Chapter 1: Life Processes

All living organisms share the same life processes (movement, respiration, sensitivity, growth, reproduction, excretion, nutrition). This chapter covers cell structure (plant vs animal), enzymes (how they work and what affects them), respiration (aerobic and anaerobic), the movement of materials into and out of cells (diffusion, osmosis, active transport) and how cells become specialised (cell division, tissues, organs, stem cells).

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THE EIGHT LIFE PROCESSES (MRS GREN / MRS H GREN)

• Movement — an action by an organism causing a change of position.
• Respiration — the chemical reaction that releases energy from food.
• Sensitivity — detecting and responding to changes in the surroundings (stimuli).
• Growth — a permanent increase in size (by cell division and cell enlargement).
• Reproduction — producing offspring.
• Excretion — removal of the waste products of metabolism (not egestion of undigested food).
• Nutrition — taking in and using food.
• (Some lists add Homeostasis — keeping internal conditions constant.)
• 💡 Exam tip: you must be able to state all eight and give an example of each.

CELL STRUCTURE

• All living things are made of cells. Simple organisms (Amoeba, bacteria, yeast) are single-celled; complex plants and animals are multicellular (countless millions of cells).
• There is no such thing as a "typical" cell — but most cells share features (organelles). Organelles are the tiny structures inside a cell that carry out particular jobs.
• A nanometre (nm) = 10⁻⁹ m (one millionth of a millimetre) — organelles are measured in nm.

ANIMAL CELL organelles (Figure 1.2)

• Nucleus — controls the cell's activities; contains chromosomes (genetic material/DNA); controls cell division.
• Cytoplasm — the jelly-like liquid where most chemical reactions happen; contains the organelles.
• Cell membrane — controls what enters and leaves the cell (partially permeable).
• Mitochondria — the site of aerobic respiration (energy release). Cells that need lots of energy (muscle cells) have many mitochondria.
• Ribosomes — tiny structures where protein synthesis happens.
• Endoplasmic reticulum (ER) — a system of membranes through the cytoplasm; rough ER is covered in ribosomes (Biology only: rough ER transports proteins made at the ribosomes; it separates reactions into different compartments so they don't interfere).

PLANT CELLS have all the above PLUS (Figure 1.2):

• Cell wall — made of cellulose; gives the cell strength and support.
• Chloroplasts — contain the green pigment chlorophyll for photosynthesis (only in photosynthesising cells — e.g. leaf cells, not root cells).
• Vacuole — a large permanent sac of cell sap (weak solution of sugars and salts) that helps support the cell (turgidity).
• KEY POINT — differences to memorise: plants have cell wall, chloroplasts, large permanent vacuole; animals do NOT. Animals store glycogen; plants store starch.
• 📊 Diagram: draw one animal cell and one plant cell side by side, label ALL organelles above, and note "plant cells also have X".

ENZYMES: CONTROLLING REACTIONS IN THE CELL

• Enzyme — a biological catalyst: a protein that speeds up a chemical reaction without being used up.
• Catalyst — a substance that speeds up a reaction but is unchanged at the end.
• Each enzyme is specific to one reaction (one substrate). The substrate fits into the enzyme's active site like a lock and key (Figure 1.5).
• Enzyme names end in -ase and usually name the substrate: amylase breaks down starch (amylose); catalase breaks down hydrogen peroxide; protease breaks down proteins; lipase breaks down lipids.
• Denatured — when an enzyme's shape changes permanently (active site destroyed) so the substrate can no longer fit; it stops working forever.

FACTORS AFFECTING ENZYMES

1. TEMPERATURE (Figure 1.6): - Rate of reaction rises with temperature up to an optimum (for human enzymes ≈ 37 °C body temperature) — particles have more energy, more collisions. - Above the optimum the enzyme denatures — rate falls rapidly to zero. - 📊 Graph: rate vs temperature — rising curve peaking at ~37 °C, then steep fall.
2. pH (Figure 1.7): - Most enzymes work best at neutral pH ~7 — this is their optimum pH. - Away from the optimum (too acidic or too alkaline), enzyme activity decreases (denaturing). - Some enzymes have different optima: pepsin in the stomach works best in acid (pH ~2). - 📊 Graph: rate vs pH — bell-shaped curve peaking at the optimum.

ACTIVITY 1 — Practical: effect of TEMPERATURE on AMYLASE (Figure 1.8)

• Test tubes of starch solution + amylase at different temperatures (e.g. 0–60 °C); sample with iodine at intervals.
• Iodine test: iodine solution turns blue-black in the presence of starch; when starch is digested, it stays orange/brown.
• Time how long until starch is gone → rate of amylase activity (e.g. at 50 °C starch all digested after X minutes). Plot rate against temperature → curve like Figure 1.6.

ACTIVITY 2 — Practical: effect of pH on CATALASE (Figure 1.9)

• Buffer solutions keep pH constant. Add catalase (e.g. potato extract) to hydrogen peroxide at different pHs and measure the rate of oxygen production (bubbles/gas volume in a syringe over water).
• At the optimum pH, most oxygen is produced fastest.

HOW THE CELL GETS ITS ENERGY — RESPIRATION

• Respiration — the chemical reaction that releases energy from glucose, happening in every living cell (NOT breathing — that is ventilation).
• Aerobic respiration (with oxygen), word equation: glucose + oxygen → carbon dioxide + water (+ energy) C6H12O6 + 6O2 → 6CO2 + 6H2O (+ energy)
• Happens in the mitochondria. Releases a LOT of energy.
• ATP — the energy 'currency' of the cell (Biology only): energy from respiration is used to make ATP from ADP + phosphate; ATP is then broken down (back to ADP) wherever the cell needs energy — e.g. muscle contraction, active transport, protein synthesis.

ANAEROBIC RESPIRATION (without oxygen) — releases less energy

• In yeast cells: glucose → ethanol + carbon dioxide (+ a little energy). (Anaerobic respiration in yeast = fermentation — used to make bread/alcohol.)
• In muscle cells: glucose → lactic acid (+ a little energy).
• Anaerobic respiration in muscles happens during a 'burst' of activity (a sprint, lifting something heavy) when oxygen is in short supply.
• The lactic acid causes muscle fatigue; it is removed by extra oxygen afterwards (oxygen debt).

ACTIVITY 3 — Practical: carbon dioxide from small living organisms (Figure 1.11)

• Small organisms (e.g. maggots/woodlice) on a gauze platform inside a tube with hydrogencarbonate indicator (or limewater).
• Hydrogencarbonate indicator: pink/red in normal air → yellow in CO₂ (more acidic); purple when CO₂ is removed.
• The organisms respire → CO₂ concentration rises → indicator turns yellow → proves living organisms produce CO₂ by respiration.

ACTIVITY 4 — Practical: heat from germinating seeds (Figure 1.12)

• Germinating peas (respiring) in a vacuum flask (insulates) with a thermometer; a control flask with boiled/dead peas.
• The temperature in the germinating flask rises — respiration releases heat energy.

MOVEMENT OF MATERIALS IN AND OUT OF CELLS

DIFFUSION

• Diffusion — the net movement of particles from a higher concentration to a lower concentration (down the concentration gradient) until evenly spread.
• It is a passive process (no energy needed).
• Examples: oxygen diffuses into cells; carbon dioxide diffuses out; food molecules absorbed in the small intestine.
• ACTIVITY 5 — Practical: diffusion in a jelly: hydrochloric acid diffuses into (and decolorises) jelly/phenolphthalein blocks — smaller blocks are coloured through faster (larger surface area:volume).

OSMOSIS

• Osmosis — the net movement of water molecules from a dilute solution (high water concentration) to a more concentrated solution (low water concentration) through a partially permeable membrane.
• It is a special case of diffusion — only water moves.
• In plant cells: osmosis moves water cell to cell; if a plant cell is placed in pure water it becomes turgid (swollen, firm — supports the plant); in a concentrated solution it becomes flaccid then plasmolysed (membrane pulls away from the wall).
• In animal cells: no cell wall — in pure water an animal cell may burst (haemolysis in red blood cells); in concentrated solution it shrinks.

ACTIVE TRANSPORT

• Active transport — the movement of particles from a lower to a higher concentration (against the concentration gradient), using energy from respiration (ATP).
• Happens in: root hair cells (absorbing mineral ions from very dilute soil water) and villi of the small intestine (absorbing glucose).
• Needs: carrier proteins in the membrane + energy.

SPECIALISED EXCHANGE SURFACES

• Big organisms need specialised exchange surfaces because diffusion alone is too slow over large distances. Adaptations (shared by alveoli of the lungs and villi of the small intestine):
• Large surface area
• Thin walls (short diffusion distance — one cell thick)
• Good blood supply (maintains the concentration gradient)
• Moist surfaces (for dissolving gases/substances)
• (Villi also have villi/microvilli; alveoli are ventilated.)

CELL DIVISION AND DIFFERENTIATION

• Organisms grow by cell division (Figure 1.15): one cell divides to form two, then four... producing countless millions of cells.
• Differentiation — cells become specialised for particular functions (e.g. a nerve cell, a muscle cell, a red blood cell, an epidermal cell in the outer layer of the skin, a root hair cell).
• Tissues — groups of cells with a similar structure and function working together (e.g. muscle tissue, xylem).
• Organs — different tissues working together (e.g. heart, stomach, lungs, leaf, root).
• Organ systems — groups of organs working together (e.g. the digestive system).

STEM CELLS

• Stem cell — an unspecialised cell that can divide to produce more cells and differentiate into specialised cells.
• Embryonic stem cells — found in embryos; can divide to become any type of cell (Figure 1.18 — scientists can isolate and culture them).
• Adult stem cells (e.g. in bone marrow) — can divide many times but only become a limited range of cells (e.g. blood cells).
• Uses (Biology only): potential to treat diseases (diabetes, paralysis, Parkinson's) by replacing damaged cells.

✅ Quick check

1. List the eight life processes. (Movement, respiration, sensitivity, growth, reproduction, excretion, nutrition [+ homeostasis].)
2. Give three differences between plant and animal cells. (Plant: cellulose cell wall, chloroplasts, large permanent vacuole.)
3. What is an enzyme? (A biological catalyst — a protein that speeds up reactions.)
4. What happens to an enzyme above its optimum temperature? (It denatures — active site changes shape permanently.)
5. Write the word equation for aerobic respiration. (Glucose + oxygen → carbon dioxide + water + energy.)
6. Distinguish diffusion, osmosis and active transport. (Diffusion = down the gradient, passive; osmosis = water through a partially permeable membrane down the water gradient; active transport = against the gradient, needs energy.)

