[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"content-index":3,"content-layer:the-digestive-system:extend":1470},{"release":4,"domains":9,"concepts":110,"edges":1358,"journeys":1467,"sources":1468,"glossary":1469,"lean":147},{"releaseId":5,"mode":6,"createdAt":7,"manifestHash":8},"remote-mubbao62","approved","2026-09-21T13:59:41.786Z","f186a6af5a4711490e544aed2c50826ebb35e4b1169c9dc3bb40b862eb1bca8c",[10,40,62,76,86,100],{"id":11,"title":12,"description":13,"order":14,"areas":15},"mathematics","Mathematics","Numbers, shapes, patterns and data — and the reasoning that connects them.",0,[16,20,24,28,32,36],{"id":17,"title":18,"description":19},"math-number","Numbers","Reading, writing and comparing large numbers, their properties, the four operations and the order we do them in.",{"id":21,"title":22,"description":23},"math-factors","Factors and multiples","Prime and composite numbers, twin primes and co-primes, HCF and LCM.",{"id":25,"title":26,"description":27},"math-patterns","Patterns","Finding the rule behind number and shape patterns, and using it to predict.",{"id":29,"title":30,"description":31},"math-geometry","Geometry","Shapes and solids, lines and rays, and the angles they make.",{"id":33,"title":34,"description":35},"math-measurement","Measurement","Measuring and constructing angles with a protractor, ruler and compass.",{"id":37,"title":38,"description":39},"math-data","Data handling","Collecting and organising data, and summarising it with mean, median, mode and range.",{"id":41,"title":42,"description":43,"order":44,"areas":45},"matter-energy","Physics","Light, sound, forces, energy and electricity — how the physical world behaves.",1,[46,50,54,58],{"id":47,"title":48,"description":49},"phys-light","Light","How light travels, what it does when it meets things, and why we see colour.",{"id":51,"title":52,"description":53},"phys-sound","Sound","Vibrations that travel through materials, and how we hear them.",{"id":55,"title":56,"description":57},"phys-forces","Forces and motion","Pushes, pulls and the force that holds moons, planets and falling apples.",{"id":59,"title":60,"description":61},"phys-electricity","Electricity and magnetism","Charge, circuits, power and magnets.",{"id":63,"title":64,"description":65,"order":66,"areas":67},"earth-space","Earth and space","Our planet, its oceans and skies, and the Sun and Moon that move them.",2,[68,72],{"id":69,"title":70,"description":71},"earth-space-astro","Sun, Moon and sky","What we see in the sky, why it changes, and what is really moving.",{"id":73,"title":74,"description":75},"earth-oceans","Oceans","Seas, coasts and the daily rise and fall of the tide.",{"id":77,"title":78,"description":79,"order":80,"areas":81},"living-world","Living world","Bodies, plants, animals and the systems that keep them alive.",3,[82],{"id":83,"title":84,"description":85},"bio-body","The human body","What is inside you, where it sits, and how the parts work together.",{"id":87,"title":88,"description":89,"order":90,"areas":91},"people-society","People and society","How people organise themselves, and what happens when they travel, trade and rule.",4,[92,96],{"id":93,"title":94,"description":95},"soc-government","Government and citizenship","Who makes the rules, who carries them out, and how people have a say.",{"id":97,"title":98,"description":99},"soc-exploration","Exploration and encounter","Why people set out into the unknown, and what followed for everyone involved.",{"id":101,"title":102,"description":103,"order":104,"areas":105},"technology","Technology","How tools, machines and computers are designed and used.",5,[106],{"id":107,"title":108,"description":109},"tech-engineering","Engineering and power","Designing machines, structures and energy systems.",[111,179,239,286,339,389,438,488,540,587,637,689,738,788,827,876,928,979,1029,1076,1125,1177,1227,1275,1311],{"id":112,"slug":112,"title":113,"question":114,"promise":115,"domains":116,"areas":117,"keywords":118,"status":139,"layers":140,"questionBank":172},"human-body-anatomy","Anatomy of the human body","What is inside you, and where exactly does it all sit?","A guided tour of the body: bones that hold you up, muscles that move you, and the organs packed inside — what each one is, where it sits, and how big it really is.",[77],[83],[119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138],"anatomy","organ","skeleton","bone","muscle","heart","lungs","brain","stomach","liver","kidney","intestine","skin","joint","ribcage","spine","diaphragm","cell","tissue","body systems","available",[141,149,155,161,167],{"depth":142,"revision":44,"title":143,"subtitle":144,"summary":145,"estimatedMinutes":146,"reviewed":147,"reviewMethod":148},"discover","A guided tour of the body you live in","What is inside you, where it sits, and how big it really is","Climb the ladder from cells to organ systems, learn the words anatomists use for where things are, meet the 206 bones and their joints, find out why a muscle can only ever pull, and take an organ-by-organ tour with real sizes and positions — then measure your own body.",38,true,"owner_bulk",{"depth":150,"revision":44,"title":151,"subtitle":152,"summary":153,"estimatedMinutes":154,"reviewed":147,"reviewMethod":148},"understand","How the body is put together","Tissues, bone, joints, muscle and the cavities that hold the organs","Go one level below the organs to the four tissue types they are built from, learn the direction words and the standard pose they are measured from, see why bone is a living composite, count the skeleton to 206, and place every major organ in its cavity with its mass.",42,{"depth":156,"revision":44,"title":157,"subtitle":158,"summary":159,"estimatedMinutes":160,"reviewed":147,"reviewMethod":148},"investigate","Predict it, then test it","Seven claims about your body, tested with paper, a tape measure and real class data","Guess before you look: does a hollow tube beat a solid rod, does height equal arm span for everyone, can a bone reveal a stranger’s height, does exercise raise every pulse equally, are you really symmetric, and does your shoulder really out-move your hip? Seven hands-on tests against real evidence.",36,{"depth":162,"revision":44,"title":163,"subtitle":164,"summary":165,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"deepen","Why it works: levers, remodelling and a history of being corrected","Lever mechanics in every joint, bone that rebuilds under load, and how anatomy overturned a thousand years of error","Treat every muscle-moved bone as a lever and see why the body favours the class that trades force for speed. Meet bone that rebuilds along its real loads, the genuine edge cases in \"206 bones\", and how Vesalius corrected centuries of Galen’s animal-based errors.",40,{"depth":168,"revision":44,"title":169,"subtitle":170,"summary":171,"estimatedMinutes":146,"reviewed":147,"reviewMethod":148},"extend","Beyond the syllabus: animals, projects, puzzles and careers","Other body plans, three things to build, puzzles worth reasoning through, and where this knowledge earns a living","Compare your body plan with a giraffe, a bird, a snake and a boneless octopus; build a working paper hand and a life-size organ map; solve puzzles spanning the whole topic; meet seven careers built on this knowledge; finish with open questions.",{"count":173,"sections":174,"levels":175},79,10,{"foundation":176,"core":177,"stretch":178,"challenge":174},22,32,15,{"id":180,"slug":180,"title":181,"question":182,"promise":183,"domains":184,"areas":185,"keywords":186,"status":139,"layers":207,"questionBank":231},"angles","Angles","How much does a door turn when it opens — and how do we measure a turn?","What an angle is, types of angles, angle pairs (complementary, supplementary, linear pairs, vertically opposite) and how to use them to find missing angles.",[11],[29],[187,188,189,190,191,192,193,194,195,196,197,198,199,200,201,202,203,204,205,206],"angle","vertex","arm","degrees","acute","right angle","obtuse","straight angle","reflex","complete angle","complementary","supplementary","linear pair","vertically opposite","adjacent angles","angles at a point","clock angles","transversal","parallel lines","angle sum of a triangle",[208,213,218,222,227],{"depth":142,"revision":44,"title":209,"subtitle":210,"summary":211,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Angles are turns","Doors, clocks, scissors and compass directions: meet the angle and learn to name its size","See an angle as a turn and as two arms meeting at a vertex. Measure turns in degrees (full 360°, half 180°, quarter 90°), sort angles into seven types, turn through N, E, S, W, read angles on a clock and meet angle partners.",35,{"depth":150,"revision":44,"title":214,"subtitle":215,"summary":216,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Naming, sorting and pairing angles","Precise definitions, the seven types, and the angle pairs that let you find what you cannot measure","Define an angle as two rays with a common vertex, name it with ∠ABC, and use degrees and landmark angles. Pin down the seven types, clock and compass angles, then adjacent, complementary, supplementary, linear-pair, vertically opposite and around-a-point angles.",45,{"depth":156,"revision":44,"title":219,"subtitle":220,"summary":221,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Is it always true? Testing angle ideas","Predict, test with labs and numbers, hunt counterexamples and find the reasons behind angle patterns","Investigate angle estimation, sums of angle types, complement and supplement patterns, linear pairs and their bisectors, crossing lines, clock-hand puzzles, turning walks around shapes and the tear-the-corners experiment, sorting claims into always, sometimes and never.",{"depth":162,"revision":44,"title":223,"subtitle":224,"summary":225,"estimatedMinutes":226,"reviewed":147,"reviewMethod":148},"Why angles behave: proofs, parallels and polygons","From Babylonian 360 to Euclid's proofs: transversals, triangle and polygon angle sums, and hard missing-angle problems","Why a full turn is 360°, how to write a proof with reasons, why vertically opposite angles are equal, the angles made by a transversal on parallel lines and their converses, the triangle and polygon angle sums, bends and zigzags between parallels, and where 180° fails.",55,{"depth":168,"revision":44,"title":228,"subtitle":229,"summary":230,"estimatedMinutes":226,"reviewed":147,"reviewMethod":148},"Angles at work and play","Clock formulas, exterior angles, bearings, radians, real-world angles, olympiad puzzles and projects","Use |30h − 5.5m| for any clock time, prove and use the exterior angle property, navigate with bearings and runway numbers, meet the radian, see angles in ramps, ladders, bowling and pie charts, and tackle olympiad-style angle chases, projects and open questions.",{"count":232,"sections":233,"levels":234},80,9,{"foundation":235,"core":236,"stretch":237,"challenge":238},20,28,21,11,{"id":240,"slug":240,"title":241,"question":242,"promise":243,"domains":244,"areas":245,"keywords":246,"status":139,"layers":261,"questionBank":281},"body-systems","Body systems and how they connect","No organ works alone — so how does a mouthful of roti reach your toes as energy?","Digestive, circulatory, respiratory, nervous, muscular, skeletal and excretory systems, and the handovers between them that keep you alive every second.",[77],[83],[247,248,249,250,251,252,253,254,255,256,257,195,258,259,260],"digestive system","circulatory system","respiratory system","nervous system","excretory system","muscular system","skeletal system","blood","oxygen","nutrients","homeostasis","heart rate","breathing","interconnected",[262,266,270,273,277],{"depth":142,"revision":44,"title":263,"subtitle":264,"summary":265,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Seven teams, one body","What each system does, and where it hands the work to the next one","Meet the organ systems one at a time — digestive, respiratory, circulatory, excretory, nervous, muscular and skeletal — then follow a roti and a breath across the hand-over points where each system passes its work to the next.",{"depth":150,"revision":44,"title":267,"subtitle":268,"summary":269,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"How the systems work, and how they hand over","One design used six times: thin wall, huge surface, steep difference","Go inside each system: enzymes and the chemical works, the pressure trick that moves air, two circuits through a four-chambered heart, filter-and-reclaim kidneys, the reflex arc and the nerve-to-muscle gap — then follow a breath all the way to a working cell.",{"depth":156,"revision":44,"title":157,"subtitle":271,"summary":272,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Reaction time, a real enzyme test, exercise data and a fever that is not a malfunction","Turn the claims from earlier layers into experiments you can actually run: a ruler-drop reaction test, an iodine test for digested starch, pulse and breathing data before and after exercise, and a look at why a fever is a controlled response rather than a failure.",{"depth":162,"revision":44,"title":274,"subtitle":275,"summary":276,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Where the tidy rule bends","The mathematics of a thin wall, bone's double life, the lymphatic system, and why some hand-overs must be prevented","Quantify why hand-over barriers must be thin, meet the lymphatic system that returns leaked fluid and carries digested fat, see bone as a blood factory and calcium bank, and look at clotting and the blood-brain barrier as hand-overs the body deliberately controls or resists.",{"depth":168,"revision":44,"title":278,"subtitle":279,"summary":280,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"History, machines and weightlessness","Harvey's arithmetic, the stethoscope and ECG, three ways to image the body, artificial hand-overs, and bodies in orbit","Meet the arithmetic that proved blood circulates, the instruments that let doctors listen to and image a living body without cutting it, machines that rebuild a failed hand-over, what microgravity does to every system at once, and a few careers and open questions this topic leads to.",{"count":173,"sections":233,"levels":282},{"foundation":176,"core":283,"stretch":284,"challenge":285},25,19,13,{"id":287,"slug":287,"title":38,"question":288,"promise":289,"domains":290,"areas":291,"keywords":292,"status":139,"layers":313,"questionBank":335},"data-handling","What is a typical value — and how can one number summarise a whole class?","Collecting and organising data, tally marks and frequency tables, bar graphs, and summarising data with mean, median, mode and range.",[11],[37],[293,294,295,296,297,298,299,300,301,302,303,304,305,306,307,308,309,310,311,312],"data","mean","median","mode","range","average","tally","frequency table","bar graph","pictograph","pie chart","double bar graph","grouped data","outlier","survey","probability","census","rainfall","batting average","raw data",[314,318,322,326,330],{"depth":142,"revision":44,"title":315,"subtitle":316,"summary":317,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Counting what matters: meeting data","From a messy list of answers to one number that tells the story","Ask a question, collect answers, and turn a jumble of raw data into tally marks, tables, pictographs and bar graphs. Then meet four friendly numbers that sum up a whole group: the fair share (mean), the middle (median), the most common (mode) and the spread (range).",{"depth":150,"revision":44,"title":319,"subtitle":320,"summary":321,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Organise, picture, summarise: how the methods work","Kinds of data, tables and graphs done properly, and exact methods for mean, median, mode and range","Tell categorical from numerical data, build self-checking frequency tables, choose a key or scale for pictographs and bar graphs, and use exact methods for mean, median (odd and even counts), mode (two modes or none) and range, even from a frequency table.",{"depth":156,"revision":44,"title":323,"subtitle":324,"summary":325,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"What happens if…? Experiments with averages","Predict, change the data, and test: outliers, shifts, missing values and datasets built to order","Treat averages like a science experiment. Predict what adding a value, an outlier, or a change to every value does to the mean, median, mode and range, then test it in the labs. Build data sets to order, hunt missing values and compare real Indian data.",{"depth":162,"revision":44,"title":327,"subtitle":328,"summary":329,"estimatedMinutes":226,"reviewed":147,"reviewMethod":148},"Why averages work, and which one to trust","Balance points, proofs, grouped data, combined groups and the art of choosing an average","Prove the mean is a balance point and how it reacts to shifts and scaling. Combine groups correctly, handle grouped data with class intervals, read double bar graphs, and choose between mean, median and mode with outliers, cricket averages and average speeds. Plus a history of statistics in India.",{"depth":168,"revision":44,"title":331,"subtitle":332,"summary":333,"estimatedMinutes":334,"reviewed":147,"reviewMethod":148},"Data in the wild: pie charts, tricks, chance and projects","Draw pie charts, catch misleading graphs, talk about chance, and investigate real Indian data","Turn data into pie charts with angles, spot graphs that mislead, describe chance from impossible to certain, and run real projects on electricity bills, the census and monsoon rain. Think about privacy and fairness in data, meet careers built on data, and try olympiad-style puzzles.",60,{"count":232,"sections":233,"levels":336},{"foundation":337,"core":338,"stretch":176,"challenge":174},18,30,{"id":340,"slug":340,"title":341,"question":342,"promise":343,"domains":344,"areas":345,"keywords":346,"status":139,"layers":362,"questionBank":383},"eclipses","Eclipses","If the Moon goes round Earth every month, why isn't there an eclipse every month?","An eclipse is a shadow falling exactly where it can be seen. Learn the geometry of umbra and penumbra, why the Moon's tilted orbit makes eclipses rare, and how to watch one safely.",[63],[69],[347,348,349,350,351,352,353,354,355,356,357,358,359,360,361],"eclipse","solar eclipse","lunar eclipse","umbra","penumbra","annular","totality","syzygy","nodes","orbit tilt","Saros","corona","blood moon","eye safety","shadow",[363,367,371,375,379],{"depth":142,"revision":44,"title":364,"subtitle":365,"summary":366,"estimatedMinutes":338,"reviewed":147,"reviewMethod":148},"An eclipse is a shadow that finds you","Two shadows, two kinds of eclipse, and how to watch one without hurting your eyes","Meet eclipses as what they really are: shadows. Learn whose shadow falls on what in solar and lunar eclipses, why the eclipsed Moon turns red, why we don't get one every month, and the safe ways to watch the Sun.",{"depth":150,"revision":44,"title":368,"subtitle":369,"summary":370,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"The geometry of a shadow in space","Umbra and penumbra, apparent sizes, nodes and seasons — and the reasons behind every safety rule","Work out the actual geometry: how long each shadow cone is, why the Moon's only just reaches us, why the discs match to 3%, how far from a node an eclipse can happen, why the Moon turns red, and the physics behind every solar viewing rule.",{"depth":156,"revision":44,"title":372,"subtitle":373,"summary":374,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Build it, test it, try to break it","A lamp-and-balls model, hands-on measurements, and predictions checked against real eclipses","Hands-on layer: build a scale model of the Earth-Moon-Sun system, test the new-moon\u002Ffull-moon rule and the shadow-width formula for yourself, find the tilt's hidden threshold, build a pinhole projector and check its numbers, and plan around three real upcoming eclipses.",{"depth":162,"revision":44,"title":376,"subtitle":377,"summary":378,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"The Saros cycle, and two eclipses that changed physics","The Saros arithmetic, the astronomers who computed it, and how a belief should really be tested","Deeper reasoning: rebuild the 1.474° eclipse limit term by term, derive the Saros and exeligmos cycles from three different lunar months, see how Aryabhata and Brahmagupta actually computed eclipses, and examine the two solar eclipses that discovered helium and tested general relativity.",{"depth":168,"revision":44,"title":380,"subtitle":381,"summary":382,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"The same shadow rule, everywhere in the Solar System","Moons too small to eclipse, a moon that eclipses constantly, transits at home, and other worlds' planets","Take the eclipse geometry beyond Earth: why Phobos and Deimos only ever transit the Sun from Mars, why Io causes true eclipses on Jupiter routinely, how Mercury and Venus transit the Sun from Earth, Venus's 243-year transit rhythm, and how the same trick finds other stars' planets.",{"count":384,"sections":385,"levels":386},68,8,{"foundation":235,"core":387,"stretch":388,"challenge":385},24,16,{"id":390,"slug":390,"title":391,"question":392,"promise":393,"domains":394,"areas":395,"keywords":396,"status":139,"layers":416,"questionBank":437},"electricity","Electricity","What actually happens between the power station and the switch under your finger?","Electricity is charge on the move. Learn what pushes it, what resists it, how it is made and delivered, what it costs, and how to stay safe around it.",[41,101],[59,107],[390,397,398,399,400,401,402,403,404,405,406,407,408,409,410,411,412,413,414,415],"voltage","current","resistance","Ohm's law","circuit","AC","DC","generator","power station","grid","transformer","kWh","electricity bill","safety","MCB","earth wire","battery","conductor","insulator",[417,421,425,429,433],{"depth":142,"revision":44,"title":418,"subtitle":419,"summary":420,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Electricity is charge on the move","From a balloon on your hair to a day that runs on it","Meet the charges hiding in every atom, see why a doorknob spark and lightning are the same idea, discover why slow electrons still light a bulb instantly, build circuits that break, and learn the first rules for staying safe.",{"depth":150,"revision":44,"title":422,"subtitle":423,"summary":424,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"The big three: voltage, current, resistance","The push, the flow and the pushback, and the one rule that ties them together","Build the pump-and-pipe picture of a circuit, then meet voltage (the push), current (the flow) and resistance (the pushback) with real numbers from AA cells to lightning. Finish with Ohm's law, V = I × R, and the mix-ups it clears up.",{"depth":156,"revision":44,"title":426,"subtitle":427,"summary":428,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Circuits you can test","Fair tests, meters, series and parallel, Ohm's law, fuses and fruit batteries","Design fair circuit tests, place