[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"content-index":3,"content-questions:the-digestive-system":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.",[],[],[],{"bank":1471,"contentHash":2415,"dependencyHashes":2416,"releaseId":2417},{"schemaVersion":44,"conceptId":1276,"revision":44,"title":1277,"intro":1277,"sections":1472,"questions":1481,"sourceIds":2407,"reviewStatus":2411,"authoring":2412},[1473,1477],{"id":1474,"title":1475,"description":1476},"core","Core practice","Practice for this topic.",{"id":1478,"title":1479,"description":1480},"stretch","Stretch","Harder practice for this topic.",[1482,1498,1512,1524,1537,1563,1583,1600,1615,1630,1653,1670,1683,1705,1720,1743,1763,1778,1800,1817,1839,1862,1885,1897,1913,1934,1946,1959,1970,1992,2005,2031,2053,2074,2096,2116,2137,2159,2182,2205,2228,2247,2265,2280,2299,2314,2327,2341,2353,2366,2378,2395],{"id":1483,"section":1474,"level":1484,"prompt":1485,"check":1486,"hints":1491,"solution":1494,"skills":1495},"the-digestive-system.q105","foundation","Which organ begins the process of mechanical digestion by chewing food into smaller pieces?",{"kind":1487,"accept":1488},"text",[1489,1490],"mouth","the mouth",[1492,1493],"Think about where food first enters your body.","Which body part contains teeth and saliva?","Food enters the digestive system through the mouth. The teeth chew food into smaller pieces (mechanical digestion), while saliva starts chemical digestion. This is the first step in breaking down food so the body can use it.",[1496,1497],"identify organs","digestive sequence",{"id":1499,"section":1474,"level":1484,"prompt":1500,"check":1501,"hints":1507,"solution":1510,"skills":1511},"the-digestive-system.q106","What is the name of the muscular tube that carries food from the mouth to the stomach?",{"kind":1487,"accept":1502},[1503,1504,1505,1506],"esophagus","oesophagus","the esophagus","the oesophagus",[1508,1509],"This tube connects the mouth to the stomach.","It uses wave-like muscle movements called peristalsis to push food down.","The esophagus (also spelled oesophagus) is a muscular tube about 25 cm long. It carries food from the mouth to the stomach using peristalsis - wave-like muscle contractions that push food downward, even when we are upside down.",[1496,1497],{"id":1513,"section":1474,"level":1484,"prompt":1514,"check":1515,"hints":1518,"solution":1521,"skills":1522},"the-digestive-system.q107","Which organ produces bile to help break down fats?",{"kind":1487,"accept":1516},[128,1517],"the liver",[1519,1520],"This is the largest internal organ in the body.","Bile is stored in the gallbladder but produced elsewhere.","The liver produces bile, a greenish-yellow fluid that helps break down fats into smaller droplets. Bile is stored in the gallbladder and released into the small intestine when needed. The liver is the largest internal organ and has many other functions too.",[1496,1523],"bile production",{"id":1525,"section":1474,"level":1484,"prompt":1526,"check":1527,"hints":1531,"solution":1534,"skills":1535},"the-digestive-system.q108","Where does most nutrient absorption into the bloodstream occur?",{"kind":1487,"accept":1528},[1529,1530],"small intestine","the small intestine",[1532,1533],"This organ has villi - tiny finger-like projections that increase surface area.","It comes after the stomach in the digestive tract.","Most nutrient absorption happens in the small intestine. The small intestine is about 6 meters long and has tiny finger-like projections called villi. These villi increase the surface area and contain blood vessels that absorb nutrients like sugars, amino acids, and fatty acids into the bloodstream.",[1496,1536],"nutrient absorption",{"id":1538,"section":1474,"level":1484,"prompt":1539,"check":1540,"hints":1556,"solution":1559,"skills":1560},"the-digestive-system.q109","What is the main function of the large intestine?",{"kind":1541,"options":1542,"correct":1555},"choice",[1543,1546,1549,1552],{"id":1544,"label":1545},"a","Break down proteins with enzymes",{"id":1547,"label":1548},"b","Absorb water and form solid waste",{"id":1550,"label":1551},"c","Produce bile for fat digestion",{"id":1553,"label":1554},"d","Begin mechanical digestion of food",[1547],[1557,1558],"Think about what happens to food after the small intestine.","Water is important to reclaim from the remaining food material.","The main function of the large intestine is to absorb water and minerals from the remaining indigestible food matter, and to form and store solid waste (feces). It does not produce enzymes like the small intestine. The waste then moves to the rectum and is eliminated through the anus.",[1561,1562],"organ functions","water absorption",{"id":1564,"section":1474,"level":1484,"prompt":1565,"check":1566,"hints":1577,"solution":1580,"skills":1581},"the-digestive-system.q110","Put these digestive organs in the correct order that food passes through them:\n\n1. Small intestine\n2. Stomach\n3. Mouth\n4. Large intestine\n5. Esophagus\n\nA) 3, 5, 2, 1, 4\nB) 3, 2, 5, 1, 4\nC) 5, 3, 2, 1, 4\nD) 3, 5, 2, 4, 1",{"kind":1541,"options":1567,"correct":1576},[1568,1570,1572,1574],{"id":1544,"label":1569},"3, 5, 2, 1, 4",{"id":1547,"label":1571},"3, 2, 5, 1, 4",{"id":1550,"label":1573},"5, 3, 2, 1, 4",{"id":1553,"label":1575},"3, 5, 2, 4, 1",[1544],[1578,1579],"Food enters through the mouth first.","The stomach is before the intestines.","The correct order is: 3 (Mouth) → 5 (Esophagus) → 2 (Stomach) → 1 (Small intestine) → 4 (Large intestine).\n\nFood is chewed in the mouth, travels down the esophagus, is churned and partially digested in the stomach, nutrients are absorbed in the small intestine, and water is absorbed in the large intestine before waste is eliminated.",[1497,1582],"organ order",{"id":1584,"section":1474,"level":1484,"prompt":1585,"check":1586,"hints":1593,"solution":1596,"skills":1597},"the-digestive-system.q111","What does the stomach secrete to help break down food?",{"kind":1487,"accept":1587},[1588,1589,1590,1591,1592],"gastric juice","acid","hydrochloric acid","stomach acid","gastric acid",[1594,1595],"The stomach produces a strong liquid that is very acidic.","This liquid contains enzymes like pepsin that digest proteins.","The stomach secretes gastric juice, which contains hydrochloric acid (HCl) and the enzyme pepsin. The acid kills bacteria and helps pepsin break down proteins into smaller pieces. The stomach lining is protected from this strong acid by a layer of mucus.",[1598,1599],"chemical digestion","stomach function",{"id":1601,"section":1474,"level":1484,"prompt":1602,"check":1603,"hints":1609,"solution":1612,"skills":1613},"the-digestive-system.q112","Which organ is a small, pear-shaped sac that stores bile until it is needed?",{"kind":1487,"accept":1604},[1605,1606,1607,1608],"gallbladder","the gallbladder","gall bladder","the gall bladder",[1610,1611],"This organ sits under the liver.","It stores something the liver makes.","The gallbladder is a small, pear-shaped organ that sits beneath the liver. It stores and concentrates bile produced by the liver. When fatty food enters the small intestine, the gallbladder releases bile through a duct to help break down those fats into smaller droplets that enzymes can more easily digest.",[1496,1614],"bile storage",{"id":1616,"section":1474,"level":1484,"prompt":1617,"check":1618,"hints":1622,"solution":1626,"skills":1627},"the-digestive-system.q113","What is the name of the tiny finger-like projections that line the small intestine and increase the surface area for nutrient absorption?",{"kind":1487,"accept":1619},[1620,1621],"villi","villus",[1623,1624,1625],"Think about structures that look like tiny fingers","The name starts with 'v'","These projections help maximize how much surface area is available for absorption","The small intestine is lined with tiny, finger-like projections called **villi** (singular: **villus**). These structures dramatically increase the surface area of the small intestine, which allows more nutrients to be absorbed into the bloodstream. Each villus contains tiny blood vessels called capillaries, so when food molecules pass through the villus, they can quickly enter the blood and be carried throughout the body. If the small intestine were smooth, it would have much less surface area and would not be able to absorb nutrients efficiently. The villi are essential for making the most of the digestive process.",[119,1628,1629],"absorption","vocabulary",{"id":1631,"section":1474,"level":1484,"prompt":1632,"check":1633,"hints":1644,"solution":1648,"skills":1649},"the-digestive-system.q114","Which of the following is NOT a function of the digestive system?",{"kind":1541,"options":1634,"correct":1643},[1635,1637,1639,1641],{"id":1544,"label":1636},"Breaking down food into usable nutrients",{"id":1547,"label":1638},"Absorbing nutrients into the bloodstream",{"id":1550,"label":1640},"Transporting oxygen to body cells",{"id":1553,"label":1642},"Eliminating waste products from the body",[1550],[1645,1646,1647],"Think about what each body system does","Oxygen transport is handled by a different system","Two of these are clearly digestive functions","The correct answer is **c) Transporting oxygen to body cells**. This is the job of the **respiratory system** (which brings oxygen into the lungs) and the **circulatory system** (which carries oxygen in blood to cells).