Chapter 2: The Variety of Living Organisms

Living organisms are classified into groups with features in common. The key division is between eukaryotic organisms (cells with a true nucleus and organelles) and prokaryotic organisms (bacteria — no true nucleus). This chapter covers the five kingdoms and viruses, with examples of each group you must recognise.

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CLASSIFICATION

• Biologists put organisms into groups according to features they have in common — classification.
• The five kingdoms are: Animals, Plants, Fungi, Protoctists (protists) and Bacteria (prokaryotes).
• Viruses are NOT in a kingdom (they are not made of cells and can only reproduce inside a host cell).

EUKARYOTIC AND PROKARYOTIC ORGANISMS

• Eukaryotic organisms — cells have a true nucleus (with a nuclear membrane), mitochondria, ribosomes and other organelles. Includes all animals, plants, fungi and protoctists.
• Prokaryotic organisms — bacteria: cells have no true nucleus (genetic material is free in the cytoplasm as a single circular loop of DNA), no mitochondria, and are much smaller. They may have a cell wall (not cellulose), and sometimes plasmids (small loops of extra DNA) and flagella.
• KEY DIFFERENCE to memorise: eukaryotic = nucleus present; prokaryotic = no nucleus.
• 💡 Exam tip: be able to state the difference and draw/sketch both cell types.

THE FIVE KINGDOMS — examples you must recognise

1. ANIMALS

• Multicellular, no cell wall, feed on other organisms (heterotrophic).
• Examples: mammals (e.g. humans, dogs, whales) and insects (e.g. housefly, butterfly).

2. PLANTS

• Multicellular, cellulose cell walls, make food by photosynthesis (autotrophic), contain chlorophyll.
• Examples: flowering plants such as maize (corn) and peas; also trees, grasses.

3. FUNGI

• Mostly multicellular (except yeast — single-celled); cell walls made of chitin (NOT cellulose); no chloroplasts; feed by saprophytic nutrition (digest food externally and absorb it) or as parasites; store glycogen.
• Examples: Mucor (a mould — multicellular, with hyphae) and yeast (single-celled fungus used in bread and alcohol making).

4. PROTOCTISTS (protozoa/protists)

• Single-celled organisms with a true nucleus (eukaryotic).
• Examples: Amoeba (moves and feeds like an animal), Chlorella (a single-celled alga with chloroplasts — photosynthesises), Plasmodium (a parasite that causes malaria, transmitted by mosquitoes).

5. BACTERIA (prokaryotes)

• Single-celled, no true nucleus (prokaryotic), small, may have a cell wall and plasmids.
• Example: Lactobacillus (used to make yoghurt from milk).

VIRUSES

• Not living cells: extremely small; consist of genetic material (DNA or RNA) inside a protein coat.
• Can only reproduce inside a living host cell (they are obligate parasites).
• Examples: influenza virus (flu), HIV (causes AIDS).
• Antibiotics do NOT work on viruses (only on bacteria).

PATHOGENS (link to disease)

• A pathogen is a microorganism that causes disease — bacteria, viruses, fungi and protoctists can all be pathogens (e.g. Plasmodium causes malaria; HIV causes AIDS; influenza virus causes flu).

✅ Quick check

1. What is the difference between eukaryotic and prokaryotic cells? (Eukaryotic cells have a true nucleus; prokaryotic (bacterial) cells do not.)
2. Name the five kingdoms. (Animals, plants, fungi, protoctists, bacteria.)
3. Give an example organism from each kingdom. (Animal: mammal/insect; plant: maize/peas; fungus: Mucor/yeast; protoctist: Amoeba/Chlorella/Plasmodium; bacterium: Lactobacillus.)
4. Why are viruses not in a kingdom? (They are not made of cells and can only reproduce inside host cells.)
5. What do Lactobacillus, Plasmodium and Mucor have in common? (They are microorganisms — bacterium, protoctist and fungus respectively — that can be pathogens or useful.)

Chapter 3: Breathing and Gas Exchange

Breathing (ventilation) moves air in and out of the lungs; gas exchange swaps oxygen and carbon dioxide between the air and the blood in the alveoli. This chapter covers the structure of the gas-exchange system, ventilation, gas exchange, the effects of exercise on breathing rate, and the harmful effects of smoking.

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RESPIRATION AND BREATHING — NOT THE SAME

• Respiration — the chemical release of energy from glucose in cells (see Chapter 1).
• Breathing / ventilation — the physical movement of air in and out of the lungs. Breathing supplies the oxygen for respiration and removes carbon dioxide.

THE STRUCTURE OF THE GAS EXCHANGE SYSTEM

Pathway of air: mouth/nose → trachea (windpipe) → bronchi (one to each lung) → bronchioles → alveoli (air sacs). - Trachea — the windpipe, kept open by rings of cartilage; lined with mucus and cilia. - Bronchi — the two main tubes branching from the trachea into each lung. - Bronchioles — smaller branching tubes. - Alveoli — tiny air sacs at the end of bronchioles where gas exchange happens. - Pleural membranes — the double membrane around each lung; the pleural fluid between them lets the lungs slide as they inflate/deflate. - EXTENSION WORK (Biology only): cartilage rings keep airways open; the diaphragm is a sheet of muscle below the lungs.

KEEPING THE AIRWAYS CLEAN

• The trachea and bronchi are lined with:
• Mucus — a sticky fluid that traps dirt, bacteria and viruses.
• Cilia — tiny hair-like structures that waft mucus (with trapped particles) up to the back of the throat, where it is swallowed (into the stomach, where acid kills microbes).
• Smoking paralyses and destroys cilia, so mucus collects — causing the "smoker's cough".

VENTILATION OF THE LUNGS (breathing in and out)

Breathing IN (inspiration): 1. The diaphragm contracts and flattens. 2. The intercostal (rib) muscles contract, pulling the ribs up and out. 3. The chest volume increases → pressure in the lungs decreases (below atmospheric). 4. Air rushes in (down the pressure gradient).

Breathing OUT (expiration): 1. The diaphragm relaxes and curves up. 2. The intercostal muscles relax, ribs move down and in. 3. Chest volume decreases → pressure increases. 4. Air is forced out.

• KEY POINT: air moves because of pressure differences, not by being "sucked" — the lungs themselves have no muscles; the rib cage and diaphragm do the work.

GAS EXCHANGE IN THE ALVEOLI

• In the alveoli, oxygen diffuses from the air into the blood (into red blood cells, combining with haemoglobin) and carbon dioxide diffuses from the blood into the air to be breathed out.
• Adaptations of the alveoli for efficient gas exchange:
• Very large surface area (millions of alveoli).
• Thin walls (one cell thick — short diffusion distance).
• Moist inner surface (gases dissolve).
• Dense network of capillaries (good blood supply — maintains the concentration gradient: blood arriving is low in O₂, high in CO₂).
• Constantly ventilated (fresh air keeps O₂ high, CO₂ low).

ACTIVITY 1 — INHALED vs EXHALED AIR

• Compare inhaled and exhaled air using limewater (exhaled air turns limewater milky/cloudy — more CO₂) and a glowing splint (exhaled air has less O₂).
• Composition of air (memorise): nitrogen ~78%, oxygen ~21% (inhaled) / ~16% (exhaled), carbon dioxide ~0.04% (inhaled) / ~4% (exhaled), water vapour higher when exhaled.

ACTIVITY 2 — Practical: effect of EXERCISE on BREATHING RATE

• Measure breathing rate (breaths per minute) at rest, then after exercise, recording at intervals during recovery.
• Result: breathing rate (and depth) increases during/after exercise because muscles respire more → more CO₂ produced → more O₂ needed → the brain detects higher CO₂ and increases ventilation.
• Plot breathing rate against time → a curve rising after exercise and falling back to resting rate (recovery).

THE EFFECTS OF SMOKING

EFFECTS OF SMOKE ON THE LINING OF THE AIR PASSAGES

• Smoke contains tar, carbon monoxide, nicotine and other chemicals.
• Tar irritates the airways → more mucus produced; destroys cilia → mucus and dirt collect → "smoker's cough"; also causes chronic bronchitis (inflamed bronchi) and emphysema (alveoli walls break down → reduced surface area for gas exchange → breathlessness).
• Nicotine is the addictive drug in tobacco; it also narrows blood vessels (raises blood pressure) and makes blood stickier (clots).

LUNG CANCER

• Tar contains carcinogens (cancer-causing chemicals). Smoking is the main cause of lung cancer — cells in the lungs divide uncontrollably, forming tumours.
• Smoking also increases the risk of cancers of the mouth, throat and bladder, and heart disease.

CARBON MONOXIDE IN SMOKE

• Carbon monoxide combines with haemoglobin (in red blood cells) more readily than oxygen — so the blood carries less oxygen around the body.
• In pregnancy it reduces oxygen to the fetus → lower birth weight.

SOME SMOKING STATISTICS (from the book)

• Smoking kills hundreds of thousands of people per year in the UK alone (e.g. over 100 000 deaths/year from smoking-related disease).
• Most smokers start young; the earlier you start, the greater the risk.

GIVING UP SMOKING

• Quitting: withdrawal symptoms (craving, irritability) but the body recovers — cilia regrow, lung function improves, risk of heart attack falls quickly, cancer risk falls over time.
• Nicotine replacement (gum, patches), counselling, and willpower all help.

✅ Quick check

1. Put in order: bronchioles, trachea, alveoli, bronchi. (Trachea → bronchi → bronchioles → alveoli.)
2. How is air moved into the lungs? (Diaphragm contracts/flattens + intercostal muscles pull ribs up/out → chest volume increases → pressure falls → air rushes in.)
3. Give four adaptations of alveoli. (Large surface area, thin walls, moist, good blood supply, ventilated.)
4. What happens to breathing rate during exercise and why? (It rises — more CO₂ produced, detected by the brain, ventilation increases.)
5. Why does carbon monoxide from smoke harm the body? (It binds to haemoglobin better than oxygen → less oxygen carried → lower birth weight, breathlessness.)

