[{"data":1,"prerenderedAt":1369},["ShallowReactive",2],{"questions:body-systems":3},{"bank":4,"contentHash":1352,"dependencyHashes":1353,"releaseId":1368},{"schemaVersion":5,"conceptId":6,"revision":5,"title":7,"intro":8,"sections":9,"questions":46,"sourceIds":1334,"reviewStatus":1348,"authoring":1349},1,"body-systems","Body systems and how they connect: question bank","Sixty-plus questions across digestion, respiration, circulation, excretion, the nervous and muscular systems, the hand-overs between them, exercise data, and the history and technology of studying the body. Every worked solution shows the reasoning, not just the answer.",[10,14,18,22,26,30,34,38,42],{"id":11,"title":12,"description":13},"systems-and-organs","Systems and organs","What an organ system is, and which organs belong where — including the ones that belong to two.",{"id":15,"title":16,"description":17},"digestion","Digestion","The food road from mouth to large intestine, enzymes, bile, and absorption at the villi.",{"id":19,"title":20,"description":21},"respiration","Respiration","Breathing mechanics, gas exchange at the alveoli, and famous numbers worth checking.",{"id":23,"title":24,"description":25},"circulation","Circulation","The double pump, blood vessels, blood itself, and the physics of branching flow.",{"id":27,"title":28,"description":29},"excretion-homeostasis","Excretion and homeostasis","Kidneys, water balance, temperature control, blood sugar and fever.",{"id":31,"title":32,"description":33},"nervous-muscles","Nervous system, muscles and bones","Reflexes, nerve speed, levers, and voluntary versus involuntary control.",{"id":35,"title":36,"description":37},"hand-overs","The hand-overs","Where systems touch, what crosses, and the three-rule pattern that explains all of them.",{"id":39,"title":40,"description":41},"exercise-data","Exercise and data","What changes when you exercise, measured with real data-handling tools.",{"id":43,"title":44,"description":45},"history-technology","History, technology and space","Harvey, the stethoscope and ECG, imaging, artificial hand-overs, and microgravity.",[47,73,92,109,128,146,165,183,202,221,239,257,275,288,305,323,340,352,369,386,403,414,432,443,461,480,497,508,526,543,553,571,582,599,618,631,649,669,687,705,718,736,753,764,781,800,818,836,847,864,876,893,910,928,945,962,979,996,1013,1031,1046,1057,1074,1091,1103,1120,1133,1150,1167,1179,1197,1215,1225,1242,1260,1273,1283,1300,1317],{"id":48,"section":11,"level":49,"prompt":50,"check":51,"hints":67,"solution":69,"skills":70},"body-systems.q001","foundation","Put these in order, from smallest to largest: organ, cell, organ system, tissue.",{"kind":52,"options":53,"correct":66},"choice",[54,57,60,63],{"id":55,"label":56},"a","cell → tissue → organ → organ system",{"id":58,"label":59},"b","cell → organ → tissue → organ system",{"id":61,"label":62},"c","tissue → cell → organ → organ system",{"id":64,"label":65},"d","organ → tissue → cell → organ system",[55],[68],"Start from the smallest living unit.","Cell is the smallest living unit. Same-kind cells make a tissue; several tissues make an organ; organs sharing a job make an organ system.",[71,72],"levels","vocabulary",{"id":74,"section":11,"level":49,"prompt":75,"check":76,"hints":87,"solution":88,"skills":89},"body-systems.q002","Which organ belongs to two systems at once: it sends digestive juice into the small intestine AND releases the hormone insulin?",{"kind":52,"options":77,"correct":86},[78,80,82,84],{"id":55,"label":79},"Liver",{"id":58,"label":81},"Pancreas",{"id":61,"label":83},"Stomach",{"id":64,"label":85},"Gall bladder",[58],[],"The pancreas is both a digestive gland (juice into the small intestine) and an endocrine gland (insulin and glucagon into the blood).",[90,91],"organs","endocrine",{"id":93,"section":11,"level":49,"prompt":94,"check":95,"hints":106,"solution":107,"skills":108},"body-systems.q003","Which of these is NOT one of the seven main organ systems described in this topic?",{"kind":52,"options":96,"correct":105},[97,99,101,103],{"id":55,"label":98},"Digestive",{"id":58,"label":100},"Respiratory",{"id":61,"label":102},"Photosynthetic",{"id":64,"label":104},"Excretory",[61],[],"Photosynthesis is how plants make food using light; it is not a human organ system. The seven here are digestive, respiratory, circulatory, excretory, nervous, muscular and skeletal.",[72],{"id":110,"section":11,"level":111,"prompt":112,"check":113,"hints":124,"solution":125,"skills":126},"body-systems.q004","core","Skin is usually classed as part of the excretory system. Why?",{"kind":52,"options":114,"correct":123},[115,117,119,121],{"id":55,"label":116},"It absorbs oxygen directly",{"id":58,"label":118},"Sweat carries out water, salt and a little urea",{"id":61,"label":120},"It digests food on its surface",{"id":64,"label":122},"It produces red blood cells",[58],[],"Sweat removes water, salt and a small amount of urea, which is why skin counts as an excretory route, alongside its roles in temperature control and defence.",[90,127],"excretion",{"id":129,"section":11,"level":111,"prompt":130,"check":131,"hints":142,"solution":143,"skills":144},"body-systems.q005","The endocrine system sends messages using hormones in the blood, while the nervous system uses electrical signals in nerves. Which best describes the trade-off between them?",{"kind":52,"options":132,"correct":141},[133,135,137,139],{"id":55,"label":134},"Hormones are always better because they last longer",{"id":58,"label":136},"Nerves are fast and precisely aimed; hormones are slower but reach the whole body and last longer",{"id":61,"label":138},"There is no real difference between them",{"id":64,"label":140},"Hormones travel faster than nerve signals",[58],[],"Nerves work like a phone call: fast, aimed at one place, brief. Hormones work like a letter posted to every address: slower, but reaching everywhere and lasting much longer.",[91,145],"nervous",{"id":147,"section":11,"level":148,"prompt":149,"check":150,"hints":160,"solution":161,"skills":162},"body-systems.q006","stretch","A doctor examining a patient notices swollen lymph nodes in the neck. Which system's activity does this most directly reflect?",{"kind":52,"options":151,"correct":159},[152,154,156,157],{"id":55,"label":153},"Skeletal",{"id":58,"label":155},"Immune (via the lymphatic system)",{"id":61,"label":98},{"id":64,"label":158},"Muscular",[58],[],"Lymph nodes are checkpoints where white blood cells multiply to fight an infection; a swollen node is a visible sign of the immune system working, not a problem with the node itself.",[163,164],"immune","lymph",{"id":166,"section":11,"level":148,"prompt":167,"check":168,"hints":179,"solution":180,"skills":181},"body-systems.q007","Why is it more accurate to say the seven organ systems are \"seven good questions to ask about a body\" rather than \"seven separate machines\"?",{"kind":52,"options":169,"correct":178},[170,172,174,176],{"id":55,"label":171},"Because organs are randomly assigned to systems",{"id":58,"label":173},"Because many real organs serve more than one system at once, like the pancreas and skin",{"id":61,"label":175},"Because the body only really has one system",{"id":64,"label":177},"Because scientists cannot agree on the number of systems",[58],[],"Nothing inside the body is labelled. The pancreas, liver and skin all serve more than one system's job at once — the systems are a useful way to organise questions, not physical walls.",[182],"reasoning",{"id":184,"section":11,"level":185,"prompt":186,"check":187,"hints":198,"solution":199,"skills":200},"body-systems.q008","challenge","The bins in a \"sort organs into systems\" game are described as \"labels, not walls\". Which