\n\nThe digestive system actually performs the other three functions:\n- **a)** It breaks down food mechanically (chewing) and chemically (enzymes and acids)\n- **b)** It absorbs nutrients through the walls of the small intestine into the bloodstream\n- **d)** It eliminates solid waste through the large intestine and rectum\n\nSo transporting oxygen is definitely NOT a digestive system function!",[1650,1651,1652],"systems","functions","differentiation",{"id":1654,"section":1474,"level":1484,"prompt":1655,"check":1656,"hints":1661,"solution":1665,"skills":1666},"the-digestive-system.q115","Arrange the following digestive processes in the correct order, from first to last:\n\n1. Absorption of nutrients\n2. Swallowing food\n3. Elimination of waste\n4. Chemical breakdown in stomach\n5. Mechanical breakdown in mouth",{"kind":1487,"accept":1657},[1658,1658,1659,1660],"2,4,1,3,5","25413","2-4-1-3-5",[1662,1663,1664],"Start with what happens when you first eat","Think about where food goes after you swallow","The last step is getting rid of what your body can't use","The correct order is: **2 → 5 → 4 → 1 → 3** (or with the numbers as listed: 2, 5, 4, 1, 3)\n\nLet me trace food through the digestive system:\n\n**Step 2:** You swallow food, pushing it down the esophagus.\n\n**Step 5:** Actually, mechanical breakdown in the mouth (chewing) happens BEFORE swallowing. Wait - let me re-read the options. The swallowing is listed as step 2 in the question's numbering.\n\nLooking at the numbered items:\n1. Absorption of nutrients\n2. Swallowing food  \n3. Elimination of waste\n4. Chemical breakdown in stomach\n5. Mechanical breakdown in mouth\n\nSo the correct chronological order is: **5, 2, 4, 1, 3**\n- **5 (Mechanical breakdown in mouth):** You chew food first\n- **2 (Swallowing):** Then you swallow\n- **4 (Chemical breakdown in stomach):** Food enters the stomach\n- **1 (Absorption):** Nutrients are absorbed in the small intestine\n- **3 (Elimination):** Waste is eliminated",[1667,1668,1669],"sequencing","processes","comprehension",{"id":1671,"section":1474,"level":1484,"prompt":1672,"check":1673,"hints":1676,"solution":1680,"skills":1681},"the-digestive-system.q116","What is the name of the flap that closes over the windpipe (trachea) when you swallow, preventing food from entering your lungs?",{"kind":1487,"accept":1674},[1675],"epiglottis",[1677,1678,1679],"This structure acts like a lid or flap","The name contains 'glottis' which relates to the voice box","It prevents choking by blocking the wrong tube","The **epiglottis** is a flap of cartilage located at the base of your tongue, near the entrance to your windpipe (trachea). When you swallow, the epiglottis closes down like a lid over the trachea, directing food and liquids into the esophagus (food pipe) instead.\n\nThis is a very important protective mechanism! Without the epiglottis, food and liquid could enter your lungs, which would cause choking or serious lung infections like pneumonia. When the epiglottis doesn't work properly, you might cough or feel like you're choking. The \"glottis\" part of the name refers to the opening of the voice box (larynx), so the epiglottis literally means \"above the glottis.\"",[119,1682,1629],"protection",{"id":1684,"section":1474,"level":1484,"prompt":1685,"check":1686,"hints":1697,"solution":1701,"skills":1702},"the-digestive-system.q117","In which part of the digestive system does food stay for the longest amount of time?",{"kind":1541,"options":1687,"correct":1696},[1688,1690,1692,1694],{"id":1544,"label":1689},"Mouth (a few minutes)",{"id":1547,"label":1691},"Stomach (2-4 hours)",{"id":1550,"label":1693},"Small intestine (about 6-8 hours)",{"id":1553,"label":1695},"Large intestine (12-48 hours)",[1553],[1698,1699,1700],"Think about which organ's main job takes the most time","Digestion takes time, but so does another process","Water absorption happens slowly over many hours","The correct answer is **d) Large intestine (12-48 hours)**.\n\nWhile food passes through the mouth in just minutes and the stomach in a few hours, and spends several hours in the small intestine, the **large intestine** holds waste material for the longest time—anywhere from **12 to 48 hours** or even longer.\n\nThis extended stay is necessary because the large intestine's main job is to **slowly absorb water and minerals** from the remaining food material. This process takes time! The water is reabsorbed into the bloodstream, which helps prevent dehydration. The longer stay also allows beneficial bacteria to break down some remaining materials and produce certain vitamins. By the time waste reaches the end of the large intestine, it has become solid feces ready for elimination.",[1703,1651,1704],"timing","large intestine",{"id":1706,"section":1474,"level":1484,"prompt":1707,"check":1708,"hints":1713,"solution":1717,"skills":1718},"the-digestive-system.q118","What is the name of the enzyme in saliva that begins breaking down starches (carbohydrates) in your mouth?",{"kind":1487,"accept":1709},[1710,1711,1712],"amylase","ptyalin","salivary amylase",[1714,1715,1716],"This enzyme starts with 'a'","It's found in your spit\u002Fsaliva","The suffix '-ase' indicates it's an enzyme that breaks things down","The enzyme is **amylase** (also called **salivary amylase** or **ptyalin**).\n\nAmylase is produced by the salivary glands and mixed with food when you chew. It begins the chemical digestion of **starches** (complex carbohydrates) by breaking them down into simpler sugars like **maltose**. This is why if you chew a piece of bread or cracker for a long time, it starts to taste slightly sweet—the amylase is breaking starch into sugar!\n\nHowever, amylase doesn't get much time to work because when you swallow, food quickly moves to the stomach where the acidic environment stops amylase from working. The breakdown of carbohydrates continues later in the small intestine with enzymes from the pancreas.",[1719,1598,1629],"enzymes",{"id":1721,"section":1474,"level":1474,"prompt":1722,"check":1723,"hints":1734,"solution":1738,"skills":1739},"the-digestive-system.q119","What is the main function of the digestive system?\n\nA) To circulate blood around the body\nB) To take in food and break it down into nutrients the body can use\nC) To remove waste from the blood\nD) To pump oxygen to the muscles",{"kind":1541,"options":1724,"correct":1733},[1725,1727,1729,1731],{"id":1544,"label":1726},"To circulate blood around the body",{"id":1547,"label":1728},"To take in food and break it down into nutrients the body can use",{"id":1550,"label":1730},"To remove waste from the blood",{"id":1553,"label":1732},"To pump oxygen to the muscles",[1547],[1735,1736,1737],"Think about what happens when you eat a meal.","The word 'digest' means to break down.","Your body needs nutrients from food for energy and growth.","The digestive system's main job is to process food so the body can use it. Let's look at each option:\n\n- A) Circulating blood is the circulatory system's job\n- B) Breaking down food into usable nutrients is exactly what the digestive system does — this is correct!\n- C) Removing waste from blood is done by the kidneys (urinary system)\n- D) Pumping oxygen to muscles involves the heart and lungs\n\nFood travels through the digestive tract where it is broken down by mechanical action (chewing, churning) and chemical action (enzymes and acids). This releases nutrients like carbohydrates, proteins, fats, vitamins, and minerals that the body absorbs.",[1740,1741,1742],"Digestive system function","Body systems identification","Nutrient absorption",{"id":1744,"section":1474,"level":1474,"prompt":1745,"check":1746,"hints":1755,"solution":1758,"skills":1759},"the-digestive-system.q120","Put the following parts of the digestive system in order from first to last in the journey of food:\n\n1. Small intestine\n2. Mouth\n3. Large intestine\n4. Stomach\n5. Oesophagus",{"kind":1487,"accept":1747},[1748,1749,1750,1751,1752,1753,1754],"2,5,4,1,3","mouth, oesophagus, stomach, small intestine, large intestine","mouth oesophagus stomach small intestine large intestine","2-5-4-1-3","2, 5, 4, 1, 3","mouth → oesophagus → stomach → small intestine → large intestine","2->5->4->1->3",[1492,1756,1757],"The tube connecting your mouth to your stomach is the oesophagus.","Waste leaves through the last part of the system.","The correct order is: **Mouth (2) → Oesophagus (5) → Stomach (4) → Small intestine (1) → Large intestine (3)**\n\nHere's what happens at each stage:\n\n1. **Mouth**: Food is chewed (mechanical digestion) and mixed with saliva which contains enzymes that start breaking down carbohydrates\n2. **Oesophagus**: A muscular tube that pushes food down to the stomach using wave-like contractions called peristalsis\n3. **Stomach**: Food is churned and mixed with gastric juices (hydrochloric acid and enzymes) to break down proteins\n4. **Small intestine**: Most digestion and absorption happens here — nutrients pass into the bloodstream. It's about 6 metres long\n5. **Large intestine**: Water is absorbed and undigested food is formed into faeces\n\nNotice the numbering given in the question: 2 → 5 → 4 → 1 → 3",[1760,1761,1762],"Digestive tract order","Food journey","Anatomy sequencing",{"id":1764,"section":1474,"level":1474,"prompt":1500,"check":1765,"hints":1769,"solution":1773,"skills":1774},"the-digestive-system.q121",{"kind":1487,"accept":1766},[1504,1503,1767,1506,1505,1768],"gullet","the gullet",[1770,1771,1772],"It starts with 'o'.","This tube uses wave-like muscle movements called peristalsis.","It's located behind your windpipe (trachea).","The answer is the **oesophagus** (also spelled 'esophagus' in American English, or sometimes called the 'gullet').