Tick off each objective as you master it. Cambridge 0610 syllabus 2026-2028.
Gas exchange occurs in the alveoli of the lungs. The lungs have four key features that make them efficient:
1. Large surface area: Millions of alveoli provide an enormous surface for diffusion. If you flattened a human lung, it would cover the size of a tennis court.
2. Thin surface: Alveolar walls are only one cell thick (simple squamous epithelium), allowing oxygen to diffuse across quickly into blood capillaries, and CO2 to diffuse out.
3. Good blood supply: Dense network of capillaries surrounding each alveolus means blood is constantly present to pick up oxygen and drop off CO2.
4. Good ventilation: The diaphragm and intercostal muscles contract to inflate the lungs with fresh air, keeping the concentration gradient high.
Air path: Larynx → Trachea → Bronchi → Bronchioles → Alveoli
Diaphragm: Sheet of muscle below lungs. Contracts downward to increase thorax volume (inspiration). Relaxes to decrease volume (expiration).
Intercostal muscles: Two sets between ribs. External intercostals pull ribs up and out (inspiration). Internal intercostals pull ribs down and in (expiration).
Cartilage in trachea: C-shaped rings keep airway open, preventing collapse during breathing.
| Gas | Inspired (%) | Expired (%) | Why? |
|---|---|---|---|
| Oxygen | 21% | 16% | Absorbed by blood in alveoli |
| CO2 | 0.04% | 4% | Released from blood into alveoli |
| Nitrogen | 78% | 78% | Inert, not used |
| Water vapour | Variable | Higher | Evaporates from alveolar lining |
Limewater turns cloudy/milky white when CO2 passes through it. Use this to test: inspired air (no change) vs expired air (turns milky).
Word equation: Glucose + Oxygen → Carbon dioxide + Water (+ Energy)
Balanced equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
Occurs in mitochondria. Releases ~2800 kJ per mole of glucose. This energy is stored as ATP.
In yeast (fermentation): Glucose → Alcohol + Carbon dioxide
In muscle during exercise: Glucose → Lactic acid
Releases much less energy (~120 kJ per mole) than aerobic. Lactic acid buildup causes muscle fatigue and oxygen debt.
Oxygen debt removal: After exercise, continued fast breathing and heart rate supply O2 to convert lactic acid back to glucose in the liver (gluconeogenesis).
A student measures breathing rate before and after running. Before: 12 breaths/min. After: 48 breaths/min. Explain why breathing rate increased.
✓ Exercise increases muscle respiration rate [1 mark]
✓ More glucose is broken down in muscles, producing more CO2 [1 mark]
✓ Increased CO2 in blood is detected by the brain, which signals faster/deeper breathing to remove CO2 [1 mark]
A sample of inspired air contains 21% oxygen. A sample of expired air contains 16% oxygen. Explain the difference.
✓ Oxygen is absorbed from the alveoli into the blood by diffusion [1 mark]
✓ This reduces the concentration of oxygen in expired air [1 mark]
A sprinter runs at maximum speed for 60 seconds. After finishing, she continues breathing heavily for several minutes. Explain what is happening.
✓ During intense exercise, muscles respire anaerobically (without sufficient oxygen) [1 mark]
✓ This produces lactic acid which accumulates, causing oxygen debt [1 mark]
✓ After exercise, the lactic acid must be oxidised back to glucose in the liver [1 mark]
✓ This requires oxygen, so breathing remains fast to supply it [1 mark]
Yeast is used to make bread. During fermentation in anaerobic conditions, glucose is converted to alcohol and CO2. Why is this process less efficient than aerobic respiration?
✓ Anaerobic respiration releases much less energy (ATP) per glucose molecule than aerobic [1 mark]
✓ Because without oxygen, glucose is only partially broken down to alcohol/lactic acid, not completely to CO2 and water [1 mark]
Which gas increases most in concentration between inspired and expired air?
What feature of alveoli makes them suitable for efficient gas exchange?
Which muscle relaxes during inspiration (breathing in)?
Describe the role of limewater in testing for carbon dioxide in expired air.
Compare aerobic and anaerobic respiration in terms of energy released.
State the word equation for aerobic respiration.
Explain why yeast cells produce alcohol during anaerobic fermentation.
A student runs at maximum speed for 2 minutes, then rests. Explain what happens to the muscles and why breathing remains heavy after stopping.
Always include: (1) Name the muscle/structure that moves, (2) Direction it moves, (3) Effect on thorax volume, (4) Effect on air pressure, (5) Direction of air flow, (6) Link to gas exchange if asked.
