Eduqas Component 3 covers gas exchange, transport, nutrition, homeostasis and the kidney, and the nervous system — and then one option chosen from A: Immunology and Disease, B: Human Musculoskeletal Anatomy, or C: Neurobiology and Behaviour. This lesson covers the core and introduces all three options.
Work through each screen, answer the questions as you go — several are A-level calculations — and collect ⭐ stars. Press Start when you are ready.
As an organism gets larger, its volume grows faster than its surface area, so the SA:V ratio falls — and the diffusion distances become greater. A single-celled organism can rely on diffusion across its body surface; a mammal cannot.
Large or metabolically active organisms therefore need a specialised exchange surface, which is always large in area, thin (a short diffusion distance), moist, and served by a mechanism that maintains the concentration gradient.
Animals: a closed double circulation. Cardiac muscle is myogenic; the SAN sets the rhythm, the AVN imposes a delay, and the bundle of His and Purkyne fibres make the ventricles contract from the apex upwards. Valves open and close purely because of pressure differences.
Haemoglobin shows cooperative binding, hence the sigmoid dissociation curve: it loads oxygen at the high partial pressure in the lungs and unloads it steeply at the low partial pressure in respiring tissue. The Bohr shift — more CO₂, lower pH — moves the curve right, so still more oxygen is released where respiration is fastest. Fetal haemoglobin has a higher affinity (curve to the left), so it takes oxygen from the maternal blood.
Plants: xylem carries water up by cohesion–tension: evaporation from the leaves creates tension, and the continuous water column is pulled up, held together by hydrogen bonding. Phloem carries sucrose by mass flow: it is actively loaded at the source, water follows by osmosis, the hydrostatic pressure rises, and sap flows to the sink where sucrose is unloaded. Xerophytes (thick cuticle, sunken stomata, rolled leaves, hairs) reduce water loss.
Modes of nutrition: autotrophic (making organic compounds from inorganic ones — photoautotrophs such as plants; chemoautotrophs such as nitrifying bacteria) and heterotrophic — holozoic (ingesting, digesting and absorbing food, as animals do), saprotrophic (secreting enzymes onto dead matter and absorbing the products, as fungi do) and parasitic.
The human gut: carbohydrates are digested by amylase and membrane-bound disaccharidases; proteins by endopeptidases (breaking internal bonds and so creating many more ends), then exopeptidases and dipeptidases; lipids are emulsified by bile salts — increasing the surface area for lipase — and absorbed as micelles.
The ileum is adapted for absorption: villi and a brush border of microvilli give an enormous surface area; the epithelium is one cell thick; there are many mitochondria for the ATP needed for co-transport; and each villus has a dense capillary network (maintaining the gradient) and a lacteal for fats.
Adaptations to diet: a herbivore has broad, ridged molars and a very long gut with a caecum housing cellulose-digesting mutualistic bacteria (mammals make no cellulase of their own). A carnivore has carnassial teeth for shearing and a much shorter gut, because meat is far easier to digest.
Ultrafiltration: the afferent arteriole is wider than the efferent, so the hydrostatic pressure in the glomerulus is high. Water, glucose, amino acids, urea and ions are forced through the fenestrations, the basement membrane (the real filter) and the podocytes. Blood cells and plasma proteins are too large to pass.
Selective reabsorption (proximal convoluted tubule): all the glucose and amino acids are reabsorbed by co-transport with Na⁺; the cells have microvilli and many mitochondria. Water follows by osmosis.
Loop of Henle: a countercurrent multiplier. Na⁺ and Cl⁻ are pumped out of the ascending limb, making the medulla progressively more negative in water potential — so water can be drawn out of the collecting duct all the way down, producing urine more concentrated than blood.
Osmoregulation: a fall in blood water potential is detected by osmoreceptors in the hypothalamus → the posterior pituitary releases ADH → ADH inserts aquaporins into the collecting duct → more water is reabsorbed → a small volume of concentrated urine. Negative feedback.
Tap a process, then tap where it happens.
Resting potential (−70 mV): the Na⁺/K⁺ pump moves 3 Na⁺ out for every 2 K⁺ in, and the membrane is far more permeable to K⁺.
Action potential: at the threshold, voltage-gated Na⁺ channels open and the membrane depolarises to about +40 mV; Na⁺ channels close, K⁺ channels open, and the membrane repolarises, with a brief hyperpolarisation. It is all-or-nothing; the refractory period ensures one-way conduction and sets the maximum firing frequency; a stronger stimulus gives a higher frequency of impulses, not a bigger one.
Saltatory conduction: myelin insulates the axon, so depolarisation occurs only at the nodes of Ranvier and the impulse jumps between them — much faster. Speed also rises with axon diameter and temperature.
Synapse: Ca²⁺ enters the pre-synaptic knob → vesicles of acetylcholine fuse with the membrane and release it → it diffuses across and binds receptors → Na⁺ channels open in the post-synaptic membrane → threshold reached. Acetylcholinesterase then hydrolyses the neurotransmitter, so the synapse is not permanently switched on.