\n\nThe oesophagus is a muscular tube about 25 cm long in adults. It connects the pharynx (throat) to the stomach. When you swallow, food enters the oesophagus. The muscles in the oesophagus wall contract in waves — this is called **peristalsis** — which pushes food downward toward the stomach. This happens automatically, so you could still swallow even if you were upside down!\n\nAt the bottom of the oesophagus is a ring of muscle called the lower oesophageal sphincter that opens to let food into the stomach and closes to prevent stomach acid flowing back up.",[1775,1776,1777],"Oesophagus structure","Peristalsis","Swallowing mechanism",{"id":1779,"section":1474,"level":1474,"prompt":1780,"check":1781,"hints":1792,"solution":1796,"skills":1797},"the-digestive-system.q122","In which organ does most of the digestion and absorption of nutrients take place?\n\nA) Stomach\nB) Large intestine\nC) Small intestine\nD) Pancreas",{"kind":1541,"options":1782,"correct":1791},[1783,1785,1787,1789],{"id":1544,"label":1784},"Stomach",{"id":1547,"label":1786},"Large intestine",{"id":1550,"label":1788},"Small intestine",{"id":1553,"label":1790},"Pancreas",[1550],[1793,1794,1795],"This organ is very long — about 6 metres in an adult.","It has a folded inner surface with tiny finger-like projections.","The stomach mainly breaks food down; another organ does most nutrient absorption.","The correct answer is **C) Small intestine**.\n\nLet's understand why:\n\n- **Stomach**: Breaks down food with acid and enzymes, but very little absorption happens here (only some water, alcohol, and certain drugs)\n- **Large intestine**: Absorbs water and minerals, and forms faeces — not where most nutrient absorption occurs\n- **Small intestine**: This is where most digestion is completed and nutrients are absorbed. It's perfectly adapted for this job:\n  - It's 6 metres long, giving lots of time for digestion\n  - Its inner wall is folded and covered in millions of tiny finger-like projections called **villi**\n  - Each villus has even tinier projections called **microvilli** (forming the 'brush border')\n  - These increase the surface area enormously — if spread out, it would cover a tennis court!\n  - Each villus contains blood capillaries and a lymph vessel to transport absorbed nutrients\n- **Pancreas**: Produces digestive enzymes and hormones, but is not where absorption happens\n\nThe huge surface area of the small intestine makes it extremely efficient at absorbing nutrients.",[1798,1799,1742],"Small intestine function","Villi structure",{"id":1801,"section":1474,"level":1474,"prompt":1802,"check":1803,"hints":1808,"solution":1812,"skills":1813},"the-digestive-system.q123","What are the tiny finger-like projections covering the inner wall of the small intestine called?",{"kind":1487,"accept":1804},[1620,1621,1805,1806,1807],"the villi","intestinal villi","small intestine villi",[1809,1810,1811],"They increase the surface area for absorption.","Each one contains blood vessels.","The singular form ends in '-us', plural ends in '-i'.","The answer is **villi** (singular: villus).\n\nVilli are tiny, finger-like projections that cover the inner surface of the small intestine. They are essential for efficient digestion and absorption because they massively increase the surface area. Here's how they work:\n\n- The small intestine is about 6 metres long, but the folds and villi increase its effective surface area to around 30 square metres\n- Each villus is about 0.5-1 mm tall\n- Villi contain a network of blood capillaries and a lymph vessel called a lacteal\n- Digested nutrients like glucose and amino acids pass through the villus cells and into the blood\n- Fats are absorbed into the lacteal (lymph vessel)\n- Each villus cell has even smaller projections on its surface called microvilli, forming a 'brush border' that increases surface area further\n\nThis structure makes the small intestine incredibly efficient at absorbing nutrients from food.",[1814,1815,1816],"Villi anatomy","Surface area adaptation","Absorption efficiency",{"id":1818,"section":1474,"level":1474,"prompt":1819,"check":1820,"hints":1831,"solution":1835,"skills":1836},"the-digestive-system.q124","What substance does the stomach produce to help break down food and kill bacteria?\n\nA) Bile\nB) Insulin\nC) Hydrochloric acid\nD) Saliva",{"kind":1541,"options":1821,"correct":1830},[1822,1824,1826,1828],{"id":1544,"label":1823},"Bile",{"id":1547,"label":1825},"Insulin",{"id":1550,"label":1827},"Hydrochloric acid",{"id":1553,"label":1829},"Saliva",[1550],[1832,1833,1834],"This substance makes the stomach very acidic.","The stomach has a pH of about 1-3.","It begins with 'H'.","The correct answer is **C) Hydrochloric acid**.\n\nLet's examine each option:\n\n- **A) Bile**: Produced by the liver and stored in the gall bladder, bile helps digest fats in the *small intestine* — not the stomach\n- **B) Insulin**: A hormone produced by the pancreas that controls blood sugar levels — not involved in stomach digestion\n- **C) Hydrochloric acid**: Correct! The stomach lining contains parietal cells that produce hydrochloric acid (HCl). This makes the stomach extremely acidic (pH 1-3), which:\n  - Activates pepsinogen into pepsin (an enzyme that digests proteins)\n  - Helps break down food physically\n  - Kills most harmful bacteria that enter with food\n- **D) Saliva**: Produced by salivary glands in the mouth, containing the enzyme amylase to start carbohydrate digestion\n\nThe stomach also produces mucus to protect its own lining from being digested by the acid. Without this protective mucus layer, the acid would damage the stomach wall.",[1837,1827,1838],"Stomach acid function","Enzyme activation",{"id":1840,"section":1474,"level":1474,"prompt":1841,"check":1842,"hints":1853,"solution":1857,"skills":1858},"the-digestive-system.q125","The liver produces a greenish-yellow fluid that helps break down fats. What is this fluid called, and where is it stored before being released into the small intestine?\n\nA) Pepsin, stored in the stomach\nB) Bile, stored in the gall bladder\nC) Lipase, stored in the pancreas\nD) Amylase, stored in the salivary glands",{"kind":1541,"options":1843,"correct":1852},[1844,1846,1848,1850],{"id":1544,"label":1845},"Pepsin, stored in the stomach",{"id":1547,"label":1847},"Bile, stored in the gall bladder",{"id":1550,"label":1849},"Lipase, stored in the pancreas",{"id":1553,"label":1851},"Amylase, stored in the salivary glands",[1547],[1854,1855,1856],"This fluid is greenish-yellow in colour.","It emulsifies fats — breaks large fat droplets into smaller ones.","Storage organ is small and pear-shaped, located under the liver.","The correct answer is **B) Bile, stored in the gall bladder**.\n\nLet me explain how this works:\n\n**Bile** is produced continuously by the **liver** — the largest internal organ in the body. Bile has several important functions:\n- It **emulsifies fats** — breaks large fat globules into tiny droplets, increasing surface area for enzymes to work on\n- Bile is **alkaline**, so it helps neutralise stomach acid when food enters the small intestine\n- It does **not** contain enzymes itself — it helps digestion mechanically, not chemically\n\nThe **gall bladder** is a small, pear-shaped organ that sits underneath the liver. It stores and concentrates bile between meals. When fatty food enters the small intestine, hormones signal the gall bladder to squeeze and release bile through a tube called the bile duct.\n\nWhy the other answers are wrong:\n- **Pepsin** is a protein-digesting enzyme in the stomach, not a fluid for fat digestion\n- **Lipase** IS a fat-digesting enzyme, but it's made by the pancreas and acts in the small intestine, not stored for release\n- **Amylase** digests carbohydrates, not fats",[1859,1860,1861],"Bile production","Fat digestion","Liver and gall bladder function",{"id":1863,"section":1474,"level":1474,"prompt":1864,"check":1865,"hints":1876,"solution":1880,"skills":1881},"the-digestive-system.q126","After food is digested in the small intestine, water and minerals are mainly absorbed in which organ, and what is the remaining undigested material called when it leaves the body?\n\nA) Small intestine; urine\nB) Large intestine; faeces\nC) Stomach; bile\nD) Liver; chyme",{"kind":1541,"options":1866,"correct":1875},[1867,1869,1871,1873],{"id":1544,"label":1868},"Small intestine; urine",{"id":1547,"label":1870},"Large intestine; faeces",{"id":1550,"label":1872},"Stomach; bile",{"id":1553,"label":1874},"Liver; chyme",[1547],[1877,1878,1879],"This organ is wider but shorter than the small intestine.","It's about 1.5 metres long.","The material that leaves the body through the anus has a specific name.","The correct answer is **B) Large intestine; faeces**.\n\nHere is the full explanation:\n\n**The Large Intestine (colon)**\n- About 1.5 metres long and wider than the small intestine\n- By the time digested food reaches here, most nutrients have already been absorbed in the small intestine\n- The large intestine's main jobs are:\n  - Absorbing water and remaining minerals (about 1.5 litres of water daily)\n  - Absorbing vitamins produced by beneficial bacteria that live there\n  - Moving the remaining material toward the rectum\n\n**What remains?**\n- Indigestible fibre (plant cell walls)\n- Dead bacteria\n- Cells shed from the gut lining\n- Some water\n\nThis material is called **faeces** (or stool). It is stored in the rectum until it leaves the body through the anus.