statement best explains what this means scientifically?",{"kind":52,"options":188,"correct":197},[189,191,193,195],{"id":55,"label":190},"Organs can be sorted into exactly one system with total confidence",{"id":58,"label":192},"A classification scheme is a human tool for organising observations, and real biology does not always respect the boundaries of that scheme",{"id":61,"label":194},"The seven systems are entirely arbitrary and could be replaced by any other number",{"id":64,"label":196},"Only the liver and pancreas break the rule; every other organ fits one system perfectly",[58],[],"Classifications like \"the seven organ systems\" are useful models built to organise understanding. Real organs like the pancreas, liver and skin regularly serve more than one system's job, which does not invalidate the scheme — it just means the scheme is a tool, not a law of nature.",[182,201],"models",{"id":203,"section":15,"level":49,"prompt":204,"check":205,"hints":216,"solution":218,"skills":219},"body-systems.q009","At which station does food actually cross into your blood?",{"kind":52,"options":206,"correct":215},[207,209,211,213],{"id":55,"label":208},"The mouth",{"id":58,"label":210},"The stomach",{"id":61,"label":212},"The villi of the small intestine",{"id":64,"label":214},"The large intestine",[61],[217],"\"Entering the body\" means crossing into the blood.","Almost all absorption happens through the villi of the small intestine, whose wall is one cell thick with a capillary inside each one.",[15,220],"handover",{"id":222,"section":15,"level":49,"prompt":223,"check":224,"hints":235,"solution":236,"skills":237},"body-systems.q010","What does saliva start breaking down, using the enzyme amylase?",{"kind":52,"options":225,"correct":234},[226,228,230,232],{"id":55,"label":227},"Protein",{"id":58,"label":229},"Starch",{"id":61,"label":231},"Fat",{"id":64,"label":233},"Vitamins",[58],[],"Amylase in saliva starts cutting starch into shorter, sweet-tasting sugar chains — which is why chewed roti or rice starts tasting sweet.",[15,238],"enzymes",{"id":240,"section":15,"level":49,"prompt":241,"check":242,"hints":253,"solution":254,"skills":255},"body-systems.q011","What does bile do?",{"kind":52,"options":243,"correct":252},[244,246,248,250],{"id":55,"label":245},"It is an enzyme that digests protein",{"id":58,"label":247},"It breaks fat into tiny droplets, with no enzyme involved",{"id":61,"label":249},"It neutralises stomach acid only",{"id":64,"label":251},"It absorbs sugar directly",[58],[],"Bile, made by the liver, contains no enzyme. It is a detergent that breaks fat into droplets, creating surface area for the pancreas's fat-digesting enzymes to work on.",[15,256],"liver",{"id":258,"section":15,"level":111,"prompt":259,"check":260,"hints":271,"solution":272,"skills":273},"body-systems.q012","Roughly how long does food take to travel from mouth to being passed out, according to this topic's figures?",{"kind":52,"options":261,"correct":270},[262,264,266,268],{"id":55,"label":263},"A few minutes",{"id":58,"label":265},"About one to three days",{"id":61,"label":267},"About one week",{"id":64,"label":269},"About one month",[58],[],"Adding up mouth, oesophagus, stomach, small intestine and large intestine gives a range of roughly 17 to 57 hours — \"about one to three days\".",[15,274],"timing",{"id":276,"section":15,"level":111,"prompt":277,"check":278,"hints":283,"solution":285,"skills":286},"body-systems.q013","A cube of food 3 cm on each side is cut into cubes 1 cm on each side. How many small cubes result?",{"kind":279,"answer":280,"tolerance":281,"unit":282},"number",27,0,"cubes",[284],"Work out how many pieces fit along one edge, then cube that number.","Along each edge, 3 ÷ 1 = 3 pieces, so the total is 3 × 3 × 3 = 27 cubes — the same amount of food with far more outside surface for enzymes to act on.",[15,287],"geometry",{"id":289,"section":15,"level":111,"prompt":290,"check":291,"hints":302,"solution":303,"skills":304},"body-systems.q014","Why does chewing food more thoroughly help digestion, according to this topic's reasoning?",{"kind":52,"options":292,"correct":301},[293,295,297,299],{"id":55,"label":294},"Chewing adds more enzymes to the food",{"id":58,"label":296},"Smaller pieces create more surface area for enzymes to act on, without adding any food",{"id":61,"label":298},"Chewing warms the food to body temperature",{"id":64,"label":300},"It makes the food weigh less",[58],[],"Cutting or grinding never changes how much food there is, but it always creates more surface. Since enzymes can only act at a surface, more surface means faster digestion.",[15,238],{"id":306,"section":15,"level":148,"prompt":307,"check":308,"hints":319,"solution":320,"skills":321},"body-systems.q015","The claim that the small intestine has \"200 to 300 square metres of surface, like a tennis court\" is now considered an overstatement. What is closer to the modern measured figure?",{"kind":52,"options":309,"correct":318},[310,312,314,316],{"id":55,"label":311},"About 3 m²",{"id":58,"label":313},"About 30 m²",{"id":61,"label":315},"About 300 m²",{"id":64,"label":317},"About 3,000 m²",[58],[],"Modern careful measurement puts the adult small intestine's absorptive surface at about 30 m² — the older 200–300 m² figure is roughly six to ten times too large.",[15,322],"misconception",{"id":324,"section":15,"level":148,"prompt":325,"check":326,"hints":337,"solution":338,"skills":339},"body-systems.q016","Digested fat is absorbed differently from sugars and amino acids at the villi. How?",{"kind":52,"options":327,"correct":336},[328,330,332,334],{"id":55,"label":329},"It is not absorbed at all and leaves in faeces",{"id":58,"label":331},"It enters a lacteal (a lymph vessel) rather than a blood capillary directly",{"id":61,"label":333},"It is absorbed in the stomach instead of the small intestine",{"id":64,"label":335},"It dissolves directly into bile and stays there",[58],[],"Fat droplets are picked up by tiny lymphatic vessels called lacteals inside each villus, and travel through the lymphatic system before joining the bloodstream — unlike sugars and amino acids, which go straight into a blood capillary.",[15,164],{"id":341,"section":15,"level":185,"prompt":342,"check":343,"hints":347,"solution":349,"skills":350},"body-systems.q017","Gut bacteria outnumber human cells by a ratio close to 1.3 to 1. If an adult has about 30 trillion human cells, roughly how many trillion bacterial cells does that suggest (to the nearest whole trillion)?",{"kind":279,"answer":344,"tolerance":345,"unit":346},39,2,"trillion",[348],"Multiply 30 trillion by the ratio 1.3.","30 trillion × 1.3 ≈ 39 trillion, close to the measured figure of about 38 trillion bacterial cells — far from the old, incorrect \"10 to 1\" claim, which would suggest 300 trillion.",[15,351],"ratio",{"id":353,"section":15,"level":185,"prompt":354,"check":355,"hints":366,"solution":367,"skills":368},"body-systems.q018","The old claim that bacteria outnumber human cells 10 to 1 was repeated for decades before being corrected. What does this best illustrate about scientific claims?",{"kind":52,"options":356,"correct":365},[357,359,361,363],{"id":55,"label":358},"Old claims are always wrong and new ones are always right",{"id":58,"label":360},"A striking, widely repeated number is not automatically an accurate one, and it can take a careful re-measurement to correct it",{"id":61,"label":362},"Bacteria counts cannot be measured accurately at all",{"id":64,"label":364},"The 10-to-1 ratio was actually correct and the 1.3-to-1 figure is wrong",[58],[],"The 2016 study that corrected the ratio to about 1.3 to 1 shows that even long-repeated, textbook-standard numbers deserve