Chapter 4: Food and Digestion

Food provides the energy and materials the body needs. A balanced diet contains carbohydrates, proteins, lipids, vitamins, minerals, water and fibre. Digestion breaks large food molecules into small, soluble ones so they can be absorbed — using mechanical breakdown, enzymes, bile, and the villi of the small intestine.

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A BALANCED DIET

• A balanced diet contains all the food groups in the right amounts for the needs of the person (age, sex, activity level).
• The food groups: 1. Carbohydrates (e.g. starch, sugars — rice, bread, potatoes): provide energy. Stored as glycogen in animals. 2. Proteins (meat, fish, eggs, beans): needed for growth and repair of cells/tissues; can be used as energy. 3. Lipids (fats and oils) (butter, oil, nuts): provide energy (more per gram than carbohydrates), insulation, and make cell membranes. 4. Vitamins (e.g. vitamin C, vitamin D): needed in small amounts for health — vitamin C prevents scurvy; vitamin D needed for calcium absorption (prevents rickets). 5. Minerals (e.g. calcium for bones and teeth; iron for haemoglobin in red blood cells — deficiency causes anaemia; iodine for the thyroid). 6. Water: needed for chemical reactions, transport, temperature control. 7. Fibre (roughage): not digested; helps food move through the gut and prevents constipation.
• Malnutrition — eating too much, too little, or an unbalanced diet (e.g. too much fat/sugar → obesity, heart disease; too little → deficiency diseases).

LIPIDS (Biology only detail)

• Fats and oils; made of fatty acids and glycerol; energy-rich (about twice the energy of carbohydrates per gram); solid fats at room temperature (animal fats), oils liquid (plant oils).

FOOD TESTS (Biology only — practicals)

• 🔬 Test for STARCH: add iodine solution → turns blue-black if starch present (stays orange/brown if not).
• 🔬 Test for GLUCOSE (reducing sugar): add Benedict's solution and heat in a water bath → turns green → yellow → brick-red if glucose present (stays blue if not). (Test sucrose only after breaking it down first.)
• 🔬 Test for PROTEIN: add biuret solution (sodium hydroxide + copper sulfate) → turns purple/lilac if protein present.
• 🔬 Test for LIPID: ethanol (alcohol) emulsion test — shake food with ethanol, pour into water → a milky white emulsion if lipid present. (Or: rub on paper → translucent grease spot.)

ENERGY FROM FOOD

• Different foods release different amounts of energy, measured in kilojoules (kJ) or kilocalories (kcal). Lipids give the most energy per gram; carbohydrates and proteins less.
• 🔬 Practical: MEASURING THE ENERGY CONTENT OF A FOOD (Biology only): burn a food sample (e.g. a peanut/crisp) under a boiling tube of water; measure the temperature rise of a known volume of water.
• Energy (J) = mass of water (g) × 4.2 × temperature rise (°C).
• This method underestimates energy because some heat escapes to the surroundings.

THE DIGESTIVE SYSTEM

• Digestion — the breakdown of large, insoluble food molecules into small, soluble molecules that can be absorbed into the blood.
• Physical (mechanical) digestion — chewing in the mouth, churning in the stomach — increases surface area.
• Chemical digestion — enzymes break molecules apart.
• Enzymes used:
• Amylase (mouth, pancreas, small intestine): starch → maltose (a sugar).
• Proteases (stomach — pepsin, pancreas): proteins → amino acids.
• Lipase (pancreas, small intestine): lipids → fatty acids + glycerol.
• Parts of the digestive system (in order): 1. Mouth — teeth chew; saliva contains amylase (starch digestion begins). 2. Oesophagus — tube carrying food to the stomach (peristalsis). 3. Stomach — churns food; secretes hydrochloric acid (kills bacteria, gives pepsin its optimum pH ~2) and the protease pepsin. 4. Small intestine (duodenum + ileum) — most digestion and absorption:
  • Pancreatic juice (from the pancreas) contains amylase, protease, lipase, and bicarbonate (neutralises stomach acid).
  • Bile (made in the liver, stored in the gall bladder) is alkaline and emulsifies fats (breaks them into tiny droplets — a bigger surface area for lipase). 5. Large intestine (colon) — water is absorbed; elimination of waste (egestion of faeces — undigested food, not excretion).

ABSORPTION IN THE ILEUM (small intestine)

• The ileum is lined with villi (finger-like projections) and each villus cell has microvilli — together giving a huge surface area.
• Villus adaptations: large surface area; thin walls (one cell thick); good blood supply (capillaries carry away absorbed glucose and amino acids); lacteals (lymph vessels) absorb fatty acids and glycerol.
• Glucose and amino acids are absorbed into the blood; some by active transport (against the concentration gradient, using energy).
• Fatty acids and glycerol pass into the lacteals (lymph).

THE LARGE INTESTINE — ELIMINATION OF WASTE

• The colon absorbs water from the remaining undigested food.
• The solid waste (faeces) is egested (removed through the anus) — egestion is NOT excretion (it is undigested food, not a product of metabolism).

✅ Quick check

1. Name the seven components of a balanced diet. (Carbohydrates, proteins, lipids, vitamins, minerals, water, fibre.)
2. Which enzyme digests starch, and to what? (Amylase — starch → maltose.)
3. What does bile do? (Made in the liver; alkaline; emulsifies fats — increases surface area for lipase.)
4. How are villi adapted for absorption? (Large surface area, thin walls, good blood supply, lacteals.)
5. Give the food tests and positive results. (Starch: iodine → blue-black. Glucose: Benedict's + heat → brick-red. Protein: biuret → purple. Lipid: ethanol emulsion → milky white.)

Chapter 5: Blood and Circulation

The circulatory system transports oxygen, nutrients, waste products and hormones around the body. This chapter covers the heart (structure and how it pumps blood), coronary heart disease, arteries, veins and capillaries, and the composition and functions of blood (plasma, red blood cells, white blood cells, platelets).

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THE NEED FOR CIRCULATORY SYSTEMS

• Large organisms need a circulatory system because diffusion alone is too slow to supply oxygen/glucose to all cells and remove waste (small organisms can rely on diffusion — e.g. Amoeba).
• The circulatory system = heart (pump) + blood vessels (tubes) + blood (transport medium).
• Double circulation (mammals): blood passes through the heart twice per circuit — once to the lungs (pulmonary circulation) and once to the rest of the body (systemic circulation). Advantage: oxygenated and deoxygenated blood never mix; high pressure can be maintained.

THE STRUCTURE AND FUNCTION OF THE HUMAN HEART

• The heart is a muscular pump with four chambers:
• Right atrium — receives deoxygenated blood from the body (via the vena cava).
• Right ventricle — pumps deoxygenated blood to the lungs (via the pulmonary artery).
• Left atrium — receives oxygenated blood from the lungs (via the pulmonary vein).
• Left ventricle — pumps oxygenated blood to the body (via the aorta). It has the thickest muscular wall (must pump blood all around the body).
• Valves (between atria and ventricles, and in arteries) prevent blood flowing backwards.
• Coronary arteries — supply the heart muscle itself with oxygenated blood (the heart needs its own blood supply!).
• Blood flow through the heart: body → vena cava → right atrium → right ventricle → pulmonary artery → lungs → pulmonary vein → left atrium → left ventricle → aorta → body.
• KEY DIAGRAM: draw the heart, label the four chambers, vena cava, pulmonary artery, pulmonary vein, aorta and valves; shade oxygenated (red) vs deoxygenated (blue) sides.

CORONARY HEART DISEASE

• Caused by fatty deposits (atheroma) narrowing the coronary arteries → less blood/oxygen to the heart muscle → angina (chest pain) or heart attack (part of the heart muscle dies).
• Risk factors: smoking, high-fat diet, lack of exercise, stress, high blood pressure, genetics.
• Treatments: statins (lower cholesterol), stents (keep arteries open), bypass surgery, healthy lifestyle.

HEART RATE

• Heart rate — number of beats per minute (about 70 at rest in adults).
• Increases with exercise (more oxygen needed by muscles), adrenaline, fear/excitement; decreases with fitness (a fit heart pumps more blood per beat).

ARTERIES, VEINS AND CAPILLARIES

	Arteries	Veins	Capillaries
Direction	Away from the heart	To the heart	Between arteries & veins
Wall	Thick, muscular, elastic	Thin, less muscular	One cell thick
Lumen	Narrow	Wide	Very narrow
Valves	No	Yes (stop backflow)	No
Blood	Oxygenated (except pulmonary artery)	Deoxygenated (except pulmonary vein)	Mixed
Pressure	High	Low	—
- Capillaries are the exchange vessels — thin walls (short diffusion distance), large total surface area; they supply cells and collect waste.

THE COMPOSITION OF BLOOD

PLASMA

• The liquid part of blood (mostly water) — transports: red/white blood cells and platelets, digested food (glucose, amino acids), carbon dioxide, urea, hormones, and heat.

RED BLOOD CELLS (erythrocytes)

• Function: carry oxygen.
• Adaptations (Biology only): biconcave disc shape (large surface area); no nucleus (more room for haemoglobin); contain haemoglobin (an iron-containing pigment that combines with oxygen to form oxyhaemoglobin — bright red); flexible (can squeeze through capillaries).

WHITE BLOOD CELLS (leucocytes)

• Function: defend the body against pathogens.
• Phagocytes — engulf and digest pathogens (phagocytosis).
• Lymphocytes — produce antibodies (which destroy pathogens/toxins) and antitoxins; involved in immunity and memory (vaccination).

PLATELETS

• Tiny fragments of cells that help blood to clot at wounds (fibrin mesh), sealing cuts and preventing blood loss/infection.

✅ Quick check

1. Name the four heart chambers and where blood goes from each. (RA ← vena cava; RV → pulmonary artery; LA ← pulmonary vein; LV → aorta.)
2. Why is the left ventricle's wall the thickest? (It pumps blood all around the body — highest pressure.)
3. Give three differences between arteries and veins. (Thick muscular walls vs thin; high vs low pressure; no valves vs valves; narrow vs wide lumen.)
4. How are red blood cells adapted to carry oxygen? (Biconcave, no nucleus, haemoglobin, flexible.)
5. What causes coronary heart disease? (Fatty deposits narrow the coronary arteries → reduced blood/oxygen to heart muscle.)
6. What is the function of platelets? (Blood clotting at wounds.)

