A quick revision summary for right before the exam: every definition, comparison and figure name, all in one place. The full notes are available separately for detailed reading.
1 Life Processes and Nutrition
Processes that together maintain the body, even when it appears to be doing nothing.
Making food from CO₂ and water using sunlight and chlorophyll (photosynthesis). Green plants, some bacteria.
Taking in complex food made by other organisms: saprophytic (bread moulds, yeast, mushrooms), holozoic, or parasitic (cuscuta, ticks, lice, leeches, tape-worms).
Equation: 6CO₂ + 12H₂O → C₆H₁₂O₆ (glucose) + 6O₂ + 6H₂O, in the presence of chlorophyll and sunlight.
Photosynthesis, three events: (i) light absorbed by chlorophyll (ii) light energy → chemical energy, water splits into H and O (iii) CO₂ reduced to carbohydrate.
Guard cells swell (water in) to open the stomatal pore, shrink to close it.
Amoeba: food vacuole via finger-like extensions. Paramoecium: cilia move food to a fixed spot.
2 Human Digestion, Organ by Organ
Mouth: teeth crush food into uniform particles; muscular tongue mixes it with saliva while chewing.
| Organ/gland | Secretion | Action |
|---|---|---|
| Salivary glands | Saliva (salivary amylase) | Starch → simple sugar |
| Gastric glands (stomach) | HCl, pepsin, mucus | Acidic medium, digests protein, protects lining |
| Liver | Bile juice | Makes food alkaline, emulsifies fat |
| Pancreas | Trypsin, lipase | Digests protein, emulsified fat |
| Small intestine wall | Intestinal juice | Protein → amino acids; carbohydrate → glucose; fat → fatty acids + glycerol |
Peristalsis: rhythmic muscular contraction pushing food along the canal.
Villi: finger-like projections in the small intestine, increase surface area for absorption.
Herbivores need a longer small intestine (cellulose takes longer to digest) than carnivores (meat digests faster).
3 Respiration
Glucose (6C) → Pyruvate (3C), in the cytoplasm, in every organism.
| Aerobic | Anaerobic | |
|---|---|---|
| Oxygen | Needed | Not needed |
| Where | Mitochondria | Cytoplasm only |
| Products | 3 CO₂ + water | Ethanol + CO₂ (yeast) or lactic acid (muscle, causes cramps) |
| Energy | More | Less |
ATP: breaking its terminal phosphate bond releases 30.5 kJ/mol; ATP powers all cell activities.
Plants: release CO₂ at night, release O₂ during the day.
Human respiratory path: nostrils (fine hairs and mucus filter the air) → throat (rings of cartilage stop the air-passage collapsing) → lungs → alveoli (gas exchange, rich blood supply; spread out they would cover about 80 m²).
Haemoglobin (in RBCs) carries O₂; CO₂ travels mostly dissolved in plasma.
4 Transportation in Humans
Heart flow: Body → right atrium → right ventricle → lungs → left atrium → left ventricle → body. Ventricles have thicker walls than atria.
| Group | Chambers | Mixing |
|---|---|---|
| Fish | 2 | Single circulation, blood through heart once |
| Amphibians/many reptiles | 3 | Some mixing tolerated |
| Birds/mammals | 4 | No mixing (right and left sides fully separated) |
Double circulation: blood passes through the heart twice in each cycle round the body in all vertebrates other than fish (once to the lungs, once to the body); in fish it passes only once.
Blood pressure: systolic ≈ 120 mm Hg, diastolic ≈ 80 mm Hg (sphygmomanometer); hypertension from arteriole constriction.
Arteries: away from heart, thick walls. Veins: to heart, have valves. Capillaries: one cell thick, exchange.
Platelets: clot blood at a leak. Lymph: tissue fluid, drains fat and excess fluid back to blood.
5 Transportation in Plants
| Xylem | Phloem | |
|---|---|---|
| Carries | Water, minerals | Food (translocation) |
| Direction | Upward only | Both directions |
| Driven by | Root pressure (night), transpiration pull (day) | ATP-driven osmotic pressure |
Transpiration: water vapour lost from aerial parts; pulls water up, and regulates temperature.
6 Excretion
Human excretory system: kidneys → ureters → urinary bladder → urethra. Waste: urea/uric acid.
Nephron: glomerulus (capillary cluster) inside Bowman’s capsule (collects filtrate) → tubule selectively re-absorbs glucose, amino acids, salts, most water.
Dialysis (artificial kidney): blood through semi-permeable tubes in dialysing fluid (same osmotic pressure as blood, no nitrogenous waste); waste diffuses out; NO re-absorption, unlike a real kidney. Filtrate ≈180 L/day made, only ≈1-2 L/day excreted.
Plants: O₂ (a photosynthesis waste), excess water via transpiration, storage in vacuoles, shed leaves, resins/gums in old xylem, excretion into soil.
7 Key Points to Revise
- Full step-by-step blood flow through all four heart chambers, in order, and why this is double circulation
- Structure and function of a nephron; compare alveoli and nephrons; compare xylem and phloem
- Difference between aerobic and anaerobic respiration, with examples