checking — repetition is not evidence.",[15,182],{"id":370,"section":19,"level":49,"prompt":371,"check":372,"hints":383,"solution":384,"skills":385},"body-systems.q019","What actually pulls air into your lungs?",{"kind":52,"options":373,"correct":382},[374,376,378,380],{"id":55,"label":375},"The lungs squeezing themselves",{"id":58,"label":377},"The heart pushing air along",{"id":61,"label":379},"The diaphragm flattening, which enlarges the chest and lowers the pressure inside",{"id":64,"label":381},"The trachea sucking",[61],[],"Lungs have no muscle of their own. The diaphragm flattens, the chest grows, pressure drops, and the atmosphere pushes air in.",[19,322],{"id":387,"section":19,"level":49,"prompt":388,"check":389,"hints":400,"solution":401,"skills":402},"body-systems.q020","Where does gas exchange (oxygen in, carbon dioxide out) actually happen?",{"kind":52,"options":390,"correct":399},[391,393,395,397],{"id":55,"label":392},"The trachea",{"id":58,"label":394},"The bronchi",{"id":61,"label":396},"The alveoli",{"id":64,"label":398},"The nose",[61],[],"The alveoli are the microscopic air sacs, about 300 million of them, where the wall is thin enough for gases to cross into and out of the blood.",[19,220],{"id":404,"section":19,"level":49,"prompt":405,"check":406,"hints":409,"solution":411,"skills":412},"body-systems.q021","A resting adult breathes about 15 times a minute. How many breaths is that in one hour?",{"kind":279,"answer":407,"tolerance":281,"unit":408},900,"breaths",[410],"Multiply breaths per minute by 60.","15 × 60 = 900 breaths in an hour.",[19,413],"arithmetic",{"id":415,"section":19,"level":111,"prompt":416,"check":417,"hints":428,"solution":429,"skills":430},"body-systems.q022","You breathe in air that is about 21% oxygen and breathe out air that is about 16% oxygen. What does this tell you?",{"kind":52,"options":418,"correct":427},[419,421,423,425],{"id":55,"label":420},"You use up almost all the oxygen you breathe in",{"id":58,"label":422},"You use only a small fraction of the oxygen you breathe in — about a quarter",{"id":61,"label":424},"Breathed-out air contains no oxygen at all",{"id":64,"label":426},"Oxygen is created inside the lungs",[58],[],"You keep only about 5 percentage points out of the 21% you started with — roughly a quarter of the oxygen available — which is exactly why rescue breathing still works.",[19,431],"gas-exchange",{"id":433,"section":19,"level":111,"prompt":434,"check":435,"hints":439,"solution":441,"skills":442},"body-systems.q023","Fresh air is about 0.04% carbon dioxide, and exhaled air is about 4% carbon dioxide. How many times more concentrated is the carbon dioxide in your breath out?",{"kind":279,"answer":436,"tolerance":437,"unit":438},100,5,"times",[440],"Divide the two percentages.","4 ÷ 0.04 = 100. Your breath carries about a hundred times more carbon dioxide than the air you breathed in.",[19,351],{"id":444,"section":19,"level":111,"prompt":445,"check":446,"hints":457,"solution":458,"skills":459},"body-systems.q024","What is your body actually reacting to when you hold your breath and feel an urgent need to breathe?",{"kind":52,"options":447,"correct":456},[448,450,452,454],{"id":55,"label":449},"Running out of oxygen",{"id":58,"label":451},"Carbon dioxide building up in the blood",{"id":61,"label":453},"The lungs collapsing",{"id":64,"label":455},"The heart slowing down",[58],[],"Sensors watch rising carbon dioxide far more closely than falling oxygen, because CO₂ changes quickly and reliably. This is why fast breathing before diving is dangerous — it removes the alarm without adding useful oxygen.",[19,460],"safety",{"id":462,"section":19,"level":148,"prompt":463,"check":464,"hints":475,"solution":477,"skills":478},"body-systems.q025","A pair of adult lungs has a gas-exchange surface of about 70 m² from around 300 million alveoli. Two smooth balloon-like bags of the same total volume, with no alveoli, would have a surface of about 0.1 m². Roughly how many times more oxygen could the real lungs absorb per breath?",{"kind":52,"options":465,"correct":474},[466,468,470,472],{"id":55,"label":467},"About 7 times more",{"id":58,"label":469},"About 70 times more",{"id":61,"label":471},"About 700 times more",{"id":64,"label":473},"No difference — volume is what matters",[61],[476],"Divide the folded surface by the smooth surface.","70 ÷ 0.1 = 700. Folding the same volume into hundreds of millions of alveoli multiplies the usable surface roughly seven hundredfold.",[19,479],"surface-area",{"id":481,"section":19,"level":148,"prompt":482,"check":483,"hints":494,"solution":495,"skills":496},"body-systems.q026","Which comparison for lung surface area is closest to the modern measured figure of about 70 m²?",{"kind":52,"options":484,"correct":493},[485,487,489,491],{"id":55,"label":486},"A doubles tennis court (about 261 m²)",{"id":58,"label":488},"A badminton court (about 82 m²)",{"id":61,"label":490},"A football pitch (thousands of m²)",{"id":64,"label":492},"The palm of one hand",[58],[],"A badminton court, at about 82 m², is much closer to the real 70 m² figure than the often-quoted tennis court, which is nearly four times too big.",[19,322],{"id":498,"section":19,"level":185,"prompt":499,"check":500,"hints":503,"solution":505,"skills":506},"body-systems.q027","At rest you use about 375 mL of oxygen a minute. During hard exercise this rises to about 3,375 mL a minute. How many times greater is that?",{"kind":279,"answer":501,"tolerance":502,"unit":438},9,0.5,[504],"Divide the exercise value by the resting value.","3,375 ÷ 375 = 9. Oxygen use rises roughly ninefold during hard exercise, closely matching the rise in cardiac output and breathing rate together.",[19,507],"exercise",{"id":509,"section":23,"level":49,"prompt":510,"check":511,"hints":522,"solution":523,"skills":524},"body-systems.q028","Why is the heart called a \"double pump\"?",{"kind":52,"options":512,"correct":521},[513,515,517,519],{"id":55,"label":514},"It beats twice for every pulse you feel",{"id":58,"label":516},"One side pumps blood to the lungs and the other pumps to the rest of the body",{"id":61,"label":518},"There are two separate hearts",{"id":64,"label":520},"It has two valves only",[58],[],"The right side sends blood a short distance to the lungs; the left side sends it everywhere else. Both sides squeeze at the same instant.",[23,525],"heart",{"id":527,"section":23,"level":49,"prompt":528,"check":529,"hints":540,"solution":541,"skills":542},"body-systems.q029","Why do veins on the back of your hand look blue-ish?",{"kind":52,"options":530,"correct":539},[531,533,535,537],{"id":55,"label":532},"Blood is blue until it meets air",{"id":58,"label":534},"Skin scatters and absorbs light unevenly; the blood inside is actually dark red",{"id":61,"label":536},"Veins have a blue lining",{"id":64,"label":538},"They carry a different fluid, not blood",[58],[],"Blood is never blue. Red light penetrates skin and is absorbed by the dark blood; blue light bounces back from upper skin layers, which is why a vein looks bluish against pinker skin.",[23,322],{"id":544,"section":23,"level":49,"prompt":545,"check":546,"hints":549,"solution":551,"skills":552},"body-systems.q030","A resting pulse of 80 beats a minute — how many beats is that in one hour?",{"kind":279,"answer":547,"tolerance":281,"unit":548},4800,"beats",[550],"Multiply beats per minute by 60.","80 × 60 = 4,800 beats in an hour.",[23,413],{"id":554,"section":23,"level":111,"prompt":555,"check":556,"hints":567,"solution":568,"skills":569},"body-systems.q031","Arteries, veins and capillaries are built very differently. Which best matches a capillary to its job?",{"kind":52,"options":557,"correct":566},[558,560,562,564],{"id":55,"label":559},"Thick