Chapter 6: Coordination

The body coordinates its actions through the nervous system — detecting stimuli with receptors, transmitting impulses along neurones, and producing rapid responses (including reflex actions). This chapter covers the central nervous system, the structure of neurones, the eye, and reflex actions.

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STIMULUS AND RESPONSE

• Stimulus — a change in the environment (light, sound, temperature, chemicals) that an organism detects.
• Receptors — cells that detect stimuli (e.g. in the eye, ear, skin, tongue, nose).
• Effectors — muscles or glands that bring about a response.
• Response — the action taken (e.g. muscle contraction, hormone release).
• Coordination — linking receptors to effectors, so the response is appropriate. This is done by the nervous system and the endocrine (hormone) system (Chapter 7).

THE CENTRAL NERVOUS SYSTEM (CNS)

• The CNS = the brain and the spinal cord.
• It receives information from receptors, processes it, and sends impulses to effectors.
• Peripheral nervous system — all the nerves (neurones) connecting the CNS to the rest of the body.
• KEY POINT: the CNS acts as the coordination centre — it does the "thinking" and decision-making for reflex and voluntary actions.

THE STRUCTURE OF NEURONES

• Neurone (nerve cell) — a cell specialised to carry electrical impulses.
• Parts: cell body (with nucleus), dendrites (receive impulses), axon (long fibre carrying the impulse away), and a myelin sheath (insulation that speeds up the impulse).
• Sensory neurones — carry impulses from receptors to the CNS.
• Motor neurones — carry impulses from the CNS to effectors (muscles/glands).
• Relay neurones — connect sensory and motor neurones within the CNS.
• Impulses pass from one neurone to the next at a synapse (a tiny gap) — chemicals (neurotransmitters) diffuse across the gap.

THE EYE

• Parts and functions:
• Cornea — transparent front; refracts (bends) light into the eye.
• Iris — coloured ring of muscle controlling the amount of light entering (the pupil size).
• Pupil — the hole in the iris through which light enters.
• Lens — focuses light onto the retina (changes shape — accommodation).
• Ciliary muscles and suspensory ligaments — change the shape of the lens.
• Retina — contains the light-sensitive receptor cells (rods and cones).
• Optic nerve — carries impulses from the retina to the brain.
• FORMING AN IMAGE: light → cornea (refracted) → pupil → lens (focused) → retina (receptors stimulated) → impulses along the optic nerve → brain interprets.
• THE IRIS REFLEX (control of pupil size):
• Bright light: circular (radial) muscles of the iris contract → pupil constricts (smaller) → less light enters (protects the retina).
• Dim light: circular muscles relax, radial muscles contract → pupil dilates (bigger) → more light enters.
• THE BLIND SPOT: where the optic nerve leaves the retina — no receptor cells, so no image is detected there.
• 💡 Exam tip: be able to label an eye diagram and explain the iris reflex in bright and dim light (which muscles contract, what happens to the pupil).

REFLEX ACTIONS

• Reflex action — a rapid, automatic response to a stimulus that does not involve conscious thought (the brain is bypassed — the impulse goes through the spinal cord).
• Reflex arc (the pathway): 1. Stimulus detected by a receptor. 2. Impulse travels along a sensory neurone to the CNS (spinal cord). 3. Relay neurone in the spinal cord connects to a motor neurone (a synapse between them). 4. Impulse travels along the motor neurone to an effector (e.g. muscle). 5. Response — the muscle contracts.
• Why reflexes are important: they are fast (protect the body from harm — e.g. pulling your hand away from something hot, the knee jerk) and they happen automatically without needing to "think", so they can't be delayed.
• Examples: blinking, pupil reflex, withdrawal from pain, coughing.

✅ Quick check

1. What are receptors and effectors? (Receptors detect stimuli; effectors (muscles/glands) produce responses.)
2. Name the three types of neurone. (Sensory, motor, relay.)
3. What is a synapse? (The tiny gap between neurones; neurotransmitters diffuse across.)
4. What happens to the pupil in bright light? (Circular muscles contract → pupil constricts → less light enters.)
5. Write the reflex arc pathway. (Stimulus → receptor → sensory neurone → relay neurone → motor neurone → effector → response.)
6. Why are reflex actions important? (Fast and automatic — protect the body from harm.)

Chapter 7: Chemical Coordination (Hormones)

The endocrine system coordinates the body using hormones — chemical messengers carried in the blood. This chapter contrasts the nervous and endocrine systems, lists the main endocrine glands, and explains two key hormones: adrenaline ("fight or flight") and insulin (control of blood glucose).

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GLANDS AND HORMONES

• Gland — an organ that makes and secretes a chemical (e.g. a hormone or enzyme).
• Hormone — a chemical messenger made by an endocrine gland, carried in the blood to a target organ, where it produces a response.
• Endocrine glands release hormones directly into the blood (ductless glands — unlike digestive glands which use ducts).
• Target organ — the organ whose activity the hormone affects.

THE DIFFERENCES BETWEEN NERVOUS AND ENDOCRINE SYSTEMS

	Nervous system	Endocrine system
Messenger	Electrical impulses (neurones)	Chemical hormones (blood)
Speed	Very fast	Relatively slow
Duration	Short-lived	Longer-lasting
Effect	Localised (one muscle/gland)	Can affect many organs
- 💡 Exam tip: this comparison table is a classic question — know all four rows.

THE ENDOCRINE GLANDS (main ones)

• Pituitary gland (in the brain) — the "master gland": produces hormones that control other glands (e.g. growth hormone, FSH/LH controlling the ovaries/testes).
• Thyroid gland (neck) — produces thyroxine, controlling metabolic rate (and growth/development).
• Adrenal glands (on top of the kidneys) — produce adrenaline.
• Pancreas — produces insulin (and glucagon) controlling blood glucose.
• Ovaries (female) — produce oestrogen and progesterone (sexual development, menstrual cycle).
• Testes (male) — produce testosterone (sexual development, sperm production).

ADRENALINE — THE "FIGHT OR FLIGHT" HORMONE

• Released by the adrenal glands in response to stress, fear or excitement (e.g. before an exam, when frightened).
• Effects (preparing the body for action):
• Heart rate and breathing rate increase (more oxygen to muscles).
• Blood glucose rises (more energy available).
• Blood diverted from skin/digestive system to muscles (vasoconstriction/dilation).
• Pupils dilate.
• These changes prepare the body to fight or run away — an evolutionary survival response.

INSULIN — CONTROL OF BLOOD GLUCOSE

• Why it matters: glucose is needed for respiration, but too much or too little is harmful. Blood glucose must be kept roughly constant.
• When blood glucose is TOO HIGH (after a carbohydrate-rich meal): 1. The pancreas detects the rise. 2. It secretes insulin. 3. Insulin causes the liver (and muscles) to take up glucose and convert it to glycogen (stored). 4. Blood glucose falls back to normal.
• When blood glucose is TOO LOW (after exercise, long gaps between meals): 1. The pancreas detects the fall and secretes glucagon. 2. Glucagon causes the liver to convert glycogen back to glucose, which is released into the blood. 3. Blood glucose rises back to normal.
• Insulin and glucagon work against each other (antagonistic) — this is a negative feedback control system.
• Diabetes: Type 1 (the pancreas produces little or no insulin — treated with insulin injections and diet control); Type 2 (body cells stop responding to insulin — linked to obesity; treated with diet/exercise, sometimes medication).
• 📊 Diagram: draw the negative-feedback loop — high glucose → insulin → liver stores glycogen → glucose falls; low glucose → glucagon → glycogen → glucose released → glucose rises.

✅ Quick check

1. What is a hormone? (A chemical messenger made by an endocrine gland, carried in the blood to a target organ.)
2. Give two differences between nervous and endocrine systems. (Nervous: fast, short-lived, electrical. Endocrine: slow, long-lasting, chemical in blood.)
3. Where is adrenaline produced and what does it do? (Adrenal glands; increases heart/breathing rate and blood glucose — fight or flight.)
4. What happens when blood glucose is too high? (Pancreas releases insulin → liver stores glucose as glycogen → glucose falls.)
5. What does glucagon do? (Converts glycogen back to glucose when blood glucose is too low.)

Chapter 8: Homeostasis and Excretion

Homeostasis keeps the internal environment constant — water content, temperature, blood glucose (Chapter 7). Excretion removes the waste products of metabolism. This chapter covers the urinary system and kidneys (Biology only: the nephron and ultrafiltration), control of water content, and control of body temperature (skin, sweating, shivering).

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HOMEOSTASIS

• Homeostasis — the maintenance of a constant internal environment (e.g. water content, temperature, blood glucose) despite external changes.
• It uses negative feedback: receptors detect a change → effectors correct it → the change is reversed.
• Examples: control of blood glucose (insulin/glucagon — Chapter 7), control of water content, control of body temperature.

EXCRETION

• Excretion — the removal of the waste products of metabolism from the body (NOT egestion of undigested food).
• Waste products: carbon dioxide (from respiration — removed by the lungs), urea (from the breakdown of excess amino acids in the liver — removed by the kidneys in urine), excess water and salts (removed by the kidneys/skin).

THE URINARY SYSTEM

• Parts: kidneys (filter the blood, produce urine) → ureters (tubes carrying urine to the bladder) → bladder (stores urine) → urethra (carries urine out).
• The kidneys' jobs: remove urea, control water content and salt content of the blood.

THE KIDNEYS — STRUCTURE OF THE NEPHRON (Biology only)

• Each kidney contains about a million nephrons — the tiny filtering units.
• Nephron structure (in order): Bowman's capsule (cup-shaped, surrounds a knot of capillaries — the glomerulus) → tubule (convoluted tubule → loop of Henle → collecting duct).
• ULTRAFILTRATION IN THE BOWMAN'S CAPSULE:
• Blood enters the glomerulus under high pressure (the arteriole entering is wider than the one leaving).
• Small molecules are forced out of the blood into the Bowman's capsule: water, glucose, urea, salts. Large molecules (proteins, blood cells) stay in the blood (they are too big to pass through the filter).
• The filtrate is called glomerular filtrate.
• CHANGES TO THE FILTRATE IN THE REST OF THE NEPHRON:
• All the glucose is reabsorbed into the blood (by active transport) in the proximal convoluted tubule — glucose should never appear in urine (it appears in diabetes).
• Most water is reabsorbed (in the loop of Henle and collecting duct) — controlled by ADH.
• Some salts reabsorbed as needed.
• Urea stays in the tubule and is excreted (some diffuses back).
• EXTENSION WORK: the loop of Henle creates a concentration gradient in the medulla, allowing water reabsorption; the collecting duct's permeability is controlled by ADH.