\n\nWhy other answers are wrong:\n- **Urine** is produced by kidneys from blood filtration, not from undigested food\n- **Bile** is a digestive fluid, not waste material\n- **Chyme** is the name for the semi-liquid food leaving the stomach, entering the small intestine",[1882,1883,1884],"Large intestine function","Water absorption","Faeces formation",{"id":1886,"section":1474,"level":1474,"prompt":1887,"check":1888,"hints":1890,"solution":1894,"skills":1895},"the-digestive-system.q127","What is the name of the long, muscular tube that connects the mouth to the stomach?",{"kind":1487,"accept":1889},[1503,1504],[1891,1892,1893],"It starts with the letter 'e'.","It uses wave-like muscle contractions called peristalsis to move food.","The American spelling starts with 'e', while British spelling starts with 'oe'.","The esophagus (spelled oesophagus in British English) is the muscular tube that carries food from the mouth down to the stomach. It is about 25 centimeters long in adults. When you swallow, muscles in the esophagus walls squeeze together in a wave-like motion called peristalsis. This pushes the food downward even if you are standing on your head! The esophagus has a special valve at the bottom called the lower esophageal sphincter that opens to let food into the stomach and then closes to prevent stomach acid from flowing back up.",[1896,1561],"digestive anatomy",{"id":1898,"section":1474,"level":1474,"prompt":1899,"check":1900,"hints":1908,"solution":1911,"skills":1912},"the-digestive-system.q128","Arrange the following organs in the correct order that food passes through them:\n\n1. Stomach\n2. Large intestine\n3. Esophagus\n4. Small intestine\n5. Mouth",{"kind":1487,"accept":1901},[1902,1903,1904,1905,1906,1907],"5, 3, 1, 4, 2","mouth, esophagus, stomach, small intestine, large intestine","5-3-1-4-2","5,3,1,4,2","5. 3. 1. 4. 2.","mouth esophagus stomach small intestine large intestine",[1492,1909,1910],"The stomach comes after the tube that carries food from the mouth.","The small intestine comes right before the large intestine.","The correct order is: 5. Mouth → 3. Esophagus → 1. Stomach → 4. Small intestine → 2. Large intestine.\n\nHere is the journey of food through the digestive system:\n\n1. **Mouth**: Food enters the body. Teeth break it into smaller pieces, and saliva begins to break down starches.\n2. **Esophagus**: A muscular tube that uses peristalsis to transport food to the stomach.\n3. **Stomach**: A muscular bag that churns food and mixes it with gastric juices. Proteins begin to break down here.\n4. **Small intestine**: The longest part of the digestive tract (about 6-7 meters long in adults). Most digestion and absorption of nutrients occurs here. Enzymes from the pancreas and bile from the liver help break down fats, proteins, and carbohydrates.\n5. **Large intestine**: Water and minerals are absorbed here, and waste is formed into feces before being eliminated through the rectum and anus.",[1497,1561],{"id":1914,"section":1474,"level":1474,"prompt":1915,"check":1916,"hints":1927,"solution":1931,"skills":1932},"the-digestive-system.q129","What is the primary role of the small intestine in digestion?",{"kind":1541,"options":1917,"correct":1926},[1918,1920,1922,1924],{"id":1544,"label":1919},"To store undigested food before elimination",{"id":1547,"label":1921},"To break down food using strong acid and kill bacteria",{"id":1550,"label":1923},"To absorb water and form solid waste",{"id":1553,"label":1925},"To complete most digestion and absorb nutrients into the bloodstream",[1553],[1928,1929,1930],"The small intestine receives help from the liver and pancreas.","It has a very large surface area due to tiny projections.","Nutrients pass through its walls into blood vessels.","The correct answer is D: To complete most digestion and absorb nutrients into the bloodstream.\n\nThe small intestine is approximately 6 to 7 meters long in adults and is where the majority of digestion and nutrient absorption takes place. Here's how it works:\n\n1. **Digestion**: The small intestine receives partially digested food from the stomach. The pancreas secretes digestive enzymes that break down carbohydrates, proteins, and fats. The liver produces bile (stored in the gallbladder) which helps break down fats.\n\n2. **Absorption**: The inner wall of the small intestine is covered with millions of tiny finger-like projections called villi. Each villus contains even smaller projections called microvilli. Together, these increase the surface area of the small intestine to about 250 square meters — roughly the size of a tennis court! This massive surface area allows for efficient absorption of nutrients (sugars, amino acids, fatty acids, vitamins, and minerals) into the bloodstream through tiny blood vessels in the villi.\n\nOptions A and C describe functions of the large intestine. Option B describes a function of the stomach.",[1933,1536],"small intestine function",{"id":1935,"section":1474,"level":1474,"prompt":1936,"check":1937,"hints":1939,"solution":1943,"skills":1944},"the-digestive-system.q130","The liver produces bile, which helps break down fats. Where is bile stored before it is released into the small intestine?",{"kind":1487,"accept":1938},[1605,1607],[1940,1941,1942],"This small, pear-shaped organ sits underneath the liver.","Its name contains the word 'gall', an old term for bile.","It contracts to squirt bile into the small intestine when fatty food arrives.","Bile is stored in the **gallbladder**.\n\nThe liver continuously produces bile, a greenish-yellow fluid that helps break down fats into smaller droplets (a process called emulsification). However, bile is not sent directly to the small intestine all the time. Instead, it flows from the liver into the gallbladder, a small, pear-shaped organ located beneath the liver that can store about 30-50 milliliters of bile.\n\nWhen you eat a meal containing fats, the gallbladder contracts and squeezes stored bile through a tube called the bile duct into the small intestine (specifically the duodenum, the first part of the small intestine). The bile mixes with fats, breaking them into tiny droplets that enzymes can more easily digest.\n\nIf someone has their gallbladder removed, bile still flows directly from the liver to the small intestine, but there is no longer a storage reservoir, so large fatty meals may be harder to digest.",[1945,1614],"liver function",{"id":1947,"section":1474,"level":1474,"prompt":1948,"check":1949,"hints":1951,"solution":1955,"skills":1956},"the-digestive-system.q131","What are the tiny, finger-like projections that cover the inner wall of the small intestine and greatly increase its surface area for absorption?",{"kind":1487,"accept":1950},[1620,1621],[1952,1953,1954],"The singular form ends in '-us' and the plural ends in '-i'.","Each one contains a network of blood capillaries.","They make the small intestine's surface look like velvet under a microscope.","These structures are called **villi** (singular: villus).\n\nVilli are tiny, finger-like projections that cover the mucosal lining of the small intestine. Each villus is approximately 0.5 to 1.5 millimeters long, and there are millions of them. The villi themselves are covered with even smaller microscopic projections called **microvilli**, which together form a structure known as the **brush border**.\n\nThis arrangement dramatically increases the surface area available for nutrient absorption. Without villi and microvilli, the small intestine would have a surface area of about 0.3 square meters. With them, the surface area expands to approximately 250 square meters — about the size of a tennis court!\n\nEach villus contains:\n- A network of blood capillaries to absorb sugars, amino acids, water, and minerals\n- A lymphatic vessel called a lacteal to absorb fatty acids and glycerol\n\nOnce nutrients pass through the cells of the villus, they enter the bloodstream and are transported to the liver for processing before being distributed to cells throughout the body.",[1957,1958],"absorption structures","surface area",{"id":1960,"section":1474,"level":1474,"prompt":1961,"check":1962,"hints":1964,"solution":1967,"skills":1968},"the-digestive-system.q132","After food is digested in the small intestine, water and minerals are mainly absorbed in which organ?",{"kind":1487,"accept":1963},[1704],[1877,1965,1966],"It is about 1.5 meters long in adults.","The remaining material becomes feces in this organ.","Water and minerals are mainly absorbed in the **large intestine** (also called the colon).\n\nAfter food passes through the small intestine, most nutrients have already been absorbed. What remains is mostly water, undigested fiber, some minerals, and bacteria. This liquid mixture enters the large intestine, which is about 1.5 meters long and 6.5 centimeters in diameter.\n\nThe large intestine performs several important functions:\n\n1. **Water absorption**: The walls of the large intestine absorb most of the remaining water (about 1 liter per day), making the waste material more solid.\n\n2. **Mineral absorption**: Important minerals such as sodium and potassium are absorbed here.\n\n3. **Bacterial action**: Trillions of beneficial bacteria live in the large intestine. They help break down some undigested fibers, produce certain vitamins (like vitamin K and some B vitamins), and protect against harmful bacteria.\n\n4. **Waste formation**: The remaining material is compacted into feces, which is stored in the rectum until it is eliminated through the anus.