and muscular, to carry blood at high pressure",{"id":58,"label":561},"Wide and floppy, with one-way valves",{"id":61,"label":563},"A wall one cell thick, so substances can cross in and out",{"id":64,"label":565},"Ringed with cartilage to stay open",[61],[],"Capillaries are built to be crossed: their wall is a single cell thick, letting oxygen, food, carbon dioxide and waste move between blood and the surrounding cells.",[23,570],"vessels",{"id":572,"section":23,"level":111,"prompt":573,"check":574,"hints":578,"solution":580,"skills":581},"body-systems.q032","The left ventricle pumps about 70 mL per beat at 72 beats a minute. How many litres does it pump in one minute?",{"kind":279,"answer":575,"tolerance":576,"unit":577},5.04,0.1,"L",[579],"Multiply mL per beat by beats per minute, then divide by 1,000.","70 mL × 72 = 5,040 mL = 5.04 L a minute — the famous \"about 5 litres a minute\" figure.",[23,413],{"id":583,"section":23,"level":111,"prompt":584,"check":585,"hints":596,"solution":597,"skills":598},"body-systems.q033","Why is the left ventricle's wall about three times thicker than the right ventricle's, even though both pump the same volume of blood per beat?",{"kind":52,"options":586,"correct":595},[587,589,591,593],{"id":55,"label":588},"The left ventricle holds more blood",{"id":58,"label":590},"The left ventricle must push blood much further, so it must push much harder",{"id":61,"label":592},"The left ventricle beats more often",{"id":64,"label":594},"The left side carries oxygen-rich blood, which weighs more",[58],[],"Both sides push the same volume — or blood would pile up — but the left side sends it all the way round the body while the right side sends it only to the nearby lungs. Further means harder, and harder means thicker muscle.",[23,525],{"id":600,"section":23,"level":148,"prompt":601,"check":602,"hints":613,"solution":615,"skills":616},"body-systems.q034","All the blood vessels in an adult body laid end to end come to about 100,000 km. Which is the best comparison for that length?",{"kind":52,"options":603,"correct":612},[604,606,608,610],{"id":55,"label":605},"The height of Mount Everest",{"id":58,"label":607},"About two and a half times around the Earth's equator",{"id":61,"label":609},"The distance from India to the USA",{"id":64,"label":611},"The length of the Ganga river",[58],[614],"Divide 100,000 by the length of Earth's equator, about 40,075 km.","Earth's equator is about 40,075 km, and 100,000 ÷ 40,075 ≈ 2.5 — so the body's vessels, laid end to end, would circle the Earth about two and a half times.",[23,617],"scale",{"id":619,"section":23,"level":148,"prompt":620,"check":621,"hints":625,"solution":628,"skills":629},"body-systems.q035","Red blood cells live about 120 days. If an adult has about 25 trillion red blood cells in total, roughly how many are made per second, on average, to replace them all over their lifespan? (Give your answer in millions per second, to the nearest whole million.)",{"kind":279,"answer":622,"tolerance":623,"unit":624},2.4,0.3,"million\u002Fs",[626,627],"Convert 120 days into seconds first.","Divide the total cell count by that number of seconds.","25,000,000,000,000 ÷ (120 × 24 × 3,600 seconds) ≈ 2.4 million new red blood cells made every second, just to keep up with the ones wearing out.",[23,630],"rates",{"id":632,"section":23,"level":185,"prompt":633,"check":634,"hints":645,"solution":646,"skills":647},"body-systems.q036","Why does a capillary need blood to keep flowing past it, rather than simply sitting full of blood?",{"kind":52,"options":635,"correct":644},[636,638,640,642],{"id":55,"label":637},"Still blood would clot immediately",{"id":58,"label":639},"Diffusion stops once both sides of a barrier are equal, so flow keeps bringing fresh, hungry blood to keep the difference alive",{"id":61,"label":641},"Blood needs to keep moving or it turns solid",{"id":64,"label":643},"It has no real effect either way",[58],[],"Diffusion only works while there is a difference to drift down. If blood sat still, the surrounding tissue and the blood would quickly reach the same oxygen level and crossing would stop; flow constantly replaces loaded blood with hungry blood, keeping the difference — and the crossing — going.",[23,648],"diffusion",{"id":650,"section":23,"level":185,"prompt":651,"check":652,"hints":663,"solution":666,"skills":667},"body-systems.q037","A vessel of cross-sectional area 2 cm² carrying blood at 30 cm\u002Fs branches into many capillaries with a combined cross-sectional area of 20 cm². What is the blood's new speed, assuming the flow rate is conserved?",{"kind":52,"options":653,"correct":662},[654,656,658,660],{"id":55,"label":655},"30 cm\u002Fs (unchanged)",{"id":58,"label":657},"10 cm\u002Fs",{"id":61,"label":659},"3 cm\u002Fs",{"id":64,"label":661},"300 cm\u002Fs",[61],[664,665],"Find the flow rate using the first vessel's numbers.","Divide that flow rate by the new combined area.","Flow rate = area × speed must stay constant: 2 × 30 = 60. New speed = 60 ÷ 20 = 3 cm\u002Fs. A bigger combined area forces a slower speed for the same flow rate.",[23,668],"flow-conservation",{"id":670,"section":27,"level":49,"prompt":671,"check":672,"hints":683,"solution":684,"skills":685},"body-systems.q038","Roughly how many litres of fluid do the kidneys filter out of the blood each day?",{"kind":52,"options":673,"correct":682},[674,676,678,680],{"id":55,"label":675},"About 1.5 L",{"id":58,"label":677},"About 18 L",{"id":61,"label":679},"About 180 L",{"id":64,"label":681},"About 1,800 L",[61],[],"The kidneys filter about 180 litres of fluid a day, then reclaim nearly all of it, leaving only about 1.5 litres of actual urine.",[127,686],"kidneys",{"id":688,"section":27,"level":49,"prompt":689,"check":690,"hints":701,"solution":702,"skills":703},"body-systems.q039","What actually cools you down when you sweat?",{"kind":52,"options":691,"correct":700},[692,694,696,698],{"id":55,"label":693},"Sweat sitting on the skin",{"id":58,"label":695},"Sweat evaporating, which removes heat from the skin",{"id":61,"label":697},"Sweat is naturally cold",{"id":64,"label":699},"Sweating has no cooling effect",[58],[],"Evaporation — sweat turning from liquid to vapour — takes a large amount of heat with it. Sweat that just sits on the skin, as on a humid day, cools you very little.",[127,704],"homeostasis",{"id":706,"section":27,"level":111,"prompt":707,"check":708,"hints":712,"solution":715,"skills":716},"body-systems.q040","Kidneys filter 180 L a day and return all but 1.5 L as urine. What percentage of the filtered fluid is reabsorbed (to 1 decimal place)?",{"kind":279,"answer":709,"tolerance":710,"unit":711},99.2,0.2,"%",[713,714],"Find how much is reabsorbed first: 180 − 1.5.","Divide by 180 and multiply by 100.","(180 − 1.5) ÷ 180 × 100 = 99.2%. Filtering nearly everything and then reclaiming almost all of it lets the kidneys handle wastes they have never specifically met before.",[127,717],"percentage",{"id":719,"section":27,"level":111,"prompt":720,"check":721,"hints":732,"solution":733,"skills":734},"body-systems.q041","A person starts a fever and feels cold and shivers, even though their temperature is only just beginning to rise. Why?",{"kind":52,"options":722,"correct":731},[723,725,727,729],{"id":55,"label":724},"The thermometer is inaccurate",{"id":58,"label":726},"Their control centre has already raised its target temperature, so their still-normal temperature now feels too low to it",{"id":61,"label":728},"Fevers always begin with a temperature drop",{"id":64,"label":730},"Shivering is what causes the fever",[58],[],"The body's temperature \"thermostat\" resets to a higher target early in a fever. The