State the percentage change for each gas, then explain WHY using diffusion/concentration gradients or cellular respiration.
Key points: (1) Anaerobic respiration during exercise, (2) Lactic acid buildup, (3) O₂ debt definition, (4) Removal mechanisms (fast breathing, heart rate, liver gluconeogenesis).
Word equations are tested in Core. Balanced equations (with C₆H₁₂O₆) are Supplement. Know both. Always include energy in word equations.
Central Nervous System (CNS): Brain + Spinal cord. Processes information and sends commands.
Peripheral Nervous System (PNS): All nerves outside CNS. Carries signals between CNS and body.
Sensory neurone: Detects stimulus, sends impulse to CNS. Long dendrite carries signal TO cell body.
Relay neurone: In CNS only. Connects sensory to motor neurone.
Motor neurone: Carries impulse FROM CNS to effector (muscle/gland). Long axon.
Stimulus → Sensory receptor → Sensory neurone → Relay neurone (in spinal cord) → Motor neurone → Effector (muscle) → Response
Reflex arcs bypass the brain for speed. Touching a hot surface: your hand pulls away BEFORE you consciously feel pain.
Synapse = junction between two neurones. Presynaptic neurone (sender) has synaptic vesicles containing neurotransmitter. Synaptic gap (~20nm) separates the two neurones. Postsynaptic neurone has receptor proteins.
Process: (1) Impulse reaches vesicles, triggering release of neurotransmitter. (2) Neurotransmitter diffuses across gap. (3) Binds to receptors on next neurone. (4) Triggers new impulse.
One-way transmission: Only presynaptic side releases neurotransmitter; only postsynaptic side has receptors.
| Structure | Function |
|---|---|
| Cornea | Refracts (bends) light to begin focusing |
| Iris | Colored muscle controlling pupil diameter |
| Pupil | Hole through which light enters (not a structure, an opening) |
| Lens | Adjusts focus on retina (accommodation) |
| Retina | Contains light receptors (rods/cones) and converts light to electrical impulses |
| Optic nerve | Carries impulses to brain |
| Blind spot | Where optic nerve exits; no photoreceptors |
Bright light: Circular muscles in iris CONTRACT → pupil narrows (less light enters). Radial muscles RELAX.
Dim light: Radial muscles in iris CONTRACT → pupil dilates (more light enters). Circular muscles RELAX.
Near object: Ciliary muscles CONTRACT → tension in suspensory ligaments decreases → lens becomes fatter (more curved) → stronger refraction for near vision.
Distant object: Ciliary muscles RELAX → ligaments pull tight → lens becomes thinner (less curved) → weaker refraction for distant vision.
Hormone: Chemical substance made by gland, carried in blood, affects specific target organs.
| Gland | Hormone | Target / Effect |
|---|---|---|
| Adrenal | Adrenaline | Fight-or-flight: ↑ heart rate, breathing, pupil size, blood glucose |
| Pancreas | Insulin | ↓ Blood glucose (cells take up glucose) |
| Pancreas | Glucagon | ↑ Blood glucose (liver breaks down glycogen) |
| Testes | Testosterone | Male sexual development, secondary characteristics |
| Ovaries | Oestrogen | Female sexual development, secondary characteristics |
Homeostasis: Maintenance of constant internal environment (temperature, blood glucose, water balance).
Negative feedback: If body strays from set point → corrective mechanism brings it back. Example: High blood glucose → Pancreas releases insulin → Glucose uptake increases → Blood glucose falls back to normal.
High glucose: Pancreatic beta cells detect it → Release insulin → Liver/muscles take up glucose and store as glycogen → Blood glucose falls.
Low glucose: Pancreatic alpha cells detect it → Release glucagon → Liver breaks down glycogen to glucose → Blood glucose rises.
Type 1 diabetes: Beta cells destroyed → Can't make insulin → Blood glucose stays high. Treatment: Insulin injection.
Skin structures: Hairs (trap insulating layer), hair erector muscles (raise hairs when cold), sweat glands (cooling), blood vessels (control blood flow to skin).
If too hot: Sweat glands release sweat (evaporative cooling). Arterioles in skin dilate (vasodilation) → more blood flow to skin surface to lose heat.
If too cold: Shivering (muscle contractions generate heat). Hair erectors contract (hairs stand up, trapping air layer). Arterioles constrict (vasoconstriction) → less blood to skin surface, conserving heat.
Phototropism: Growth toward light source. Caused by unequal distribution of auxin (more on shaded side → cells elongate more → shoot bends toward light).
Gravitropism: Root grows DOWN (positive geotropism); shoot grows UP (negative geotropism). Auxin concentration changes in response to gravity.