ammeters and voltmeters correctly, compare series and parallel bulbs, test Ohm's law and see a filament bulb break it, work out when an MCB trips, and build a safe lemon battery.",{"depth":162,"revision":44,"title":430,"subtitle":431,"summary":432,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"How it's made and how it reaches you","From Faraday's spinning magnets to the socket on your wall","Follow electricity from a spinning magnet in a power station, through transformers and 765 kV lines, down to the 230 V socket in your room. Learn why the grid runs on AC at 50 Hz, why it transmits at high voltage, and why supply must match demand every second.",{"depth":168,"revision":44,"title":434,"subtitle":435,"summary":436,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Power, bills, safety and the future","From watts on a rating plate to units on your bill, the milliamps that matter, and the grid that is coming","Use P = V × I and E = P × t to read rating plates and work out a real electricity bill in units (kWh). Learn why current through the body is what injures, how earth pins, MCBs and RCCBs protect you, what to do in a shock emergency, and how solar, storage and smart meters are changing the grid.",null,{"id":439,"slug":439,"title":440,"question":441,"promise":442,"domains":443,"areas":444,"keywords":445,"status":139,"layers":463,"questionBank":485},"exploration","Exploration: reasons and consequences","What made people sail into oceans they could not map — and who paid for it?","Curiosity, trade, faith, gold and rivalry sent people across oceans. Follow the voyages, the technology that made them possible, and the consequences — for those who travelled and for those already there.",[87],[97],[439,446,447,448,449,450,451,452,453,454,455,456,457,458,459,460,461,462],"voyage","navigation","trade route","spices","Vasco da Gama","Columbus","Zheng He","Silk Road","colonisation","Columbian exchange","monsoon winds","astrolabe","compass","cartography","empire","consequences","indigenous peoples",[464,468,473,477,481],{"depth":142,"revision":44,"title":465,"subtitle":466,"summary":467,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Why sail into an ocean nobody has mapped?","Reasons, routes and results, told from both ends of the voyage","Meet exploration honestly: what the word means and why 'discovery' misleads, six reasons people set out, the busy Indian Ocean world before European ships, how sailors found their way, four voyages worth knowing, and what followed - new foods, new maps, disease, slavery and empire.",{"depth":150,"revision":44,"title":469,"subtitle":470,"summary":471,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"How the navigator's toolkit actually works","Mechanisms behind the voyages: instruments, sails, clocks, charts and the economics of a monopoly","Go under Discover's story to the mechanisms: how a compass, kamal, astrolabe, lateen sail and sternpost rudder actually work, why longitude needed a clock and took decades to solve, how flat maps must distort a round Earth, and why a royal charter let a trading company become a ruler.",50,{"depth":156,"revision":44,"title":474,"subtitle":475,"summary":476,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Predict it, try it, compare it, test it","Lab-heavy investigations that check what the Discover layer told you","Compare stated reasons with actual results for Columbus and Zheng He, run a monsoon 'what if', judge whether one number sums up a disputed history, sort evidence against a claim about da Gama, read a paraphrased passage from two sides, and test sweeping generalisations against real voyages.",{"depth":162,"revision":44,"title":478,"subtitle":479,"summary":480,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Mechanism, harder numbers, and how historians know","Why the monsoon reverses, how clock drift compounds, and the method behind contested figures","Go beneath Discover's facts into mechanism and method: why the monsoon reverses, how clock drift compounds over a long voyage, an edge case in kamal readings, how historians back-project contested figures, how to weigh one account against another, and what shipwreck years teach about mean vs median.",{"depth":168,"revision":44,"title":482,"subtitle":483,"summary":484,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Beyond the horizon: exploration to today","Cook, the poles, space, the deep sea, and the questions nobody has answered yet","Carries exploration from Cook's Pacific voyage to today: the race to the poles and the treaty that followed, leaving Earth's gravity for the Moon and beyond, the deepest ocean trench, and the hardest open questions - who owns what nobody lives on, and who decides.",{"count":486,"sections":233,"levels":487},75,{"foundation":178,"core":236,"stretch":176,"challenge":174},{"id":489,"slug":489,"title":490,"question":491,"promise":492,"domains":493,"areas":494,"keywords":495,"status":139,"layers":515,"questionBank":536},"four-operations","Four operations","When should you add, subtract, multiply or divide — and how do you know your answer makes sense?","Addition, subtraction, multiplication and division with large numbers, choosing the right operation in real problems, and checking answers by estimating and by inverse operations.",[11],[17],[496,497,498,499,500,501,502,503,504,505,506,507,508,509,510,511,512,513,514],"addition","subtraction","multiplication","division","word problems","estimation","inverse operations","quotient","remainder","dividend","divisor","product","sum","difference","regrouping","long division","long multiplication","unitary method","word problems in rupees",[516,520,524,528,532],{"depth":142,"revision":44,"title":517,"subtitle":518,"summary":519,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Four ways to change a number","Adding, subtracting, multiplying and dividing: what each one means and when to use it","Meet the four operations through a kirana-shop trip, cricket scores, egg trays and shared laddoos. Learn what each operation means, how they undo each other, how to pick the right one from a story, and how to check that an answer is sensible.",{"depth":150,"revision":44,"title":521,"subtitle":522,"summary":523,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"How the column methods work","Carrying, borrowing, long multiplication and long division, and why every step is allowed","Learn the exact name for every part of a calculation, then master column addition and subtraction up to crores, long multiplication, long division with remainders and zeros in the quotient, checking with inverse operations, and working with money and units.",{"depth":156,"revision":44,"title":525,"subtitle":526,"summary":527,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Predict, test, check","Estimating first, changing the numbers, making sense of remainders and catching keyword traps","Predict before you calculate and test with labs and tables: estimate sums and products, see what happens when numbers change, decide what a remainder means in a story, catch misleading keywords and check answers by undoing them.",{"depth":162,"revision":44,"title":529,"subtitle":530,"summary":531,"estimatedMinutes":226,"reviewed":147,"reviewMethod":148},"Why the methods work","Regrouping, the distributive property, the division algorithm, checks, proportion and the history behind them","Prove why carrying, borrowing, long multiplication and long division work, meet the division algorithm and why dividing by zero is impossible, check with casting out nines, use the unitary method wisely, and solve India-sized multi-step problems.",{"depth":168,"revision":44,"title":533,"subtitle":534,"summary":535,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"Other ways to calculate, and harder puzzles","Lattices, Vedic-style shortcuts, doubling, binary, classic puzzles, olympiad problems and real projects","Try the lattice, Napier's bones, Vedic-style shortcuts and Russian peasant multiplication and see why each works. Crack classic puzzles and olympiad problems, then plan real projects: a trip budget, a kirana bill, a harvest and a run chase.",{"count":537,"sections":385,"levels":538},74,{"foundation":178,"core":539,"stretch":176,"challenge":385},29,{"id":541,"slug":541,"title":542,"question":543,"promise":544,"domains":545,"areas":546,"keywords":547,"status":139,"layers":563,"questionBank":584},"gravity","Gravity","Why does everything fall down — and what is the Moon falling towards?","The force that pulls an apple to the ground is the same one that keeps the Moon circling Earth. Meet mass and weight, free fall, orbits and why astronauts float.",[41],[55],[541,548,549,550,551,552,553,554,555,556,557,558,559,560,561,562],"mass","weight","free fall","orbit","force","Newton","air resistance","g","acceleration","satellite","weightlessness","planet","tides","escape velocity","centre of mass",[564,568,572,576,580],{"depth":142,"revision":44,"title":565,"subtitle":566,"summary":567,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Why does everything fall down?","Meet the pull that drops a pencil, bends the Moon’s path and holds the sky together","Start with a dropped pencil and end with galaxies. Discover what a force is, why heavy things do not fall faster, how air changes everything, the real difference between mass and weight, and the true reason astronauts float.",{"depth":150,"revision":44,"title":569,"subtitle":570,"summary":571,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"How gravity works: weight, falling and orbits","Mass against weight, g against speed, drag against gravity — and why an orbit is a permanent miss","Turn the story into rules you can use: weight = mass × g, distance = ½ g t², why mass cancels in free fall, how drag sets terminal velocity, Newton’s universal law in words, and the real reason astronauts float.",{"depth":156,"revision":44,"title":573,"subtitle":574,"summary":575,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Test it: predictions, ramps, pendulums and Newton’s own proof","Predict, try, compare and ask \"is it always true?\" — with a ramp, a pendulum, a leaking cup and a spacecraft","Turn gravity into hands-on science: rebuild Galileo’s ramp, design fair tests for mass and shape, weigh the Earth with a pendulum, check whether Newton’s law survives the trip to the Moon, hunt for orbital speed by binary search, and see how ISRO climbs to the Moon and Mars one burn at a time.",{"depth":162,"revision":44,"title":577,"subtitle":578,"summary":579,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"The mathematics behind every number in this topic","G, orbits derived from first principles, Newton’s Moon test in full, and the coincidence Einstein could not ignore","Meet Newton’s law with its constant G, derive orbital and escape speed from scratch, redo Newton’s Moon test in full, explore why gravitational and inertial mass are equal, see why g is not uniform on Earth, and look at the mechanics behind ISRO’s orbit-raising missions.",{"depth":168,"revision":44,"title":581,"subtitle":582,"summary":583,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Curved spacetime, black holes and the questions nobody has answered yet","Einstein’s radical idea, tested and confirmed — and an honest look at where gravity’s biggest mysteries still are","Go beyond Newton to Einstein: gravity as curved spacetime, the rubber-sheet picture and its flaws, the tests that confirmed general relativity, black holes, gravitational waves, orbital puzzles from tidal locking to dark matter, and open questions with real projects.",{"count":585,"sections":233,"levels":586},70,{"foundation":388,"core":387,"stretch":235,"challenge":174},{"id":588,"slug":588,"title":589,"question":590,"promise":591,"domains":592,"areas":593,"keywords":594,"status":139,"layers":613,"questionBank":634},"hcf-and-lcm","HCF and LCM","When will two blinking lights flash together again — and what is the biggest tile that fits a floor exactly?","Highest common factor and lowest common multiple by listing, prime factorisation and division, their link HCF × LCM = product, and real problems that need them.",[11],[21],[595,596,597,598,599,600,601,602,603,604,605,606,607,608,609,610,500,611,612],"HCF","LCM","GCD","GCF","highest common factor","lowest common multiple","least common multiple","common factors","common multiples","prime factorisation","Venn diagram","long division method","Euclid's algorithm","common division method","co-prime","HCF × LCM","remainder problems","fractions",[614,618,622,626,630],{"depth":142,"revision":44,"title":615,"subtitle":616,"summary":617,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Sharing and meeting: meet the HCF and LCM","The biggest equal pieces and the next time things line up","Start from two puzzles, the biggest tile for a courtyard and the next time two lights flash together, and discover factors, multiples, common factors, common multiples, the HCF and the LCM, and how to tell which one a problem needs.",{"depth":150,"revision":44,"title":619,"subtitle":620,"summary":621,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Four ways to find the HCF and LCM","Listing, prime factors, long division and the ladder, and why they work","Precise definitions, then four methods: listing, prime factorisation with a Venn picture, long (continued) division for the HCF and common division for the LCM. Three numbers, the rule HCF × LCM = product, co-primes, fractions and the classic mix-ups.",{"depth":156,"revision":44,"title":623,"subtitle":624,"summary":625,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Predict, test and explain: HCF and LCM patterns","Always, sometimes or never? Find out with your own experiments","Make predictions and test them: when the LCM equals the product, why neighbours are co-prime, how HCF × LCM = a × b holds for two numbers but not three, what scaling does, how remainder puzzles work, and how changing a word problem changes the answer.",{"depth":162,"revision":44,"title":627,"subtitle":628,"summary":629,"estimatedMinutes":226,"reviewed":147,"reviewMethod":148},"Why it works: proofs, Euclid and the edges","Unique prime recipes, the product rule, Euclid’s algorithm and Bézout","Proofs in plain language: unique prime factorisation, why HCF takes smallest powers and LCM largest, why HCF × LCM = a × b (and why not for three numbers), why Euclid’s method works and how fast it is, Bézout’s identity, edge cases, harder problems and history.",{"depth":168,"revision":44,"title":631,"subtitle":632,"summary":633,"estimatedMinutes":334,"reviewed":147,"reviewMethod":148},"Cycles, gears and puzzles: HCF and LCM in the wild","Calendars, cicadas, tabla, bicycles, jugs, screens and olympiad problems","Expeditions beyond the textbook: cycles with head starts, calendars and planetary alignments (and why they are not LCMs), prime-cycle cicadas, gears and bicycle chains, tala rhythms, water jugs, ancient remainder puzzles, screen ratios, fractions, olympiad problems, careers and open questions.",{"count":173,"sections":385,"levels":635},{"foundation":235,"core":636,"stretch":337,"challenge":174},31,{"id":638,"slug":638,"title":639,"question":640,"promise":641,"domains":642,"areas":643,"keywords":644,"status":139,"layers":665,"questionBank":686},"government-india","How government works in India","Who decides what a country does — and where does a citizen fit in?","Parliament, the President and the Prime Minister, states and panchayats, courts and elections: how India makes its laws, carries them out and settles disputes, and how people have a say.",[87],[93],[645,646,647,648,649,650,651,652,653,654,655,656,657,658,659,660,661,662,663,664],"government","democracy","Parliament","Lok Sabha","Rajya Sabha","President","Prime Minister","Supreme Court","election","vote","constitution","panchayat","municipality","state","federal","law","rights","duties","citizen","judiciary",[666,670,674,678,682],{"depth":142,"revision":44,"title":667,"subtitle":668,"summary":669,"estimatedMinutes":338,"reviewed":147,"reviewMethod":148},"Who decides the rules?","From an hour in the school hall to a republic of a hundred and forty crore people","Start with thirty children, one football and no rules, and discover the three jobs every group has to invent: making rules, carrying them out and settling disputes. Then meet India's version — the Constitution, three organs, three levels, and the vote.",{"depth":150,"revision":44,"title":671,"subtitle":672,"summary":673,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"How each part actually works","Parliament's machinery, a bill's journey, the courts' ladder, and the levels beneath the Union","Go inside the institutions Discover introduced: how Parliament questions ministers, how a bill becomes an Act, what a President does that a Prime Minister does not, how courts check Parliament, and how the Union, States, Union Territories and local bodies share the work.",{"depth":156,"revision":44,"title":675,"subtitle":676,"summary":677,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Test it yourself: does the arithmetic hold up?","Seat share against vote share, real turnout data, and edge cases in how a bill becomes an Act","Put the rules from Understand under pressure: work through seat-versus-vote-share examples, test what happens when the two Houses disagree over a money bill, analyse real turnout data with mean, median and range, and sort everyday problems by the level of government actually responsible.",{"depth":162,"revision":44,"title":679,"subtitle":680,"summary":681,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Why it is built this way","The amendment procedure's arithmetic, the basic structure doctrine, and the freedom movement's fingerprints","Go after the reasoning: the arithmetic of amending the Constitution, the basic structure doctrine, how judges come to be chosen, the freedom movement's own arguments becoming institutions, and a few genuine edge cases put under pressure.",{"depth":168,"revision":44,"title":683,"subtitle":684,"summary":685,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Build it, test it, take it further","A mini-constitution, a mock Parliament, coalition puzzles, other countries' choices, and where this knowledge leads","Put the whole topic to work: draft and stress-test a mini-constitution, run a mock Parliament, prove a coalition-counting puzzle, compare India's design with other countries', research your own representatives, and meet real careers and open questions this knowledge connects to.",{"count":687,"sections":385,"levels":688},76,{"foundation":176,"core":636,"stretch":178,"challenge":385},{"id":690,"slug":690,"title":48,"question":691,"promise":692,"domains":693,"areas":694,"keywords":695,"status":139,"layers":713,"questionBank":735},"light","What is light, how does it travel, and why can you see this page at all?","Light travels in straight lines at extraordinary speed, bounces, bends, splits into colours and lets you see. Find out how, and why shadows, mirrors and rainbows behave as they do.",[41],[47],[690,696,697,698,361,699,700,701,702,703,704,705,706,707,708,709,710,350,711,712],"luminous","reflection","refraction","mirror","spectrum","colour","transparent","opaque","translucent","ray","speed of light","rainbow","prism","lens","eye","scattering","laser",[714,718,722,726,730],{"depth":142,"revision":44,"title":715,"subtitle":716,"summary":717,"estimatedMinutes":338,"reviewed":147,"reviewMethod":148},"Light: how you can see anything at all","Sources, straight lines, shadows, mirrors, bent straws and the colours hiding inside white","Meet light as the messenger that carries the world to your eyes: what makes its own light and what only reflects it, why light travels dead straight, how that one fact explains shadows, and first looks at mirrors, bending and the colours inside white light.",{"depth":150,"revision":44,"title":719,"subtitle":720,"summary":721,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"How light behaves: rays, angles and rules you can use","Shadow arithmetic, the law of reflection, what refraction really is, and the two kinds of colour mixing","Turn the facts of Discover into rules that predict. Work out shadow sizes with similar triangles, meet umbra and penumbra, apply the law of reflection to mirrors and periscopes, see why light bends when its speed changes, and separate the two opposite kinds of colour mixing.",{"depth":156,"revision":44,"title":723,"subtitle":724,"summary":725,"estimatedMinutes":154,"reviewed":147,"reviewMethod":148},"Chasing light: measuring, mirroring and bending it on purpose","How fast is light, and how would you find out? Predict and test curved mirrors, lenses, TIR and rainbows.","Step into the shoes of Rømer and Fizeau to measure something that seemed instant, then turn detective on curved mirrors, lenses pushed to a magnifier, total internal reflection in a diamond and a fibre-optic cable, and finally the exact geometry that puts a rainbow at 42 degrees from the Sun.",{"depth":162,"revision":44,"title":727,"subtitle":728,"summary":729,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Precise light: derivations, corrective lenses and the shape of a rainbow","Beyond the syllabus: derive the mirror formula, correct short and long sight, and see why a rainbow sits at 42 degrees.","Follow the speed of light to its modern exact definition, derive the mirror\u002Flens formula from similar triangles, work out lens powers for short and long sight, put numbers on fibre-optic latency, and see why the rainbow's angle is a genuine minimum.",{"depth":168,"revision":44,"title":731,"subtitle":732,"summary":733,"estimatedMinutes":734,"reviewed":147,"reviewMethod":148},"Waves, particles and the light you cannot see","Beyond visible light: wave versus particle, a real chocolate-bar experiment, and looking into the past with light-years.","Step past visible light into the wider spectrum, meet the wave-versus-particle debate (light is genuinely both), measure light's speed with a microwave and a chocolate bar, see how bending stretches every day, and use light-years to look into the past.",44,{"count":232,"sections":233,"levels":736},{"foundation":284,"core":737,"stretch":284,"challenge":178},27,{"id":739,"slug":739,"title":740,"question":741,"promise":742,"domains":743,"areas":744,"keywords":745,"status":139,"layers":763,"questionBank":784},"lines","Lines, rays and line segments","What is the difference between a line, a ray and a segment — and why do railway tracks never meet?","Points, lines, rays and line segments, intersecting, parallel and perpendicular lines, and where we see them in the world.",[11],[29],[746,747,705,748,749,750,751,752,205,753,754,204,755,756,757,758,759,760,761,762],"point","line","line segment","plane","collinear","concurrent","intersecting lines","perpendicular lines","perpendicular bisector","skew lines","horizontal and vertical","measuring segments","parallax error","Euclid's postulates","parallel postulate","vanishing point","railway tracks",[764,768,772,776,780],{"depth":142,"revision":44,"title":765,"subtitle":766,"summary":767,"estimatedMinutes":283,"reviewed":147,"reviewMethod":148},"Straight