\n\nWithout the large intestine's water absorption, we would lose too much water and become dehydrated very quickly.",[1969,1562],"large intestine function",{"id":1971,"section":1474,"level":1474,"prompt":1972,"check":1973,"hints":1984,"solution":1988,"skills":1989},"the-digestive-system.q133","Which two organs produce substances that help break down food in the small intestine, but are NOT part of the tube that food actually travels through?",{"kind":1541,"options":1974,"correct":1983},[1975,1977,1979,1981],{"id":1544,"label":1976},"Stomach and liver",{"id":1547,"label":1978},"Liver and pancreas",{"id":1550,"label":1980},"Pancreas and gallbladder",{"id":1553,"label":1982},"Esophagus and large intestine",[1547],[1985,1986,1987],"These are called 'accessory organs' because they assist digestion from outside the main digestive tract.","One produces bile; the other produces digestive enzymes and bicarbonate.","The gallbladder only stores a substance made by another organ.","The correct answer is B: Liver and pancreas.\n\nThe liver and pancreas are known as **accessory organs** of the digestive system. They produce substances essential for digestion, but food does not pass through them — they are connected to the small intestine by ducts.\n\n**The Liver:**\n- Produces bile, which breaks down fats into tiny droplets (emulsification)\n- Processes nutrients absorbed from the small intestine\n- Detoxifies harmful substances\n\n**The Pancreas:**\n- Produces pancreatic juice containing digestive enzymes that break down carbohydrates (amylase), proteins (trypsin), and fats (lipase)\n- Produces bicarbonate to neutralize stomach acid when it enters the small intestine\n- Produces hormones insulin and glucagon that regulate blood sugar (endocrine function)\n\nThe **gallbladder** (Option C) is also an accessory organ, but it only stores and concentrates bile — it does not produce it. The stomach and esophagus (Options A and D) are part of the digestive tube itself that food passes through.",[1990,1991],"accessory organs","enzyme production",{"id":1993,"section":1474,"level":1474,"prompt":1994,"check":1995,"hints":1998,"solution":2002,"skills":2003},"the-digestive-system.q134","What is the name of the wavelike muscle contractions that push food through the digestive tract?",{"kind":1487,"accept":1996},[1997],"peristalsis",[1999,2000,2001],"This process also pushes a ball of food down the esophagus when you swallow upside down.","The word starts with 'p' and ends with '-sis'.","It involves circular muscles contracting behind food and relaxing in front of it.","These wavelike muscle contractions are called **peristalsis**.\n\nPeristalsis is an involuntary process, meaning you cannot consciously control it. It works through a coordinated sequence of muscle contractions:\n\n1. **Circular muscles** behind the food contract, squeezing it forward.\n2. **Longitudinal muscles** ahead of the food contract, shortening that section of the tube.\n3. The muscles behind then relax, allowing the tube to expand and receive more food.\n\nThis creates a wave-like motion that propels food along the entire digestive tract — from the esophagus to the stomach, through the small intestine, and into the large intestine.\n\nPeristalsis continues even if you are upside down, which is why you can swallow food or drink while standing on your head! The muscles are strong enough to overcome gravity.\n\nIn the esophagus, peristalsis moves food at about 2-4 centimeters per second, taking about 6-10 seconds for food to reach the stomach after swallowing. In the small intestine, peristalsis is slower and mixes food with digestive juices while gradually pushing it toward the large intestine — a journey that takes 3-5 hours.",[1997,2004],"muscle contractions",{"id":2006,"section":1474,"level":1474,"prompt":2007,"check":2008,"hints":2022,"solution":2026,"skills":2027},"the-digestive-system.q135","The digestive system breaks food down into simpler nutrients the body can absorb. Put these five stages in the correct order from start to finish:\n\nA) Elimination of waste\nB) Mechanical breakdown in the mouth\nC) Chemical digestion in the stomach\nD) Nutrient absorption in the small intestine\nE) Water absorption in the large intestine\n\nWhich answer shows the correct sequence?",{"kind":1541,"options":2009,"correct":2021},[2010,2012,2014,2016,2018],{"id":1544,"label":2011},"A → B → C → D → E",{"id":1547,"label":2013},"B → C → D → E → A",{"id":1550,"label":2015},"B → D → C → E → A",{"id":1553,"label":2017},"C → B → D → E → A",{"id":2019,"label":2020},"e","B → C → E → D → A",[1547],[2023,2024,2025],"Think about what happens first when you take a bite of food.","Where does food go after leaving the stomach?","What is the very last thing that happens to undigested food?","1. **B) Mechanical breakdown in the mouth** — Food is chewed and mixed with saliva. This is always the first step.\n2. **C) Chemical digestion in the stomach** — The chewed food passes down the esophagus to the stomach, where acid and enzymes break it down further.\n3. **D) Nutrient absorption in the small intestine** — From the stomach, food moves to the small intestine, where most nutrients are absorbed into the bloodstream.\n4. **E) Water absorption in the large intestine** — Next, remaining material enters the large intestine, where water and minerals are absorbed.\n5. **A) Elimination of waste** — Finally, solid waste is stored and then removed from the body.\n\nThe correct order is **B → C → D → E → A**, which is answer **B**.",[2028,2029,2030],"Sequence recall","Digestive anatomy","Process understanding",{"id":2032,"section":1474,"level":1474,"prompt":2033,"check":2034,"hints":2045,"solution":2049,"skills":2050},"the-digestive-system.q136","The pancreas and salivary glands are both **accessory organs** of the digestive system. What does \"accessory organ\" mean in this context?\n\nA) They are the most important organs for digestion.\nB) They help with digestion but are not part of the continuous digestive tube that food passes through.\nC) They are only needed for digesting special types of food.\nD) They store food before it is digested.",{"kind":1541,"options":2035,"correct":2044},[2036,2038,2040,2042],{"id":1544,"label":2037},"They are the most important organs for digestion.",{"id":1547,"label":2039},"They help with digestion but are not part of the continuous digestive tube that food passes through.",{"id":1550,"label":2041},"They are only needed for digesting special types of food.",{"id":1553,"label":2043},"They store food before it is digested.",[1547],[2046,2047,2048],"Food travels through a tube from mouth to anus. Does food go through the pancreas?","The salivary glands release saliva into the mouth, but does food pass through the glands themselves?","Think about whether these organs are inside the path food follows, or outside helping from nearby.","The digestive system includes one long, continuous tube called the **alimentary canal** (or gastrointestinal tract), which runs from the mouth to the anus. Food physically passes through this tube.\n\n**Accessory organs** are organs that help with digestion but are **not part of this continuous tube**. Instead, they produce substances that are released into the tube at various points:\n- **Salivary glands** produce saliva, which enters the mouth through ducts.\n- **The pancreas** produces digestive enzymes that flow into the small intestine.\n- **The liver** produces bile, which is stored in the gallbladder and released into the small intestine.\n\nFood never passes directly through any of these organs. Therefore, the correct answer is **B**: they help with digestion but are not part of the continuous digestive tube that food passes through.\n\nAnswer **A** is incorrect because the small intestine is arguably the most important site for absorption. Answer **C** is incorrect because these organs help with everyday digestion of all foods. Answer **D** is incorrect because storage is the job of the stomach and large intestine, not these glands.",[2051,2029,2052],"Vocabulary in context","Classification",{"id":2054,"section":1478,"level":1478,"prompt":2055,"check":2056,"hints":2067,"solution":2071,"skills":2072},"the-digestive-system.q137","In the human digestive system, food passes through several organs in a specific order. Which of the following shows the **correct** path of food from start to finish?\n\nA) Mouth → Stomach → Esophagus → Small intestine → Large intestine\n\nB) Mouth → Esophagus → Stomach → Small intestine → Large intestine\n\nC) Mouth → Esophagus → Stomach → Large intestine → Small intestine\n\nD) Mouth → Stomach → Esophagus → Large intestine → Small intestine",{"kind":1541,"options":2057,"correct":2066},[2058,2060,2062,2064],{"id":1544,"label":2059},"Mouth → Stomach → Esophagus → Small intestine → Large intestine",{"id":1547,"label":2061},"Mouth → Esophagus → Stomach → Small intestine → Large intestine",{"id":1550,"label":2063},"Mouth → Esophagus → Stomach → Large intestine → Small intestine",{"id":1553,"label":2065},"Mouth → Stomach → Esophagus → Large intestine → Small intestine",[1547],[2068,2069,2070],"Think about what happens right after you swallow food.","The esophagus is the tube that connects the mouth to the stomach.","The small intestine comes before the large intestine in the digestive process.","The correct order is: Mouth → Esophagus → Stomach → Small intestine → Large intestine.\n\nHere's why: When you eat, food first enters the **mouth** where it is chewed and mixed with saliva. When you swallow, the food travels down the **esophagus** (a muscular tube) to reach the **stomach**. In the stomach, food is mixed with acid and enzymes. From the stomach, partially digested food moves to the **small intestine**, where most digestion and nutrient absorption occurs. Finally, remaining waste passes to the **large intestine** (colon), where water is absorbed and waste is prepared for elimination.