actual temperature has not caught up yet, so the body reacts as if it is too cold — shivering and feeling chilled — until it does.",[704,735],"fever",{"id":737,"section":27,"level":111,"prompt":738,"check":739,"hints":750,"solution":751,"skills":752},"body-systems.q042","Which of these is a genuine example of negative feedback?",{"kind":52,"options":740,"correct":749},[741,743,745,747],{"id":55,"label":742},"Blood sugar rises, so the liver releases even more sugar",{"id":58,"label":744},"Body temperature rises, so the body sweats and cools down",{"id":61,"label":746},"You feel thirsty, so you feel more and more thirsty",{"id":64,"label":748},"You run, so your muscles produce more heat",[58],[],"Negative feedback always pushes back in the opposite direction to the change. A temperature rise triggers a cooling response — the others either push the same way as the change or are the disturbance itself.",[704],{"id":754,"section":27,"level":148,"prompt":755,"check":756,"hints":759,"solution":761,"skills":762},"body-systems.q043","On an ordinary day, a body loses about 1.5 L as urine, 0.5 L as sweat, 0.4 L as water vapour in breath and 0.1 L in faeces. What is the total water lost, in litres?",{"kind":279,"answer":757,"tolerance":758,"unit":577},2.5,0.05,[760],"Add up all four routes.","1.5 + 0.5 + 0.4 + 0.1 = 2.5 L lost across four different routes in one day, matched on the \"in\" side by drinking, food and water made inside cells.",[704,763],"water-balance",{"id":765,"section":27,"level":148,"prompt":766,"check":767,"hints":778,"solution":779,"skills":780},"body-systems.q044","Why do kidneys filter nearly everything out of the blood and then reclaim most of it, rather than filtering out only the waste directly?",{"kind":52,"options":768,"correct":777},[769,771,773,775],{"id":55,"label":770},"It is simply an inefficient design with no advantage",{"id":58,"label":772},"A bulk filter-then-reclaim system can remove wastes it has never specifically encountered before, including new medicines",{"id":61,"label":774},"It saves the kidneys energy compared with a targeted filter",{"id":64,"label":776},"It is required to keep blood pressure high",[58],[],"A general filter does not need a specific detector for every possible waste chemical. Reclaiming a short list of things worth keeping (water, sugar, most salt) handles anything else automatically, including substances the body has never met before.",[704,686,182],{"id":782,"section":27,"level":185,"prompt":783,"check":784,"hints":795,"solution":797,"skills":798},"body-systems.q045","A capillary bed swells with extra fluid after an injury, pushing capillaries roughly four times further from nearby cells than normal. Given that diffusion time scales with the square of distance, roughly how much longer would a substance take to diffuse across the swollen gap?",{"kind":52,"options":785,"correct":794},[786,788,790,792],{"id":55,"label":787},"About 4 times as long",{"id":58,"label":789},"About 8 times as long",{"id":61,"label":791},"About 16 times as long",{"id":64,"label":793},"No change — distance does not affect diffusion time",[61],[796],"Square the distance multiple.","Diffusion time scales with distance squared. Four times the distance means 4² = 16 times the time — a real, physical reason swollen tissue can heal and feel sluggish.",[704,648,799],"scaling",{"id":801,"section":31,"level":49,"prompt":802,"check":803,"hints":814,"solution":815,"skills":816},"body-systems.q046","In a reflex like pulling your hand off something hot, what does the brain do?",{"kind":52,"options":804,"correct":813},[805,807,809,811],{"id":55,"label":806},"Decides to move the hand",{"id":58,"label":808},"Nothing, ever",{"id":61,"label":810},"Is informed afterwards, after the spinal cord has already ordered the movement",{"id":64,"label":812},"Sends the pain signal to the hand",[61],[],"The spinal cord completes the reflex circuit on its own. A copy of the signal reaches the brain slightly later, which is why you feel pain after your hand has already moved.",[145,817],"reflex",{"id":819,"section":31,"level":49,"prompt":820,"check":821,"hints":832,"solution":833,"skills":834},"body-systems.q047","What can a single muscle, acting alone, never do?",{"kind":52,"options":822,"correct":831},[823,825,827,829],{"id":55,"label":824},"Contract",{"id":58,"label":826},"Pull a tendon",{"id":61,"label":828},"Lengthen itself back out again",{"id":64,"label":830},"Get tired",[61],[],"A muscle can only shorten, or \"pull\". Lengthening it back out needs an opposing muscle (or gravity) pulling the other way.",[835],"muscles",{"id":837,"section":31,"level":49,"prompt":838,"check":839,"hints":842,"solution":844,"skills":845},"body-systems.q048","A nerve signal travels at up to 120 m\u002Fs. How many kilometres per hour is that?",{"kind":279,"answer":840,"tolerance":437,"unit":841},432,"km\u002Fh",[843],"Multiply metres per second by 3.6 to get kilometres per hour.","120 × 3.6 = 432 km\u002Fh.",[145,846],"units",{"id":848,"section":31,"level":111,"prompt":849,"check":850,"hints":861,"solution":862,"skills":863},"body-systems.q049","Why is a spinal reflex so much faster than a voluntary reaction to something you see?",{"kind":52,"options":851,"correct":860},[852,854,856,858],{"id":55,"label":853},"Nerve signals travel faster during a reflex",{"id":58,"label":855},"A reflex skips the time-consuming step of the brain recognising, deciding and ordering a response",{"id":61,"label":857},"Reflexes do not use nerves at all",{"id":64,"label":859},"The muscle contracts faster during a reflex",[58],[],"Nerve travel speed is about the same either way. The big time cost in a voluntary reaction is the brain's recognise-decide-order process, which a reflex bypasses entirely by deciding in the spinal cord.",[145,817,182],{"id":865,"section":31,"level":111,"prompt":866,"check":867,"hints":870,"solution":873,"skills":874},"body-systems.q050","The biceps attaches about 4 cm from the elbow joint; a weight held in the hand is about 32 cm from the joint. To hold a 5 kg weight, roughly how many kilograms-worth of force must the biceps produce?",{"kind":279,"answer":868,"tolerance":345,"unit":869},40,"kg-worth",[871,872],"Find the ratio of the two distances first.","Multiply the load by that ratio.","The lever ratio is 32 ÷ 4 = 8. Force needed = 5 × 8 = 40 kg-worth — the muscle works much harder than the load itself weighs, in exchange for speed and range of movement.",[835,875],"levers",{"id":877,"section":31,"level":111,"prompt":878,"check":879,"hints":890,"solution":891,"skills":892},"body-systems.q051","Why do muscles almost always work in opposing pairs, like the biceps and triceps?",{"kind":52,"options":880,"correct":889},[881,883,885,887],{"id":55,"label":882},"A single muscle is too weak to move a joint",{"id":58,"label":884},"A muscle can only pull, so a second muscle pulling the other way is needed to reverse the movement",{"id":61,"label":886},"Pairs simply look more symmetrical",{"id":64,"label":888},"One muscle in a pair always rests while the other works all day",[58],[],"Since a muscle's entire vocabulary is \"pull\", moving a joint in both directions needs two muscles, arranged on opposite sides, each undoing what the other one does.",[835],{"id":894,"section":31,"level":148,"prompt":895,"check":896,"hints":907,"solution":908,"skills":909},"body-systems.q052","Which statement about voluntary and involuntary control is most accurate?",{"kind":52,"options":897,"correct":906},[898,900,902,904],{"id":55,"label":899},"Everything the body does is either fully voluntary or fully involuntary, with no middle ground",{"id":58,"label":901},"Breathing, blinking and swallowing run automatically but accept a