Auxin: Plant hormone made in shoot tip. Diffuses toward darker/lower side → causes cell elongation on that side → bending response.
A student touches a hot surface and quickly pulls their hand away. Explain how a reflex arc allows this rapid response without conscious thought.
✓ Heat detected by receptors in skin → sensory neurone carries impulse [1 mark]
✓ Sensory neurone synapse with relay neurone in spinal cord [1 mark]
✓ Relay neurone synapses with motor neurone [1 mark]
✓ Motor neurone sends impulse to arm muscle → contraction → hand withdraws (all before brain processes conscious pain) [1 mark]
Explain how the pupil reflex protects the retina from bright light damage.
✓ Bright light detected by retina → signals sent to brain [1 mark]
✓ Brain sends impulses to circular muscles in iris → they contract [1 mark]
✓ Pupil narrows (constricts) → less light enters the eye → protects retina from overexposure [1 mark]
A student's blood glucose level rises to 150 mg/100ml (above normal). Describe how negative feedback maintains blood glucose.
✓ High blood glucose detected by pancreatic beta cells [1 mark]
✓ Pancreas secretes insulin into blood [1 mark]
✓ Insulin causes liver and muscle cells to take up glucose → stored as glycogen [1 mark]
✓ Blood glucose level falls back to normal (negative feedback corrects the change) [1 mark]
A plant shoot grows toward a window (light source). Explain how auxin causes this phototropic response.
✓ Light causes unequal distribution of auxin → more auxin on shaded side of shoot [1 mark]
✓ Higher auxin concentration stimulates cell elongation on shaded side more than lit side → shoot bends toward light [1 mark]
Which neurone type carries impulses FROM the central nervous system TO an effector?
How does a synapse ensure that nerve impulses travel in only one direction?
In dim light, what happens to the pupil?
Describe what happens to the lens when focusing on a nearby object.
Explain how the body maintains a constant temperature when the environmental temperature is very cold.
Which hormone is released by the adrenal gland in response to fear or excitement?
Explain the role of auxin in phototropism of a plant shoot.
Compare nervous and hormonal control of body functions.
Label all components (receptor, sensory neurone, relay neurone, motor neurone, effector, synapses). Arrows show direction of impulse. Always mention that reflex bypasses conscious brain control for speed.
Use the term "negative feedback" explicitly. Show the SET POINT, the DETECTOR, the CORRECTIVE MECHANISM, and how the system returns to normal.
State: (1) Which gland secretes it, (2) Stimulus for release, (3) Target organ/tissue, (4) Specific effect. Avoid vague language like "it affects the body."
Always mention: (1) Stimulus (light/gravity), (2) Unequal auxin distribution, (3) Differential cell elongation, (4) Direction of bending. Don't just say "the plant grows toward light."
Excretion: Removal of metabolic waste products (CO₂, urea, excess water) produced by cells.
Egestion: Removal of undigested food (faeces) — not waste from metabolism.
Lungs: Carbon dioxide (from respiration)
Kidneys: Urea (from amino acid breakdown), excess water and ions
Liver: Converts nitrogenous waste from protein breakdown to urea (safer, less toxic)
Cortex: Outer layer; site of ultrafiltration (first step)
Medulla: Inner layer; site of selective reabsorption (second step)
Pelvis: Funnel-shaped structure collecting urine → enters ureter
Step 1 — Ultrafiltration (in Bowman's capsule): High blood pressure forces water, glucose, urea, and ions out of capillaries into Bowman's capsule. Large molecules (proteins, red blood cells) remain in blood.
Step 2 — Selective reabsorption (in proximal convoluted tubule and loop of Henle): All glucose (useful), some ions, and most water are reabsorbed back into blood. Urea remains in filtrate.
Step 3 — Urine formation: Remaining filtrate (containing urea, excess ions, excess water) = urine. Flows down collecting duct → ureter → bladder → urethra → expelled.
Excess amino acids cannot be stored. The liver removes the amino group (-NH₂) from amino acids via deamination. The nitrogenous part is converted to urea (less toxic). The carbohydrate part can be used for respiration or glycogen synthesis.
Urea is toxic if accumulated in blood. Regular excretion via kidneys removes this poison. Inability to excrete (kidney failure) causes uremia (urea poisoning in blood), requiring dialysis.
Explain why glucose is present in the filtrate at Bowman's capsule but absent in urine.
✓ Glucose is small enough to be filtered out of the blood during ultrafiltration in Bowman's capsule [1 mark]
✓ Glucose is a useful substance needed by cells [1 mark]
✓ It is selectively reabsorbed back into the blood in the proximal convoluted tubule [1 mark]
Explain why people with diabetes may have glucose in their urine.