\n\nOption A is wrong because the stomach comes after the esophagus, not before. Option C is wrong because the small intestine comes before the large intestine. Option D has multiple errors in ordering.",[1760,2073],"Organ function sequencing",{"id":2075,"section":1478,"level":1478,"prompt":2076,"check":2077,"hints":2088,"solution":2092,"skills":2093},"the-digestive-system.q138","The **small intestine** is where most digestion and nutrient absorption occurs. It is divided into three parts. What are these three parts, in order from where food first enters to where it exits?\n\nA) Ileum, Jejunum, Duodenum\n\nB) Duodenum, Ileum, Jejunum\n\nC) Duodenum, Jejunum, Ileum\n\nD) Jejunum, Duodenum, Ileum",{"kind":1541,"options":2078,"correct":2087},[2079,2081,2083,2085],{"id":1544,"label":2080},"Ileum, Jejunum, Duodenum",{"id":1547,"label":2082},"Duodenum, Ileum, Jejunum",{"id":1550,"label":2084},"Duodenum, Jejunum, Ileum",{"id":1553,"label":2086},"Jejunum, Duodenum, Ileum",[1550],[2089,2090,2091],"The first part connects directly to the stomach.","The names are alphabetical in order: D, J, I.","The duodenum receives enzymes from the pancreas and bile from the liver.","The three parts of the small intestine, in order, are: **Duodenum → Jejunum → Ileum**.\n\nAfter leaving the stomach, food first enters the **duodenum**, which is the shortest section (about 25-30 cm long). Here, food mixes with bile from the gallbladder and digestive enzymes from the pancreas. Next, food moves to the **jejunum**, where most nutrient absorption takes place. Finally, food reaches the **ileum**, which absorbs remaining nutrients, especially vitamin B12 and bile salts, before passing to the large intestine.\n\nA helpful memory trick: the order is alphabetical — **D**uodenum, **J**ejunum, **I**leum.",[2094,2095],"Small intestine anatomy","Nutrient absorption locations",{"id":2097,"section":1478,"level":1478,"prompt":2098,"check":2099,"hints":2108,"solution":2112,"skills":2113},"the-digestive-system.q139","Which organ produces **bile**, a substance that helps digest fats?\n\nA) Gallbladder\n\nB) Pancreas\n\nC) Liver\n\nD) Stomach",{"kind":1541,"options":2100,"correct":2107},[2101,2103,2104,2106],{"id":1544,"label":2102},"Gallbladder",{"id":1547,"label":1790},{"id":1550,"label":2105},"Liver",{"id":1553,"label":1784},[1550],[2109,2110,2111],"This organ is the largest internal organ in the human body.","The gallbladder stores something but does not produce it.","Bile is a greenish-yellow fluid.","The **liver** produces bile.\n\nThe liver is the largest internal organ in the human body and has many functions. One important function is producing **bile**, a greenish-yellow fluid that helps break down fats into smaller droplets that enzymes can more easily digest. \n\nAfter the liver produces bile, it is stored and concentrated in the **gallbladder**. When fatty food enters the duodenum, the gallbladder releases this stored bile. The **pancreas** produces digestive enzymes but not bile. The **stomach** produces gastric acid and pepsin for protein digestion, not bile.\n\nSo while the gallbladder is involved with bile, it only stores it — the liver is the producer.",[1859,2114,2115],"Liver functions","Accessory organ roles",{"id":2117,"section":1478,"level":1478,"prompt":2118,"check":2119,"hints":2130,"solution":2134,"skills":2135},"the-digestive-system.q140","The enzyme **pepsin** breaks down proteins in the stomach. What is the optimal pH for pepsin to work, and why is this p level important?\n\nA) pH 7 (neutral), because most enzymes work best at neutral pH\n\nB) pH 2 (very acidic), because pepsin needs hydrochloric acid to be activated\n\nC) pH 10 (basic), because alkaline conditions help unfold proteins\n\nD) pH 5 (slightly acidic), because this is the average pH of the human body",{"kind":1541,"options":2120,"correct":2129},[2121,2123,2125,2127],{"id":1544,"label":2122},"pH 7 (neutral), because most enzymes work best at neutral pH",{"id":1547,"label":2124},"pH 2 (very acidic), because pepsin needs hydrochloric acid to be activated",{"id":1550,"label":2126},"pH 10 (basic), because alkaline conditions help unfold proteins",{"id":1553,"label":2128},"pH 5 (slightly acidic), because this is the average pH of the human body",[1547],[2131,2132,2133],"The stomach produces a strong acid.","Think about what 'gastric acid' means.","Pepsin is specifically adapted to the stomach environment.","The correct answer is **pH 2 (very acidic)**, because pepsin needs hydrochloric acid to be activated.\n\nThe stomach lining contains **parietal cells** that produce **hydrochloric acid (HCl)**, making the stomach environment extremely acidic with a pH between 1.5 and 3.5. This acidity serves multiple purposes: it kills harmful bacteria in food, helps break down food physically, and most importantly for this question — **activates pepsinogen into pepsin**.\n\nPepsinogen is the inactive form of the enzyme. Only in the presence of HCl does it become active pepsin. Pepsin then breaks protein chains into smaller peptides. If the pH were neutral or basic, pepsin would not activate and would actually be denatured (destroyed). This is why pepsin works only in the stomach and not in the small intestine, where pH becomes neutral to slightly basic due to bicarbonate from the pancreas.",[1838,1837,2136],"pH and digestion",{"id":2138,"section":1478,"level":1478,"prompt":2139,"check":2140,"hints":2151,"solution":2155,"skills":2156},"the-digestive-system.q141","The **villi** and **microvilli** in the small intestine greatly increase surface area for absorption. About how much does the small intestine's internal surface area increase due to these structures, compared to a smooth tube of the same length?\n\nA) About 2 times larger\n\nB) About 10 times larger\n\nC) About 100 times larger\n\nD) About 600 times larger",{"kind":1541,"options":2141,"correct":2150},[2142,2144,2146,2148],{"id":1544,"label":2143},"About 2 times larger",{"id":1547,"label":2145},"About 10 times larger",{"id":1550,"label":2147},"About 100 times larger",{"id":1553,"label":2149},"About 600 times larger",[1553],[2152,2153,2154],"Consider that there are two levels of folding: villi and then microvilli on top of those.","The small intestine is only about 6 meters long but has a surface area of roughly 200-250 square meters.","Think about the vast surface needed to absorb all nutrients efficiently.","The correct answer is **about 600 times larger**.\n\nThe small intestine is only about 6 meters (20 feet) long and 2.5-3 cm in diameter. If it were a simple smooth tube, its surface area would be quite small. However, three structural adaptations massively increase this:\n\n1. **Circular folds (plicae circulares)**: These permanent ridges triple the surface area.\n\n2. **Villi**: These are finger-like projections covering the entire inner surface, increasing area by another factor of about 10. Each villus contains blood capillaries and a lacteal (lymph vessel) to absorb nutrients.\n\n3. **Microvilli**: These are microscopic hair-like projections on each villus cell, creating a \"brush border\" that increases surface area by another factor of about 20.\n\nCombined, these structures increase the surface area from about 0.3 m² (smooth tube) to approximately **200-250 m²** — roughly the size of a tennis court! This massive surface area is essential for efficient nutrient absorption, as food spends only 3-6 hours in the small intestine.",[1815,2157,2158],"Villus structure","Efficiency of absorption",{"id":2160,"section":1478,"level":1478,"prompt":2161,"check":2162,"hints":2173,"solution":2177,"skills":2178},"the-digestive-system.q142","During digestion, carbohydrates are broken down into simple sugars. What is the **final enzyme** that completes the digestion of carbohydrates in the small intestine, and what does it produce?\n\nA) Amylase, producing glucose\n\nB) Maltase, producing glucose\n\nC) Sucrase, producing fructose and glucose\n\nD) Lactase, producing galactose and glucose",{"kind":1541,"options":2163,"correct":2172},[2164,2166,2168,2170],{"id":1544,"label":2165},"Amylase, producing glucose",{"id":1547,"label":2167},"Maltase, producing glucose",{"id":1550,"label":2169},"Sucrase, producing fructose and glucose",{"id":1553,"label":2171},"Lactase, producing galactose and glucose",[1547],[2174,2175,2176],"The question asks for the enzyme that completes digestion, acting on the final intermediate products.","Amylase starts carbohydrate digestion but does not finish it.","Maltose is a disaccharide that needs to be split into single units.","The correct answer is **maltase, producing glucose**.\n\nCarbohydrate digestion happens in stages:\n\n1. **Salivary amylase** in the mouth and **pancreatic amylase** in the small intestine break down starch into shorter chains (maltose, maltotriose, and limit dextrins).\n\n2. Brush border enzymes on the microvilli then **complete** digestion. The main enzyme that finishes this process is **maltase**, which breaks maltose (a disaccharide of two glucose units) into **glucose** — the simplest form that can be absorbed into the blood.\n\nWhile **sucrase** breaks sucrose into fructose and glucose, and **lactase** breaks lactose into galactose and glucose, these enzymes act on specific sugars. **Maltase** is the enzyme that handles the most common intermediate product from starch digestion (maltose) and produces glucose, the final simple sugar that cells can directly use for energy.\n\nAmylase is incorrect because it only partially digests carbohydrates and produces maltose, not glucose.",[2179,2180,2181],"Carbohydrate digestion","Enzyme specificity","Glucose production",{"id":2183,"section":1478,"level":1478,"prompt":2184,"check":2185,"hints":2196,"solution":2200,"skills":2201},"the-digestive-system.q143","The **large intestine** (colon) has several regions. Starting from where the small intestine connects, what is the correct order of these regions?