conscious override, unlike the heartbeat or sweating",{"id":61,"label":903},"The heartbeat can be consciously stopped with enough practice",{"id":64,"label":905},"Voluntary and involuntary actions use completely different kinds of nerve cells",[58],[],"Some actions — breathing, blinking, swallowing — sit in between: automatic by default, but able to accept a conscious override up to a point. The heartbeat, sweating, and pupil size cannot be consciously controlled at all.",[145,182],{"id":911,"section":31,"level":148,"prompt":912,"check":913,"hints":924,"solution":925,"skills":926},"body-systems.q053","A dropped ruler falls only about 0.2 cm in the time a knee-jerk reflex (about 20 ms) takes. What does this best explain?",{"kind":52,"options":914,"correct":923},[915,917,919,921],{"id":55,"label":916},"Reflexes are actually too slow to be useful",{"id":58,"label":918},"The ruler-drop test cannot measure something this fast; a tendon-tap test is used instead",{"id":61,"label":920},"Gravity does not act during a reflex",{"id":64,"label":922},"The ruler would need to be heavier to fall faster",[58],[],"A couple of millimetres of fall is far too small to read reliably with a ruler and a human catch, so reflex speed is tested a different way entirely — by tapping a tendon and watching for a jerk.",[145,927],"measurement",{"id":929,"section":31,"level":185,"prompt":930,"check":931,"hints":942,"solution":943,"skills":944},"body-systems.q054","A biceps lever (4 cm muscle arm, 32 cm load arm) trades strength for speed. The jaw-closing muscle is arranged the opposite way, with its muscle arm relatively long compared with the load arm at the back teeth. What should this predict about how the jaw moves and how hard it can bite?",{"kind":52,"options":932,"correct":941},[933,935,937,939],{"id":55,"label":934},"Fast movement, weak bite",{"id":58,"label":936},"Slow movement, very strong bite",{"id":61,"label":938},"No difference from the arm",{"id":64,"label":940},"Fast movement, and equally strong bite",[58],[],"A lever with a proportionally longer muscle arm trades speed for force — the opposite of the biceps. This matches how a jaw actually works: it closes over a small range, relatively slowly, but with enough force to crack something firm.",[835,875,182],{"id":946,"section":35,"level":49,"prompt":947,"check":948,"hints":959,"solution":960,"skills":961},"body-systems.q055","Which feature do all of the body's hand-over points share?",{"kind":52,"options":949,"correct":958},[950,952,954,956],{"id":55,"label":951},"A thick, strong wall",{"id":58,"label":953},"A pump to push things across",{"id":61,"label":955},"A very thin wall, a very large folded surface, and a steep difference across it",{"id":64,"label":957},"They are all located in the chest",[61],[],"Alveoli, villi and capillaries are the same design solved three times: thin barrier, huge surface, and a difference that keeps material moving on its own.",[220],{"id":963,"section":35,"level":49,"prompt":964,"check":965,"hints":976,"solution":977,"skills":978},"body-systems.q056","What crosses the alveolus wall, and in which direction?",{"kind":52,"options":966,"correct":975},[967,969,971,973],{"id":55,"label":968},"Only oxygen, into the blood",{"id":58,"label":970},"Only carbon dioxide, out of the blood",{"id":61,"label":972},"Oxygen into the blood and carbon dioxide out of it, at the same time",{"id":64,"label":974},"Blood itself, into the air sac",[61],[],"Both gases cross the same wall at the same moment, in opposite directions, each drifting from where it is crowded to where it is not.",[220,19],{"id":980,"section":35,"level":111,"prompt":981,"check":982,"hints":993,"solution":994,"skills":995},"body-systems.q057","Which TWO of these hand-overs involve the circulatory system on at least one side?",{"kind":52,"options":983,"correct":992},[984,986,988,990],{"id":55,"label":985},"Alveolus to blood",{"id":58,"label":987},"Nerve to muscle",{"id":61,"label":989},"Villus to blood",{"id":64,"label":991},"Muscle to bone",[55,61],[],"Both the alveolus (gases) and the villus (nutrients) hand their cargo directly to the blood. The nerve-to-muscle and muscle-to-bone hand-overs do not directly involve blood.",[220],{"id":997,"section":35,"level":111,"prompt":998,"check":999,"hints":1010,"solution":1011,"skills":1012},"body-systems.q058","Why does blood have to keep flowing past an alveolus rather than sitting still?",{"kind":52,"options":1000,"correct":1009},[1001,1003,1005,1007],{"id":55,"label":1002},"To keep the lungs warm",{"id":58,"label":1004},"Diffusion stops once both sides are equal, so flow keeps carrying loaded blood away and bringing hungry blood in",{"id":61,"label":1006},"Still blood would freeze",{"id":64,"label":1008},"It does not matter either way",[58],[],"Flow maintains the difference diffusion needs. Without it, blood and air would reach the same oxygen level and crossing would stop.",[220,648],{"id":1014,"section":35,"level":148,"prompt":1015,"check":1016,"hints":1027,"solution":1028,"skills":1029},"body-systems.q059","A roti's glucose reaches a working calf muscle. Put these hand-overs in the correct order it passes through.",{"kind":52,"options":1017,"correct":1026},[1018,1020,1022,1024],{"id":55,"label":1019},"Villus → blood, then blood → muscle cell",{"id":58,"label":1021},"Blood → muscle cell, then villus → blood",{"id":61,"label":1023},"Villus → blood, then muscle cell → blood",{"id":64,"label":1025},"Alveolus → blood, then villus → blood",[55],[],"Glucose first crosses the villus wall into the blood (digestive → circulatory), then later crosses a capillary wall into a muscle cell (circulatory → muscular).",[220,15,1030],"sequence",{"id":1032,"section":35,"level":148,"prompt":1033,"check":1034,"hints":1043,"solution":1044,"skills":1045},"body-systems.q060","Which hand-over in this topic carries a force rather than a substance?",{"kind":52,"options":1035,"correct":1042},[1036,1037,1038,1040],{"id":55,"label":985},{"id":58,"label":987},{"id":61,"label":1039},"Muscle to bone (via the tendon)",{"id":64,"label":1041},"Blood to kidney filter",[61],[],"Every other hand-over here carries a substance or a chemical signal. The tendon at a joint carries a pull — force — from muscle to bone, and only in that one direction.",[220,835],{"id":1047,"section":35,"level":185,"prompt":1048,"check":1049,"hints":1051,"solution":1054,"skills":1055},"body-systems.q061","A dialysis machine copies the kidney's filtering hand-over for about 4 hours a session, 3 sessions a week. What percentage of a full week (168 hours) does that represent, to one decimal place?",{"kind":279,"answer":1050,"tolerance":710,"unit":711},7.1,[1052,1053],"Find total hours on the machine first.","Divide by the total hours in a week and convert to a percentage.","4 × 3 = 12 hours a week on the machine. 