paths: points, lines, rays and segments","Meet the alphabet of geometry in torch beams, railway tracks and cricket creases","Meet points, line segments, rays and lines through everyday things, then see how two lines can cross, meet at square corners or run side by side forever.",{"depth":150,"revision":44,"title":769,"subtitle":770,"summary":771,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Names, notation and rules for lines","Precise definitions, careful measuring and the mix-ups they clear up","Pin down point, line and plane; name lines, rays and segments correctly; measure without parallax error; and define collinear, concurrent, parallel and perpendicular lines precisely.",{"depth":156,"revision":44,"title":773,"subtitle":774,"summary":775,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Test it: predictions about points and lines","Count, fold, measure and hunt for counterexamples","Predict and count how many lines, segments, rays and crossing points some points and lines can make; run a measuring experiment; beat optical illusions; and sort claims into always, sometimes and never true.",{"depth":162,"revision":44,"title":777,"subtitle":778,"summary":779,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"Why it must be so: reasoning about lines","Euclid's rules, proofs, counting arguments and the puzzle of parallels","Build geometry from Euclid's postulates, prove key facts about intersecting, parallel and perpendicular lines, count with pairs, and follow the 2,000-year story of the parallel postulate from Alexandria to curved space.",{"depth":168,"revision":44,"title":781,"subtitle":782,"summary":783,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"Lines in the wider world","Perspective, skew lines, maps, sport, careers, puzzles and open questions","See parallel lines meet in perspective drawings, find skew lines in rooms and solids, read lines on maps and sports grounds, meet people who use lines at work, and tackle puzzles from pizza cuts to string art.",{"count":232,"sections":233,"levels":785},{"foundation":786,"core":539,"stretch":176,"challenge":787},17,12,{"id":789,"slug":789,"title":790,"question":790,"promise":791,"domains":792,"areas":793,"keywords":794,"status":139,"layers":800,"questionBank":823},"magnets","Magnets: why do some things stick to a magnet and others do not?","A new science topic for learners aged 10 to 12 (Class 5-6, India). Cover: what a magnet is; poles, attraction and repulsion; which materials are magnetic (iron, nickel, cobalt, steel) and which are not (wood, plastic, copper, aluminium); th",[41],[59],[789,795,796,797,798,799],"some","things","stick","magnet","others",[801,807,811,815,819],{"depth":142,"revision":44,"title":802,"subtitle":803,"summary":804,"estimatedMinutes":805,"reviewed":147,"reviewMethod":806},"The Invisible Grip: How Magnets Pull and Push","A journey from fridge magnets to Earth's hidden force — why some things stick and others slip away","This lesson introduces magnets through everyday objects, explains how poles attract and repel, and shows how to test materials for magnetism. Readers will map invisible magnetic fields, make a simple compass, and connect it all to Earth acting as a giant magnet.",90,"per_lesson",{"depth":150,"revision":44,"title":808,"subtitle":809,"summary":810,"estimatedMinutes":805,"reviewed":147,"reviewMethod":806},"The Hidden Army Inside a Magnet","How tiny atomic teams line up to pull, stick or snap — and why heat or a hard knock sends them tumbling","This lesson reveals the invisible world of magnetic domains: why iron sticks but copper slips, how stroking or electricity organises atoms into a magnet, and why heat or hammering destroys that order. It also covers common mix-ups like 'all metals attract' and how to test unknown",{"depth":156,"revision":44,"title":812,"subtitle":813,"summary":814,"estimatedMinutes":805,"reviewed":147,"reviewMethod":806},"The Magnet Investigation Lab","How changing conditions, careful measurement and fair tests reveal what magnets really do","This lesson puts every magnet claim to the test. Learners plan fair comparisons, predict outcomes, gather evidence and use it to decide how magnets behave, how they weaken, and how an electromagnet's design changes its power.",{"depth":162,"revision":44,"title":816,"subtitle":817,"summary":818,"estimatedMinutes":805,"reviewed":147,"reviewMethod":806},"The Invisible Architecture of Magnetism","How atoms, domains, and field lines explain why some materials obey the magnet and others refuse","This lesson traces magnetism from everyday fridge magnets to atomic arrangements and magnetic domains, explaining why iron rushes to a magnet while copper stays still. Readers learn to predict magnetic behaviour, interpret field-line patterns, and calculate simple field relations",{"depth":168,"revision":44,"title":820,"subtitle":821,"summary":822,"estimatedMinutes":805,"reviewed":147,"reviewMethod":806},"The Invisible Push: Magnets at Work and at Scale","From iron filings to maglev trains — how hidden fields, domains and electromagnets shape our world","This lesson explores how magnetic domains explain why some materials become magnets and others do not, then builds to electromagnets, real engineering uses, and how to test magnetism fairly at home. It closes with open questions about magnetic storage and levitation that learners",{"count":824,"sections":66,"levels":825},52,{"foundation":826,"core":337,"stretch":787,"challenge":385},14,{"id":828,"slug":828,"title":829,"question":830,"promise":831,"domains":832,"areas":833,"keywords":834,"status":139,"layers":853,"questionBank":874},"constructing-angles","Measuring and constructing angles","How do you draw an exact 60° angle with only a compass and a ruler?","Reading a protractor correctly, measuring and drawing angles, and constructing 60°, 120°, 90°, 30° and 45° angles and bisectors with a ruler and compass.",[11],[33,29],[835,458,836,837,754,838,839,840,841,842,843,844,845,846,847,848,849,850,851,852],"protractor","construction","angle bisector","60 degrees","90 degrees","120 degrees","45 degrees","30 degrees","geometry box","set square","divider","measuring angles","drawing angles","reflex angle","inner and outer scale","ruler and compass","trisection","constructing triangles",[854,858,862,866,870],{"depth":142,"revision":44,"title":855,"subtitle":856,"summary":857,"estimatedMinutes":338,"reviewed":147,"reviewMethod":148},"Angles you can measure and make","The geometry box, the protractor and the compass trick for an exact 60°","Open the geometry box, learn what a degree is, estimate angles by eye, measure and draw angles with a protractor, and discover how a compass alone can make an exact 60° angle.",{"depth":150,"revision":44,"title":859,"subtitle":860,"summary":861,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Reading the protractor and the compass constructions","Why the two scales exist, how to measure and draw any angle, and why 60°, 90°, 30° and 45° constructions work","Learn the precise protractor method (and the wrong-scale trap), measure and draw reflex angles, copy lengths with a compass, and construct 60°, 120°, 90°, 30° and 45° angles and perpendicular bisectors with the reason each one works.",{"depth":156,"revision":44,"title":863,"subtitle":864,"summary":865,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Test it: estimates, radii and angle recipes","Predict, try and check: what really changes an angle, and what never does","Predict and test: does arm length matter, what does a wrong-scale reading look like, how good is your eye, does the compass radius matter, which angles can bisecting and set squares reach, how accurate can a check be, and why bisectors always work.",{"depth":162,"revision":44,"title":867,"subtitle":868,"summary":869,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Why the constructions work","Proofs behind the recipes, edge cases, accuracy and the problems the Greeks could not solve","Find out why each compass construction is exact: equilateral triangles for 60°, congruent triangles for bisectors, equidistant points for perpendiculars. Then test edge cases, measure reflex angles, analyse errors and meet the impossible trisection problem.",{"depth":168,"revision":44,"title":871,"subtitle":872,"summary":873,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"Triangles, polygons and the impossible angle","Build triangles and regular polygons, meet Gauss's 17-gon, and find out why 20° can never be constructed","Construct triangles from SSS, SAS and ASA, draw regular polygons from a circle, discover which polygons and whole-degree angles are constructible (multiples of 3°), meet the trisection problem, and use angles in projects, puzzles and careers.",{"count":537,"sections":233,"levels":875},{"foundation":178,"core":338,"stretch":284,"challenge":174},{"id":877,"slug":877,"title":878,"question":879,"promise":880,"domains":881,"areas":882,"keywords":883,"status":139,"layers":903,"questionBank":924},"patterns","Number and shape patterns","How can you predict the 100th term without drawing 100 pictures?","Spotting rules in number sequences and growing shape patterns, describing them in words and symbols, and using the rule to predict.",[11],[25],[877,884,885,886,887,888,889,890,891,892,893,894,895,896,897,898,899,900,901,902],"sequence","rule","term","nth term","repeating patterns","growing patterns","arithmetic sequence","geometric sequence","square numbers","cube numbers","triangular numbers","Fibonacci","Pascal's triangle","matchstick patterns","odd numbers","even numbers","magic squares","kolam","algebra",[904,908,912,916,920],{"depth":142,"revision":44,"title":905,"subtitle":906,"summary":907,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"What comes next? Meeting patterns","Bangles, kolam borders, calendars, matchsticks and the rules that make them","Meet repeating and growing patterns in beads, rangoli, calendars and the hundred square. Find the unit, find the difference, describe the rule in words, and use jumps to predict terms far ahead.",{"depth":150,"revision":44,"title":909,"subtitle":910,"summary":911,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Rules, terms and sequences","Arithmetic and geometric sequences, special numbers, digit patterns and shape rules","Learn the precise language of sequences, the difference method for finding rules, arithmetic and geometric sequences, square, cube, triangular and Fibonacci numbers, digit patterns, and the rules behind growing matchstick and dot patterns.",{"depth":156,"revision":44,"title":913,"subtitle":914,"summary":915,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"Pattern detectives: predict, test, explain","Matchstick challenges, Gauss’s trick, calendar magic, growth races and patterns that fool you","Investigate growing patterns like a detective: predict first, collect small cases, find the rule, test it and explain why it works. Includes far predictions, working backwards, odd sums, Gauss’s pairing, grid tricks and always-sometimes-never reasoning.",{"depth":162,"revision":44,"title":917,"subtitle":918,"summary":919,"estimatedMinutes":334,"reviewed":147,"reviewMethod":148},"Why patterns work: rules, algebra and proof","nth terms, equivalent expressions, picture proofs, Pingala’s rhythms, Meru Prastara and patterns that break","Turn rules into algebra and prove them: why the step becomes the coefficient of n, why odd numbers make squares, sums of powers and cubes, the Indian discovery of the Fibonacci numbers and Meru Prastara, why digit patterns stop, and why patterns that look certain can break.",{"depth":168,"revision":44,"title":921,"subtitle":922,"summary":923,"estimatedMinutes":334,"reviewed":147,"reviewMethod":148},"Pattern hunters: puzzles, projects and open questions","Magic squares from Khajuraho, tessellations, figurate numbers, cycles, olympiad problems and unsolved mysteries","Take patterns into the wider world: Lo Shu, Khajuraho and Ramanujan magic squares, tessellations and symmetry, figurate numbers, cycles of last digits and weekdays, the chessboard legend and binary, olympiad problems, patterns in music and careers, projects, and open questions like Collatz.",{"count":925,"sections":233,"levels":926},81,{"foundation":178,"core":927,"stretch":387,"challenge":233},33,{"id":929,"slug":929,"title":930,"question":931,"promise":932,"domains":933,"areas":934,"keywords":935,"status":139,"layers":955,"questionBank":976},"number-system","Number system","How do we read, write and compare really big numbers — and why do Indians and the rest of the world put commas in different places?","Place value, number names, expanded form, predecessors and successors, the Indian and International systems, and rounding — the toolkit for every large number you will ever meet.",[11],[17],[936,937,938,939,940,941,942,943,944,945,946,947,501,948,949,950,951,952,953,954],"place value","number names","expanded form","predecessor","successor","Indian number system","International number system","lakh","crore","million","billion","rounding","comparing numbers","face value","Roman numerals","arab and kharab","Hindu-Arabic numerals","binary","expanded form with powers of ten",[956,960,964,968,972],{"depth":142,"revision":44,"title":957,"subtitle":958,"summary":959,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Big numbers all around us","Ten digits, a few clever places, and every number you will ever need","Meet place value through bundles of sticks, cricket crowds and rupee notes. Learn to read and write big numbers the Indian way (lakh, crore) and the international way (million, billion), find the number just before and after, compare, round and even read Roman numerals.",{"depth":150,"revision":44,"title":961,"subtitle":962,"summary":963,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"How place value works, and how to use it","Precise rules for names, commas, comparing, forming, rounding and estimating","Exact rules for place and face value, expanded form, number names and both comma systems, with many worked examples. Then reliable methods for converting, comparing, ordering, forming numbers, rounding, estimating and Roman numerals, plus the mix-ups to avoid.",{"depth":156,"revision":44,"title":965,"subtitle":966,"summary":967,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Testing big-number ideas","Predict first, then try it: shifting digits, rollovers, rounding traps and estimation errors","Make predictions about place value and then test them: what moving a digit does, how many numbers of each size exist, when a successor gains a digit, which numbers round to the same value, how far off an estimate can be, and why 6174 keeps appearing.",{"depth":162,"revision":44,"title":969,"subtitle":970,"summary":971,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"Why place value works","Powers of ten, proofs of the rules, error bounds and the Indian story of zero","Powers of ten, and proofs that the rules for comparing, rounding and forming numbers always work. Bound estimate errors, meet Sanskrit names for powers of ten, follow our digits from Brahmi to Aryabhata to Baghdad to Europe, and see metric units as place value.",{"depth":168,"revision":44,"title":973,"subtitle":974,"summary":975,"estimatedMinutes":226,"reviewed":147,"reviewMethod":148},"Beyond a billion, and beyond base ten","Arab, kharab and trillion; ISRO distances; binary and other bases; puzzles and projects","Stretch the number system in every direction: bigger names in both systems, real Indian large numbers from elections to Mars, number systems of the Babylonians, Maya and Egyptians, binary as a place-value system, olympiad-style puzzles, Fermi estimates, projects and open questions.",{"count":977,"sections":233,"levels":978},83,{"foundation":235,"core":338,"stretch":176,"challenge":238},{"id":980,"slug":980,"title":981,"question":982,"promise":983,"domains":984,"areas":985,"keywords":986,"status":139,"layers":1006,"questionBank":1027},"order-of-operations","Order of operations","Is 2 + 3 × 4 equal to 20 or 14 — and who decides?","Why we need an agreed order, the DMAS \u002F BODMAS rule, brackets, and how the distributive property explains it all.",[11],[17],[987,988,989,990,991,992,993,994,995,996,997,998,999,1000,1001,1002,500,1003,1004,1005],"DMAS","BODMAS","BIDMAS","PEMDAS","order of operations","brackets","simplify","expression","terms","left to right","precedence","vinculum","of","implied multiplication","four fours","24 game","calculator","distributive property","nested brackets",[1007,1011,1015,1019,1023],{"depth":142,"revision":44,"title":1008,"subtitle":1009,"summary":1010,"estimatedMinutes":338,"reviewed":147,"reviewMethod":148},"One line of maths, one answer","Why 2 + 3 × 4 is 14 everywhere in the world, and the simple rules that make it so","Meet the puzzle 2 + 3 × 4 through a shopping bill, learn why everyone needs one agreed order, and practise the three rules: brackets first, then × and ÷, then + and −, with partners going left to right.",{"depth":150,"revision":44,"title":1012,"subtitle":1013,"summary":1014,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"The rule, precisely","Terms, memory words, three kinds of brackets, “of”, word problems and error-spotting","Make the order of operations precise: split expressions into terms, see why DMAS, BODMAS and PEMDAS all mean one rule, handle nested brackets and \"of\", write expressions from word problems and find mistakes in working.",{"depth":156,"revision":44,"title":1016,"subtitle":1017,"summary":1018,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Brackets under the microscope","Predict, test and explain: moving brackets, missing signs, calculators and targets","Experiment with the order of operations: count how many values brackets can make, find when brackets change nothing, test always\u002Fsometimes\u002Fnever statements, fill in missing signs, compare calculators and hit targets.",{"depth":162,"revision":44,"title":1020,"subtitle":1021,"summary":1022,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Why the rule is the rule","Repeated addition, the distributive property, powers, the vinculum, history and how machines read maths","Justify the order of operations: why × comes before + (repeated addition, the distributive property), why partners go left to right (negatives and reciprocals), where powers fit, the vinculum and history of brackets, expression trees, RPN and edge cases.",{"depth":168,"revision":44,"title":1024,"subtitle":1025,"summary":1026,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Puzzles, arguments and the wider world","Viral puzzles, four fours, the 24 game, olympiad problems, code and open questions","Take the order of operations further: why 8 ÷ 2(2 + 2) starts arguments, the four fours and 24 puzzles, olympiad problems, how code and spreadsheets differ, other notations, projects and open questions.",{"count":486,"sections":385,"levels":1028},{"foundation":284,"core":636,"stretch":786,"challenge":385},{"id":1030,"slug":1030,"title":1031,"question":1032,"promise":1033,"domains":1034,"areas":1035,"keywords":1036,"status":139,"layers":1053,"questionBank":1074},"phases-of-the-moon","Phases of the Moon","Why does the Moon change shape — and why is it never really a different shape at all?","Half the Moon is always lit. What changes is how much of the lit half faces us. Follow the monthly cycle, learn the names, and find out why the Moon is up in the daytime too.",[63],[69],[1037,1038,1039,1040,1041,1042,1043,1044,1045,1046,551,1047,1048,1049,1050,1051,1052],"moon","phases","new moon","full moon","crescent","gibbous","waxing","waning","lunar month","synodic","tithi","Purnima","Amavasya","terminator","earthshine","far side",[1054,1058,1062,1066,1070],{"depth":142,"revision":44,"title":1055,"subtitle":1056,"summary":1057,"estimatedMinutes":338,"reviewed":147,"reviewMethod":148},"The shape that changes — except it never does","Why the Moon looks different every night, and what is really going on","Meet the Moon's monthly cycle: borrowed sunlight, a ball that is always half lit, and eight named phases. Learn to tell waxing from waning tonight, find out why the Moon is up in the daytime, and kill the biggest myth in astronomy — that the phases are Earth's shadow.",{"depth":150,"revision":44,"title":1059,"subtitle":1060,"summary":1061,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Reading the Moon: one angle explains everything","Elongation, lit fraction, rise times, the terminator and why one face always faces us","Turn the phase picture into a tool. Learn to go from the Sun-Earth-Moon angle to the shape, the fraction lit and the rise and set times; find out why craters show best at quarter moon, what earthshine is, and why the Moon keeps one face towards Earth.",{"depth":156,"revision":44,"title":1063,"subtitle":1064,"summary":1065,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Put the Moon on trial","Eight investigations, from an orange and a lamp to a month-long diary","Stop reading and start checking. Build a working model of the phases with a ball and a lamp, keep a month-long moon diary, measure the fifty-minute daily lag against your own rooftop, hunt earthshine, and predict a festival moonrise well enough to announce it.",{"depth":162,"revision":44,"title":1067,"subtitle":1068,"summary":1069,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"The chase, the wobble and the brake","Deriving 29.53 days, the elastic tithi, adhik maas, eclipse rarity and the recession, from first principles","Go past the rules to the reasoning: derive the synodic month from two orbital speeds, see why a tithi stretches and shrinks, work out how often adhik maas is needed, derive eclipse rarity from the 5.1-degree tilt, and follow the torque that locked the Moon and is now pushing it away.",{"depth":168,"revision":44,"title":1071,"subtitle":1072,"summary":1073,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"To the wobble, the far side and the far future","Libration, Chandrayaan-3 and the south pole, deep time, other calendars, puzzles and open questions","Push past the settled parts of the topic: measure libration for yourself, trace the far side from Luna 3 to Chandrayaan-3, work out why total eclipses have an expiry date, compare world calendars, and take on puzzles and open questions nobody has fully answered.",{"count":486,"sections":233,"levels":1075},{"foundation":284,"core":387,"stretch":337,"challenge":826},{"id":1077,"slug":1077,"title":1078,"question":1079,"promise":1080,"domains":1081,"areas":1082,"keywords":1083,"status":139,"layers":1102,"questionBank":1123},"prime-and-composite","Prime and composite numbers","Why are some numbers impossible to split into equal groups?","Factors and multiples, prime and composite numbers, the Sieve of Eratosthenes, divisibility tests, twin primes and co-primes.",[11],[21],[1084,1085,1086,1087,1088,609,1089,1090,604,1091,1092,1093,1094,1095,1096,1097,1098,1099,1100,1101],"prime number","composite number","factor","multiple","twin primes","sieve of Eratosthenes","divisibility rules","factor tree","1 is neither","relatively