\n\nA) Ascending colon → Transverse colon → Descending colon → Sigmoid colon\n\nB) Transverse colon → Ascending colon → Descending colon → Sigmoid colon\n\nC) Descending colon → Transverse colon → Ascending colon → Sigmoid colon\n\nD) Sigmoid colon → Descending colon → Transverse colon → Ascending colon",{"kind":1541,"options":2186,"correct":2195},[2187,2189,2191,2193],{"id":1544,"label":2188},"Ascending colon → Transverse colon → Descending colon → Sigmoid colon",{"id":1547,"label":2190},"Transverse colon → Ascending colon → Descending colon → Sigmoid colon",{"id":1550,"label":2192},"Descending colon → Transverse colon → Ascending colon → Sigmoid colon",{"id":1553,"label":2194},"Sigmoid colon → Descending colon → Transverse colon → Ascending colon",[1544],[2197,2198,2199],"Think about the anatomical position: 'ascending' means going up.","Food enters the large intestine on the lower right side of the abdomen.","The path follows an inverted U or frame shape around the abdomen.","The correct answer is **Ascending colon → Transverse colon → Descending colon → Sigmoid colon**.\n\nThe ileum (end of small intestine) connects to the **cecum** in the lower right abdomen. From there:\n\n1. **Ascending colon**: Travels upward on the **right side** of the abdomen.\n\n2. **Transverse colon**: Crosses horizontally **across the upper abdomen** below the stomach.\n\n3. **Descending colon**: Travels downward on the **left side** of the abdomen.\n\n4. **Sigmoid colon**: Forms an S-shaped curve in the **lower left abdomen**, connecting to the rectum.\n\nThis path forms a frame-like shape around the abdominal cavity. The names are directional clues: ascending = going up, transverse = going across, descending = going down. The sigmoid colon is named for its S-shape (sigma-like). Together, these regions move waste slowly (12-48 hours) while absorbing water and electrolytes to form solid feces.",[2202,2203,2204],"Large intestine anatomy","Colon regions","Waste movement",{"id":2206,"section":1478,"level":1478,"prompt":2207,"check":2208,"hints":2219,"solution":2223,"skills":2224},"the-digestive-system.q144","**Peristalsis** is the wave-like muscle contraction that moves food through the digestive tract. Which type of muscle tissue is primarily responsible for peristalsis in the esophagus, and what makes this muscle special?\n\nA) Skeletal muscle, because it is under voluntary control\n\nB) Smooth muscle, because it contracts involuntarily and can maintain contraction for long periods\n\nC) Cardiac muscle, because it has automatic rhythmic contractions\n\nD) Striated muscle, because it is found in both voluntary and involuntary forms in the digestive tract",{"kind":1541,"options":2209,"correct":2218},[2210,2212,2214,2216],{"id":1544,"label":2211},"Skeletal muscle, because it is under voluntary control",{"id":1547,"label":2213},"Smooth muscle, because it contracts involuntarily and can maintain contraction for long periods",{"id":1550,"label":2215},"Cardiac muscle, because it has automatic rhythmic contractions",{"id":1553,"label":2217},"Striated muscle, because it is found in both voluntary and involuntary forms in the digestive tract",[1547],[2220,2221,2222],"The esophagus works even when you are asleep.","Think about whether you can control digestion consciously.","Cardiac muscle is only found in one place in the body.","The correct answer is **smooth muscle, because it contracts involuntarily and can maintain contraction for long periods**.\n\nThe digestive tract from the esophagus to the anus contains layers of **smooth muscle** in its walls. This muscle differs from skeletal muscle in several important ways:\n\n- **Involuntary control**: You cannot consciously start or stop peristalsis — it is controlled by the autonomic nervous system.\n\n- **Slow, sustained contractions**: Smooth muscle can maintain contraction (tone) for long periods without tiring, unlike skeletal muscle which fatigues quickly.\n\n- **Wavelike coordination**: Circular and longitudinal muscle layers coordinate to squeeze food forward while relaxing behind it.\n\nWhile the **upper esophagus** does contain some skeletal muscle (allowing voluntary initiation of swallowing), most of the esophagus and the entire rest of the digestive tract uses smooth muscle. **Cardiac muscle** is found only in the heart. The esophagus's smooth muscle capability for sustained, rhythmic, involuntary contraction makes peristalsis efficient for moving material through the 9-meter total digestive tract.",[2225,2226,2227],"Peristalsis mechanism","Smooth muscle properties","Involuntary digestion control",{"id":2229,"section":1478,"level":1478,"prompt":2230,"check":2231,"hints":2238,"solution":2242,"skills":2243},"the-digestive-system.q145","In the human digestive system, most chemical digestion is completed in a specific organ before nutrients are absorbed. Which organ produces a digestive juice containing **bicarbonate** to neutralize stomach acid, plus enzymes that break down carbohydrates, proteins, and fats?\n\nA) Stomach\nB) Liver\nC) Pancreas\nD) Gallbladder",{"kind":1541,"options":2232,"correct":2237},[2233,2234,2235,2236],{"id":1544,"label":1784},{"id":1547,"label":2105},{"id":1550,"label":1790},{"id":1553,"label":2102},[1550],[2239,2240,2241],"Think about which organ has both an exocrine function (producing digestive enzymes) and an endocrine function.","The organ sits behind the stomach and connects to the duodenum via a duct.","Bicarbonate raises pH so that enzymes can work effectively in the small intestine.","The correct answer is **C) Pancreas**.\n\nThe **pancreas** produces pancreatic juice containing:\n- **Bicarbonate**: This alkaline substance neutralizes the highly acidic chyme coming from the stomach, raising the pH from about 2 to around 7-8. This creates a suitable environment for enzymes to function.\n- **Enzymes**: The pancreas secretes enzymes for all major macronutrients:\n  - **Amylase** — breaks down carbohydrates\u002Fstarch into maltose\n  - **Trypsin** — breaks down proteins into smaller peptides\n  - **Lipase** — breaks down fats into fatty acids and glycerol\n\nThe liver (B) produces bile but no bicarbonate or digestive enzymes. The stomach (A) produces acid and pepsin, not bicarbonate. The gallbladder (D) only stores and concentrates bile.",[2244,2245,2246],"Human biology","Digestive system","Organ functions",{"id":2248,"section":1478,"level":1478,"prompt":2249,"check":2250,"hints":2258,"solution":2262,"skills":2263},"the-digestive-system.q146","The **epiglottis** plays a crucial protective role during swallowing. What happens if the epiglottis fails to close properly when food is swallowed, and what structure could food enter as a result?",{"kind":1487,"accept":2251},[2252,2253,2254,2255,2256,2257],"food enters the trachea\u002Fwindpipe","food enters the larynx","aspiration into the airway","choking risk\u002Ffood goes down the wrong pipe","food enters the respiratory tract","aspiration pneumonia risk",[2259,2260,2261],"The epiglottis acts as a flap or lid during swallowing.","If it doesn't close, food goes down the 'wrong pipe' instead of the esophagus.","The windpipe is the tube that carries air to and from the lungs.","If the **epiglottis** fails to close properly, food can enter the **trachea** (windpipe) instead of the esophagus (food pipe).\n\n**Normal swallowing process:**\n1. The tongue pushes food to the back of the throat\n2. The epiglottis flips down to cover the opening of the larynx (voice box)\n3. This directs food into the esophagus behind the trachea\n\n**If the epiglottis fails:**\n- Food enters the **trachea** and may block the airway\n- This causes **choking** as the airway is obstructed\n- Small particles may reach the lungs and cause **aspiration pneumonia**\n- The body triggers the **cough reflex** to try to expel the material\n\nThis is why you should not talk or laugh while swallowing — these actions can prevent proper epiglottis closure.",[2244,2245,2264],"Protective mechanisms",{"id":2266,"section":1478,"level":1478,"prompt":2267,"check":2268,"hints":2273,"solution":2277,"skills":2278},"the-digestive-system.q147","During digestion, proteins are broken down into smaller molecules. Starting from a protein in food, trace the complete breakdown sequence: first name the smaller chains formed in the stomach, then the even smaller units formed in the small intestine, and finally state the end product that can be absorbed.\n\nEnter your answer as three terms separated by commas (e.g., 'term1, term2, term3').",{"kind":1487,"accept":2269},[2270,2271,2272],"polypeptides, peptides, amino acids","polypeptide, peptide, amino acid","peptides, amino acids, amino acids",[2274,2275,2276],"In the stomach, pepsin breaks proteins into medium-sized chains.","In the small intestine, trypsin and other enzymes further break these chains.","The final absorbable units are the building blocks of proteins.","The correct sequence is: **polypeptides, peptides, amino acids**.