✓ Blood glucose concentration is very high [1 mark]
✓ More glucose is filtered into the filtrate than the proximal convoluted tubule can reabsorb, so excess glucose remains in urine [1 mark]
Explain why deamination occurs in the liver and why urea is produced.
✓ Excess amino acids cannot be stored; the liver must break them down [1 mark]
✓ The amino group is removed (deamination) producing ammonia/nitrogen waste [1 mark]
✓ This nitrogenous waste is converted to urea, which is less toxic and can be excreted safely by the kidneys [1 mark]
Which of the following is NOT excreted by the kidneys?
Describe the role of the kidney in maintaining homeostasis.
In which part of the nephron does ultrafiltration occur?
Why is deamination important for the body?
Which kidney structure collects urine from the nephrons?
Definition: Production of genetically identical offspring from one parent. Offspring are clones.
Examples: Vegetative propagation (runners in strawberries, bulbs in daffodils, fragmentation in starfish, binary fission in bacteria).
Advantages: Offspring are identical to parent (no variation), faster than sexual reproduction, no need to find mate.
Disadvantages: No genetic variation → population cannot adapt to environmental change; all organisms equally susceptible to disease.
Definition: Fusion of nuclei from two gametes (male and female) to form a zygote. Offspring are genetically different.
Advantages: Genetic variation → population can adapt to environmental changes; individuals differ in disease resistance.
Disadvantages: Slower than asexual; genetic variation may produce unfavorable traits; requires finding a mate.
| Part | Structure | Function |
|---|---|---|
| Sepals | Green leaf-like | Protect flower bud |
| Petals | Colorful, scented | Attract insects |
| Stamens | Male organs: anther + filament | Produce pollen (male gametes) |
| Carpel | Female organ: stigma + style + ovary | Contain ovules (female gametes) |
| Feature | Insect-Pollinated | Wind-Pollinated |
|---|---|---|
| Petals | Large, colorful, scented | Small or absent |
| Pollen grains | Sticky, large | Light, powdery, smooth |
| Anthers | Inside flower | Outside flower, exposed |
| Stigma | Small, sticky | Large, feathery, exposed |
| Nectar | Present (insect food) | Absent |
| Examples | Rose, bee orchid, sunflower | Grass, wheat, hazel |
Pollination: Transfer of pollen from anther to stigma.
Self-pollination: Pollen from anther of flower A to stigma of flower A (or different flower on same plant). Results in inbreeding.
Cross-pollination: Pollen from flower A to stigma of flower B (different plant, same species). Results in genetic variation.
Fertilisation: Pollen tube grows down style. Pollen nucleus fuses with ovule nucleus in ovary → zygote forms → becomes seed.
Water: Activates enzymes; allows root growth; dissolves nutrients.
Oxygen: Required for aerobic respiration in growing cells.
Temperature: Activates enzymes; different seeds have different optimal temperatures.
Explain why cross-pollination is preferable to self-pollination for wild plant populations.
✓ Cross-pollination produces genetic variation in offspring [1 mark]
✓ Variation allows the population to adapt if the environment changes [1 mark]
✓ Self-pollination produces identical offspring → no variation → population cannot adapt [1 mark]
Describe two structural differences between insect-pollinated and wind-pollinated flowers.
✓ Insect flowers have large, colorful petals; wind flowers have small or no petals [1 mark]
✓ Insect flowers have sticky pollen; wind flowers have light, powdery pollen [1 mark]
Why is water essential for seed germination?
✓ Water activates enzymes necessary for metabolism and growth [1 mark]
✓ Water is absorbed, allowing the seed to swell and the root to emerge; it dissolves nutrients for transport [1 mark]
Which type of reproduction produces genetically identical offspring?
Explain why genetic variation from sexual reproduction is important for a species' survival.
Which part of the flower contains the ovules (female gametes)?
Describe two environmental factors required for seed germination.