prime","prime triplet","trial division","fundamental theorem of arithmetic","Euclid","Goldbach conjecture","Mersenne prime","perfect number","periodical cicadas",[1103,1107,1111,1115,1119],{"depth":142,"revision":44,"title":1104,"subtitle":1105,"summary":1106,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Numbers that will not make rectangles","Factors, multiples and the numbers that can only stand in a single line","Share laddoos, set out chairs and build rectangles from tiles to meet factors and multiples. Discover prime numbers, composite numbers, the odd case of 1, the Sieve of Eratosthenes, twin primes and co-primes.",{"depth":150,"revision":44,"title":1108,"subtitle":1109,"summary":1110,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Factors, primes and how to test them","Precise definitions, reliable methods and the mix-ups to avoid","Find every factor with the factor-pair method, sieve to 100 and see why you can stop at 7, test any number for primality by trial division up to its square root, use divisibility rules, and meet twin primes, co-primes and factor trees.",{"depth":156,"revision":44,"title":1112,"subtitle":1113,"summary":1114,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"Hunting patterns among the primes","Predict, test and decide: which prime patterns are real, and which ones fool you?","Test claims about primes like a mathematician: how fast primes thin out, the 6-column grid, last digits, twin prime hunts, why 3, 5, 7 stands alone, co-prime experiments, patterns that break, prime deserts and numbers with the most factors.",{"depth":162,"revision":44,"title":1116,"subtitle":1117,"summary":1118,"estimatedMinutes":226,"reviewed":147,"reviewMethod":148},"Why it all works: proofs about primes","Unique factorisation, the square-root rule, the reasons behind divisibility tests, and Euclid’s endless primes","Prove that every number is built from primes in exactly one way, see a world where that fails, count factors from a factorisation, explain the square-root rule and every divisibility test, follow Euclid’s proof that primes never end, and prove facts about co-primes and twin primes.",{"depth":168,"revision":44,"title":1120,"subtitle":1121,"summary":1122,"estimatedMinutes":334,"reviewed":147,"reviewMethod":148},"Primes in the wild: cicadas, codes and unsolved puzzles","From insect life cycles and online banking to record primes, perfect numbers and problems nobody has solved","Take primes into the world: prime cicada cycles, the prime-based codes behind online payments, Mersenne primes and perfect numbers, Goldbach’s and the twin prime conjectures, Indian mathematicians, other number bases, olympiad puzzles and projects.",{"count":173,"sections":233,"levels":1124},{"foundation":235,"core":236,"stretch":176,"challenge":233},{"id":1126,"slug":1126,"title":1127,"question":1128,"promise":1129,"domains":1130,"areas":1131,"keywords":1132,"status":139,"layers":1153,"questionBank":1174},"properties-of-numbers","Properties of numbers","Why does 7 × 8 equal 8 × 7, and how can such rules make mental maths easy?","The closure, commutative, associative and distributive properties, the special roles of 0 and 1, and how they turn hard calculations into easy ones.",[11],[17],[1133,1134,1135,1136,1137,1138,1139,1140,1141,1142,1143,1144,1145,1146,1147,1148,1149,1150,1151,1152],"commutative","associative","distributive","closure","identity","additive identity","multiplicative identity","natural numbers","whole numbers","number line","mental maths","properties of zero","properties of one","division by zero","even and odd","counterexample","always sometimes never","area model","integers","clock arithmetic",[1154,1158,1162,1166,1170],{"depth":142,"revision":44,"title":1155,"subtitle":1156,"summary":1157,"estimatedMinutes":338,"reviewed":147,"reviewMethod":148},"Rules that numbers always follow","Turn-around facts, friendly groups, breaking apart and the magic of 0 and 1","Meet the properties of numbers through chairs, laddoos, kirana bills and socks: why 4 × 6 = 6 × 4, why you can add in any order, how breaking numbers apart makes sums easy, and what 0 and 1 do.",{"depth":150,"revision":44,"title":1159,"subtitle":1160,"summary":1161,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"The properties, precisely","Closure, commutative, associative and distributive laws, and the special numbers 0 and 1","State each property of whole numbers exactly, in words and with letters; see why it holds for + and × but fails for − and ÷; learn why division by zero is undefined; and use the properties for fast, reliable mental maths.",{"depth":156,"revision":44,"title":1163,"subtitle":1164,"summary":1165,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Always, sometimes or never?","Predict, test and explain: counterexamples, grouping gaps, parity patterns and shortcut showdowns","Test claims about whole numbers the way mathematicians do: predict, hunt for counterexamples, measure how badly subtraction and division fail to swap or regroup, discover patterns and shortcuts, and explain why the true ones must be true.",{"depth":162,"revision":44,"title":1167,"subtitle":1168,"summary":1169,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"Why the rules must be true","Proofs with arrays and boxes, the distributive law behind every method, zero through history, and the road to algebra","Prove the commutative, associative and distributive laws for every whole number, see why long multiplication and divisibility tests work, show why division by zero would make 0 = 1, prove parity facts with letters, and meet the properties as the rules of algebra.",{"depth":168,"revision":44,"title":1171,"subtitle":1172,"summary":1173,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"Properties beyond the whole numbers","Integers, fractions, clocks, computers, puzzles and the problems nobody has solved","Take the properties into new worlds: integers and fractions that repair closure, clock arithmetic, non-commutative everyday actions, rounding inside computers, olympiad puzzles built on parity and the distributive law, projects to try and open questions like Goldbach.",{"count":1175,"sections":385,"levels":1176},85,{"foundation":237,"core":212,"stretch":284,"challenge":174},{"id":1178,"slug":1178,"title":1179,"question":1180,"promise":1181,"domains":1182,"areas":1183,"keywords":1184,"status":139,"layers":1204,"questionBank":1225},"shape-and-space","Shape and space","What makes a square a square, and how many edges does a cube really have?","2D shapes and their properties, 3D solids and their faces, edges and vertices, nets, views from different sides, and symmetry.",[11],[29],[1185,1186,1187,1188,1189,1190,1191,708,1192,1193,1194,1195,1196,1197,1198,1199,1200,1201,1202,1203],"polygon","triangle","quadrilateral","circle","diagonals","cube","cuboid","pyramid","faces edges vertices","net","views","line symmetry","rotational symmetry","Euler","Platonic solids","tangram","tessellation","2D","3D",[1205,1209,1213,1217,1221],{"depth":142,"revision":44,"title":1206,"subtitle":1207,"summary":1208,"estimatedMinutes":338,"reviewed":147,"reviewMethod":148},"Shapes all around us","Flat shapes, solid shapes, and how to count, fold, view and mirror them","Meet 2D and 3D shapes through things you know: carrom boards, dice, laddoos, honeycombs, the Ashoka Chakra and the Taj Mahal. Learn to name polygons, count faces, edges and corners, unfold a box into a net, and find lines of symmetry.",{"depth":150,"revision":44,"title":1210,"subtitle":1211,"summary":1212,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Naming shapes precisely","Definitions, properties and the mix-ups they clear up","Give every shape an exact definition: polygons and diagonals, triangles by sides and angles, the quadrilateral family tree, the parts of a circle, perimeter, prisms and pyramids, nets, views and line symmetry, with worked examples and common mix-ups.",{"depth":156,"revision":44,"title":1214,"subtitle":1215,"summary":1216,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Test it, fold it, count it","Predictions and experiments with diagonals, triangles, nets, views, symmetry and π","Predict, then test: how fast diagonals multiply, which three sticks make a triangle, what polygon angles add up to, which statements are always true, the F + V − E pattern, which six-square shapes fold into a cube, symmetry in letters, measuring π and which shapes tile a floor.",{"depth":162,"revision":44,"title":1218,"subtitle":1219,"summary":1220,"estimatedMinutes":472,"reviewed":147,"reviewMethod":148},"Why shapes behave as they do","Proofs, edge cases and history: diagonals, angle sums, inequality, Euler and symmetry","Turn patterns into proofs: the diagonal formula, why angles add to 180° and (n − 2) × 180°, the triangle inequality, quadrilateral inheritance, why wheels are round, a sketch proof of Euler’s formula and where it fails, cube-net rules, symmetry orders, and the history of π.",{"depth":168,"revision":44,"title":1222,"subtitle":1223,"summary":1224,"estimatedMinutes":226,"reviewed":147,"reviewMethod":148},"Projects, puzzles and the wider world of shape","Platonic solids, all 11 cube nets, rotational symmetry, tilings, olympiad problems and open questions","Build the five Platonic solids and hunt all 11 cube nets, design rangoli with rotational symmetry, explore tangram paradoxes and semi-regular tilings, count a football, see geometry in Indian monuments and nature, solve olympiad-style problems, and meet questions still unsolved.",{"count":232,"sections":233,"levels":1226},{"foundation":284,"core":636,"stretch":284,"challenge":238},{"id":1228,"slug":1228,"title":52,"question":1229,"promise":1230,"domains":1231,"areas":1232,"keywords":1233,"status":139,"layers":1252,"questionBank":1273},"sound","Why does a drum you cannot touch still reach your ears?","Sound is a vibration travelling through air, water and solids. Learn what makes a sound high or low, loud or soft, why space is silent, and how your ears turn shaking air into music.",[41],[51],[1228,1234,1235,1236,1237,1238,1239,1240,1241,1242,1243,1244,1245,1246,1247,1248,1249,1250,1251],"vibration","wave","pitch","frequency","amplitude","loudness","decibel","echo","medium","ultrasound","hertz","eardrum","resonance","speed of sound","noise","music","sonar","vacuum",[1253,1257,1261,1265,1269],{"depth":142,"revision":44,"title":1254,"subtitle":1255,"summary":1256,"estimatedMinutes":338,"reviewed":147,"reviewMethod":148},"Everything that sounds is shaking","Find the vibration behind every sound, follow it to your ear, and learn why space is silent","Feel your own throat buzz, watch a tuning fork throw water, and follow the shaking from a tabla skin across the room to the hair cells in your ear. Meet pitch, loudness, echoes and the thunder rule, and find out why nothing at all can be heard in space.",{"depth":150,"revision":44,"title":1258,"subtitle":1259,"summary":1260,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"Compressions, rarefactions and the wave equation","What is really travelling, how fast, and how the ear turns it into a signal","See what a sound wave actually is: a train of squashed and stretched air marching outwards. Meet longitudinal waves on a slinky, the equation v = f × λ, why steel beats air by seventeen times, how decibels multiply, and the engineering of the human ear.",{"depth":156,"revision":44,"title":1262,"subtitle":1263,"summary":1264,"estimatedMinutes":212,"reviewed":147,"reviewMethod":148},"Predict it, try it: resonance, echoes and everyday sound technology","Test resonance with a swing and a singing glass, then use echoes the way sonar, ultrasound, bats and dolphins do","Push a swing at the wrong rhythm, make a wine glass sing, and find the sympathetic strings that ring inside a sitar untouched. Time an echo the way sonar and a hospital scanner do, compare a bat's call with a dolphin's, and see why India's noise rules are stricter near a hospital than in a market.",{"depth":162,"revision":44,"title":1266,"subtitle":1267,"summary":1268,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Why resonance, harmonics and reverberation work the way they do","Damping, aeroelastic flutter, singing granite pillars, harmonics and a physicist with 300 cushions","Find out why resonance cannot grow forever, why two famous bridge wobbles had different causes, and why 56 granite pillars at Hampi ring with different notes. Meet Wallace Sabine, who found the reverberation formula with borrowed cushions, and the arithmetic of combining decibels.",{"depth":168,"revision":44,"title":1270,"subtitle":1271,"summary":1272,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Doppler shifts, digital recording and listening to the Earth","The physics of a passing siren, why your recorded voice sounds strange, and how earthquakes get located","Work out how much a siren's pitch shifts as it passes, find out why your recorded voice sounds strange (a real anatomical reason), and see why 44,100 Hz was not an arbitrary choice. Try two projects, solve combined puzzles, and use sound's own reasoning to locate an earthquake.",{"count":687,"sections":233,"levels":1274},{"foundation":388,"core":927,"stretch":337,"challenge":233},{"id":1276,"slug":1276,"title":1277,"question":1277,"promise":1278,"domains":1279,"areas":1280,"keywords":1281,"status":139,"layers":1284,"questionBank":1309},"the-digestive-system","The digestive system","How digestive system work, what are various parts.",[77],[83],[1282,1283],"digestive","system",[1285,1290,1295,1300,1304],{"depth":142,"revision":44,"title":1286,"subtitle":1287,"summary":1288,"estimatedMinutes":734,"reviewed":1289,"reviewMethod":437},"From Bite to Flush: Your Food's Journey","How your body breaks a roti into the tiny packets your cells can use.","This lesson follows food from the first bite to the final exit, meeting each organ that cuts, dissolves and absorbs it. You will learn why digestion is really a long assembly line of physical crushing and chemical dissolving.",false,{"depth":150,"revision":44,"title":1291,"subtitle":1292,"summary":1293,"estimatedMinutes":1294,"reviewed":1289,"reviewMethod":437},"Food's Journey: From Bite to Energy","How your digestive system breaks down every meal into the nutrients that power your body","This lesson follows food from the first bite to the final exit, explaining how each organ mechanically and chemically transforms food into absorbable nutrients. Learners will distinguish digestion from absorption and clear up common misconceptions about which organs do what.",39,{"depth":156,"revision":44,"title":1296,"subtitle":1297,"summary":1298,"estimatedMinutes":1299,"reviewed":1289,"reviewMethod":437},"How Your Body Unpacks a Meal","An engineer's journey through the digestive tract: break, mix, absorb, and adapt","Follow food from bite to bloodstream and discover how each digestive organ changes conditions to speed or slow the work. Use a model gut to test how chewing, enzymes, and diet type shape what your body can extract.",51,{"depth":162,"revision":44,"title":1301,"subtitle":1302,"summary":1303,"estimatedMinutes":472,"reviewed":1289,"reviewMethod":437},"Journey Through the Gut: How Your Body Turns Food into Fuel","From the first bite to the bloodstream — the mechanics, chemistry, and math of human digestion","Follow a meal through the human digestive tract to see how mechanical churning, enzymes, and acids break food into absorbable nutrients. Learn why villi matter more than you think, and how your body coordinates every step.",{"depth":168,"revision":44,"title":1305,"subtitle":1306,"summary":1307,"estimatedMinutes":1308,"reviewed":1289,"reviewMethod":437},"From Bite to Bloodstream: The Journey of a Meal","How mechanical forces, chemical reactions, and specialised organs transform the food on your plate into fuel for your bo","This lesson follows a complete meal through the human digestive tract, explaining how each organ contributes to mechanical and chemical breakdown, how enzymes speed up reactions, and how lifestyle choices affect this process. It includes a design challenge for testing enzyme acti",47,{"count":824,"sections":66,"levels":1310},{"foundation":826,"core":337,"stretch":787,"challenge":385},{"id":560,"slug":560,"title":1312,"question":1313,"promise":1314,"domains":1315,"areas":1316,"keywords":1317,"status":139,"layers":1334,"questionBank":1355},"Tides","Why does the sea climb up the beach and slide back, twice a day, forever?","The Moon's pull stretches the ocean into two bulges and Earth turns through them. Learn why there are two high tides a day, why they arrive later each day, and what makes a spring tide.",[63],[73],[1318,1319,1320,1321,1322,1323,1324,541,1325,1326,1327,1328,1329,1330,1331,1332,1333],"tide","high tide","low tide","spring tide","neap tide","tidal range","bulge","Moon","Sun","tidal bore","estuary","tide table","coast","fishing","Chandipur","Hooghly",[1335,1339,1343,1347,1351],{"depth":142,"revision":44,"title":1336,"subtitle":1337,"summary":1338,"estimatedMinutes":338,"reviewed":147,"reviewMethod":148},"Tides: the sea's daily rise and fall","Why the whole ocean leans towards the Moon, twice a day, forever","Meet the tide: not a wave but the whole sea rising and falling. Find out how the Moon's pull makes two bulges, why most coasts get two high tides a day, why the tide is 50 minutes later each day, and what spring and neap tides are.",{"depth":150,"revision":44,"title":1340,"subtitle":1341,"summary":1342,"estimatedMinutes":166,"reviewed":147,"reviewMethod":148},"How the Moon builds two bulges","Difference, not strength: the mechanism behind every tide","Work out why a pull towards the Moon makes a bulge away from it, where 24 h 50 min comes from, why the Sun's tide is only 46% of the Moon's, and why the same Moon gives Kochi one metre and Bhavnagar ten.",{"depth":156,"revision":44,"title":1344,"subtitle":1345,"summary":1346,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Investigate: predicting, classifying and staying safe","Test the ideas from Understand against a real tide table, real coasts and real disasters","Predict and check a day of tide heights, learn to tell semidiurnal, diurnal and mixed tides apart, meet the Hooghly bore and storm surges, see how tidal power and INCOIS's predictions work, and test the funnelling and resonance ideas with real numbers.",{"depth":162,"revision":44,"title":1348,"subtitle":1349,"summary":1350,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Deepen: the mathematics and history behind a tide table","Newton, Laplace, harmonic waves, closed-pipe resonance, and the physics of a bore","Trace the two-hundred-year path from Newton's equilibrium theory to Laplace's ocean waves and Kelvin's tide-predicting machine, meet the harmonic constituents that a real tide is built from, derive why a bay resonates at a quarter wavelength, and quantify Earth's own solid and atmospheric tides.",{"depth":168,"revision":44,"title":1352,"subtitle":1353,"summary":1354,"estimatedMinutes":217,"reviewed":147,"reviewMethod":148},"Extend: deep time, deep space, and open questions","Tidal friction across hundreds of millions of years, tides on other worlds, and what is still unknown","Follow tidal friction from a subtle offset in Earth's bulge to a shorter Cretaceous day, a measurably receding Moon, tidal heating on Io, Europa and Enceladus, and a set of open questions and careers built on this one idea.",{"count":1356,"sections":385,"levels":1357},71,{"foundation":786,"core":283,"stretch":284,"challenge":174},[1359,1362,1364,1367,1369,1371,1373,1375,1377,1379,1381,1383,1386,1389,1391,1393,1395,1397,1399,1401,1403,1405,1407,1409,1411,1413,1415,1417,1419,1421,1423,1425,1427,1429,1431,1433,1435,1437,1439,1441,1443,1445,1447,1449,1451,1453,1455,1457,1459,1461,1463,1465],{"from":929,"to":489,"relation":1360,"reason":1361},"helps_understand","Place value is what makes column addition, carrying and long division work.",{"from":929,"to":287,"relation":1360,"reason":1363},"Reading, comparing and rounding numbers comes first when you sort data and round a mean.",{"from":929,"to":877,"relation":1365,"reason":1366},"related_to","Place-value charts are full of patterns: each place is ten times the one to its right.",{"from":1126,"to":489,"relation":1360,"reason":1368},"Commutative, associative and distributive properties are the shortcuts behind fast, accurate calculation.",{"from":1126,"to":980,"relation":1360,"reason":1370},"The distributive property explains why multiplication is done before addition and how brackets change a result.",{"from":1126,"to":877,"relation":1365,"reason":1372},"Many number patterns — like the sum of consecutive odd numbers — are properties of numbers in disguise.",{"from":489,"to":980,"relation":1360,"reason":1374},"Once each operation is reliable, the next question is which one to do first when several appear together.",{"from":489,"to":1077,"relation":1360,"reason":1376},"Testing whether a number is prime is just careful division: does anything divide it exactly?",{"from":489,"to":287,"relation":1360,"reason":1378},"Finding a mean means adding every value and dividing by how many there are.",{"from":980,"to":877,"relation":1365,"reason":1380},"A pattern rule such as 3 × n + 1 is an expression — you need the order of operations to use it.",{"from":1077,"to":588,"relation":1360,"reason":1382},"Prime factorisation is the fastest route to both the HCF and the LCM.",{"from":1077,"to":877,"relation":1384,"reason":1385},"contrasts_with","Primes famously refuse to follow a simple pattern, unlike even numbers, squares or multiples.",{"from":588,"to":877,"relation":1387,"reason":1388},"applied_in","Two repeating cycles line up again after their LCM — the pattern behind blinking lights and bus timetables.",{"from":588,"to":1178,"relation":1387,"reason":1390},"The largest square tile that fits a rectangular floor exactly has a side equal to the HCF of its length and width.",{"from":877,"to":1178,"relation":1365,"reason":1392},"Growing shape patterns — matchstick squares, dot triangles — are geometry and number at the same time.",{"from":1178,"to":739,"relation":1365,"reason":1394},"Every polygon is built from line segments, and its sides can be parallel or perpendicular.",{"from":1178,"to":180,"relation":1365,"reason":1396},"The corners of shapes are angles: a square has four right angles and a triangle's angles add to 180°.",{"from":739,"to":180,"relation":1360,"reason":1398},"An angle is two rays that share an end point; intersecting lines make angle pairs.",{"from":739,"to":828,"relation":1360,"reason":1400},"Constructions rely on drawing straight lines, perpendiculars and bisectors accurately.",{"from":180,"to":828,"relation":1360,"reason":1402},"Knowing angle types and pairs tells you what you are measuring and checks if your construction is sensible.",{"from":180,"to":287,"relation":1387,"reason":1404},"In a pie chart each slice's angle shows a share of the data: 360° stands for the whole.",{"from":828,"to":1178,"relation":1387,"reason":1406},"Drawing accurate triangles, squares and regular polygons needs measured or constructed angles.",{"from":287,"to":390,"relation":1387,"reason":1408},"A