12 ÷ 168 × 100 ≈ 7.1% — a striking contrast with a healthy kidney, which performs the same hand-over continuously, all week, every week.",[220,1056],"technology",{"id":1058,"section":35,"level":185,"prompt":1059,"check":1060,"hints":1071,"solution":1072,"skills":1073},"body-systems.q062","Digested fat crossing into a lacteal, rather than a blood capillary, is sometimes described as an \"exception\" to the general hand-over rule at the villi. In what sense is it still consistent with the topic's three-rule pattern (thin wall, big surface, steep difference)?",{"kind":52,"options":1061,"correct":1070},[1062,1064,1066,1068],{"id":55,"label":1063},"It is not consistent at all — fat absorption ignores all three rules",{"id":58,"label":1065},"The lacteal is still a thin-walled, high-surface vessel inside the villus — only the destination network differs",{"id":61,"label":1067},"Fat does not actually need to cross any wall",{"id":64,"label":1069},"The three-rule pattern only applies to gases, not to fat",[58],[],"The lacteal is a thin, absorptive vessel just like a blood capillary, sitting inside the same folded, high-surface-area villus. What changes is which network receives the substance afterwards (lymph rather than blood directly), not the fundamental thin-wall, high-surface design.",[220,182,164],{"id":1075,"section":39,"level":49,"prompt":1076,"check":1077,"hints":1088,"solution":1089,"skills":1090},"body-systems.q063","When you run hard, what mostly triggers the faster breathing?",{"kind":52,"options":1078,"correct":1087},[1079,1081,1083,1085],{"id":55,"label":1080},"Your brain deciding you need more air",{"id":58,"label":1082},"Rising carbon dioxide in your blood",{"id":61,"label":1084},"Your muscles pulling on the ribs",{"id":64,"label":1086},"Falling body temperature",[58],[],"Sensors watch carbon dioxide closely because it changes fast and reliably — the same signal that makes holding your breath uncomfortable.",[507,704],{"id":1092,"section":39,"level":49,"prompt":1093,"check":1094,"hints":1097,"solution":1099,"skills":1100},"body-systems.q064","A class's resting pulses are 72, 76, 80, 68, 84, 78 bpm. What is the mean, to one decimal place?",{"kind":279,"answer":1095,"tolerance":710,"unit":1096},76.3,"bpm",[1098],"Add all the values, then divide by how many there are.","(72+76+80+68+84+78) ÷ 6 = 458 ÷ 6 ≈ 76.3 bpm.",[1101,1102],"data-handling","mean",{"id":1104,"section":39,"level":111,"prompt":1105,"check":1106,"hints":1117,"solution":1118,"skills":1119},"body-systems.q065","A class measures pulse and breathing rate before and after one minute of star jumps. What does this topic's data show?",{"kind":52,"options":1107,"correct":1116},[1108,1110,1112,1114],{"id":55,"label":1109},"Only pulse rises",{"id":58,"label":1111},"Only breathing rises",{"id":61,"label":1113},"Both rise by a similar factor, roughly doubling",{"id":64,"label":1115},"Neither reliably changes",[61],[],"Pulse rose by a factor of about 1.74 and breathing by about 1.89 in the sample data — both roughly double, from the same rising-carbon-dioxide trigger.",[507,1101],{"id":1121,"section":39,"level":111,"prompt":1122,"check":1123,"hints":1127,"solution":1130,"skills":1131},"body-systems.q066","A ruler-drop reaction test gives a class mean of 19.5 cm. Using d = ½gt² with g = 9.8 m\u002Fs², roughly what reaction time (in milliseconds) does this correspond to?",{"kind":279,"answer":1124,"tolerance":1125,"unit":1126},199,15,"ms",[1128,1129],"Convert the distance to metres first.","Rearrange d = ½gt² to solve for t.","t = √(2d ÷ g) = √(2 × 0.195 ÷ 9.8) ≈ 0.199 s ≈ 199 ms — closely matching the roughly 200 ms often used for a voluntary reaction time.",[507,1132],"physics",{"id":1134,"section":39,"level":111,"prompt":1135,"check":1136,"hints":1147,"solution":1148,"skills":1149},"body-systems.q067","During hard exercise, why does blood flow to the muscles rise by a much bigger factor (about ×16) than the pulse does (about ×1.7)?",{"kind":52,"options":1137,"correct":1146},[1138,1140,1142,1144],{"id":55,"label":1139},"Pulse and blood flow to muscle are actually unrelated",{"id":58,"label":1141},"A rise in total cardiac output compounds with a redirected share of blood going to muscle instead of the gut",{"id":61,"label":1143},"It is a measurement error in the data",{"id":64,"label":1145},"Muscles create their own separate blood supply during exercise",[58],[],"Cardiac output itself rises (about ×4), and on top of that a bigger share of that blood is redirected to muscle and away from the gut, and the two multipliers compound to give the much larger combined rise.",[507,23,182],{"id":1151,"section":39,"level":148,"prompt":1152,"check":1153,"hints":1164,"solution":1165,"skills":1166},"body-systems.q068","Two people reach the same peak pulse after identical exercise. One recovers to their resting pulse in 4 minutes, the other in 12 minutes. What is the fairest conclusion?",{"kind":52,"options":1154,"correct":1163},[1155,1157,1159,1161],{"id":55,"label":1156},"The slower-recovering person is definitely unwell",{"id":58,"label":1158},"On this one measure, the faster-recovering person is currently fitter — nothing more dramatic than that",{"id":61,"label":1160},"Recovery time is meaningless and random",{"id":64,"label":1162},"The faster-recovering person has a smaller heart",[58],[],"Recovery time reflects how efficiently the whole system settles back to resting mode, and it genuinely improves with regular exercise — but a single reading says nothing else about a person's health or worth.",[507,182],{"id":1168,"section":39,"level":148,"prompt":1169,"check":1170,"hints":1173,"solution":1176,"skills":1177},"body-systems.q069","At rest, oxygen use is about 375 mL a minute, costing about 1.88 kcal a minute at roughly 5 kcal per litre of oxygen. During hard exercise, oxygen use rises to about 3,375 mL a minute. Roughly how many kcal a minute does that cost (to 1 decimal place)?",{"kind":279,"answer":1171,"tolerance":502,"unit":1172},16.9,"kcal\u002Fmin",[1174,1175],"Convert millilitres to litres.","Multiply by 5 kcal per litre.","3,375 mL = 3.375 L; 3.375 × 5 ≈ 16.9 kcal a minute — about nine times the resting energy cost, matching the ninefold rise in oxygen use.",[507,1178],"energy",{"id":1180,"section":39,"level":185,"prompt":1181,"check":1182,"hints":1193,"solution":1194,"skills":1195},"body-systems.q070","In an experiment testing whether saliva digests starch, cup A gets rice plus saliva and cup B gets rice with nothing added. What is cup B's scientific role?",{"kind":52,"options":1183,"correct":1192},[1184,1186,1188,1190],{"id":55,"label":1185},"It is the important result to report",{"id":58,"label":1187},"It is the control, showing what \"no digestion happened\" looks like so cup A can be meaningfully compared",{"id":61,"label":1189},"It is a backup in case cup A is spilled",{"id":64,"label":1191},"It tests the iodine solution, not the rice",[58],[],"Without a control, a colour change in cup A could have several explanations. Cup B isolates the one thing that differs — the saliva — so any difference in colour can only be explained by it.",[507,1196],"fair-test",{"id":1198,"section":43,"level":49,"prompt":1199,"check":1200,"hints":1211,"solution":1212,"skills":1213},"body-systems.q071","What did William Harvey demonstrate in 1628?",{"kind":52,"options":1201,"correct":1210},[1202,1204,1206,1208],{"id":55,"label":1203},"That blood is made in the liver and used up by the tissues",{"id":58,"label":1205},"That blood circulates around the body in a closed loop, pumped by the heart",{"id":61,"label":1207},"The existence of capillaries, seen under a microscope",{"id":64,"label":1209},"How to record the heart's electrical signal",[58],[],"Harvey showed, mainly through arithmetic, that far too much blood is pumped every hour for it to be freshly made and destroyed — it must be circulating and reused.",[1214],"history",{"id":1216,"section":43,"level":111,"prompt":1217,"check":1218,"hints":1221,"solution":1223,"skills":1224},"body-systems.q072","Harvey estimated about 56.8 mL of blood pumped per beat, at about 4,320 beats an hour. Roughly how many litres of blood does that give per hour?",{"kind":279,"answer":1219,"tolerance":1220,"unit":577},245,10,[1222],"Multiply mL per beat by beats per hour, then convert to litres.","56.8 × 4,320 ≈ 245,376 mL ≈ 245 L in one hour — around 49 times the whole body's actual blood supply of about 5 L, which only makes sense if the same blood is reused repeatedly.",[1214,413],{"id":1226,"section":43,"level":111,"prompt":1227,"check":1228,"hints":1239,"solution":1240,"skills":1241},"body-systems.q073","What