CONTROL OF THE BODY'S WATER CONTENT

• Water is gained by drinking and in food; lost in urine, sweat, breath and faeces.
• Antidiuretic hormone (ADH) — produced by the pituitary gland:
• Too little water in the blood (dehydration): more ADH released → kidneys reabsorb more water → concentrated urine (small volume).
• Too much water in the blood: less ADH → kidneys reabsorb less water → dilute urine (large volume).
• This is a negative feedback loop.

CONTROL OF BODY TEMPERATURE

• Human body temperature is kept at about 37 °C (optimum for enzymes).
• MONITORING BODY TEMPERATURE: the thermoregulatory centre in the brain (hypothalamus) monitors blood temperature; the skin has temperature receptors (monitoring the surroundings).
• THE SKIN AND TEMPERATURE:
• Too HOT:
  • Vasodilation: blood vessels near the skin surface widen → more blood flows near the surface → more heat lost by radiation (skin looks red).
  • Sweating: sweat glands produce sweat; as sweat evaporates it takes heat from the skin → cools the body.
  • (Hairs lie flat.)
• Too COLD:
  • Vasoconstriction: blood vessels near the skin surface narrow → less blood at the surface → less heat lost (skin looks pale).
  • Shivering: muscles contract rapidly → respiration releases heat.
  • Hairs stand up (erector muscles contract — traps an insulating layer of air; little effect in humans).
  • (Reduced sweating.)
• 📊 Diagram: label skin layers, sweat gland, hair/erector muscle, blood vessels; explain hot and cold responses.

✅ Quick check

1. Define homeostasis. (Maintaining a constant internal environment using negative feedback.)
2. Name the organs of the urinary system in order. (Kidneys → ureters → bladder → urethra.)
3. Where is urea made and what from? (In the liver, from excess amino acids.)
4. What happens in ultrafiltration? (High pressure forces water, glucose, urea and salts out of the glomerulus into the Bowman's capsule; proteins and cells stay in the blood.)
5. How does ADH control water content? (More ADH → more water reabsorbed → concentrated urine; less ADH → dilute urine.)
6. Give two responses to being too hot and two to being too cold. (Hot: vasodilation, sweating. Cold: vasoconstriction, shivering.)

Chapter 9: Reproduction in Humans

Sexual reproduction involves the fusion of male and female gametes, producing genetically different offspring. This chapter compares sexual and asexual reproduction, covers the reproductive organs and gametes, the transfer of sperm, the human life cycle, and the hormones controlling the menstrual cycle.

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SEXUAL AND ASEXUAL REPRODUCTION COMPARED

	Sexual reproduction	Asexual reproduction
Gametes	Two gametes fuse (fertilisation)	None
Genetic material	From both parents — offspring genetically different	From one parent — offspring genetically identical (clones)
Variation	High (variation)	None (except mutation)
Time/energy	Slower, costly (finding mates)	Fast, cheap
Examples	Humans, most animals and plants	Bacteria (binary fission), yeast (budding), runners in strawberries
- Advantage of sexual reproduction: genetic variation → species can adapt to changing environments (disease resistance).
- Advantage of asexual reproduction: rapid, no mate needed, all offspring suited to a stable environment.

SEXUAL REPRODUCTION IN HUMANS

• Gametes (sex cells): sperm (male) and egg/ovum (female) — haploid (half the chromosomes).
• Fertilisation — the fusion of a sperm nucleus with an egg nucleus → a zygote (diploid) → divides by mitosis → embryo → fetus → baby.
• Male organs: testes (make sperm and testosterone), sperm ducts (carry sperm), penis (delivers sperm), prostate/seminal vesicles (add fluid).
• Female organs: ovaries (make eggs and oestrogen/progesterone), oviducts (fallopian tubes — where fertilisation happens), uterus (womb — where the embryo develops), vagina (receives sperm), cervix.

PRODUCTION OF GAMETES

• Sperm — small, motile (tail for swimming), produced continuously in large numbers in the testes from puberty.
• Eggs — large (contain food stores/cytoplasm), non-motile; one (or occasionally more) released each menstrual cycle from the ovaries.

TRANSFER OF THE SPERM TO THE EGG

• During sexual intercourse, sperm are deposited in the vagina; they swim through the cervix and uterus into the oviduct, where one sperm may fertilise the egg.
• Fertilisation happens in the oviduct; the zygote then travels to the uterus and implants in the lining (uterus wall).

SUMMARY OF THE HUMAN LIFE CYCLE

• Childhood → puberty (sexual maturity, ~11–14) → adulthood → gametes produced → fertilisation → zygote → embryo (first 8 weeks) → fetus → birth → baby → childhood…
• Key stages: gamete production → transfer → fertilisation → implantation → development of embryo/fetus (placenta, amniotic fluid protects it) → birth → growth.

HORMONES CONTROLLING REPRODUCTION

• Testosterone (testes) — male secondary sexual characteristics, sperm production.
• Oestrogen (ovaries) — female secondary sexual characteristics; thickens the uterus lining; controls the menstrual cycle.
• Progesterone (ovaries — corpus luteum, then placenta in pregnancy) — maintains the uterus lining (in pregnancy, keeps it thick).

HORMONES AND THE MENSTRUAL CYCLE

• The cycle is about 28 days, controlled by four hormones: 1. FSH (follicle-stimulating hormone) — made by the pituitary; causes an egg to mature in the ovary and stimulates oestrogen production. 2. Oestrogen — made by the ovaries; thickens the uterus lining; inhibits FSH and stimulates LH. 3. LH (luteinising hormone) — made by the pituitary; triggers ovulation (release of the egg). 4. Progesterone — made by the ovary (corpus luteum); maintains the uterus lining; inhibits FSH and LH.
• Negative feedback: high oestrogen → inhibits FSH; high progesterone → inhibits FSH and LH (this is how the contraceptive pill works — keeps FSH/LH low so no egg matures/releases).
• Menstruation: if no fertilisation, the uterus lining breaks down and is shed (period) — day 1 of the cycle.

EXTENSION WORK (Biology only)

• IVF (in vitro fertilisation) uses FSH and LH-like hormones to stimulate egg production, fertilisation outside the body, then implantation of embryos.

✅ Quick check

1. Give two differences between sexual and asexual reproduction. (Sexual: two parents, gametes fuse, variation. Asexual: one parent, no gametes, identical clones.)
2. Where does fertilisation happen? (In the oviduct.)
3. What is a gamete? (A sex cell — sperm or egg — with half the chromosomes.)
4. Which hormones control the menstrual cycle and what do they do? (FSH matures egg, oestrogen thickens lining, LH triggers ovulation, progesterone maintains lining.)
5. How does the contraceptive pill work? (Oestrogen/progesterone inhibit FSH and LH → no egg matures or is released.)

Chapter 10: Plants and Food (Photosynthesis)

Photosynthesis is how plants make food — using light energy to convert carbon dioxide and water into glucose (stored as starch) and oxygen. This chapter covers the word and symbol equations, leaf structure, the factors affecting the rate of photosynthesis, what the plant does with glucose, and mineral nutrition (with the starch-test and pondweed practicals).

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PHOTOSYNTHESIS — THE KEY EQUATIONS

• Photosynthesis — the process by which plants make glucose using light energy, carbon dioxide and water.
• Word equation: carbon dioxide + water →(light energy, chlorophyll)→ glucose + oxygen
• Symbol equation: 6CO2 + 6H2O →(light, chlorophyll)→ C6H12O6 + 6O2
• Conditions needed: light energy, chlorophyll (in chloroplasts), carbon dioxide and water.

PLANTS MAKE STARCH

• Plants store the glucose they make as starch (insoluble — doesn't affect water balance).
• 🔬 Practical: TESTING LEAVES FOR STARCH (proves photosynthesis has happened): 1. Boil the leaf in water (kills it, stops enzyme action). 2. Boil in ethanol (removes chlorophyll — the leaf becomes white/pale). ⚠️ Do this in a water bath, turn off the Bunsen burner — ethanol is flammable! 3. Rinse in cold water (softens the leaf). 4. Add iodine solution → blue-black = starch present (photosynthesis happened); stays orange/brown = no starch.
• Testing the light requirement: a destarched plant (kept in the dark 48h), cover part of a leaf with black paper, expose to light, then test — only the exposed parts turn blue-black.

THE STRUCTURE OF LEAVES (adaptations for photosynthesis)

• Waxy cuticle — waterproof layer, reduces water loss.
• Upper epidermis — transparent (light passes through).
• Palisade mesophyll — tall cells packed with chloroplasts at the top of the leaf — the main photosynthesis site.
• Spongy mesophyll — air spaces for gas exchange (CO₂ diffuses in, O₂ out).
• Stomata (singular: stoma) — pores (mostly in the lower epidermis) that let CO₂ in and O₂/water out; controlled by guard cells.
• Veins (vascular bundles) — xylem (water in) and phloem (glucose out).

INVESTIGATING PHOTOSYNTHESIS

🔬 Practical: effect of LIGHT on gas exchange by a leaf

• Pondweed/canadian pondweed (Elodea) exposed to light gives off oxygen bubbles (collected in a test tube; a glowing splint relights = oxygen).
• In the dark, no bubbles — photosynthesis needs light.

🔬 Practical: MEASURING THE RATE OF PHOTOSYNTHESIS USING PONDWEED

• Count bubbles per minute (or collect gas volume) from pondweed at different light intensities (move a lamp closer/further).
• Rate increases with light intensity up to a plateau (another factor becomes limiting — CO₂ or temperature).