family's monthly electricity use varies; the mean, median and range of a year of bills show what is typical.",{"from":929,"to":390,"relation":1387,"reason":1410},"Power stations are rated in megawatts and India uses lakhs of crores of units a year: reading such numbers needs place value and the Indian system.",{"from":489,"to":390,"relation":1387,"reason":1412},"An electricity bill is units × rate per unit, plus fixed charges, minus subsidies — all four operations in one sheet of paper.",{"from":180,"to":390,"relation":1387,"reason":1414},"A generator's coil turns through 360° every cycle — 50 full turns a second on India's 50 Hz supply.",{"from":1077,"to":390,"relation":1387,"reason":1416},"The encryption that protects smart meters and grid control systems relies on the difficulty of factorising huge numbers into primes.",{"from":690,"to":340,"relation":1360,"reason":1418},"An eclipse is a shadow, and shadows need light that travels in straight lines.",{"from":690,"to":1030,"relation":1360,"reason":1420},"The Moon has no light of its own: we see the half of it the Sun is lighting.",{"from":690,"to":112,"relation":1387,"reason":1422},"The eye is a lens, a screen and a shutter — optics built out of living tissue.",{"from":690,"to":1228,"relation":1384,"reason":1424},"Both travel as waves and carry energy, but light needs no material and races a million times faster than sound.",{"from":1228,"to":112,"relation":1387,"reason":1426},"The ear turns shaking air into signals a nerve can carry: a drum, three tiny bones and a spiral of fluid.",{"from":541,"to":1030,"relation":1360,"reason":1428},"Gravity is what keeps the Moon in the orbit that produces the monthly cycle of phases.",{"from":541,"to":560,"relation":1360,"reason":1430},"Tides are gravity made visible: the Moon pulls the near ocean harder than the far ocean.",{"from":541,"to":340,"relation":1360,"reason":1432},"Eclipses happen only because the Sun, Earth and Moon move on fixed gravitational paths we can predict.",{"from":1030,"to":340,"relation":1360,"reason":1434},"Eclipses can only happen at new moon or full moon — the two phases where the three bodies line up.",{"from":1030,"to":560,"relation":1365,"reason":1436},"Spring and neap tides follow the phases: the biggest tides come at new and full moon.",{"from":112,"to":240,"relation":1360,"reason":1438},"Once you know where each organ sits, you can follow how they pass work to each other.",{"from":240,"to":541,"relation":1365,"reason":1440},"Bones, muscles and blood pressure are all built for a life spent pulling against Earth's gravity — which is why astronauts weaken in orbit.",{"from":439,"to":638,"relation":1360,"reason":1442},"The empires that grew out of the voyages shaped the constitution and the freedoms India wrote for itself afterwards.",{"from":439,"to":560,"relation":1387,"reason":1444},"Sailing ships left harbour on the tide, and monsoon winds and currents set the whole calendar of Indian Ocean trade.",{"from":439,"to":1030,"relation":1387,"reason":1446},"Before clocks and satellites, the Moon and stars were how a navigator knew where they were.",{"from":638,"to":287,"relation":1387,"reason":1448},"A census, an election result and a budget are all data: counted, summarised and argued over.",{"from":638,"to":929,"relation":1387,"reason":1450},"Election results and budgets are read in lakhs and crores — place value with real consequences.",{"from":690,"to":390,"relation":1365,"reason":1452},"A bulb, an LED and a solar panel are all conversions between electricity and light.",{"from":1228,"to":390,"relation":1365,"reason":1454},"Microphones and speakers turn sound into current and current back into sound.",{"from":439,"to":1178,"relation":1387,"reason":1456},"Maps, globes and navigation are geometry: a round Earth flattened onto paper without lying too much.",{"from":340,"to":180,"relation":1387,"reason":1458},"Whether an eclipse is total or partial comes down to angles: the Moon's tilted orbit and the apparent size of two discs.",{"from":560,"to":287,"relation":1387,"reason":1460},"A tide table is a data set: measure the water twice a day for years, and the pattern lets you predict it.",{"from":112,"to":287,"relation":1387,"reason":1462},"Heart rate, height and lung capacity across a class are real data to collect, average and compare.",{"from":541,"to":489,"relation":1387,"reason":1464},"Weight on another world is your mass times that world's gravity — multiplication with an astonishing answer.",{"from":240,"to":287,"relation":1387,"reason":1466},"Pulse and breathing rate before and after exercise are real class data to average, compare and graph.",[],[],[],{"layer":1471,"contentHash":2647,"dependencyHashes":2648,"approval":2649,"releaseId":2651,"sources":2652},{"schemaVersion":44,"conceptId":1276,"locale":1472,"depth":168,"revision":44,"title":1305,"subtitle":1306,"summary":1307,"objectives":1473,"estimatedMinutes":1308,"plate":1479,"blocks":1499,"sourceIds":2642,"reviewStatus":2643,"authoring":2644},"en",[1474,1475,1476,1477,1478],"Analyze how mechanical and chemical digestion work together to break down food into absorbable nutrients.","Compare the structure and function of each major digestive organ and explain how they interconnect.","Design an investigation to test factors affecting enzyme activity in the stomach or small intestine.","Evaluate how lifestyle choices or disorders impact digestive efficiency and overall health.","Construct an accurate model or diagram showing the path of food through the entire digestive tract with labeled processes.",{"title":1480,"rows":1481},"Extend",[1482,1484,1487,1490,1493,1496],{"label":1483,"value":1480},"Depth",{"label":1485,"value":1486},"Reading time","About 47 minutes",{"label":1488,"value":1489},"Chapters","10",{"label":1491,"value":1492},"Prior knowledge","Cells, tissues, basic chemistry of acids and bases, enzymes",{"label":1494,"value":1495},"Activities","Build a peristalsis model; design a pepsin activity investig",{"label":1497,"value":1498},"Core sources","NCERT Class 7 Science, Chapter 2; Human digestive system; Hu",[1500,1504,1510,1513,1519,1541,1552,1572,1590,1593,1598,1601,1625,1629,1639,1674,1698,1703,1706,1711,1714,1733,1738,1741,1751,1755,1777,1780,1785,1788,1812,1817,1820,1855,1866,1870,1892,1897,1900,1922,1931,1935,1960,1963,1980,1983,1988,1991,2007,2011,2041,2051,2055,2077,2080,2111,2121,2126,2129,2133,2156,2170,2174,2184,2208,2234,2256,2259,2264,2267,2301,2305,2315,2318,2341,2344,2349,2352,2356,2361,2371,2395,2414,2441,2446,2449,2557,2560,2564,2575,2588,2635],{"id":1501,"type":1502,"markdown":1503},"prose-1","prose","Every time you eat a dosa, a samosa, or a mango, your body performs an extraordinary transformation. That solid food must become tiny molecules that can slip through your gut wall into your blood — otherwise, it might as well stay on the plate. This journey, called digestion, involves crushing, soaking, dissolving, and chemical chopping that takes over 24 hours to complete.\n\nIn this lesson, you will travel with a bite of food from mouth to large intestine, understanding not just *what* each organ does, but *how* it works. You will design a real experiment to test how stomach enzymes behave, and you will judge how common habits — skipping breakfast, eating too fast, or drinking very little water — change the efficiency of your own digestive system.",{"id":1505,"type":1506,"title":1507,"eyebrow":1508,"navLabel":1509},"chapter-2","chapter","The Unnoticed Work of Eating: What Happens Before Swallowing","Chapter 01","Where digestion begins",{"id":1511,"type":1502,"markdown":1512},"prose-3","You have just finished your lunch—maybe roti, dal, and a piece of mango. You swallow, and the food is gone from your mind. But your body has only begun. Before that first gulp even leaves your mouth, a hidden factory has already started dismantling your meal. This chapter is about the unnoticed work: what happens between the first bite and the moment the food slides down your throat. We will see why chewing matters more than most people think, how saliva is a chemical tool and not just spit, and why a soft ball called a bolus is one of the cleverest pieces of food engineering your body performs.",{"id":1514,"type":1515,"variant":1516,"title":1517,"markdown":1518},"callout-4","callout","misconception","Wrong: digestion starts in the stomach","Many people believe the stomach is where digestion begins. It is not. The moment starch from your roti, rice, or potato touches your tongue, salivary amylase starts clipping long starch chains into shorter sugar pieces. If you swallow too quickly, you miss this early chemical head start. The stomach's acid later *stops* amylase activity, so the mouth is your only chance for this particular starch attack.",{"id":1520,"type":1521,"title":1522,"items":1523},"steps-5","steps","From bite to bolus in your mouth",[1524,1528,1532,1535,1538],{"title":1525,"tag":1526,"text":1527},"Bite and tear","mechanical","Incisors slice, canines grip, molars grind. Food is crushed into smaller fragments.",{"title":1529,"tag":1530,"text":1531},"Saliva floods in","chemical","Three pairs of salivary glands release water, mucus, and salivary amylase. About 1–1.5 litres of saliva are produced per day.",{"title":1533,"tag":1530,"text":1534},"Enzyme attack begins","Salivary amylase starts breaking starch into maltose, a smaller sugar. This only works in the mouth's neutral pH.",{"title":1536,"tag":1526,"text":1537},"Tongue shapes the bolus","The tongue presses food against the palate, mixing and rolling it into a soft, slippery ball.",{"title":1539,"text":1540},"Swallowing trigger","Once the bolus is smooth and small enough, the brain triggers swallowing. The epiglottis covers your windpipe so food enters the oesophagus, not your lungs.",{"id":1542,"type":1543,"title":1544,"problem":1545,"steps":1546},"worked-example-6","worked_example","How Chewing Affects Surface Area","A child swallows a single cube of boiled potato measuring 1 cm on each side. Her sister chews the same size cube into 64 tiny cubes, each 2.5 mm (0.25 cm) on a side. How much more starch-exposing surface area did the sister create?",[1547,1548,1549,1550,1551],"Calculate the surface area of the original cube: 6 faces × (1 cm × 1 cm) = 6 cm².","Each small cube has side 0.25 cm. Surface area of one small cube = 6 × (0.25 cm × 0.25 cm) = 6 × 0.0625 cm² = 0.375 cm².","Total surface area of 64 small cubes = 64 × 0.375 cm² = 24 cm².","Compare: 24 cm² ÷ 6 cm² = 4. The chewed potato has 4 times the surface area of the swallowed cube.","More surface area means more starch molecules are exposed to salivary amylase at once, so chemical breakdown starts faster and more thoroughly before the food reaches the stomach.",{"id":1553,"type":1554,"tone":1555,"items":1556},"spec-7","spec","amber",[1557,1560,1563,1566,1569],{"label":1558,"value":1559},"Saliva per day","1 to 1.5 litres",{"label":1561,"value":1562},"Salivary amylase optimal pH","around 7 (neutral)",{"label":1564,"value":1565},"Average chews per bite","5 to 10 times",{"label":1567,"value":1568},"Recommended thorough chews","20 to 30 times",{"label":1570,"value":1571},"Time saliva needs to work","about 30 seconds to 1 minute",{"id":1573,"type":1574,"prompt":1575,"options":1576,"explanation":1589},"prediction-8","prediction","You eat two identical platefuls of plain rice. On Monday you chew each bite 5 times and swallow quickly. On Tuesday you chew each bite 25 times. What is the most likely difference in how your body handles the two meals?",[1577,1580,1583,1586],{"id":1578,"label":1579},"a","The Tuesday meal reaches your bloodstream as glucose much faster because chewing releases insulin directly from the jaw.",{"id":1581,"label":1582},"b","The Monday meal gives you more vitamins because less chewing preserves fragile nutrients.",{"id":1584,"label":1585},"c","The Tuesday meal has more starch broken down early, so your stomach and small intestine do less work overall.",{"id":1587,"label":1588},"d","There is no difference; the stomach acid completely replaces whatever the mouth started.","Option c is correct. More chewing exposes more starch surface area to salivary amylase, so more starch is pre-digested into sugars before reaching the stomach. This does not mean glucose enters your bloodstream instantly—insulin is not released by chewing—but it does reduce the workload for later digestive organs. Option a confuses chewing with an insulin trigger. Option b is wrong because vitamins are not destroyed by chewing. Option d repeats the common misconception: stomach acid actually *stops* amylase, so the mouth's head start is lost forever if you swallow too fast.",{"id":1591,"type":1502,"markdown":1592},"prose-9","Think of your mouth as a kitchen prep station. A chef who throws whole potatoes into a pot will wait hours for them to cook through. A chef who dices them finely gets even cooking in minutes. Your enzymes are like heat: they work best when they can reach every corner. Chewing is your knife. The bolus is your carefully portioned dumpling, shaped so it will slide down the right pipe. Every swallow you take without chewing thoroughly is a missed opportunity to let your mouth do work your stomach would otherwise have to handle later. In the next chapter, we will follow that bolus into a muscular highway with no wheels: the oesophagus.",{"id":1594,"type":1506,"title":1595,"eyebrow":1596,"navLabel":1597},"chapter-10","The Oesophagus: A Muscular Highway with No Wheels","Chapter 02","Swallowing and peristals",{"id":1599,"type":1502,"markdown":1600},"prose-11","You have just bitten into a warm aloo paratha. Chewing turns it into a soft, wet lump called a **bolus** — a term that simply means a rounded mass of food ready for swallowing. Once you swallow, the bolus does not fall down into your stomach like water poured into a funnel. Instead, it enters a muscular tube about 25 cm long in adults: the **oesophagus** (or food pipe). This tube runs behind your windpipe, through your chest, and passes through a dome-shaped muscle called the **diaphragm** before reaching your stomach. The oesophagus has no bones, no cilia like your windpipe, and no gravity-fed slope. Yet it moves every swallowed bite reliably downward, whether you are standing in a cricket field, lying flat on a train berth, or doing a handstand. The secret is a process called **peristalsis** — a coordinated wave of muscle contractions that squeezes the bolus along like toothpaste through a tube.",{"id":1602,"type":1521,"title":1603,"items":1604},"steps-12","How peristalsis moves one bolus",[1605,1609,1613,1617,1621],{"title":1606,"tag":1607,"text":1608},"Step 1: Circular muscles behind contract","Squeeze","Muscles in the oesophagus wall just behind the bolus tighten, narrowing the tube and pushing the food forward.",{"title":1610,"tag":1611,"text":1612},"Step 2: Circular muscles ahead relax","Open path","Muscles in front of the bolus loosen, widening the tube so the bolus has somewhere to go.",{"title":1614,"tag":1615,"text":1616},"Step 3: The wave travels downward","Propagation","The contraction-relaxation pattern repeats like a travelling wave, moving the bolus about 2–4 cm each second.",{"title":1618,"tag":1619,"text":1620},"Step 4: Sphincter opens at the stomach","Gate","The lower oesophageal sphincter — a ring of muscle at the stomach entrance — relaxes to let the bolus enter.",{"title":1622,"tag":1623,"text":1624},"Step 5: Sphincter snaps shut","Seal","The sphincter contracts again, sealing the stomach to stop acidic contents from flowing back up.",{"id":1626,"type":1515,"variant":1516,"title":1627,"markdown":1628},"callout-13","\"Food just falls down because of gravity\"","Many people imagine the oesophagus as a simple slide. If that were true, astronauts in space would starve — yet they eat normally. On Earth, you can swallow water while standing on your head, and it still reaches your stomach. Experiments with X-ray tracking (using barium-labelled food) show the bolus moves upward briefly during neck extension, then continues downward regardless of body position. Gravity helps when you are upright, but peristalsis is the engine that works in every orientation.",{"id":1630,"type":1543,"title":1631,"problem":1632,"steps":1633},"worked-example-14","Timing a swallow from sip to stomach","An adult's oesophagus is about 25 cm long. Peristalsis moves a bolus at roughly 3 cm per second. How long does one swallow take to reach the stomach? And if the person stands on their head, does the time change?",[1634,1635,1636,1637,1638],"Write what you know: distance = 25 cm; speed = 3 cm\u002Fs.","Use the relationship: time = distance ÷ speed.","Calculate: 25 ÷ 3 ≈ 8.3 seconds. Round to about 8 seconds for a typical swallow.","Consider orientation: peristalsis is involuntary and gravity-independent. The circular muscle wave still contracts behind and relaxes ahead. So standing on your head does not change the time significantly.","Double-check: even with gravity assisting slightly when upright, the muscular wave dominates. The answer stays roughly 8 seconds either way.",{"id":1640,"type":1641,"caption":1642,"columns":1643,"rows":1648},"table-15","table","Oesophagus compared to a simple pipe and to the trachea",[1644,1645,1646,1647],"Feature","Oesophagus","A garden hose (gravity pipe)","Trachea (windpipe)",[1649,1654,1659,1664,1669],[1650,1651,1652,1653],"Wall structure","Muscular, can actively squeeze","Passive, no muscles","Held open by C-shaped cartilage rings",[1655,1656,1657,1658],"Movement of contents","Peristalsis: active wave","Flows down if tilted; stalls if flat","Cilia push mucus upward (!)",[1660,1661,1662,1663],"Direction control","Always toward stomach","Depends on tilt","Always toward mouth for mucus",[1665,1666,1667,1668],"Works upside down?","Yes","No flow without pressure","Still works — cilia beat upward",[1670,1671,1672,1673],"Sealing at bottom","Sphincter prevents backflow","Open end, no seal","No equivalent seal at bottom",{"id":1675,"type":1676,"itemId":1677,"prompt":1678,"check":1679,"hints":1691,"feedback":1695},"practice-16","practice","the-digestive-system.p001","Raj lies flat on his bed and drinks a glass of water. What is the MAIN reason the water still reaches his stomach?",{"kind":1680,"options":1681,"correct":1690},"choice",[1682,1684,1686,1688],{"id":1578,"label":1683},"Gravity pulls the water down because the bed is slightly tilted.",{"id":1581,"label":1685},"The water evaporates and condenses in the stomach.",{"id":1584,"label":1687},"Peristalsis in the oesophagus actively pushes it downward.",{"id":1587,"label":1689},"Air pressure from breathing forces it down.",[1584],[1692,1693,1694],"Think about what would happen in space with no gravity at all.","Remember which structure has walls made of muscle.","Consider whether gravity is necessary for swallowing.",{"correct":1696,"incorrect":1697},"Exactly. Peristalsis is an involuntary muscular wave that propels food and liquid regardless of body position — flat, upright, or even upside down.","Peristalsis is the key. Gravity may help when upright, but the muscular wave of the oesophagus is what moves the bolus. Even flat on a bed or in space, swallowing works.",{"id":1699,"type":1515,"variant":1700,"title":1701,"markdown":1702},"callout-17","careful","The sphincter is not a door you control","The lower oesophageal sphincter opens and closes automatically. You cannot will it open or shut. Sometimes it weakens or relaxes at the wrong time, letting stomach acid slip upward — this is **acid reflux** or heartburn. Eating very large meals, lying down immediately after eating, or excess pressure from tight clothing can make this more likely. The sphincter's automatic design normally keeps acid out of the oesophagus, but it is not perfect.",{"id":1704,"type":1502,"markdown":1705},"prose-18","Understanding peristalsis matters beyond biology class. Doctors treating patients who cannot swallow after a stroke use this knowledge to design exercises that strengthen the remaining muscle coordination. Engineers designing pill-sized cameras for stomach examination mimic peristalsis to move devices through the gut. And when ISRO plans long-duration space missions, they know astronauts need normal digestion without gravity — which is only possible because the oesophagus brings its own motor. The next time you swallow a sip of water before a cricket match, remember: you are not just letting it drop. You are launching it down a 25 cm muscular highway, driven by one of the most reliable transport systems in your body.",{"id":1707,"type":1506,"title":1708,"eyebrow":1709,"navLabel":1710},"chapter-19","The Stomach: Acid Kitchen and Protein Chopper","Chapter 03","Gastric digestion",{"id":1712,"type":1502,"markdown":1713},"prose-20","Think about the last time you ate rajma-chawal or a paneer roll. Between swallowing and feeling full, your food vanished into a silent, hidden room inside your body: the stomach. That room is roughly the size of your fist when empty, yet it can stretch to hold a litre or more after a festival meal. But the stomach is far more than a storage bag. It is a kitchen with three jobs: mash the food, flood it with acid strong enough to clean a old coin, and chop long protein chains into smaller pieces using a specialised enzyme called pepsin. In this chapter we will walk through each job, see why the stomach does not digest itself, and work through the chemistry of that acid bath.",{"id":1715,"type":1554,"tone":1555,"items":1716},"spec-21",[1717,1721,1725,1729],{"label":1718,"big":1719,"value":1720},"Internal pH","1.5–3.5","More acidic than lemon juice (pH ~2.2) or vinegar (pH ~2.5); close to battery acid.",{"label":1722,"big":1723,"value":1724},"Acid produced daily","2–3 litres","Of gastric juice, containing hydrochloric acid, mucus, salts, and pepsinogen.",{"label":1726,"big":1727,"value":1728},"Residence time","2–4 hours","For a mixed meal; liquids may leave faster, fatty meals slower.",{"label":1730,"big":1731,"value":1732},"Pepsin optimal pH","1.5–2","The enzyme works fastest here and becomes inactive above pH 5.",{"id":1734,"type":1515,"variant":1735,"title":1736,"markdown":1737},"callout-22","definition","Enzyme, substrate and active site","An **enzyme** is a protein molecule that speeds up a chemical reaction without being used up. The molecule it works on is called the **substrate**. Pepsin's substrate is protein from your food. The **active site** is the specific pocket on the enzyme where the substrate fits, like a key in a lock. The bond only forms when conditions—here, strong acid—are right.",{"id":1739,"type":1502,"markdown":1740},"prose-23","The acid comes from **gastric glands** in the stomach wall. Cells called **parietal cells** pump hydrogen ions (H⁺) into the stomach cavity using energy, creating hydrochloric acid. This is not a gentle trickle; it is an active, energy-consuming process, which is why you feel tired after a very large meal. Meanwhile, **chief cells** release an inactive precursor called **pepsinogen**. Only when pepsinogen meets the acid does it snap into its active form, pepsin. This safety catch prevents the enzyme from digesting the