\n\n**Step-by-step protein digestion:**\n\n1. **In the stomach (pH 1.5-3.5):**\n   - **Pepsin** breaks long protein chains into shorter chains called **polypeptides**\n   - Pepsin cleaves bonds between specific amino acids\n\n2. **In the small intestine (pH raised by bicarbonate):**\n   - **Trypsin** (from pancreas) breaks polypeptides into even smaller **peptides** (oligopeptides and dipeptides)\n   - Other pancreatic enzymes (chymotrypsin, carboxypeptidase) assist\n\n3. **Final breakdown at intestinal lining:**\n   - Brush border enzymes on microvilli break peptides into single **amino acids**\n   - Dipeptidases and aminopeptidases complete this process\n\n4. **Absorption:**\n   - Amino acids are absorbed into the bloodstream through capillaries in the villi\n   - They travel to the liver via the hepatic portal vein\n\nAmino acids are the fundamental building blocks that cells use to synthesize new proteins for growth and repair.",[2244,2245,2279],"Biochemistry",{"id":2281,"section":1478,"level":1478,"prompt":2282,"check":2283,"hints":2292,"solution":2296,"skills":2297},"the-digestive-system.q148","The digestive system contains both **mechanical** and **chemical** digestion. For each of the following actions, identify whether it is mechanical or chemical digestion:\n\n1. Teeth chewing food into smaller pieces\n2. Salivary amylase breaking starch into maltose\n3. The stomach churning to mix food with gastric juice\n4. Hydrochloric acid denaturing proteins\n\nFormat your answer as four letters in order, M for mechanical or C for chemical (e.g., 'M, C, M, C').",{"kind":1487,"accept":2284},[2285,2286,2287,2288,2289,2290,2291],"M, C, M, C","M,C,M,C","mc","MC","mcmc","MCMC","M C M C",[2293,2294,2295],"Mechanical digestion breaks food into smaller pieces without changing chemical structure.","Chemical digestion uses enzymes or acids to change molecular structure.","Churning and chewing are physical processes; enzymes and acids are chemical processes.","The correct answer is **M, C, M, C** (or equivalent formats).\n\n**Detailed breakdown:**\n\n1. **Teeth chewing food — MECHANICAL**\n   - Physical breakdown into smaller pieces\n   - Increases surface area for enzyme action\n   - No chemical bonds are broken; food is still the same material\n\n2. **Salivary amylase breaking starch — CHEMICAL**\n   - The enzyme amylase catalyzes hydrolysis of starch into maltose\n   - This changes the chemical structure (polysaccharide → disaccharide)\n   - A new substance with different properties is formed\n\n3. **Stomach churning — MECHANICAL**\n   - Smooth muscle contractions mix food with gastric juice\n   - Creates semi–liquid chyme\n   - Physical mixing, not chemical change by itself\n\n4. **Hydrochloric acid denaturing proteins — CHEMICAL**\n   - HCl unfolds (denatures) protein structure\n   - This exposes peptide bonds for pepsin to attack\n   - Changes the protein's shape and prepares it for enzymatic digestion; also kills bacteria\n\n**Summary:** Mechanical digestion reduces particle size, while chemical digestion alters molecular structure through chemical reactions.",[2244,2245,2298],"Physical vs chemical change",{"id":2300,"section":1474,"level":2301,"prompt":2302,"check":2303,"hints":2308,"solution":2312,"skills":2313},"the-digestive-system.q149","challenge","The human digestive system is a long tube starting at the mouth and ending at the anus. If the total length of the digestive tract is about 9 meters and the small intestine makes up approximately 2\u002F3 of this length, how long is the small intestine in meters?",{"kind":2304,"answer":2305,"tolerance":2306,"unit":2307},"number",6,0.1,"meters",[2309,2310,2311],"Find 2\u002F3 of 9 meters","Multiply 9 × 2\u002F3","9 ÷ 3 = 3, then 3 × 2 = ?","To find 2\u002F3 of the total length: 9 × 2\u002F3 = (9 × 2) ÷ 3 = 18 ÷ 3 = 6 meters. The small intestine is approximately 6 meters long.",[612,498,500],{"id":2315,"section":1474,"level":2301,"prompt":2316,"check":2317,"hints":2320,"solution":2324,"skills":2325},"the-digestive-system.q150","Salivary glands produce about 1.5 liters of saliva per day. If a person sleeps for 8 hours and produces almost no saliva during sleep, how many milliliters of saliva are produced per waking hour? (1 liter = 1000 milliliters)",{"kind":2304,"answer":2318,"tolerance":2306,"unit":2319},93.75,"mL\u002Fhour",[2321,2322,2323],"Convert liters to milliliters first","Calculate waking hours in a day","Divide total saliva by waking hours","First, convert 1.5 liters to milliliters: 1.5 × 1000 = 1500 mL. Waking hours = 24 - 8 = 16 hours. Saliva per waking hour = 1500 ÷ 16 = 93.75 mL\u002Fhour.",[2326,499,500],"unit conversion",{"id":2328,"section":1474,"level":2301,"prompt":2329,"check":2330,"hints":2334,"solution":2338,"skills":2339},"the-digestive-system.q151","The stomach typically holds about 1 liter when full but can expand to hold up to 4 liters. By what percentage does the stomach's capacity increase from its typical full state to its maximum expansion?",{"kind":2304,"answer":2331,"tolerance":2332,"unit":2333},300,0.5,"percent",[2335,2336,2337],"Find the increase in capacity: 4 - 1 = 3 liters","Divide the increase by the original amount","Convert to percentage","The increase is 4 - 1 = 3 liters. Percentage increase = (increase ÷ original) × 100 = (3 ÷ 1) × 100 = 300%. The stomach's capacity increases by 300%.",[2340,497,499],"percentages",{"id":2342,"section":1478,"level":2301,"prompt":2343,"check":2344,"hints":2347,"solution":2351,"skills":2352},"the-digestive-system.q152","Food takes about 6 to 8 hours to pass through the stomach and small intestine. If a meal spends 3\u002F5 of this time in the small intestine and the total transit time is 7 hours, how many hours does the food spend in the stomach?",{"kind":2304,"answer":2345,"tolerance":2306,"unit":2346},2.8,"hours",[2348,2349,2350],"Calculate time in small intestine: 7 × 3\u002F5","Subtract this from total time for stomach time","Or find the fraction in stomach first","Time in small intestine = 7 × 3\u002F5 = 21\u002F5 = 4.2 hours. Time in stomach = 7 - 4.2 = 2.8 hours. Alternatively, fraction in stomach = 1 - 3\u002F5 = 2\u002F5, so time in stomach = 7 × 2\u002F5 = 14\u002F5 = 2.8 hours.",[612,497,500],{"id":2354,"section":1478,"level":2301,"prompt":2355,"check":2356,"hints":2358,"solution":2362,"skills":2363},"the-digestive-system.q153","The liver produces about 500 to 1000 mL of bile per day. If bile is stored and concentrated 5 times in the gallbladder (from 500 mL to 100 mL), what is the concentration factor? In other words, how many times more concentrated is the stored bile compared to the original bile?",{"kind":2304,"answer":104,"tolerance":14,"unit":2357},"times",[2359,2360,2361],"Concentration factor = original volume ÷ final volume","500 mL is reduced to 100 mL","Calculate 500 ÷ 100","The concentration factor is found by dividing the original volume by the final stored volume: 500 ÷ 100 = 5. The bile is concentrated 5 times in the gallbladder.",[499,2364,2365],"ratios","concentration",{"id":2367,"section":1478,"level":2301,"prompt":2368,"check":2369,"hints":2371,"solution":2375,"skills":2376},"the-digestive-system.q154","The surface area of the small intestine is increased by finger-like projections called villi. If each villus increases surface area by a factor of 10, and microvilli on the villi increase it by another factor of 20, what is the total surface area multiplication factor compared to a smooth tube?",{"kind":2304,"answer":2370,"tolerance":14,"unit":2357},200,[2372,2373,2374],"Multiply the two factors together","10 × 20 = total factor","This is why absorption is so efficient","Total surface area multiplication = factor from villi × factor from microvilli = 10 × 20 = 200. The small intestine has approximately 200 times more surface area than a smooth tube of the same length, which greatly increases nutrient absorption.",[498,1958,2377],"biology application",{"id":2379,"section":1474,"level":2301,"prompt":2380,"check":2381,"hints":2388,"solution":2392,"skills":2393},"the-digestive-system.q155","Which organ produces enzymes that break down carbohydrates, proteins, and fats, and also produces bicarbonate to neutralize stomach acid?",{"kind":1541,"options":2382,"correct":2387},[2383,2384,2385,2386],{"id":1544,"label":1784},{"id":1547,"label":2105},{"id":1550,"label":1790},{"id":1553,"label":2102},[1550],[2389,2390,2391],"Think about which organ sends digestive juices to the small intestine","This organ is located behind the stomach","It has both endocrine and exocrine functions","The pancreas (c) produces pancreatic amylase for carbohydrates, trypsin for proteins, and lipase for fats. It also produces bicarbonate to neutralize the acidic chyme from the stomach, raising the pH for enzyme activity in the small intestine. The stomach produces pepsin and acid, the liver produces bile, and the gallbladder only stores bile.",[1561,1719,2394],"pH balance",{"id":2396,"section":1478,"level":2301,"prompt":2397,"check":2398,"hints":2399,"solution":2403,"skills":2404},"the-digestive-system.q156","The large intestine absorbs water and forms feces. If chyme enters the large intestine with 500 mL of water and 85% of this water is absorbed, leaving 100 mL in the feces plus additional solid material, is this possible? If not, what percentage would actually need to be absorbed to leave 100 mL?",{"kind":2304,"answer":232,"tolerance":2332,"unit":2333},[2400,2401,2402],"Check if 85% absorption leaves 100 mL","Calculate 15% of 500 mL","Find what percentage of 500 equals 100 mL","If 85% is absorbed, 15% remains: 500 × 0.15 = 75 mL, not 100 mL. So 85% absorption is NOT correct. To leave 100 mL: 100 ÷ 500 = 0.20 = 20% remains. Therefore, absorption = 100% - 20% = 80%. The correct absorption percentage is 80%.",[2340,2405,2406],"verification","inverse problems",[2408,2409,2410],"body-systems-britannica-digestive","body-systems-britannica-respiratory","digestive-system-ncert-science-7-ch2","needs_review",{"generatedBy":2413,"notes":2414},"claude-code","generated from work item wi-29051418","8d520ac2bea10573d3b7b2f1ab616d196de4c6232584483f98e6951c885d5467",{},"generation-4c1a594b-3e08-4931-b878-9bd6c2c6c83b"]