FACTORS AFFECTING THE RATE OF PHOTOSYNTHESIS

1. Light intensity — rate rises as light increases, then plateaus (light no longer limiting).
2. Carbon dioxide concentration — rate rises with CO₂, then plateaus.
3. Temperature — rate rises with temperature up to the optimum (~35–40 °C), then falls as enzymes denature (above ~45 °C). - Limiting factor — the factor that is in shortest supply and therefore controls the rate (at night: light; in a sealed greenhouse: CO₂; in winter: temperature). - Farmers/greenhouses use this: add CO₂, extra light, optimum temperature, to raise yield.

THE PLANT'S USES FOR GLUCOSE

• Respiration (energy).
• Stored as starch (in roots, seeds, leaves).
• Cellulose for cell walls.
• Proteins (combined with nitrate ions from the soil).
• Fats/oils (in seeds).
• Growth (new cells and tissues).

MINERAL NUTRITION

• Plants need mineral ions from the soil (absorbed by root hairs by active transport):
• Nitrates (nitrogen) — for proteins and growth. Deficiency: stunted growth, yellow older leaves.
• Magnesium — needed to make chlorophyll. Deficiency: chlorosis (yellow leaves).
• (Also phosphorus, potassium, calcium in smaller amounts.)
• WATER CULTURE EXPERIMENTS (Biology only): grow plants in solutions missing one mineral at a time — the deficiency symptoms identify what each mineral does.

✅ Quick check

1. Write the word equation for photosynthesis. (Carbon dioxide + water → glucose + oxygen, using light and chlorophyll.)
2. What is the test for starch and the positive result? (Iodine solution → blue-black.)
3. Give three leaf adaptations. (Palisade cells with chloroplasts, transparent epidermis, stomata, air spaces, waxy cuticle.)
4. Name the three limiting factors. (Light intensity, CO₂ concentration, temperature.)
5. What are nitrates and magnesium needed for? (Nitrates → proteins/growth; magnesium → chlorophyll.)

Chapter 11: Transport in Plants

Plants transport water and minerals up the xylem and sugars around the plant in the phloem. Water moves into roots by osmosis and is lost from leaves by transpiration (through stomata). This chapter covers osmosis in plant cells, root uptake, transpiration, xylem/phloem structure, and the factors affecting transpiration (potometer practical).

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OSMOSIS IN PLANT CELLS

• Osmosis — net movement of water from a dilute solution (high water concentration) to a concentrated solution (low water concentration) through a partially permeable membrane.
• Plant cell in pure water (dilute): water enters → cell becomes turgid (swollen, pushes against the cell wall — supports the plant). The cell wall stops it bursting.
• Plant cell in concentrated solution: water leaves → cell becomes flaccid; if severe, the cell membrane pulls away from the wall — plasmolysis (cells are plasmolysed).
• 🔬 Activity 1 — ONION EPIDERMIS CELLS: mount onion epidermis in salt solution → observe cytoplasm pulling away from the cell wall (plasmolysis) under a microscope.
• 🔬 Activity 2 — POTATO TUBER TISSUE: weigh potato chips in pure water vs concentrated salt solution — gain mass in water (turgid), lose mass in salt (flaccid/plasmolysed).

UPTAKE OF WATER BY ROOTS

• Root hair cells are specialised for absorption:
• Large surface area (long, thin extensions).
• Thin walls (short diffusion distance).
• High concentration of solutes in the cell sap → water enters by osmosis from the dilute soil water.
• Mineral ions are absorbed by active transport (against the concentration gradient, using energy).
• Water then moves across the root to the xylem.

TRANSPORT IN THE XYLEM

• Xylem transports water and dissolved minerals from the roots up the plant (one direction).
• Xylem vessels: dead cells, hollow tubes, strengthened with lignin (rings/spirals) — also gives support to the stem.
• The movement of water up the xylem is driven by transpiration pull (evaporation from leaves creates a pull/negative pressure) + cohesion between water molecules.

LOSS OF WATER BY THE LEAVES — TRANSPIRATION

• Transpiration — the loss of water vapour from the leaves (through the stomata) by evaporation and diffusion.
• Why it happens: stomata must be open for CO₂ to enter for photosynthesis → water vapour inevitably escapes.
• Transpiration stream: water evaporates from leaf cells → replaced by water from the xylem → a continuous column of water is pulled up from the roots.

TRANSPORT IN THE PHLOEM

• Phloem transports sugars (sucrose) and amino acids from where they are made (leaves — sources) to where they are used/stored (roots, fruits, growing tips — sinks).
• Phloem is made of living cells (sieve tubes with sieve plates, companion cells).
• Movement in phloem is both directions (unlike xylem's one-way flow) — this is translocation.

STRUCTURE OF A STEM

• Cross-section: xylem toward the inside, phloem toward the outside (arranged in vascular bundles); in roots xylem is central, phloem around it.

CONTROL OF TRANSPIRATION BY STOMATA

• Stomata are pores, mostly on the lower leaf surface, surrounded by guard cells.
• Guard cells open the stoma when turgid (water enters) and close it when flaccid. They close at night and in very dry/hot conditions to save water.

FACTORS AFFECTING THE RATE OF TRANSPIRATION

1. Temperature ↑ → faster evaporation → transpiration rate rises.
2. Humidity ↑ (more water in the air) → smaller diffusion gradient → rate falls.
3. Wind ↑ → water vapour blown away → gradient maintained → rate rises.
4. Light ↑ → stomata open (for photosynthesis) → rate rises. - 💡 Exam tip: plants lose MORE water on hot, dry, windy, bright days; LESS on cool, humid, still, dark days.

MEASURING THE RATE OF TRANSPIRATION — POTOMETERS

• A potometer measures water uptake by a leafy shoot: as the shoot loses water by transpiration, an air bubble moves along a capillary tube; measure the distance the bubble moves per unit time.
• 🔬 Practical: ENVIRONMENTAL FACTORS AND TRANSPIRATION (simple potometer): 1. Cut a leafy shoot under water (prevents air locks), insert into the potometer. 2. Record the bubble's movement per minute in still air (control). 3. Repeat with a fan (wind), a lamp (light/heat), a polythene bag over the leaves (humidity), and in different temperatures. 4. Results: wind and light/heat increase the rate; high humidity decreases it.
• EXTENSION WORK: potometer measures water uptake, which approximates transpiration (some water is used in photosynthesis).

✅ Quick check

1. What is transpiration? (Loss of water vapour from leaves through stomata.)
2. What does the xylem transport and in which direction? (Water and minerals, from roots up.)
3. What does the phloem transport? (Sugars and amino acids, both directions — translocation.)
4. How do root hair cells absorb water? (Osmosis — large surface area, high solute concentration, thin walls.)
5. Give four factors affecting transpiration rate. (Temperature, humidity, wind, light.)
6. What is a potometer used for? (Measuring the rate of water uptake/transpiration of a shoot.)

Chapter 12: Chemical Coordination in Plants (Plant Hormones)

Plants coordinate their responses to stimuli (especially light and gravity) using hormones called auxins. Auxins control growth — making shoots grow toward light (phototropism) and roots grow downward (gravitropism/geotropism). This chapter covers how plants detect and respond to stimuli, tropisms, and how auxins cause them.

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PLANT STIMULI AND RESPONSES

• Plants respond to stimuli by growing toward or away from them (growth responses are called tropisms).
• Phototropism — response to light: shoots grow toward light (positive phototropism).
• Gravitropism (geotropism) — response to gravity: roots grow downward (positive gravitropism); shoots grow upward (negative gravitropism).
• These responses keep shoots in the light (for photosynthesis) and roots in the soil (for water/minerals/anchorage).

DETECTING THE LIGHT STIMULUS — PLANT HORMONES (AUXINS)

• Auxin — a plant hormone (e.g. IAA) produced mainly at the tip of shoots and roots; it controls growth by making cells elongate.
• How phototropism works (shoot toward light): 1. Light is detected at the shoot tip. 2. Auxin moves (diffuses) to the shaded side of the shoot. 3. The shaded side has more auxin → cells elongate faster there. 4. The shoot bends toward the light.
• How gravitropism works (root downward): 1. Gravity is detected at the root tip. 2. Auxin accumulates on the lower side. 3. In roots, high auxin inhibits cell elongation → the upper side grows faster → the root bends downward.
• KEY POINT — the same hormone has opposite effects: in shoots high auxin promotes elongation (grows toward light); in roots high auxin inhibits elongation (grows downward).
• 💡 Exam tip: state WHERE auxin is made (tip), WHERE it moves (shaded/lower side), and the EFFECT (cells elongate faster on that side).

EXTENSION WORK

• Clinostat experiment: a rotating clinostat cancels the effect of gravity — seedlings on it grow straight, while control seedlings (not rotating) bend. This shows gravity (not another factor) causes the response.

✅ Quick check

1. What is a tropism? (A growth response of a plant to a stimulus.)
2. Define positive phototropism. (Shoots growing toward light.)
3. What is auxin and where is it produced? (A plant growth hormone produced at shoot/root tips.)
4. Explain why a shoot bends toward light. (Auxin moves to the shaded side → cells there elongate faster → shoot bends toward light.)
5. Why does a root grow downward? (Auxin accumulates on the lower side and inhibits elongation in roots → the top side grows faster → root bends down.)

Chapter 13: Reproduction in Plants

Plants reproduce both asexually (runners, bulbs, cuttings — producing clones) and sexually (flowers → pollination → fertilisation → seeds and fruits). This chapter covers both methods, gamete production, seed and fruit formation, and the conditions needed for germination.

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SEXUAL AND ASEXUAL REPRODUCTION

	Asexual	Sexual
Parents	One	Two
Gametes	None	Pollen + ovule (egg) fuse
Offspring	Clones (identical)	Genetically different
Examples	Runners (strawberries), bulbs (daffodils), cuttings, tubers (potatoes)	Flowering plants

ASEXUAL REPRODUCTION IN PLANTS

• Runners (e.g. strawberry): horizontal stems grow out and root at intervals → new plants (clones).
• Bulbs (e.g. daffodil): underground storage organs that produce new bulbs.
• Tubers (e.g. potato): underground stems store starch; "eyes" grow into new plants.
• Cuttings: humans take a stem/leaf cutting which grows roots (used by gardeners).
• Advantages: fast, no mate needed, all offspring suited to the environment.
• Disadvantage: no variation → all offspring vulnerable to the same disease/change.