very cells that make it.",{"id":1742,"type":1543,"title":1743,"problem":1744,"steps":1745},"worked-example-24","Could stomach acid dissolve a steel nail?","Stomach acid is roughly 0.1 M HCl. A small iron nail has a mass of about 2 g. Hydrochloric acid reacts with iron to produce iron chloride and hydrogen gas. Suppose 1 litre of fresh gastric juice is present. Is there enough acid to dissolve the nail completely?",[1746,1747,1748,1749,1750],"The reaction is: Fe + 2 HCl → FeCl₂ + H₂. Each mole of iron needs 2 moles of HCl.","Molar mass of iron is about 56 g\u002Fmol. Moles of iron in the nail = 2 g ÷ 56 g\u002Fmol ≈ 0.036 mol.","Moles of HCl needed = 2 × 0.036 mol = 0.072 mol.","Available HCl = 0.1 mol (from 0.1 M in 1 litre). Since 0.1 > 0.072, there is barely enough acid in principle.","In reality, the stomach lining is protected by mucus, the nail would not sit in acid for days, and the body would neutralise pH spikes. Our calculation is a simplified model; it shows the acid is surprisingly strong, but conditions inside the stomach are controlled.",{"id":1752,"type":1515,"variant":1516,"title":1753,"markdown":1754},"callout-25","\"The stomach digests itself\"","It does not—normally. The inner surface is coated by a **mucus layer** half a millimetre thick, rich in bicarbonate that neutralises acid right at the wall. The stomach lining also replaces its surface cells every few days. Only when the mucus barrier fails does acid attack the wall, creating open sores called **ulcers**. For decades doctors blamed spicy food and stress; we now know the bacterium *Helicobacter pylori* is a major cause because it damages the mucus layer. Another cause is overuse of certain pain medicines (NSAIDs) that reduce protective prostaglandins.",{"id":1756,"type":1676,"itemId":1757,"prompt":1758,"check":1759,"hints":1770,"feedback":1774},"practice-26","the-digestive-system.p002","A test-tube contains a protein solution at pH 7. A student adds pepsin and keeps the tube at body temperature (37 °C). After 30 minutes, hardly any protein has broken down. What single change is most likely to make the enzyme active?",{"kind":1680,"options":1760,"correct":1769},[1761,1763,1765,1767],{"id":1578,"label":1762},"Add more pepsin",{"id":1581,"label":1764},"Add a little hydrochloric acid to lower the pH to 2",{"id":1584,"label":1766},"Raise the temperature to 50 °C",{"id":1587,"label":1768},"Shake the tube vigorously",[1581],[1771,1772,1773],"Remember where pepsin normally works.","Pepsin needs to be activated from pepsinogen. What triggers that?","The stomach is not neutral; think about its acidic environment.",{"correct":1775,"incorrect":1776},"Correct. Pepsin is inactive at pH 7 and only becomes fully active once the pH drops to around 1.5–2. Adding acid mimics the stomach conditions.","Not quite. Pepsin is already present; shaking or more enzyme won't help if conditions are wrong. And 50 °C would damage the protein structure. The missing factor is acid.",{"id":1778,"type":1502,"markdown":1779},"prose-27","After two to four hours of churning and acid chopping, the stomach releases its contents through the **pyloric sphincter**, a ring-shaped muscle that opens a few millimetres at a time. What exits is **chyme** (kime)—a creamy, semi-liquid acid soup of partly digested food. No longer recognisable as roti or sabzi, it enters the small intestine in squirts, where the next stage of chemical processing begins. The stomach's job is preparation, not completion: proteins are shortened but not absorbed, and carbohydrates and fats are barely touched. That division of labour keeps the system efficient and protects the delicate intestine from acid damage.",{"id":1781,"type":1506,"title":1782,"eyebrow":1783,"navLabel":1784},"chapter-28","How the Small Intestine Steals the Show","Chapter 04","Absorption centre",{"id":1786,"type":1502,"markdown":1787},"prose-29","If someone asked you to absorb all the nutrients from a full plate of rajma-chawal into your body through a surface the size of a postcard, you would call it impossible. Yet your small intestine does something close to this miracle every single day. Tightly coiled in your abdomen like a garden hose packed into a bucket, this roughly 6-metre tube is where digestion finishes and absorption begins in earnest. The stomach may get the fame for growling, but the small intestine is where the real work of feeding your cells happens. In this chapter, we will see how its shape, its partnerships with the liver and pancreas, and its microscopic architecture make it the star of the digestive show.",{"id":1789,"type":1554,"tone":1790,"items":1791},"spec-30","blue",[1792,1796,1800,1804,1808],{"label":1793,"big":1794,"value":1795},"Length (adult)","~6 m","Coiled in the abdomen; about 5× your body height if stretched",{"label":1797,"big":1798,"value":1799},"Surface multiplier","~600×","Compared to a smooth tube of the same length, due to folds, villi, and microvilli",{"label":1801,"big":1802,"value":1803},"Transit time","3–5 hr","How long a meal typically spends in the small intestine",{"label":1805,"big":1806,"value":1807},"Inner pH","7–8","Neutral to slightly alkaline, allowing enzyme action after the stomach's acid",{"label":1809,"big":1810,"value":1811},"Villi per square mm","20–40","Finger-like projections covering the inner wall",{"id":1813,"type":1515,"variant":1814,"title":1815,"markdown":1816},"callout-31","model_limit","A Simplified Picture of Surface Area","The figure \"600 times\" is a widely used teaching estimate based on measurements of intestinal folds (plicae), villi, and microvilli under microscopes. Real absorption also depends on blood flow, how long food stays, and what you ate. Think of the 600× as a useful model, not a precise measurement for every person or every meal.",{"id":1818,"type":1502,"markdown":1819},"prose-32","The small intestine does not work alone. Two organs that never touch your food directly—the liver and the pancreas—pour critical chemicals into its upper section, called the duodenum. The liver makes bile, a greenish fluid stored in the gall bladder and released when fats arrive. Bile does not digest fat itself; it *emulsifies* it, which means it breaks large fat droplets into tiny droplets, the way dish soap breaks oil on a tawa. This gives fat-digesting enzymes far more surface to attack. Meanwhile, the pancreas secretes a juice rich in bicarbonate to neutralise stomach acid, plus three key enzymes: pancreatic amylase for carbohydrates, lipase for fats, and proteases for proteins. Without this pH shift, the intestine's own enzymes would be destroyed by the acid chyme arriving from the stomach.",{"id":1821,"type":1641,"caption":1822,"columns":1823,"rows":1828},"table-33","Enzymes and secretions entering the small intestine",[1824,1825,1826,1827],"Source","Secretion","What it does","Target nutrient",[1829,1834,1839,1843,1846,1850],[1830,1831,1832,1833],"Liver (stored in gall bladder)","Bile","Emulsifies fats (breaks large droplets into tiny ones)","Fats",[1835,1836,1837,1838],"Pancreas","Bicarbonate-rich juice","Raises pH from ~2 to ~7-8","Acid chyme",[1835,1840,1841,1842],"Pancreatic amylase","Breaks starch into maltose","Carbohydrates",[1835,1844,1845,1833],"Lipase","Breaks fats into fatty acids and glycerol",[1835,1847,1848,1849],"Trypsin and other proteases","Break proteins into shorter peptides","Proteins",[1851,1852,1853,1854],"Small intestine wall","Maltase, peptidases, etc.","Finish breaking molecules into absorbable units","Carbohydrates and proteins",{"id":1856,"type":1543,"title":1857,"problem":1858,"steps":1859},"worked-example-34","Tracing a Fatty Acid from Bite to Lacteal","A teenager eats a plate of paratha with ghee. Follow one fatty acid molecule from the moment it leaves the stomach until it enters the bloodstream.",[1860,1861,1862,1863,1864,1865],"In the duodenum, the arriving acidic chyme triggers the gall bladder to squeeze bile into the intestine. The bile salts wrap around large fat droplets and split them into tiny droplets—emulsification.","Pancreatic lipase now attacks the droplets, breaking triglycerides into fatty acids and monoglycerides. This is true chemical digestion, not just physical splitting.","These smaller molecules cluster with bile salts into tiny spheres called micelles, which ferry them to the surface of the intestinal epithelial cells.","The fatty acids and monoglycerides slip through the cell membrane. Inside the cell, they are reassembled into triglycerides and packaged with proteins into particles called chylomicrons.","The chylomicrons are too large for blood capillaries. Instead, they enter the lacteal—a lymph vessel inside each villus. The lymph eventually drains into the bloodstream near the heart.","This fatty acid has now joined the blood, but it took a detour through the lymphatic system, unlike sugars or amino acids which go straight to blood capillaries.",{"id":1867,"type":1515,"variant":1516,"title":1868,"markdown":1869},"callout-35","Bile Is Not an Enzyme","Many students say bile \"digests\" fat. It does not. Bile contains no enzymes. It emulsifies fat—purely physical separation into droplets—so that lipase enzymes can do the chemical cutting. Confusing the two is like saying a knife cooks food because it makes pieces small enough to cook faster. The cutting and the cooking are different jobs.",{"id":1871,"type":1676,"itemId":1872,"prompt":1873,"check":1874,"hints":1885,"feedback":1889},"practice-36","the-digestive-system.p003","A student says: \"Villi are like tiny sponges that just soak up nutrients passively.\" What is wrong with this statement? Choose the best critique.",{"kind":1680,"options":1875,"correct":1884},[1876,1878,1880,1882],{"id":1578,"label":1877},"Nothing is wrong; villi do simply soak passively",{"id":1581,"label":1879},"Villi are not sponges; they are muscular tubes that squeeze food",{"id":1584,"label":1881},"Villi are finger-like projections, but absorption involves both passive diffusion and active transport requiring energy",{"id":1587,"label":1883},"Villi only absorb water, not nutrients",[1584],[1886,1887,1888],"Think about whether all nutrients move by simple diffusion or if some need cellular energy.","Consider the structure: villi increase surface area, but what happens at the cell membrane?","Glucose absorption against a concentration gradient requires ATP—this is active transport.",{"correct":1890,"incorrect":1891},"Exactly. Villi multiply surface area, but absorption includes both passive diffusion (some lipids) and active transport (glucose, amino acids against gradients). The 'sponge' model misses the energy-requiring cellular work.","Try again. Villi are indeed finger-like projections, but the soaking analogy hides an important truth: many nutrients are pulled into cells using energy, not just drifting in.",{"id":1893,"type":1506,"title":1894,"eyebrow":1895,"navLabel":1896},"chapter-37","The Large Intestine: Water Scout and Bacteria Hotel","Chapter 05","Waste and water recovery",{"id":1898,"type":1502,"markdown":1899},"prose-38","Picture yourself standing in the queue at the railway station on a sweltering May afternoon. You buy a nimbu paani for ₹20, but as you reach the platform, half the glass spills. That lost water stings because water is precious—your body thinks the same way. After the small intestine has extracted most sugars, amino acids, and fats from your meal, what remains is a watery, sludgy mixture that still carries something your body refuses to waste: water itself, plus dissolved salts and a few remaining minerals. The large intestine, or colon, is where this recovery happens. It is about 1.5 metres long—roughly the height of a tall 12-year-old—yet noticeably wider than the small intestine. Unlike its longer cousin, the colon is not lined with millions of villi for nutrient absorption. Instead, it behaves like a careful accountant, tallying every millilitre of water and every gram of salt it can reclaim. The material entering the large intestine from the small intestine is called chyme; by the time it exits, it has been transformed into faeces. This transformation takes anywhere from 12 to 48 hours, which is why the food you ate at lunch on Tuesday might not leave your body until Wednesday evening. The large intestine also hosts trillions of bacteria—more than the number of cells in your own body—forming a bustling community known as the gut microbiota. These microscopic residents do not merely freeload; they ferment fibres you cannot digest, manufacture vitamins you need, and even talk to your immune system. Understanding this final stretch of the digestive journey shows how digestion is less about destruction and more about salvage, cooperation, and precision recycling.",{"id":1901,"type":1554,"tone":1790,"items":1902},"spec-39",[1903,1907,1911,1914,1918],{"label":1904,"big":1905,"value":1906},"Length","≈ 1.5 m","About as long as an adult's arm span from wrist to opposite shoulder",{"label":1908,"big":1909,"value":1910},"Daily water recovery","≈ 1.5 L","Enough to fill three standard 500 ml water bottles you carry to cricket practice",{"label":1801,"big":1912,"value":1913},"12–48 h","Highly variable; fibre-rich meals move faster, low-fibre meals slower",{"label":1915,"big":1916,"value":1917},"Bacterial count","~10¹¹ \u002Fg","Over 100 billion bacteria per gram of colon contents in the lower gut",{"label":1919,"big":1920,"value":1921},"Main absorbable","Water + salts","Almost no digested nutrients like glucose or amino acids enter here",{"id":1923,"type":1543,"title":1924,"problem":1925,"steps":1926},"worked-example-40","Tracking Water Through Priya's Day","Priya, 13, drinks about 2.5 litres of water and eats meals containing another 1 litre of water from rice dal, sabzi, and fruit. Secretions from her digestive organs add roughly 1.5 litres. Of the 5 litres total entering her digestive tract, her small intestine absorbs about 3.5 litres into her bloodstream. How much water reaches her large intestine, and what happens to it?",[1927,1928,1929,1930],"Calculate total water entering the tract: 2.5 L (drinks) + 1.0 L (food) + 1.5 L (secretions) = 5.0 L.","Find what reaches the large intestine: 5.0 L total − 3.5 L absorbed by small intestine = 1.5 L remaining in chyme.","The large intestine's job is to reclaim this water. It absorbs approximately 1.3 to 1.4 litres of the 1.5 litres, leaving only about 0.1 to 0.2 litres to exit with faeces. Without this recovery, Priya would need to drink several extra bottles of water daily just to stay hydrated.","If Priya has diarrhoea, the large intestine cannot absorb water quickly enough. What should be 1.4 litres absorbed might drop to 0.5 litres, meaning 1.0 litre extra leaves the body—exactly why ORS (oral rehydration solution) is critical during loose motions.",{"id":1932,"type":1515,"variant":1516,"title":1933,"markdown":1934},"callout-41","\"Nutrients are absorbed in the large intestine\"","This is a very common guess, but it is wrong for almost all digested nutrients. By the time chyme reaches the colon, nearly all glucose, amino acids, fatty acids, vitamins, and minerals that your enzymes could break down have already been absorbed through the villi of the small intestine. The colon *can* absorb some vitamin K and B vitamins *made by bacteria* there, plus short-chain fatty acids produced from fibre fermentation—but these are bacterial gifts, not direct food nutrients. Treating the large intestine as a second small intestine is a model that fails; think of it instead as a water-recovery plant and bacteria-powered refinery.",{"id":1936,"type":1937,"title":1938,"items":1939},"timeline-42","timeline","A Day in the Life of Your Colon",[1940,1944,1948,1952,1956],{"time":1941,"title":1942,"text":1943},"0–4 h","Chyme arrives from ileum","The ileocaecal valve opens, releasing watery chyme into the caecum. Bacteria begin mixing with the material.",{"time":1945,"title":1946,"text":1947},"4–12 h","Ascending colon climb","Upward movement on the right side; water absorption begins in earnest. Some fibre fermentation starts.",{"time":1949,"title":1950,"text":1951},"12–24 h","Transverse crossing","Material moves across the upper abdomen. Bacteria produce increasing amounts of gases and vitamins.",{"time":1953,"title":1954,"text":1955},"24–36 h","Descending descent","Left side passage; faeces become firmer as more water is withdrawn. The sigmoid colon stores material.",{"time":1957,"title":1958,"text":1959},"36–48 h","Rectal storage","The rectum fills. Nerve signals create the urge to defecate. Elimination completes the journey.",{"id":1961,"type":1502,"markdown":1962},"prose-43","The bacteria in your colon deserve their own recognition. When you eat a banana or bhindi, your own enzymes cannot break down every type of carbohydrate fibre. The bacteria feast on what you cannot use, and in exchange they manufacture vitamin K—essential for blood clotting so a scraped knee stops bleeding—and several B vitamins that support your nerves and energy metabolism. They also produce short-chain fatty acids, small molecules that nourish the cells lining your colon and help keep the gut barrier strong. This is not passive residence; it is a partnership. However, this partnership depends on what you feed it. A diet heavy in refined flour and sugar gives bacteria little fibre to ferment, reducing the helpful by-products they create. In contrast, a thali with whole-wheat roti, lentils, vegetables, and a raw salad provides varied fibre that supports a diverse bacterial community. The faeces you finally pass are roughly 75% water, with the remainder being dead bacteria, undigested plant fibre, shed cells from the gut lining, and bile pigments that give the characteristic brown colour. Faeces is not simply \"waste food\"—most food was digested long before arrival. It is, instead, the ledger of what your body could not use and what your bacterial tenants left behind.",{"id":1964,"type":1574,"prompt":1965,"options":1966,"explanation":1979},"prediction-44","Rahul, 14, is on a camping trip. He eats mostly packaged biscuits and instant noodles for three days, with almost no vegetables, fruit, or whole grains. What is most likely to happen in his large intestine during this time?",[1967,1970,1973,1976],{"id":1968,"label":1969},"faster","His colon will absorb water faster because there is less fibre to block absorption",{"id":1971,"label":1972},"slower","His colon will move material more slowly and faeces will become harder, because low-fibre diets reduce bulk and water-holding capacity",{"id":1974,"label":1975},"vitamins","His bacteria will produce extra vitamins to compensate for the poor diet",{"id":1977,"label":1978},"same","Nothing changes; the large intestine works the same regardless of diet","The correct prediction is that movement slows and faeces hardens. Dietary fibre absorbs water and adds bulk, which stimulates the colon walls to contract and push material forward. Without fibre, the colon lacks this stimulus, transit slows, and more water than usual gets extracted—leading to harder, drier faeces. Bacteria cannot magically produce extra vitamins without fibre to ferment, and water absorption is actually less efficient in a sluggish colon because material sits too long, though the end result is still dehydration of stool. This is why fibre-poor travel diets often cause constipation.",{"id":1981,"type":697,"prompt":1982},"reflection-45","Think about your own meals yesterday. List one food that provided fibre for your gut bacteria, one source of water that your large intestine could reclaim, and one habit (like drinking enough water or eating on a regular schedule) that helps your colon do its job well. If you cannot identify these easily, what small change could you make at today's dinner?",{"id":1984,"type":1506,"title":1985,"eyebrow":1986,"navLabel":1987},"chapter-46","The Liver and Pancreas: Chemical Factories Behind the Scenes","Chapter 06","Accessory organs",{"id":1989,"type":1502,"markdown":1990},"prose-47","Think of a busy railway station like Mumbai CST or Howrah. Thousands of people arrive, but the station does not run on passengers alone. Behind the platforms, an army of workers refuel the engines, clean the coaches, and signal the trains. Your digestive tract is similar. The tube from mouth to anus is the platform where food travels, but two organs — the liver and the pancreas — do much of the real preparation without ever touching the food directly. They sit behind the scenes, drop chemicals into the small intestine through tubes, and make the difference between a meal that nourishes you and one that passes through unused. In this chapter we will see exactly what each factory produces, why bile is not what most people think it is, and what happens when one of these factories shuts down.",{"id":1992,"type":1554,"tone":1555,"items":1993},"spec-48",[1994,1997,2001,2004],{"label":1995,"value":1996},"Location","Liver: upper right abdomen, under the rib cage. Pancreas: behind the stomach, about 15 cm long in adults.",{"label":1998,"big":1999,"value":2000},"Daily output","~1 litre","Bile produced by the liver; ~500 mL pancreatic juice released into the intestine.",{"label":2002,"value":2003},"Key products","Liver: bile (no enzymes). Pancreas: amylase, lipase, proteases, bicarbonate.",{"label":2005,"value":2006},"Gall bladder role","Stores and concentrates bile 5–10×; releases it when fatty food enters the duodenum.",{"id":2008,"type":1515,"variant":1516,"title":2009,"markdown":2010},"callout-49","Bile does NOT digest fat","Many textbooks and charts group bile with \"digestive juices,\" so students assume it contains enzymes that chop fat molecules. It does not. Bile is a mixture of water, salts, pigments, and cholesterol-based **bile salts** that act like soap. They coat large fat droplets and break them into tiny droplets — a physical change called **emulsification** — so that the enzyme lipase can actually attack the fat. Without bile, lipase would sit uselessly on top of an oil slick. With bile, the same oil becomes thousands of tiny targets. Emulsification is preparation, not digestion. Digestion requires breaking chemical bonds; emulsification only changes the size of the droplets.",{"id":2012,"type":1641,"caption":2013,"columns":2014,"rows":2017},"table-50","Comparing the liver and pancreas in digestion",[1644,2015,2016],"Liver","Pancreas (exocrine part)",[2018,2021,2025,2029,2033,2037],[2019,1831,2020],"Main secretion","Pancreatic juice",[2022,2023,2024],"Enzymes present?","None","Amylase (starch), lipase (fat), trypsin (protein)",[2026,2027,2028],"How it reaches intestine","Via bile duct","Via pancreatic duct",[2030,2031,2032],"Secretion triggered by","Fatty food in duodenum","Acidic chyme entering duodenum",[2034,2035,2036],"Also functions as","Chemical factory, blood filter, storage site","Endocrine gland: insulin and glucagon released into blood",[2038,2039,2040],"Failure symptom","Steatorrhoea (pale, greasy stools), vitamin deficiency","Same plus sugar balance problems from endocrine failure",{"id":2042,"type":1543,"title":2043,"problem":2044,"steps":2045},"worked-example-51","Tracing the path of a paratha","You eat an aloo paratha for