Disease: pathogens include bacteria (TB, cholera), viruses (HIV, influenza), fungi and protoctists (malaria — Plasmodium, carried by the female Anopheles mosquito). Disease may be endemic (always present), epidemic or pandemic.
Antibiotics: bactericidal antibiotics kill (penicillin prevents the cross-linking of murein, so the wall fails and the cell bursts by osmosis); bacteriostatic ones inhibit growth. They do not work on viruses, which have no cell wall, no ribosomes of their own and no metabolism. Resistance evolves by natural selection: a chance mutation (e.g. producing β-lactamase) is favoured by the selection pressure of the antibiotic, and the allele spreads — including horizontally, on plasmids, between species.
Immune response: non-specific defences (barriers, inflammation, phagocytosis) and then the specific response — the cell-mediated response (T helper, T killer and T memory cells) and the humoral response (B plasma cells secreting antibodies; B memory cells giving a faster, larger secondary response). Vaccination creates that memory without the illness, and high uptake gives herd immunity.
Skeletal tissues: compact bone is built from Haversian systems (osteons) — concentric lamellae of mineralised matrix around a central canal carrying blood vessels, with osteocytes in lacunae connected by canaliculi. Cartilage (hyaline, at joint surfaces) has chondrocytes in a firm but flexible matrix and no blood supply — which is why it heals so poorly.
The skeleton: the axial skeleton (skull, vertebral column, ribs, sternum) protects and supports; the appendicular skeleton (limbs and girdles) provides for movement. Its functions are support, protection, movement (a system of levers), mineral storage (calcium and phosphate) and blood cell production in the red marrow.
Joints: a synovial joint has articular cartilage, a synovial membrane secreting synovial fluid, and a fibrous capsule. Ligaments (bone to bone) are slightly elastic; tendons (muscle to bone) are inelastic, so the whole contraction is transmitted. Muscles work in antagonistic pairs (biceps = flexor, triceps = extensor), because muscles can only pull.
Contraction: the sliding filament mechanism — Ca²⁺ → troponin → tropomyosin moves → cross-bridges → power stroke → ATP detaches and re-cocks the myosin head. Osteoporosis (loss of bone density) and osteoarthritis (degeneration of the articular cartilage) are the conditions to know.
The brain: the cerebrum (conscious thought, memory, language, voluntary movement, sensory processing — with its motor and sensory areas mapped as the homunculus); the cerebellum (balance, posture, fine coordination); the hypothalamus (homeostasis, and control of the pituitary); the medulla oblongata (heart rate, breathing, blood pressure).
Imaging: CT and MRI show structure (MRI without ionising radiation); fMRI and PET show function — which regions are active during a task, by tracking blood oxygenation or a radioactive tracer.
Neuroscience: synaptic transmission and neurotransmitters; plasticity — connections that are used are strengthened and those that are not are pruned, which is why the critical period in visual development matters so much.
Behaviour: innate behaviour is inherited, stereotyped and needs no learning — a taxis is a directional response (a woodlouse moving away from light is negative phototaxis), while a kinesis is a non-directional change in the rate of movement or turning (a woodlouse moves faster and turns less in dry air, so by chance it spends more time in damp air). Learned behaviour includes habituation (a declining response to a repeated harmless stimulus — which saves energy), imprinting, classical and operant conditioning, and insight learning.
Tap a topic on the left, then the Eduqas option it belongs to.
SA:V ratio falls as an organism gets bigger, so large or active organisms need specialised exchange surfaces and a ventilation mechanism and mass transport system.
Gas exchange surfaces are large, thin and moist, with a maintained concentration gradient: alveoli, gills (countercurrent flow), tracheae, and the leaf mesophyll with its stomata.
Transport: cardiac output = stroke volume × heart rate. Haemoglobin gives a sigmoid dissociation curve; the Bohr shift unloads more oxygen in respiring tissue. Plants: xylem (cohesion-tension) and phloem (mass flow).
Kidney: ultrafiltration → selective reabsorption (PCT) → the loop of Henle sets up the medullary gradient → ADH controls water reabsorption in the collecting duct. Negative feedback.
Nervous system: resting potential −70 mV; action potential (Na⁺ in, then K⁺ out); all-or-nothing; saltatory conduction; synaptic transmission by acetylcholine.
Option A — Immunology and Disease: pathogens, antibiotics and antibiotic resistance, phagocytosis, the humoral and cell-mediated responses, antibodies, vaccination.
Option B — Human Musculoskeletal Anatomy: bone and cartilage, the axial and appendicular skeleton, joints, and the sliding filament mechanism.
Option C — Neurobiology and Behaviour: brain structure and imaging, neuroscience, and innate and learned behaviour.
You have covered the Eduqas Component 3 core and all three options. Press Finish to see your score.
You have worked through Component 3 — Requirements for Life at full A-level depth. 🎉
Your stars: 0 / 0
Next: test yourself in the Evaluate stage Confidence Quiz, then lock it in with Verify.