SEXUAL REPRODUCTION IN PLANTS

• The flower's parts: petals (attract pollinators), sepals, stamen (male: anther makes pollen + filament), carpel/pistil (female: stigma, style, ovary containing ovules).
• Gametes: pollen grains (male gametes, made in the anther) and ovules/egg cells (female gametes, in the ovary).

POLLINATION AND FERTILISATION

• Pollination — the transfer of pollen from the anther to the stigma.
• Insect-pollinated flowers: large, colourful, scented petals, nectar, sticky pollen.
• Wind-pollinated flowers: small, no petals/scent, light pollen produced in large amounts, feathery stigmas.
• Fertilisation — the fusion of the pollen (male) nucleus with the egg (female) nucleus in the ovule. The pollen grain grows a pollen tube down the style to the ovule.

SEED AND FRUIT FORMATION

• After fertilisation: the ovule becomes the seed, the ovary becomes the fruit.
• A seed contains the embryo (young plant) + food store (cotyledons/endosperm) + seed coat (testa).
• Seed dispersal — spreading seeds away from the parent (by wind, animals, water, explosion) — reduces competition.
• Fruits help dispersal: fleshy fruits (animals eat them, seeds pass through), winged fruits (wind), hooks (animal fur).

THE CONDITIONS NEEDED FOR GERMINATION (seed germination)

1. Water — for chemical reactions/enzymes and to swell the seed.
2. Oxygen — for respiration (energy for growth).
3. Warmth — optimum temperature for enzymes. - NOT light — seeds germinate in the dark (most seeds). - 🔬 Practical: INVESTIGATING THE CONDITIONS NEEDED FOR GERMINATION: set up test tubes with cotton wool and cress seeds: (1) water + air + warm, (2) no water + air + warm, (3) water + no air (oil layer) + warm, (4) water + air + cold. Only tube 1 germinates → shows all three conditions are needed.

✅ Quick check

1. Give three examples of asexual reproduction in plants. (Runners, bulbs, tubers, cuttings.)
2. Where are the male and female gametes made? (Pollen in the anther; egg cells in ovules in the ovary.)
3. What is pollination? (Transfer of pollen from anther to stigma.)
4. What happens after fertilisation? (Ovule → seed, ovary → fruit.)
5. Name the three conditions for germination. (Water, oxygen, warmth.)

Chapter 14: Ecosystems

An ecosystem is a community of organisms and their environment. This chapter covers the components of ecosystems, sampling with quadrats, biotic and abiotic factors, feeding relationships (food chains/webs, pyramids), the flow of energy, and the cycling of nutrients (carbon cycle and nitrogen cycle).

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THE COMPONENTS OF ECOSYSTEMS

• Ecosystem — all the organisms (community) living in an area, together with the non-living (abiotic) environment.
• Habitat — the place where an organism lives.
• Population — all the organisms of ONE species in a habitat.
• Community — all the populations of DIFFERENT species in a habitat.
• Producer — an organism that makes its own food by photosynthesis (green plants/algae).
• Consumer — an organism that eats other organisms (herbivore = primary consumer, carnivore = secondary/tertiary).
• Decomposer — organisms (bacteria and fungi) that break down dead material and waste, returning nutrients to the soil.

USING QUADRATS TO SAMPLE A HABITAT (Biology only)

• A quadrat is a square frame (e.g. 0.25 m² or 1 m²) used to sample plants (or slow animals).
• Random sampling: throw the quadrat at random positions (or use random coordinates) to get a representative sample; count the number of each species.
• 🔬 Practical 1: COMPARING THE SIZE OF A PLANT POPULATION IN TWO AREAS OF A FIELD: place quadrats randomly in both areas, count a species in each, calculate the mean per quadrat and estimate the total population (mean × area ÷ quadrat area).
• 🔬 Practical 2: COMPARING BIODIVERSITY OF PLANTS IN TWO HABITATS: count the number of different species per quadrat in each habitat — the habitat with more species per quadrat has higher biodiversity.
• EXTENSION WORK: abundance can be estimated as frequency, percentage cover, or count.

INTERACTIONS IN ECOSYSTEMS

BIOTIC AND ABIOTIC FACTORS

• Abiotic factors (non-living): light, temperature, water, pH, soil type, oxygen, salinity.
• Biotic factors (living): competition for food/light/space, predation, disease.

FEEDING RELATIONSHIPS

• Food chain: e.g. grass → rabbit → fox. Shows the flow of energy.
• Food web: many interlinked food chains.
• Ecological pyramids show the relationship between organisms at each trophic level:
• Pyramid of numbers (count of organisms — can look odd when one big tree supports many insects).
• Pyramid of biomass (mass of living material — always roughly pyramid-shaped).
• Pyramid of energy (energy available — always a pyramid; ~10% passes between levels).
• WHY ARE DIAGRAMS OF FEEDING RELATIONSHIPS NOT ALWAYS PYRAMIDS? (Biology only): a single large producer (a tree) can feed thousands of insects — so the pyramid of numbers is inverted at the bottom; biomass/energy pyramids are the reliable ones.

THE FLOW OF ENERGY THROUGH ECOSYSTEMS

• Energy enters as sunlight, fixed by photosynthesis into producers.
• Energy is transferred along food chains, but most is lost at each trophic level (as heat from respiration, movement, undigested material) — only about 10% passes to the next level.
• This is why food chains are usually short (max ~5 links) and why top carnivores need huge territories.

CYCLING NUTRIENTS THROUGH ECOSYSTEMS

• Nutrients are recycled: decomposers release them from dead matter back into the soil, where producers take them up again.

THE CARBON CYCLE

• Key processes: 1. Photosynthesis — plants remove CO₂ from the air, making glucose (carbon enters food chains). 2. Respiration — all living organisms release CO₂ back into the air. 3. Decomposition — decomposers respire, releasing CO₂ from dead material. 4. Combustion — burning fossil fuels (coal, oil, gas) releases CO₂.
• I COMPOUNDS / FOSSIL FUELS: carbon is locked up long-term in fossil fuels (and limestone); burning them returns it to the air (→ enhanced greenhouse effect).

THE NITROGEN CYCLE

• Nitrogen is needed to make proteins and DNA — but most organisms cannot use nitrogen gas (N₂) from the air.
• Key processes: 1. Nitrogen fixation — bacteria (in root nodules of legumes — Rhizobium, and free-living soil bacteria) convert N₂ → nitrates. (Also lightning fixes a little.) 2. Decay/decomposition — decomposers break down proteins in dead organisms and waste → ammonium compounds. 3. Nitrification — nitrifying bacteria convert ammonium → nitrites → nitrates (usable by plants). 4. Absorption — plants take up nitrates to make proteins; animals get nitrogen by eating plants. 5. Denitrification — denitrifying bacteria (in waterlogged/airless soil) convert nitrates → N₂ gas (lost to the air).
• Decomposers and bacteria are essential — without them nitrogen would stay locked in dead matter.

✅ Quick check

1. Define ecosystem, population, community. (Ecosystem = community + environment; population = one species in a habitat; community = all populations in a habitat.)
2. What is a quadrat used for? (Sampling plants to estimate population size or biodiversity.)
3. Give two biotic and two abiotic factors. (Biotic: competition, predation, disease. Abiotic: light, temperature, water, pH.)
4. Why is energy lost between trophic levels? (Respiration/heat, movement, undigested food.)
5. Name the four processes of the carbon cycle. (Photosynthesis, respiration, decomposition, combustion.)
6. What do nitrifying and denitrifying bacteria do? (Nitrifying: ammonium → nitrates; denitrifying: nitrates → nitrogen gas.)

Chapter 15: Human Influences on the Environment

Humans affect the environment through agriculture (fertilisers, pesticides, fish farming), air pollution (CO₂, carbon monoxide, sulfur dioxide) and water pollution (sewage, fertilisers). This chapter covers modern food production, the problems and solutions (including biological control), global warming, and pollution — with their ecological effects.

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MODERN AGRICULTURE — PRODUCING THE FOOD WE NEED

• The growing human population needs more food — farmers increase yields using:
• Fertilisers (add minerals to the soil).
• Pesticides (kill pests that eat crops).
• Machinery, selective breeding, greenhouses (control temperature/light/CO₂).

IMPROVING YIELDS FROM CROP PLANTS

• Glasshouses and polythene tunnels (from the book's learning objectives): trap heat, raise temperature and CO₂, protect from wind/pests → higher photosynthesis rate → higher yields.
• Fertilisers increase crop yields: they replace nitrates, phosphates, potassium removed by harvesting — but overuse causes pollution (below).

CYCLING NUTRIENTS ON A FARM

• In natural ecosystems nutrients recycle (Chapter 14). On a farm, crops are removed (not decomposed), so nutrients must be replaced — with fertilisers (natural manure or artificial) or crop rotation (legumes fix nitrogen).

PEST CONTROL

• Pests — organisms that reduce crop yield (insects eat crops, weeds compete, fungi cause disease).
• Pesticides — chemicals that kill pests (insecticides, herbicides, fungicides).

PROBLEMS WITH PESTICIDES

1. Kill useful organisms (e.g. bees that pollinate, natural predators of the pest).
2. Bioaccumulation: pesticides that don't break down build up in food chains — top carnivores get the highest (most toxic) concentrations (e.g. DDT in birds of prey).
3. Pests develop resistance — they survive and reproduce, needing ever stronger chemicals.
4. Pollution of soil and water.

BIOLOGICAL CONTROL

• Using a natural predator/parasite of the pest instead of chemicals (e.g. ladybirds eat aphids; a parasitic wasp controls whitefly).
• Advantages: no chemical pollution; doesn't harm non-target species; pests don't easily develop resistance.
• Disadvantages: slow to work; the control organism may itself become a pest (or eat useful species); hard to control.

FISH FARMING

• Fish are farmed in cages/pens to provide food.
• Advantages: reliable supply, controlled conditions (feeding, disease control), reduces pressure on wild fish stocks.
• Problems: pollution from waste/food; disease spreading between caged fish; escaped fish breeding with wild fish (genetic effects); needs feeding with fish meal (can deplete wild stocks).