breakfast: starch from the dough, fat from the ghee, protein from the wheat and potato. By the time the partly-broken food reaches your duodenum, the stomach has already turned it into acidic chyme. Describe exactly what the liver and pancreas contribute before any nutrient can enter your blood.",[2046,2047,2048,2049,2050],"The acidic chyme entering the duodenum triggers enteroendocrine cells to release two hormones: secretin and cholecystokinin (CCK).","Secretin tells the pancreas to release bicarbonate-rich fluid. This alkaline jet neutralises stomach acid, raising the pH from ~2 to ~7–8. Without this, the intestinal enzymes would be destroyed.","CCK tells the gall bladder to squeeze stored bile into the duodenum through the bile duct. The bile salts emulsify the ghee fat into microscopic droplets.","The pancreas simultaneously releases pancreatic amylase to resume starch digestion, lipase to attack the now-emulsified fat, and trypsin to continue protein breakdown.","Only after these secretions have done their work can the small intestine lining absorb sugars, amino acids, and fatty acids into the blood. The liver and pancreas never touched the paratha, but without them, the nutrients would be locked inside.",{"id":2052,"type":1515,"variant":1814,"title":2053,"markdown":2054},"callout-52","Simplified model: ducts as one-way streets","We describe the bile duct and pancreatic duct as simple pipes that open into the duodenum. In reality, the human body shows variation: sometimes the two ducts join into a single **hepatopancreatic ampulla** before entering the intestine; sometimes they have separate openings. The sphincter of Oddi, a muscular valve, controls release timing and prevents intestine contents from flowing backward into the ducts. We omit this valve in basic diagrams to keep the flow concept clear, but in surgery and medicine it matters greatly.",{"id":2056,"type":1676,"itemId":2057,"prompt":2058,"check":2059,"hints":2070,"feedback":2074},"practice-53","the-digestive-system.p004","A 12-year-old patient has a blocked bile duct due to a gallstone. Their doctor notices pale, bulky stools that float and leave an oily film in the toilet. The patient is also developing night blindness and bone pain. Which deficiency best explains these symptoms?",{"kind":1680,"options":2060,"correct":2069},[2061,2063,2065,2067],{"id":1578,"label":2062},"Starch, because without bile the pancreas cannot release amylase",{"id":1581,"label":2064},"Fat and fat-soluble vitamins A and D, because bile emulsification is missing",{"id":1584,"label":2066},"Protein, because bile contains proteases that are now blocked",{"id":1587,"label":2068},"Vitamin C, because the liver normally stores citrus compounds",[1581],[2071,2072,2073],"Recall that bile has no enzymes — so options mentioning enzymes in bile are wrong.","Night blindness is linked to vitamin A; bone pain can signal vitamin D problems.","Both A and D are fat-soluble vitamins. What happens to fat absorption when emulsification fails?",{"correct":2075,"incorrect":2076},"Exactly. Without bile, fat cannot be emulsified, so lipase cannot digest it. The fat passes out, carrying the fat-soluble vitamins A, D, E, and K with it. Night blindness (vitamin A) and bone pain (vitamin D) are classic consequences.","Look again: bile contains no enzymes at all, so it cannot be needed for starch or protein digestion. Vitamin C is water-soluble and unrelated to bile. The floating, oily stools are unabsorbed fat — and fat-soluble vitamins go with it.",{"id":2078,"type":1502,"markdown":2079},"prose-54","The pancreas deserves special attention because it works two shifts. Its **exocrine** tissue — about 99% of the gland — manufactures digestive enzymes and ships them down the pancreatic duct. The remaining 1%, scattered as **islets of Langerhans**, is **endocrine**: it releases insulin and glucagon straight into the bloodstream to regulate blood sugar. This is why pancreatitis or pancreatic cancer can cripple a person in two ways at once: poor digestion from enzyme shortage, and diabetes from insulin shortage. The liver, too, has a blood-sugar role — it stores glucose as glycogen and releases it between meals — but its digestive contribution is strictly the production of bile. When liver cells are damaged by hepatitis or long-term alcohol exposure, bile production falls, and the same fatty-stool syndrome appears even though the pancreas may be perfectly healthy.",{"id":2081,"type":2082,"title":2083,"questions":2084},"quiz-55","quiz","Check your understanding",[2085,2098],{"itemId":2086,"prompt":2087,"options":2088,"correct":1581,"why":2097},"the-digestive-system.q005","Which statement correctly distinguishes bile from pancreatic juice?",[2089,2091,2093,2095],{"id":1578,"label":2090},"Both contain enzymes that digest food.",{"id":1581,"label":2092},"Bile contains no enzymes; pancreatic juice does.",{"id":1584,"label":2094},"Bile digests fat; pancreatic juice digests protein only.",{"id":1587,"label":2096},"Both are stored in the gall bladder before release.","Bile contains bile salts for emulsification but no enzymes. Pancreatic juice contains amylase, lipase, and proteases. The gall bladder stores only bile.",{"itemId":2099,"prompt":2100,"options":2101,"correct":1587,"why":2110},"the-digestive-system.q006","A patient with severe chronic pancreatitis is likely to show all of these EXCEPT:",[2102,2104,2106,2108],{"id":1578,"label":2103},"Greasy, hard-to-flush stools",{"id":1581,"label":2105},"Difficulty controlling blood sugar",{"id":1584,"label":2107},"Poor starch digestion",{"id":1587,"label":2109},"Inability to produce bile","Bile is made by the liver, not the pancreas. Pancreatitis causes steatorrhoea (fatty stools), possible diabetes from insulin loss, and poor starch digestion from missing amylase — but bile production continues unless the liver itself is damaged.",{"id":2112,"type":2113,"title":2114,"points":2115},"summary-56","summary","Key takeaways",[2116,2117,2118,2119,2120],"The liver continuously produces bile; the gall bladder only stores and concentrates it, releasing bile when fat arrives in the duodenum.","Bile contains no enzymes. Its bile salts emulsify fat — breaking large droplets into tiny ones — so that pancreatic lipase can digest the fat chemically.","The pancreas secretes bicarbonate to neutralise stomach acid, plus amylase, lipase, and proteases to digest starch, fat, and protein.","The pancreas is both exocrine (digestive enzymes into the intestine) and endocrine (insulin and glucagon into the blood).","Blockage or disease of either organ causes steatorrhoea — pale, greasy, floating stools — and deficiencies in fat-soluble vitamins A, D, E, and K.",{"id":2122,"type":1506,"title":2123,"eyebrow":2124,"navLabel":2125},"chapter-57","Design Your Own: Testing Pepsin Under Different Conditions","Chapter 07","Enzyme experiment design",{"id":2127,"type":1502,"markdown":2128},"prose-58","After six chapters of following food through the human body, you now know that pepsin is the enzyme that chops proteins in the stomach. But here is a question most people never ask: how do we *know* pepsin works best at body temperature and in strong acid? Someone had to test it. In this chapter, you become that investigator. You will design a controlled experiment to find out how either temperature or pH affects pepsin speed, using ordinary egg white or gelatine as your protein target. A controlled experiment means you change only one factor at a time and keep everything else identical, so you can be sure that factor caused the result. This is exactly how scientists at food labs, dairy research centres, and even ISRO's food technology teams check how proteins behave under different conditions.",{"id":2130,"type":1515,"variant":1735,"title":2131,"markdown":2132},"callout-59","Enzyme, substrate, and the lock-and-key model","An **enzyme** is a protein that speeds up a chemical reaction without being used up. The molecule it acts upon is called the **substrate**. Pepsin is the enzyme; the protein in egg white or gelatine is its substrate. The **lock-and-key model** says an enzyme has a specific shape (the lock) that fits only its substrate (the key). If heat or pH warps that shape, the lock jams and the reaction slows or stops.",{"id":2134,"type":1554,"tone":1790,"items":2135},"spec-60",[2136,2140,2144,2148,2152],{"label":2137,"big":2138,"value":2139},"Optimum temperature","≈37°C","Human body temperature; pepsin shape holds steady here",{"label":2141,"big":2142,"value":2143},"Optimum pH","≈2","Strongly acidic, matching stomach acid (hydrochloric acid)",{"label":2145,"big":2146,"value":2147},"Inactive pH","7","Neutral pH; enzyme denatures and loses shape",{"label":2149,"big":2150,"value":2151},"Substrate options","2","Egg white albumen or gelatine strips; both rich in protein",{"label":2153,"big":2154,"value":2155},"Safety gear","Goggles","Always; plus gloves if using strong acid or base solutions",{"id":2157,"type":1574,"prompt":2158,"options":2159,"explanation":2169},"prediction-61","You will test pepsin at three temperatures: 5°C (iced water), 37°C (warm water bath), and 60°C (hot water bath). All tubes contain pepsin solution and egg-white cubes. Before reading further, choose what you expect:",[2160,2163,2166],{"id":2161,"label":2162},"cold","The coldest tube dissolves egg white fastest because cold preserves the enzyme.",{"id":2164,"label":2165},"body","The 37°C tube dissolves egg white fastest because this matches body conditions.",{"id":2167,"label":2168},"hot","The hottest tube dissolves egg white fastest because heat always speeds reactions.","The body-temperature tube should win. Enzymes are proteins; too little heat keeps molecules sluggish, but too much heat warps the enzyme's shape permanently (denaturation). At 60°C, pepsin unravels like a messed-up paperclip and stops working. At 5°C, it merely slows down. Only near 37°C does pepsin keep its shape while moving fast enough to chop proteins efficiently.",{"id":2171,"type":1515,"variant":1700,"title":2172,"markdown":2173},"callout-62","One variable at a time — no cheating!","A common mistake is changing both temperature and pH together. If you make one tube colder *and* less acidic, and it dissolves egg white slowly, you cannot tell which factor caused the delay. Scientists call this a **confounded experiment**. Decide before you start: are you testing temperature OR pH? The other factor must stay locked at the optimum value for every single tube.",{"id":2175,"type":1543,"title":2176,"problem":2177,"steps":2178},"worked-example-63","Designing a pH test with controlled variables","Riya wants to test whether pepsin works faster at pH 2, pH 4, or pH 7. She has pepsin powder, distilled water, 0.1 M hydrochloric acid (for low pH), sodium hydroxide solution (for neutral pH), egg-white cubes, a stopwatch, and test tubes. What should stay the same, and what should change?",[2179,2180,2181,2182,2183],"Independent variable (the one that changes): pH level — three values: 2, 4, and 7. Riya prepares buffer solutions at each pH.","Dependent variable (the measurement): time in seconds for the egg-white cube to become cloudy and finally disappear, or else a clarity scale from 1 to 5 if full dissolving takes too long.","Controlled variables (kept identical): volume of pepsin solution (say 5 mL), concentration of pepsin (same mass dissolved per mL), size of egg-white cube (measure with a ruler, 1 cm × 1 cm × 1 cm), total volume in each tube, temperature of the water bath (37°C for all tubes), and timing of the stopwatch start.","Step-by-step: label three tubes A, B, C. Add pH 2 buffer to A, pH 4 to B, pH 7 to C. Add equal pepsin solution to each. Drop in one measured egg-white cube per tube. Place all three in the same 37°C water bath. Start the stopwatch together. Check every two minutes and record observations until 20 minutes pass or the cube vanishes.","Fair-test check: if tube A has a 2 cm cube by accident, Riya cannot fairly compare times. She must discard the run and repeat with matched cubes.",{"id":2185,"type":1521,"title":2186,"items":2187},"steps-64","Your experimental procedure (temperature version)",[2188,2192,2196,2200,2204],{"title":2189,"tag":2190,"text":2191},"Prepare identical samples","Step 1","Cut three egg-white cubes, 1 cm each side. Prepare three tubes with 5 mL pepsin solution buffered at pH 2.",{"title":2193,"tag":2194,"text":2195},"Set temperatures","Step 2","Place tube A in iced water at 5°C, tube B in a 37°C water bath, tube C in a 60°C water bath. Wait 5 minutes so the liquid inside each tube reaches the bath temperature.",{"title":2197,"tag":2198,"text":2199},"Start the reaction","Step 3","Drop one egg-white cube into each tube simultaneously. Start the stopwatch. Record the state of each cube at 2, 5, 10, 15, and 20 minutes.",{"title":2201,"tag":2202,"text":2203},"Record results","Step 4","Note whether the cube is intact, softened, cloudy, or fully dissolved. Use a simple scale: 4 = gone, 3 = mostly gone, 2 = soft edges, 1 = unchanged.",{"title":2205,"tag":2206,"text":2207},"Clean up safely","Step 5","Wash tubes with detergent. Dispose of pepsin liquid down the sink with running water. Wipe benches. Never pour acids or bases together in one waste pot.",{"id":2209,"type":1641,"caption":2210,"columns":2211,"rows":2214},"table-65","What to control and what to measure in two versions of the test",[1644,2212,2213],"Temperature test","pH test",[2215,2219,2223,2226,2230],[2216,2217,2218],"What you deliberately change","Temperature: 5°C, 37°C, 60°C","pH: 2, 4, 7",[2220,2221,2222],"What you keep identical","pH 2 buffer in every tube; same pepsin concentration","37°C for every tube; same pepsin concentration",[2224,2225,2225],"What you measure","Time or clarity scale for egg-white breakdown",[2227,2228,2229],"Why it matters","Tests whether pepsin needs body heat to work","Tests whether stomach acid level really is best",[2231,2232,2233],"Risk to watch","60°C water can scald; use tongs for tubes","Acid and base both irritate skin; goggles essential",{"id":2235,"type":1676,"itemId":2236,"prompt":2237,"check":2238,"hints":2249,"feedback":2253},"practice-66","the-digestive-system.p007","Arjun runs a pepsin experiment but makes these mistakes: (1) his hot-water tube sits on a sunny windowsill while the others are in shade, (2) he uses larger egg-white cubes in the cold tube, and (3) he forgets to buffer the neutral tube, so its pH drifts to 5. Which of these mistakes breaks the 'one variable at a time' rule?",{"kind":1680,"options":2239,"correct":2248},[2240,2242,2244,2246],{"id":1578,"label":2241},"Only mistake 1, because sunlight is extra heat.",{"id":1581,"label":2243},"Mistakes 1 and 2, because both add extra unplanned variables.",{"id":1584,"label":2245},"All three, because each introduces a difference beyond the intended change.",{"id":1587,"label":2247},"Only mistake 3, because pH drift changes the intended variable.",[1584],[2250,2251,2252],"Think about what 'controlled' means: everything except your chosen independent variable must match.","Mistake 1 adds light and uneven heat. Mistake 2 adds different cube size. Mistake 3 adds uncontrolled pH shift.","If any tube differs in an extra way, you cannot trust the comparison.",{"correct":2254,"incorrect":2255},"Correct. Every mistake introduces an extra uncontrolled variable. Arjun would not know whether results came from temperature, cube size, or pH drift. A fair test demands that only one factor differs across tubes.","Not quite. Review what 'controlled variable' means. Any extra difference between tubes — light exposure, cube size, or drifting pH — ruins the fair test, not just the one you planned to study.",{"id":2257,"type":1502,"markdown":2258},"prose-67","Once you collect your data, draw a bar chart: temperature or pH on the horizontal axis, and your clarity score or dissolving time on the vertical axis. Expect a peak at 37°C and pH 2, with sharp drops on both sides. If your results look messy — perhaps the 60°C tube dissolved faster than expected — do not hide it. Scientists repeat experiments. Check whether your water bath actually reached 60°C (maybe the thermometer was faulty) or whether the egg-white cube was smaller. Honest repeats are how real labs work, from university kitchens to the food-quality checks run before meals are packed for Indian Railways or space missions. The skill you practised here — isolating one variable, predicting, controlling, measuring — is the same skill used to test medicines, design safer cooking oils, and even check whether spices aid digestion. Hold onto it.",{"id":2260,"type":1506,"title":2261,"eyebrow":2262,"navLabel":2263},"chapter-68","When Digestion Goes Wrong: Disorders and Daily Habits","Chapter 08","Health and lifestyle",{"id":2265,"type":1502,"markdown":2266},"prose-69","You have spent the last several chapters watching a perfect digestive system at work: teeth tearing, the oesophagus squeezing, the stomach acid chopping proteins, villi greedily absorbing nutrients, and bacteria finishing the leftovers. But real bodies are not always this tidy. In this chapter we look at what happens when parts of the system break, when enzymes go missing, and when daily habits quietly sabotage the whole pipeline. Some problems are visible under a microscope; others leave no trace yet still cause real pain. Understanding these disorders and habits is not about memorising scary names — it is about learning to read the signals your own body sends.",{"id":2268,"type":1641,"caption":2269,"columns":2270,"rows":2276},"table-70","Four digestive problems: what changes, what you feel, what helps",[2271,2272,2273,2274,2275],"Condition","Damaged or Missing?","Key change inside","Typical symptoms","Management clue",[2277,2283,2289,2295],[2278,2279,2280,2281,2282],"Coeliac disease","Structural damage","Immune attack flattens villi in small intestine; absorption surface shrinks","Chronic fatigue, diarrhoea, weight loss despite eating","Strict gluten-free diet (no wheat, barley, rye)",[2284,2285,2286,2287,2288],"Lactose intolerance","Missing enzyme","Small intestine makes too little lactase; lactose reaches colon unchanged","Bloating, cramps, diarrhoea after milk or paneer","Limit dairy or use lactase tablets",[2290,2291,2292,2293,2294],"Irritable Bowel Syndrome (IBS)","Functional — no visible damage","Nerve and muscle signals in gut are hypersensitive; motility is erratic","Abdominal pain relieved by stool, alternating constipation and diarrhoea","Stress management, regular meals, trigger-food diary",[2296,2297,2298,2299,2300],"Chronic dehydration and fast eating","Habits, not disease","Chewing time drops; colon reabsorbs too much water from slow-moving waste","Hard stools, constipation, occasional heartburn","Slow down, sip water through the day, fibre-rich meals",{"id":2302,"type":1515,"variant":1516,"title":2303,"markdown":2304},"callout-71","Gluten sensitivity is not the same as wheat allergy","Many people say they are \"allergic to gluten,\" but coeliac disease is **not** a food allergy. In a true allergy, the immune system releases histamine fast — think of a nut allergy causing swelling within minutes. In coeliac disease, the immune system slowly attacks the body's own villi every time gluten appears. **Human digestive system** calls this an autoimmune-like reaction. A wheat allergy can exist separately, but the two conditions need different tests and different worries.",{"id":2306,"type":1543,"title":2307,"problem":2308,"steps":2309},"worked-example-72","Tracing a glass of lassi in a lactose-intolerant person","Priya drinks a large glass of lassi (yoghurt drink) at a Mumbai street stall. She has mild lactose intolerance. Trace what happens hour by hour, and explain why her symptoms differ from coeliac disease.",[2310,2311,2312,2313,2314],"Hour 0–1: Mouth and stomach. Lactase is supposed to be made in the small intestine, so nothing unusual happens yet. The lassi is churned with stomach acid and pepsin, turning milk proteins into shorter chains.","Hour 1–3: Small intestine. Normally lactase would split lactose into glucose and galactose for absorption. Priya's villi are structurally healthy — no flattening — but they simply do not make enough lactase. Most lactose molecules stay whole and slide past the villi undigested.","Hour 3–6: Large intestine. The undigested lactose reaches the colon, where resident bacteria ferment it enthusiastically. Fermentation releases gases (hydrogen, carbon dioxide, methane) and short-chain fatty acids. The gas causes bloating and cramps; the acidic, osmotic load pulls water into the colon lumen, producing watery diarrhoea.","Why this is not coeliac disease: coeliac disease damages the villi themselves, so *all* nutrients — fats, proteins, vitamins — are poorly absorbed, leading to malnutrition and chronic fatigue. Priya's problem is a missing enzyme, not missing surface area. Her villi are intact; only one sugar is escaping absorption.","Management: Priya could choose smaller portions, pick fermented products with lower lactose (some yoghurts), take a lactase tablet with the drink, or switch to a plant-based alternative.",{"id":2316,"type":1502,"markdown":2317},"prose-73","If structure and enzymes explain only part of the story, what about the mind? Irritable Bowel Syndrome is the textbook case of a **functional disorder** — the gut looks normal during endoscopy or scans, yet it behaves badly. Stress hormones like cortisol alter how fast the colon contracts and how loudly pain signals are amplified. **Nutrition in Animals — NCERT Class 7 Science, Chapter 2** reminds us that digestion is not only chemistry; it is also coordination. When exam stress or family tension hits, some students feel \"butterflies,\" while others get genuine cramps or sudden diarrhoea. The nervous system and digestive system share wiring so thoroughly that scientists now call the gut a \"second brain.