Compare the structure of pollen from insect-pollinated and wind-pollinated flowers.
| Structure | Function |
|---|---|
| Testes | Produce sperm and testosterone |
| Scrotum | Keeps testes at lower temperature for sperm production |
| Sperm ducts | Transport sperm from testes toward penis |
| Prostate gland | Secretes seminal fluid (nutrients, motility) |
| Urethra | Carries sperm and urine (at different times) |
| Penis | Deposits sperm into female tract |
| Structure | Function |
|---|---|
| Ovaries | Produce eggs and hormones (oestrogen, progesterone) |
| Oviducts | Transport egg from ovary to uterus; site of fertilisation |
| Uterus | Implantation site; fetal development |
| Cervix | Narrows during pregnancy; dilates during labor |
| Vagina | Receives sperm; birth canal |
| Feature | Sperm | Egg |
|---|---|---|
| Size | Tiny (~0.05 mm) | Large (~0.1 mm) |
| Motility | Highly motile (flagellum) | Non-motile |
| Number | Millions per ejaculate | One per ovulation |
| Mitochondria | Many (power flagellum) | Many (energy for early development) |
| Nucleus | Haploid (n) | Haploid (n) |
| Acrosome | Contains enzymes to penetrate egg coat | Zona pellucida (jelly coat hardens after fertilisation) |
Fertilisation: Sperm nucleus fuses with egg nucleus → diploid zygote (2n) with 46 chromosomes.
Embryo development: Zygote divides by mitosis → ball of cells (morula) → implants into uterus lining after ~6 days.
Placenta: Grows from trophoblast. Exchanges oxygen, nutrients, and waste between mother and fetus WITHOUT mixing blood.
Umbilical cord: Connects fetus to placenta. Contains two arteries and one vein.
Amniotic sac: Membrane surrounding fetus.
Amniotic fluid: Cushions fetus, maintains constant temperature, allows movement.
Testosterone (in males): Promotes development of male secondary characteristics: facial/body hair, muscle development, deep voice, penis enlargement.
Oestrogen (in females): Promotes development of female secondary characteristics: breast development, hip widening, menstruation.
Follicular phase (days 1-14): FSH from pituitary stimulates ovary to produce follicles and oestrogen. Oestrogen builds uterus lining (endometrium).
Ovulation (day 14): LH surge triggers release of mature egg from ovary.
Luteal phase (days 15-28): Corpus luteum (remnant of follicle) produces progesterone. Progesterone maintains endometrium. If no fertilisation, progesterone/oestrogen drop → menstruation.
hCG (human chorionic gonadotropin): Produced by embryo; maintains corpus luteum to continue progesterone production.
Progesterone: Maintains pregnancy; inhibits uterus contractions.
Oestrogen: Increases throughout pregnancy; promotes uterus growth.
Definition: Infections transmitted through sexual contact.
HIV (Human Immunodeficiency Virus): Attacks immune cells (T cells); can lead to AIDS. Transmission: blood, sexual contact, mother-to-child. No cure; treatment: antiretroviral drugs.
Prevention: Condoms (barrier), testing, monogamy, safe practices with blood (don't share needles).
Explain how the structure of a sperm cell relates to its function.
✓ Sperm has a flagellum (tail) for swimming through female reproductive tract [1 mark]
✓ Sperm has many mitochondria to provide ATP energy for flagellum movement [1 mark]
✓ Sperm has acrosome containing enzymes to penetrate egg coat [1 mark]
Explain the role of the placenta in fetal development.
✓ Placenta allows exchange of oxygen and nutrients from mother's blood to fetus [1 mark]
✓ Placenta also allows removal of fetal waste (CO₂, urea) to mother's blood for excretion [1 mark]
Describe how progesterone and oestrogen control the menstrual cycle after ovulation.
✓ After ovulation, corpus luteum produces progesterone [1 mark]
✓ Progesterone maintains the endometrium (uterus lining) [1 mark]
✓ If no fertilisation occurs, progesterone/oestrogen levels drop → endometrium sheds → menstruation [1 mark]
Which hormone is secreted by the testes and promotes male secondary characteristics?
At what stage does a fertilized egg implant into the uterus lining?
Explain the function of the umbilical cord during pregnancy.
Which hormone causes ovulation in the menstrual cycle?
Describe the difference between the follicular and luteal phases of the menstrual cycle.
What is the term for an infection transmitted through sexual contact?
Explain how HIV affects the immune system and leads to AIDS.
State two methods of preventing the transmission of HIV.
Explain why the amniotic fluid is important during pregnancy.
Compare the structure of a sperm cell to an egg cell in terms of size and number.
Always clearly distinguish between asexual (one parent, clones) and sexual (two parents, variation). Know the advantages/disadvantages of each for exam success.
Name the three key structures: placenta (exchange), umbilical cord (transport), amniotic fluid (protection). Examiners test understanding of why each is essential.
Use a timeline: Days 1-14 (follicular), day 14 (ovulation), days 15-28 (luteal). Link each phase to the hormone changes (FSH→oestrogen→LH→progesterone).
Know HIV specifically: pathogen type, routes of transmission (sexual, blood, mother-to-child), symptoms, and prevention. Avoid vague language.