The Biology Challenge doesn't test obscure trivia — it tests whether a Year 9 or 10 biologist really knows the KS3 core: cells, photosynthesis and respiration, the heart and blood, chromosomes, natural selection, food chains, pathogens and classification. We build our own KS3 biology flashcards for Biology Challenge practice, and pulling together the facts behind those cards makes a genuinely useful revision list — useful whether or not your child's school enters this year. For the background on the competition itself, see our full guide to the Biology Challenge.

Cells built for a job: the leaf and the root hair

A specialised cell is a shape built to solve one problem. A leaf's palisade cells are packed with chloroplasts, tiny structures containing the pigment chlorophyll, which traps light energy near the top of the leaf where the light is strongest. Down at the roots, cells just behind the growing tip grow a long, hair-like extension — the root hair cell — that hugely increases the surface area available to take in water and dissolved minerals from the soil. Water moves in by osmosis, from the dilute water in the soil into the more concentrated cell; minerals need energy, which is why root hair cells are unusually rich in mitochondria. Same principle both times: shape follows job.

Photosynthesis and respiration: two reactions running in opposite directions

Photosynthesis is the leaf's food-making reaction: carbon dioxide plus water, using light energy trapped by chlorophyll, makes glucose plus oxygen. Aerobic respiration runs the opposite way in every living cell, day and night: glucose plus oxygen makes carbon dioxide plus water, releasing usable energy. Because photosynthesis only happens in daylight while respiration never stops, a plant is a net taker of carbon dioxide during the day and a net giver at night — and that exchange, repeated across every plant and animal on Earth, drives the carbon cycle.

When a cell can't get enough oxygen — a sprinting muscle, for instance — it falls back on anaerobic respiration instead: glucose breaks down into lactic acid, releasing far less energy, and the lactic acid has to be cleared afterwards, which is why you keep panting once you stop running. Yeast does something different when oxygen runs short: glucose becomes ethanol and carbon dioxide, a process called fermentation, and it's what makes bread dough rise.

Digestion: enzymes that each do exactly one job

Digestion is chemical, not just mechanical. Amylase, an enzyme in saliva, starts breaking starch down into sugars the moment you begin chewing, and the pancreas adds more amylase further along the gut. Two other enzyme families finish the job elsewhere: proteases break protein down into amino acids, and lipase breaks fat down into fatty acids and glycerol. Each enzyme fits only its own substrate — amylase never touches protein — which is exactly the kind of pairing a multiple-choice paper likes to test.

The heart and blood: two pumps and four passengers

The heart is really two pumps side by side. The right side sends blood on the short journey to the lungs; the left side sends it all the way round the body, so the left ventricle has by far the thickest, most muscular wall of the four chambers — and on a diagram facing you, it sits on the right-hand side, because "left" means the patient's left, not the viewer's.

Blood itself carries four things. Red blood cells carry oxygen, bound to the iron-rich pigment haemoglobin; they have no nucleus and a biconcave shape, both of which make more room for haemoglobin and more surface area for gas exchange. White blood cells fight infection, platelets help blood clot, and plasma carries everything else dissolved — food, carbon dioxide, hormones, heat. A red blood cell lives only around 120 days before the spleen recycles it.

Chromosomes: why a gamete carries half

Every human body cell holds 46 chromosomes, arranged as 23 pairs — one chromosome of each pair from each parent. A gamete, an egg or a sperm, carries only 23. That halving matters: when a sperm fertilises an egg, the two half-sets combine to restore the full 46, and the chromosome number stays stable from one generation to the next.

Natural selection, happening in real time

Antibiotic resistance is one of the fastest, most watchable examples of natural selection there is. Nothing in the bacteria decides to resist a drug — in any large population, a few cells already carry a chance mutation that lets them survive it. The antibiotic kills the rest; the survivors multiply; the next generation is mostly resistant. Variation, selection, inheritance: Darwin's three ingredients, just running with a twenty-minute generation time instead of a twenty-year one. The same logic explains the peppered moth's colour change and the shape of the Galápagos finches' beaks.

Food chains: what the arrow actually means

In a food chain, the arrow always points from the organism that gets eaten to the one that eats it — grass → rabbit → fox — because the arrow shows the direction energy is transferred, not who is chasing whom. Only a small fraction of the energy at each level passes up to the next; most is lost as heat from respiration, in movement, and in waste. That's why food chains rarely run more than four or five links, and why a pyramid of biomass narrows sharply towards the top.

Pathogens: four kinds, and only one that antibiotics can touch

Pathogens fall into four groups: bacteria, viruses, fungi and protists. Flu, colds and measles are viral; tuberculosis and Salmonella food poisoning are bacterial; athlete's foot is fungal; malaria is caused by a protist. Antibiotics kill bacteria and nothing else — which is why a doctor won't prescribe them for flu, and why taking them when they can't help simply breeds more resistant bacteria.

Classifying vertebrates: five classes and one bridge

Vertebrates split into five classes: fish (gills, scales), amphibians (moist permeable skin, jelly-covered eggs laid in water), reptiles (dry scaly skin, shelled eggs laid on land), birds (feathers, hard-shelled eggs) and mammals (fur, milk). Amphibians are the bridge between water and land — a frog starts life as a gilled tadpole and ends it as a lung-breathing adult, which is why it has to return to water to breed.

Where these facts come from — and where to go next

This list is built from our own KS3 biology flashcard deck written for Biology Challenge practice — twelve cards covering cells, energy, the body, genetics, ecosystems and classification. Unlike some competitions, the Biology Challenge doesn't publish past papers with answers, so there's no year-by-year archive to mine for recurring themes; instead, see how these topics connect to the KS3 curriculum for the bigger picture.

Knowing a fact once and being able to recall it instantly under pressure are different skills. For the mistakes that come from almost knowing these facts — the swapped diagram, the muddled process, the misremembered rule — see Biology Challenge: common mistakes and misconceptions. And for how regular, spaced review turns a shaky fact into a solid one, see preparing for the Biology Challenge with spaced repetition.

FAQ

Do I need to enter the Biology Challenge for this list to be useful?

No. Every fact here is core KS3 biology — cells, photosynthesis and respiration, the heart and blood, chromosomes, natural selection, food chains, pathogens and classification. It's useful revision whether or not your child's school takes part this year.

Is this list exhaustive — is this everything the Biology Challenge could ask?

No, and we wouldn't claim it is. Unlike some competitions, UK Biology Competitions doesn't publish past Biology Challenge papers with their answers, so there's no archive of past questions to draw on. What's here are the facts behind our own Biology Challenge practice deck — one set of twelve cards, not a syllabus.

My child struggles to remember all these facts — what actually helps?

Spaced repetition, reviewed little and often, works far better than reading a list once. See our companion piece on preparing for the Biology Challenge with spaced repetition for how that works in practice.

Duke Harewood runs aitutors.me and built its KS3 science tutors, including Professor Darwin for biology.