\" This does not mean IBS is imaginary; it means the damage is in the software, not the hardware.",{"id":2319,"type":1676,"itemId":2320,"prompt":2321,"check":2322,"hints":2333,"feedback":2338},"practice-74","the-digestive-system.p008","A 14-year-old student eats lunch in 4 minutes during the school break, then drinks barely two glasses of water all day. He complains of hard stools, occasional stomach burn, and feeling \"heavy\" after meals. Which single habit change is most likely to help first, and why?",{"kind":1680,"options":2323,"correct":2332},[2324,2326,2328,2330],{"id":1578,"label":2325},"Drink two litres of water within ten minutes at 3 pm",{"id":1581,"label":2327},"Chew each bite at least 15 times and sip water steadily through the day",{"id":1584,"label":2329},"Skip lunch entirely to rest the digestive system",{"id":1587,"label":2331},"Take antacid tablets before every meal",[1581],[2334,2335,2336,2337],"Think about which problem appears earliest in the digestive pipeline.","Eating fast shortens both mechanical breakdown (chewing) and exposure to salivary enzymes.","Water spread through the day reaches the colon gradually; a sudden flood mostly becomes urine.","The student has no ulcer diagnosis, so routine antacids are not the first step.",{"correct":2339,"incorrect":2340},"Correct. Slow chewing gives salivary amylase time to start starch digestion and signals the stomach to prepare acid. Steady hydration keeps colonic contents soft without overwhelming the kidneys. These changes address the root habits, not just symptoms.","Not the best first step. A water flood at 3 pm will mostly be excreted as urine and may not reach the colon in time. Skipping lunch stresses the system more. Routine antacids without diagnosis mask symptoms rather than fix habits.",{"id":2342,"type":697,"prompt":2343},"reflection-75","Think of one meal you ate yesterday. Which part of your digestive system had the hardest job — chewing quickly, handling spice or oil, absorbing nutrients, or forming stool? Name one small habit you could adjust today to make that part's job easier.",{"id":2345,"type":1506,"title":2346,"eyebrow":2347,"navLabel":2348},"chapter-76","A Day in Indian Cuisine: Mapping Your Own Meal","Chapter 09","Personal digestion map",{"id":2350,"type":1502,"markdown":2351},"prose-77","Imagine sitting down to a typical Indian lunch: a plate of steamed rice, a bowl of yellow dal, two warm rotis, a small bowl of seasonal sabzi, and a spoon of ghee melting over the rice. You have tasted this meal countless times, but after studying the digestive system, you can now see it as a set of chemical puzzles your body must solve. Each ingredient carries a different nutrient, and each nutrient follows a different path through the same plumbing. In this chapter, you will map that entire journey, clock the timing, and discover why your dal and rice do not get digested in the same place or at the same speed. This is where theory meets your thali.",{"id":2353,"type":1515,"variant":1735,"title":2354,"markdown":2355},"callout-78","Key terms for this meal map","- **Starch**: a long chain of glucose units found in rice, wheat, and potatoes; your body must break it into single glucose molecules to absorb it.\n- **Polysaccharide**: a carbohydrate made of many sugar units linked together; starch is the main polysaccharide in this meal.\n- **Emulsify**: to break large fat droplets into tiny droplets so enzymes can reach them; bile from the liver does this in the small intestine.\n- **Transit time**: the hours or days a meal spends travelling from mouth to rectum; it varies widely between people and even between meals.",{"id":2357,"type":1515,"variant":2358,"title":2359,"markdown":2360},"callout-79","nuance","Why starch seems to restart, not continue","Students often imagine starch digestion as one smooth conveyor belt from mouth to small intestine. It is not. Salivary amylase and pancreatic amylase are different enzymes with similar names, made by different organs. The first enzyme is destroyed by acid before the second takes over. There is a genuine pause in starch breakdown inside the stomach, lasting roughly one to three hours depending on stomach contents. Only when the acidic chyme exits the stomach and pancreatic bicarbonate neutralises it does starch digestion resume. Model this as a relay race with a dropped baton, not a single runner.",{"id":2362,"type":1543,"title":2363,"problem":2364,"steps":2365},"worked-example-80","Tracking one roti from bite to bloodstream","A plain wheat roti contains mainly starch with a small amount of plant protein and almost no fat. Follow its starch through the digestive tract, naming each stage, the approximate time spent there, and what happens to the starch molecule.",[2366,2367,2368,2369,2370],"Mouth (0-1 minute): Chewing mixes the roti with saliva. Salivary amylase clips long starch chains into shorter maltose and dextrin fragments. You may notice a faint sweetness if you hold chewed roti on your tongue.","Oesophagus (5-10 seconds): No chemical change. The muscular wall pushes the soft bolus down to the stomach by peristalsis.","Stomach (1-4 hours): Gastric acid inactivates salivary amylase. Starch digestion pauses completely. Meanwhile stomach pepsin begins working on the small amount of wheat protein. The roti starch sits as intact fragments in acidic chyme.","Small intestine (3-5 hours): Pancreatic amylase pours in from the pancreatic duct and resumes cutting starch into maltose. Brush-border enzymes on the intestinal surface then split maltose into glucose. Glucose crosses the intestinal lining into blood capillaries and travels to the liver via the hepatic portal vein.","Large intestine (12-48 hours): Any resistant starch or fibre that escaped earlier arrives here. Bacteria ferment some of it. Water and minerals are absorbed. The remainder becomes faeces.",{"id":2372,"type":1937,"title":2373,"items":2374},"timeline-81","Approximate transit of an Indian mixed meal",[2375,2379,2383,2387,2391],{"time":2376,"title":2377,"text":2378},"0-2 min","Mouth and oesophagus","Starch breakdown begins with salivary amylase. Protein and fat untouched. Bolus swallowed quickly.",{"time":2380,"title":2381,"text":2382},"1-4 hr","Stomach","Protein digestion starts with pepsin. Starch digestion pauses. Acid begins unfolding all food structures.",{"time":2384,"title":2385,"text":2386},"3-6 hr","Small intestine","Pancreatic amylase, trypsin, and lipase finish most chemical breakdown. Nutrients absorbed into blood.",{"time":2388,"title":2389,"text":2390},"12-48 hr","Large intestine","Water reclaimed. Fibre fermented by bacteria. Waste compacted into stool. Transit varies widely.",{"time":2392,"title":2393,"text":2394},"24-72 hr","Total mouth to rectum","Highly individual. Fibre-rich meals take longer. Hydration and activity level both shift the timing.",{"id":2396,"type":1521,"title":2397,"items":2398},"steps-82","Build your own meal map",[2399,2402,2405,2408,2411],{"title":2400,"text":2401},"List your foods","Write down each item on your plate: rice, rajma, bhindi, raita, mango, chapati.",{"title":2403,"text":2404},"Tag each nutrient","Identify the dominant nutrient: starch, protein, fat, fibre, or sugar. Some foods have two.",{"title":2406,"text":2407},"Mark start points","Starch starts in mouth. Protein starts in stomach. Fat and fibre start later. Note pauses.",{"title":2409,"text":2410},"Assign transit times","Use the timeline ranges. Remember liquids move faster than solids; fat slows stomach emptying.",{"title":2412,"text":2413},"Check the hand-offs","Where does one organ stop and another begin? Mark enzyme switches like amylase to amylase.",{"id":2415,"type":1676,"itemId":2416,"prompt":2417,"check":2418,"hints":2433,"feedback":2438},"practice-83","the-digestive-system.p009","You eat a lunch of rice, dal, and ghee-laden roti. Which nutrient type spends the longest time waiting before its primary digestive enzyme becomes active?",{"kind":1680,"options":2419,"correct":2432},[2420,2423,2426,2429],{"id":2421,"label":2422},"starch","Starch from rice and roti",{"id":2424,"label":2425},"protein","Protein from dal",{"id":2427,"label":2428},"fat","Fat from ghee",{"id":2430,"label":2431},"fibre","Fibre from vegetables",[2427],[2434,2435,2436,2437],"Think about where each enzyme first acts, not where digestion finishes.","Salivary amylase starts starch breakdown in the mouth immediately.","Pepsin starts protein breakdown as soon as food reaches the stomach.","Fat needs bile emulsification before lipase can work effectively.",{"correct":2439,"incorrect":2440},"Correct. Fat from ghee must wait until food reaches the small intestine, where bile emulsifies it before pancreatic lipase can begin. Starch starts in the mouth; protein starts in the stomach; fibre is never digested by human enzymes at all.","Not quite. Starch digestion begins in the mouth with salivary amylase. Protein digestion begins in the stomach with pepsin. Fat is the only major nutrient that waits all the way until the small intestine for bile and lipase to become active.",{"id":2442,"type":1506,"title":2443,"eyebrow":2444,"navLabel":2445},"chapter-84","Check Yourself, and What Comes Next","Chapter 10","Quiz and next steps",{"id":2447,"type":1502,"markdown":2448},"prose-85","You have travelled the full digestive highway—from the first chew to the final flush. Now it is time to test whether you can steer on your own. This chapter has three parts: a quiz that mixes recall with reasoning, a look at where your new knowledge leads next, and a concise map of everything that matters. Treat the quiz as a diagnostic tool, not a score to chase. If a question traps you, return to the relevant chapter, because these ideas will reappear when biology links digestion to breathing and energy release in living cells.",{"id":2450,"type":2082,"title":2451,"questions":2452},"quiz-86","Digestive Highway Check",[2453,2465,2478,2495,2512,2527,2542],{"itemId":2454,"prompt":2455,"options":2456,"correct":1584,"why":2464},"the-digestive-system.q010","Arrange these events in the order they actually occur from mouth to large intestine: (a) starch broken to maltose, (b) proteins broken to peptides, (c) water absorbed, (d) food mixed with bile.",[2457,2459,2461,2462],{"id":1578,"label":2458},"a → b → d → c",{"id":1581,"label":2460},"b → d → a → c",{"id":1584,"label":2458},{"id":1587,"label":2463},"a → d → b → c","Salivary amylase starts starch→maltose in the mouth (a). Pepsin breaks proteins→peptides in the stomach (b). Bile from the liver mixes with food in the small intestine (d). Water absorption peaks in the large intestine (c). Sequence: a → b → d → c.",{"itemId":2466,"prompt":2467,"options":2468,"correct":2473,"why":2477},"the-digestive-system.q011","Where does the food actually enter—pass through the wall into—the organ's own tissue or ducts?",[2469,2470,2472,2474],{"id":128,"label":2015},{"id":2471,"label":1835},"pancreas",{"id":2473,"label":2385},"si",{"id":2475,"label":2476},"gb","Gall bladder","Digestion is extracellular inside the alimentary canal. The small intestine's lumen is continuous with the outside world; only small intestine villus cells absorb nutrients into blood. Liver, pancreas and gall bladder are accessory organs—food never enters them.",{"itemId":2479,"prompt":2480,"options":2481,"correct":2489,"why":2494},"the-digestive-system.q012","Pepsin is secreted by gastric glands in the stomach. Which conditions does it need to work effectively?",[2482,2485,2488,2491],{"id":2483,"label":2484},"acid","Alkaline pH and room temperature",{"id":2486,"label":2487},"base","Neutral pH and 0 °C",{"id":2489,"label":2490},"right","Acidic pH (around 2) and body temperature (about 37 °C)",{"id":2492,"label":2493},"warm","Acidic pH and 60 °C","Pepsin is a protein-digesting enzyme adapted to the stomach's hydrochloric acid environment. Its optimum pH is roughly 1.5–2.0, and like human enzymes generally, it functions near body temperature. Too cold slows molecular motion; too hot denatures the protein shape.",{"itemId":2496,"prompt":2497,"options":2498,"correct":2503,"why":2511},"the-digestive-system.q013","A finger-like villus in the small intestine has many microvilli on its surface. What is the main advantage of this 'folds on folds' design?",[2499,2502,2505,2508],{"id":2500,"label":2501},"speed","It speeds up peristaltic churning",{"id":2503,"label":2504},"area","It greatly increases surface area for absorption",{"id":2506,"label":2507},"enzyme","It stores extra digestive enzymes inside",{"id":2509,"label":2510},"water","It pumps water out into the lumen","Nutrient absorption is limited by contact surface. Villi and microvilli are pure structure-function geometry: more membrane exposed to digested food means faster diffusion and transport of amino acids, fatty acids and sugars into blood. This matches observations in Human digestive system.",{"itemId":2513,"prompt":2514,"options":2515,"correct":1554,"why":2526},"the-digestive-system.q014","In the Chapter 7 experiment, test tubes of boiled egg white (protein) were placed with pepsin at different pH values. At pH 7, the egg white stayed cloudy; at pH 2, it cleared fastest. What does this show?",[2516,2519,2521,2524],{"id":2517,"label":2518},"temp","Temperature matters more than pH",{"id":1554,"label":2520},"Enzyme action depends on matching pH to the enzyme's specificity",{"id":2522,"label":2523},"all","Enzymes work the same at any pH",{"id":2483,"label":2525},"Acid alone digests protein without enzymes","The controlled comparison isolates pH while holding enzyme and substrate constant. Clearing indicates protein breakdown. Result: pepsin is specialised for acidic conditions. This is the enzyme-substrate specificity principle, not a general acid effect—hydrochloric acid without pepsin clears egg white very slowly.",{"itemId":2528,"prompt":2529,"options":2530,"correct":2536,"why":2541},"the-digestive-system.q015","Which daily habit most directly protects the mucus lining of the stomach from self-digestion?",[2531,2533,2535,2538],{"id":2509,"label":2532},"Drinking 3 litres of water with every meal",{"id":2430,"label":2534},"Eating high-fibre daal and roti",{"id":2536,"label":2537},"regular","Eating regular, moderate meals rather than very large infrequent ones",{"id":2539,"label":2540},"spicy","Avoiding all spices completely","The stomach lining renews its mucus blanket constantly. Very large meals stretch the stomach and trigger prolonged, heavy acid release, which can overwhelm局部 (local) repair. Regular moderate meals keep acid load steady and allow mucosal recovery. Fibre helps the large intestine, not primarily the stomach wall.",{"itemId":2543,"prompt":2544,"options":2545,"correct":2473,"why":2556},"the-digestive-system.q016","A train passenger eats a Mumbai vada pav: bread (starch), potato (starch plus some protein), chutney (fibre and water), and oil. Where is the oil first chemically broken down?",[2546,2549,2551,2553],{"id":2547,"label":2548},"mouth","Mouth by salivary amylase",{"id":127,"label":2550},"Stomach by pepsin and acid",{"id":2473,"label":2552},"Small intestine by pancreatic lipase with bile assistance",{"id":2554,"label":2555},"li","Large intestine by bacteria","Fats are not digested until the small intestine. Bile from the liver emulsifies large oil droplets into tiny ones; pancreatic lipase then clips triglycerides into fatty acids and glycerol. Mouth and stomach enzymes attack carbohydrates and proteins, not lipids.",{"id":2558,"type":1502,"markdown":2559},"prose-87","If you scored six or seven correctly, the digestive model is yours. If two or more tripped you, revisit the specific organ chapters before moving on. Now for the bridge forward. Every nutrient that crosses a villus enters a blood vessel in the intestinal wall. That blood travels first to the liver through the hepatic portal vein. The liver screens and converts molecules, then releases them into general circulation. Finally, each cell in your muscles, brain and bones receives those nutrients. But a cell cannot unlock energy from glucose by digestion alone. It needs oxygen. Oxygen arrives from the air through the respiratory system, which you will study next. Digestion breaks food down; respiration combines those breakdown products with oxygen to release usable energy. The two systems are inseparable partners, and the link is the bloodstream that leaves your small intestine.",{"id":2561,"type":1515,"variant":1516,"title":2562,"markdown":2563},"callout-88","\"Food Digests Itself\"","A common mix-up is imagining that digestion is passive—food simply falls apart in acid or alkali. In reality, every main step is driven by specific enzymes, which are proteins with exact shapes matching exact substrates. No enzyme, no targeted breakdown. Acid alone can damage tissue, but it does not systematically cleave starch to maltose or proteins to peptides. This active, enzyme-driven model is what separates biological digestion from mere rotting.",{"id":2565,"type":1543,"title":2566,"problem":2567,"steps":2568},"worked-example-89","Predicting an Experiment: Cold Pepsin","A student sets up two tubes with identical egg-white strips and pepsin solution at pH 2. Tube A is kept in a 37 °C water bath; Tube B is placed in an ice bath at 5 °C. After 20 minutes, which tube shows more digestion, and why?",[2569,2570,2571,2572,2573,2574],"Identify the variable: temperature is the only deliberate difference; pH, enzyme type and substrate are controlled.","Recall enzyme mechanism: pepsin must collide with protein substrate; its shape must fit.","Apply kinetic energy principle: at 37 °C, molecules move faster and collide more frequently; the enzyme's shape is stable at body temperature.","Predict Tube A outcome: frequent successful collisions mean visible breakdown (clearing or softening of egg white).","Predict Tube B outcome: at 5 °C, kinetic energy is low; collisions are rare and weak. Digestion is very slow or absent.","State the answer clearly: Tube A shows more digestion because enzyme-substrate interaction depends on molecular motion and correct temperature, not merely the presence of acid and enzyme.",{"id":2576,"type":2113,"title":2577,"points":2578},"summary-90","The Full Model: From Bite to Bloodstream",[2579,2580,2581,2582,2583,2584,2585,2586,2587],"Ingestion: food enters the mouth; teeth and tongue begin mechanical breakdown while salivary amylase starts starch digestion.","Propulsion: peristalsis—wave-like muscle contractions—pushes the bolus through oesophagus, stomach and intestines without gravity dependence.","Mechanical breakdown: churning in the stomach and segmentation in the small intestine increase physical surface area exposed to enzymes.","Enzymatic breakdown: specific enzymes at specific pH values chop carbohydrates, proteins and fats into absorbable units; this is active, shape-driven chemistry, not passive dissolving.","Accessory supply: liver produces bile for fat emulsification; pancreas secretes digestive enzymes and bicarbonate; gall bladder stores bile. Food never enters these organs.","Absorption: villi and microvilli in the small intestine provide massive surface area; nutrients pass into blood and lymph.","Water recovery: the large intestine reabsorbs water and minerals; resident bacteria synthesise some vitamins.","Defaecation: undigested fibre, dead bacteria and water form faeces, expelled through the rectum and anus.","Integration: absorbed nutrients travel via hepatic portal vein to the liver, then to all body cells, where they await oxygen-driven energy release.",{"id":2589,"type":2590,"title":2591,"terms":2592},"glossary-91","glossary","Key Terms of the Lesson",[2593,2597,2601,2604,2608,2612,2615,2619,2623,2627,2631],{"term":2594,"meaning":2595,"example":2596},"Alimentary canal","The continuous muscular tube from mouth to anus through which food passes; also called the gastrointestinal tract.","Oesophagus, stomach, small intestine and large intestine are all parts of the alimentary canal.",{"term":2598,"meaning":2599,"example":2600},"Amylase","An enzyme that breaks starch into simpler sugars such as maltose.","Salivary amylase begins starch digestion in the mouth; pancreatic amylase continues it in the small intestine.",{"term":1831,"meaning":2602,"example":2603},"A greenish fluid produced by the liver, stored in the gall bladder, that emulsifies fats so lipase can act.","Bile does not digest fat chemically; it breaks large oil droplets into tiny ones.",{"term":2605,"meaning":2606,"example":2607},"Enzyme","A biological catalyst, usually a protein, that speeds up a specific chemical reaction without being consumed.","Pepsin is an enzyme that breaks proteins into peptides in the stomach.",{"term":2609,"meaning":2610,"example":2611},"Hepatic portal vein","The blood vessel that carries nutrient-rich blood from the small intestine to the liver for processing.","After a meal, this vein delivers absorbed glucose directly to the liver before it reaches the rest of the body.",{"term":1844,"meaning":2613,"example":2614},"An enzyme that breaks fats (lipids) into fatty acids and glycerol.","Pancreatic lipase acts in the small intestine after bile has emulsified the fat.",{"term":2616,"meaning":2617,"example":2618},"Microvilli","Tiny hair-like projections on the surface of villus cells that massively increase absorption surface area.","A single villus cell may have thousands of microvilli, forming the 'brush border'.",{"term":2620,"meaning":2621,"example":2622},"Mucus","A slippery secretion that protects and lubricates the inner lining of the digestive tract.","Gastric mucus shields the stomach wall from being digested by its own acid and pepsin.",{"term":2624,"meaning":2625,"example":2626},"Peristalsis","Rhythmic, wave-like muscle contractions that move material through tubes such as the oesophagus and intestines.","You can swallow upside down because peristalsis pushes food toward the stomach regardless of gravity.",{"term":2628,"meaning":2629,"example":2630},"Substrate","The specific molecule upon which an enzyme acts.","For salivary amylase, starch is the substrate; for pepsin, proteins are the substrate.",{"term":2632,"meaning":2633,"example":2634},"Villus (plural: villi)","A small, finger-like projection in the small intestine wall that increases surface area for nutrient absorption.","Each villus contains blood capillaries and a lacteal to collect absorbed nutrients.",{"id":2636,"type":2637,"sourceIds":2638},"sources-92","sources",[2639,2640,2641],"body-systems-britannica-digestive","body-systems-britannica-respiratory","digestive-system-ncert-science-7-ch2",[2639,2640,2641],"needs_review",{"generatedBy":2645,"notes":2646},"claude-code","generated from work item wi-29051418 (10 chapters)","f79c623d2236f835c535d1f90e84f8517b3906585c0beb640724cdfbe1e6d198",{},{"state":2650},"unreviewed","generation-4c1a594b-3e08-4931-b878-9bd6c2c6c83b",[2653,2661,2665],{"id":2639,"title":2654,"publisher":2655,"url":2656,"kind":2657,"accessed":2658,"usage":2659,"verification":2660},"Human digestive system","Encyclopaedia Britannica","https:\u002F\u002Fwww.britannica.com\u002Fscience\u002Fhuman-digestive-system","reference","2026-09-20","Supports the order of the digestive tract, chewing and saliva, salivary amylase as the first enzyme, peristalsis, stomach acid and pepsin, the roles of liver, gall bladder and pancreas, absorption at the villi, water recovery in the large intestine, and transit times of roughly one to three days.","unverified",{"id":2640,"title":2662,"publisher":2655,"url":2663,"kind":2657,"accessed":2658,"usage":2664,"verification":2660},"Human respiratory system","https:\u002F\u002Fwww.britannica.com\u002Fscience\u002Fhuman-respiratory-system","Supports the air path from nose to alveoli, warming and filtering of air in the nose, the diaphragm and rib muscles doing the work of breathing, a tidal volume of about 500 mL, resting breathing rates, and the composition of inhaled versus exhaled air (about 21%\u002F16% oxygen, 0.04%\u002F4% carbon dioxide).",{"id":2641,"title":2666,"publisher":2667,"url":2668,"kind":2669,"accessed":2670,"usage":2671,"verification":2672},"Nutrition in Animals — NCERT Class 7 Science, Chapter 2 (the digestive system)","NCERT","https:\u002F\u002Fncert.nic.in\u002Ftextbook\u002Fpdf\u002Fgesc102.pdf","educational","2026-09-21","The digestive system: mouth, teeth, saliva, stomach, small and large intestine, absorption, digestion in grass-eating animals and amoeba","machine_checked"]