can an ECG detect that a stethoscope cannot?",{"kind":52,"options":1229,"correct":1238},[1230,1232,1234,1236],{"id":55,"label":1231},"The sound of blood flow",{"id":58,"label":1233},"The heart's own electrical signal",{"id":61,"label":1235},"Blood pressure directly",{"id":64,"label":1237},"The exact size of the heart",[58],[],"A stethoscope hears sound (valves and flow); an ECG records the heart's self-generated electrical signal, picked up from sensors on the skin.",[1214,1056],{"id":1243,"section":43,"level":111,"prompt":1244,"check":1245,"hints":1256,"solution":1257,"skills":1258},"body-systems.q074","Why is X-ray usually tried first for a suspected broken bone, rather than MRI?",{"kind":52,"options":1246,"correct":1255},[1247,1249,1251,1253],{"id":55,"label":1248},"X-ray shows more soft-tissue detail",{"id":58,"label":1250},"X-ray is fast and inexpensive, and bone is exactly the tissue it images best",{"id":61,"label":1252},"MRI cannot be used on bones at all",{"id":64,"label":1254},"X-ray uses no radiation, unlike MRI",[58],[],"X-ray is quick, cheap and shows dense bone clearly. MRI gives better soft-tissue detail but is slower and more expensive — a better fit for different questions.",[1056,1259],"imaging",{"id":1261,"section":43,"level":148,"prompt":1262,"check":1263,"hints":1270,"solution":1271,"skills":1272},"body-systems.q075","A dialysis machine mainly rebuilds which hand-over from this topic?",{"kind":52,"options":1264,"correct":1269},[1265,1266,1267,1268],{"id":55,"label":985},{"id":58,"label":1041},{"id":61,"label":987},{"id":64,"label":991},[58],[],"It copies the kidney's filtering hand-over: blood on one side of a thin membrane, cleaning fluid on the other, waste crossing by diffusion.",[1056,220],{"id":1274,"section":43,"level":148,"prompt":1275,"check":1276,"hints":1278,"solution":1280,"skills":1281},"body-systems.q076","Without exercise, astronauts can lose bone mineral at about 1% a month in microgravity. Over a 6-month mission, roughly what percentage would this come to if it continued unchecked?",{"kind":279,"answer":1277,"tolerance":502,"unit":711},6,[1279],"Multiply the monthly rate by the number of months.","1% × 6 = 6% over six months — a genuinely large loss, which is exactly why ISS astronauts exercise against resistance machines for a couple of hours almost every day.",[1282,413],"space",{"id":1284,"section":43,"level":148,"prompt":1285,"check":1286,"hints":1297,"solution":1298,"skills":1299},"body-systems.q077","Why do many wrist-worn fitness bands need a snug fit and can give unreliable readings during fast, jerky movement?",{"kind":52,"options":1287,"correct":1296},[1288,1290,1292,1294],{"id":55,"label":1289},"They use a stethoscope, which needs good contact",{"id":58,"label":1291},"They measure tiny changes in reflected light caused by blood pulses, which a loose fit or motion easily disrupts",{"id":61,"label":1293},"They record an ECG, which needs a wire touching the heart",{"id":64,"label":1295},"They measure body temperature, which changes slowly",[58],[],"These sensors shine light into the skin and detect a tiny, repeating dimming caused by extra blood arriving with each heartbeat — a signal easily disturbed by a loose strap or vigorous movement.",[1056],{"id":1301,"section":43,"level":185,"prompt":1302,"check":1303,"hints":1314,"solution":1315,"skills":1316},"body-systems.q078","India was certified polio-free by the WHO in 2014, after the last wild polio case in 2011. What does this best illustrate about vaccination?",{"kind":52,"options":1304,"correct":1313},[1305,1307,1309,1311],{"id":55,"label":1306},"A single national vaccination event is always enough",{"id":58,"label":1308},"The same individual immune-memory mechanism, applied repeatedly and reliably across a whole population over years, can eliminate a disease at national scale",{"id":61,"label":1310},"Polio disappeared without any vaccination effort",{"id":64,"label":1312},"Certification happens automatically a fixed number of years after the last case, regardless of ongoing vaccination",[58],[],"Eliminating a disease across a whole country requires the same basic immune-memory trick as an individual vaccination, delivered reliably and repeatedly to enough of the population that the germ can no longer find enough unprotected people to spread between.",[1214,163,182],{"id":1318,"section":43,"level":185,"prompt":1319,"check":1320,"hints":1331,"solution":1332,"skills":1333},"body-systems.q079","Harvey proved circulation using arithmetic decades before Malpighi actually saw a capillary under a microscope. What does this sequence best demonstrate about scientific reasoning?",{"kind":52,"options":1321,"correct":1330},[1322,1324,1326,1328],{"id":55,"label":1323},"Arithmetic is always more reliable than direct observation",{"id":58,"label":1325},"A sound logical argument can establish that something must be true well before the direct physical evidence for it is available",{"id":61,"label":1327},"Harvey's claim was not actually accepted until Malpighi's discovery",{"id":64,"label":1329},"Microscopes were not needed at all once Harvey had done his arithmetic",[58],[],"Harvey's argument showed that only continuous circulation makes arithmetic sense, without ever seeing how arteries connected to veins. Malpighi's later microscope observation confirmed the missing physical link Harvey's reasoning had already required.",[1214,182],[1335,1336,1337,1338,1339,1340,1341,1342,1343,1344,1345,1346,1347],"body-systems-britannica-digestive","body-systems-britannica-respiratory","body-systems-britannica-cardiovascular","body-systems-britannica-renal","body-systems-britannica-nervous","body-systems-helander-surface","body-systems-wiki-alveolus","body-systems-wiki-homeostasis","body-systems-sender-cells","body-systems-nasa-humans-in-space","body-systems-britannica-history-medicine","body-systems-britannica-dialysis","body-systems-who-immunization","needs_review",{"generatedBy":1350,"notes":1351},"claude-code","Draft generated locally; pending owner review.","c188fe4e6efca82c3f962ef3ab0c67e989146a0d78be63c74bf9cc7ac847a5df",{"logic:questions":1354,"source:body-systems-britannica-cardiovascular":1355,"source:body-systems-britannica-dialysis":1356,"source:body-systems-britannica-digestive":1357,"source:body-systems-britannica-history-medicine":1358,"source:body-systems-britannica-nervous":1359,"source:body-systems-britannica-renal":1360,"source:body-systems-britannica-respiratory":1361,"source:body-systems-helander-surface":1362,"source:body-systems-nasa-humans-in-space":1363,"source:body-systems-sender-cells":1364,"source:body-systems-who-immunization":1365,"source:body-systems-wiki-alveolus":1366,"source:body-systems-wiki-homeostasis":1367},"e7fd7c240a65bea1bff6277f7af7cca65e2c7fcb13c6d756cb943d53f3cbc948","8b7278004bfe64d7ad3e369fbfa62cada6c2ca19bdda240520d8cb96569d40a7","f84d9e2a5ffc9a1351da1e245ac71000e5564ac0ac9c1bebb262fab02e1b1b64","8b28eef54dd7327ab08588678c32674f0a6615182ae48d49d272ad156d0ad122","fe1a4e43d20072580424c152ced7e693b4b96fbd453bddd8de4a914b2f062c9e","07d4488afad056b326893d48a8ecd74894b1e87c5b23c8f0bbd1268b77fdf252","5aac5e4ba60a1b43234a3f40d1a2f4a1fae961d335628e57236d7e84bd5073f3","dd8e7c0348ffd73f06866939a2804a19b80938f30a21e7c2b3e4ac922cb96f65","315ae0ee433a382e063169419964f84379d552e5957655fd04ced507ff2a6940","02b80a915fbee98479fc55757f037cca24b091dd7844fee0cb6a54fb141040f2","275141a01bad918372489d869091a22c69fcb823ac1a7a523ba14b5ab8494acc","9b61cc1683dd013de90da0ab1067e4bd122ff090c0383f4d64355890022d25e0","43da85a71de8cdd85dad5ae87aa0c57897396ecc1b5efde1f672fe7289321ecf","0e7d85baebb026691fbe6a4ef3c8aeaf14bd5c792553e4d59439acce7e4f81b3","preview-7e1cbbcc4f",1789899599608]