AIR POLLUTION

CARBON DIOXIDE AND GLOBAL WARMING

• Burning fossil fuels (and deforestation) increases atmospheric CO₂.
• CO₂ is a greenhouse gas: it traps heat in the atmosphere (the greenhouse effect — necessary for life) — but the enhanced greenhouse effect from extra CO₂ causes global warming.
• Consequences: climate change, rising sea levels (melting ice), extreme weather, reduced crop yields, habitats destroyed, species at risk.
• Reducing it: renewable energy, energy efficiency, reforestation, carbon taxes, international agreements.

CARBON MONOXIDE

• From incomplete combustion of fossil fuels (e.g. car engines).
• Toxic — it combines with haemoglobin (better than oxygen), reducing oxygen transport → poisoning/fatal at high levels.

SULFUR DIOXIDE

• From burning fossil fuels containing sulfur (coal, oil).
• Causes acid rain (dissolves in rain → sulfuric acid): kills aquatic life in lakes, damages trees and buildings, harms soil.

WATER POLLUTION

POLLUTION OF WATER BY SEWAGE

• Sewage contains organic matter (and bacteria). When it enters rivers: 1. Decomposers (bacteria) multiply to break down the organic matter — they use up oxygen. 2. Oxygen concentration falls → fish and other aerobic organisms die. 3. The water becomes anoxic and polluted (eutrophication-like effect).
• Also toxic: untreated sewage carries disease-causing pathogens (cholera, typhoid).

POLLUTION OF WATER BY FERTILISERS (EUTROPHICATION)

1. Nitrates/phosphates from farmland (or sewage) wash into rivers/lakes.
2. Algae bloom — algae grow rapidly on the surface.
3. Algae block light → plants below die.
4. Decomposers multiply breaking down dead plants → use up oxygen.
5. Fish and other organisms die from lack of oxygen. - This sequence is eutrophication — a classic 5-step exam answer.

✅ Quick check

1. Give three problems caused by pesticides. (Kill useful organisms, bioaccumulation, resistance, pollution.)
2. What is biological control? (Using a natural predator/parasite to control pests.)
3. What causes global warming? (Extra CO₂ (and other greenhouse gases) from burning fossil fuels/deforestation — enhanced greenhouse effect.)
4. What does carbon monoxide do? (Combines with haemoglobin → less oxygen carried → toxic.)
5. What causes acid rain? (Sulfur dioxide from burning fossil fuels.)
6. Write the 5 steps of eutrophication. (Fertilisers → algae bloom → light blocked → plants die → decomposers use oxygen → fish die.)

Chapter 16: Chromosomes, Genes and DNA

DNA carries the genetic information that controls the cell. It is organised into chromosomes, which carry genes. This chapter covers the structure of DNA (the double helix, bases), DNA replication, the genetic code, protein synthesis, gene mutations (Biology only), and the basics of genes and alleles.

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THE STRUCTURE OF CHROMOSOMES

• Chromosomes — thread-like structures in the nucleus, made of DNA tightly coiled around proteins.
• Humans have 46 chromosomes (23 pairs) in each body cell.
• Chromosomes exist in pairs (one from each parent) — homologous pairs.

GENES AND ALLELES

• Gene — a section of DNA that codes for a particular protein (e.g. a characteristic like eye colour or a protein like insulin). Genes are found at specific positions (loci) on chromosomes.
• Allele — a different version of the same gene (e.g. the gene for eye colour has a brown and a blue allele). One allele is inherited from each parent.

THE STRUCTURE OF DNA (Biology only)

• DNA (deoxyribonucleic acid) — the molecule that carries genetic information.
• Shape: a double helix (two strands twisted together — like a twisted ladder).
• The "rungs" are base pairs. There are four bases:
• Adenine (A) pairs with Thymine (T)
• Cytosine (C) pairs with Guanine (G)
• KEY POINT — complementary base pairing: A–T and C–G always pair (the order of bases along the strand is the genetic code).

DNA REPLICATION

• Before a cell divides, DNA copies itself so each new cell gets identical DNA: 1. The double helix unzips (the two strands separate). 2. Each strand acts as a template; free nucleotides line up using complementary base pairing (A–T, C–G). 3. Two identical DNA molecules result.

THE GENETIC CODE

• The order of bases (A, T, C, G) along the DNA is the genetic code.
• Bases are read in groups of three (triplets/codons) — each triplet codes for one amino acid.
• The sequence of amino acids builds a protein (e.g. a specific sequence of ~150 bases codes for a protein of 50 amino acids).

THE STAGES OF PROTEIN SYNTHESIS (Biology only)

1. The DNA code is copied into messenger RNA (mRNA) in the nucleus (transcription).
2. mRNA carries the code out of the nucleus to the ribosomes (in the cytoplasm).
3. At the ribosome, the code is read in triplets, and amino acids are joined in the right order (translation) to build the protein. - Proteins then fold into their shape; some become enzymes, structural proteins, hormones, etc.

GENE MUTATIONS — WHEN DNA MAKES MISTAKES (Biology only)

• Mutation — a change in the base sequence of DNA (a "mistake" in copying).
• A change of even one base can change the triplet → a different amino acid → a different protein → a changed characteristic.
• Most mutations are harmful or have no effect; occasionally they are beneficial (basis of evolution — see Chapter 19).
• Example: sickle-cell anaemia is caused by one base change in the haemoglobin gene.

✅ Quick check

1. Where is DNA found and what is its shape? (In chromosomes in the nucleus; a double helix.)
2. Which bases pair together? (A–T and C–G.)
3. What is a gene? (A section of DNA coding for a protein.)
4. What is an allele? (A different version of the same gene.)
5. How many chromosomes do humans have? (46 — 23 pairs.)
6. What is a gene mutation? (A change in the base sequence of DNA.)

Chapter 17: Cell Division

Cells divide by mitosis (making identical copies — growth and repair) and meiosis (making gametes with half the chromosomes — for sexual reproduction). This chapter also explains why sexual reproduction produces variation while asexual reproduction produces clones, and how genes and environment both cause variation.

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MITOSIS (for growth and repair)

• Mitosis — the type of cell division that produces two genetically identical daughter cells (clones) with the same number of chromosomes as the parent (diploid, 2n).
• What happens (KEY POINT): before division the DNA replicates; the chromosomes line up and are pulled apart; the cell divides once → two identical cells, each with a full set of chromosomes.
• Where/why: growth, repairing damaged tissue, replacing worn-out cells (skin, blood cells), asexual reproduction in simple organisms, and in embryos.
• Diagram summary: 1 parent cell → 2 identical daughter cells (same chromosome number).

MEIOSIS (for making gametes)

• Meiosis — the type of cell division that produces four genetically different daughter cells (gametes) with half the chromosome number (haploid, n).
• What happens: DNA replicates; the cell divides twice; chromosomes (and their alleles) are shuffled between pairs (crossing over) and separated randomly → each gamete gets a different mix.
• Where: in the ovaries (eggs) and testes (sperm) of animals; in the anthers/ovaries of plants.
• Why it matters: gametes fuse at fertilisation, restoring the full chromosome number — and the shuffling produces genetic variation.

MITOSIS vs MEIOSIS (memorise this table)

	Mitosis	Meiosis
Purpose	Growth, repair	Gamete production
Number of divisions	One	Two
Daughter cells	2	4
Chromosomes	Same as parent (diploid, 2n)	Half (haploid, n)
Genetically	Identical (clones)	Different (variation)
Where	Body cells	Ovaries/testes (anthers/ovaries in plants)

SEXUAL REPRODUCTION AND VARIATION

• Why sexual reproduction produces variation: 1. Meiosis shuffles alleles (crossing over + random separation) — each gamete is unique. 2. Random fertilisation — any sperm can fuse with any egg → huge numbers of combinations.
• Example: children of the same parents look different (except identical twins — from ONE fertilised egg splitting by mitosis).

ASEXUAL REPRODUCTION AND CLONING

• Asexual reproduction uses mitosis only → offspring are genetically identical to the parent and each other (clones).
• Examples: bacteria (binary fission), yeast (budding), strawberry runners, cuttings taken by gardeners.
• Cloning — producing identical copies of an organism (genetically identical).
• KEY POINT: no gametes, no fertilisation, no variation (except mutation).

GENES AND ENVIRONMENT BOTH PRODUCE VARIATION

• Genetic causes of variation: different alleles (from meiosis/fertilisation), mutations.
• Environmental causes of variation: diet, climate, light, soil, lifestyle (e.g. plants grown in different soils; body weight affected by diet).
• Most characteristics are caused by both genes and environment interacting (e.g. height is genetic but affected by nutrition).
• 💡 Exam tip: "explain why organisms vary" → genes + environment — give an example of each.

✅ Quick check

1. What is mitosis and what does it produce? (Division producing 2 genetically identical diploid cells — growth/repair.)
2. What is meiosis and what does it produce? (Division producing 4 genetically different haploid cells — gametes.)
3. Why does sexual reproduction cause variation? (Meiosis shuffles alleles + random fertilisation.)
4. What are clones? (Genetically identical organisms — from asexual reproduction/mitosis.)
5. Give one genetic and one environmental cause of variation. (Genetic: alleles/mutation. Environmental: diet/climate.)

Chapter 18: Genes and Inheritance

Inheritance is how characteristics are passed from parents to offspring through genes. This chapter covers Gregor Mendel's experiments, monohybrid inheritance (dominant/recessive alleles, Punnett squares), the test cross, sex determination, and polygenic inheritance — with the genetic diagrams you must be able to draw.

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GREGOR MENDEL (Biology only)

• Gregor Mendel — an Austrian monk (1800s) who discovered the basic rules of inheritance by breeding pea plants.
• Mendel's experiments on peas: he crossed plants with different characteristics (e.g. tall vs short, green vs yellow seeds) and counted the offspring in each generation.
• What he found: characteristics are controlled by factors (now called genes) that come in pairs (one from each parent) and are passed on unchanged; some factors are dominant (show up even with one copy), some recessive (need two copies).
• KEY POINT: his results showed inheritance is particulate (factors don't blend) — e.g. crossing tall × short gives all tall in the F1, then tall and short reappear in the F2 in a 3:1 ratio.

EXPLAINING MENDEL'S RESULTS — MONOHYBRID INHERITANCE

• Key terms:
• Gene — section of DNA coding for a characteristic.
• Allele — a version of a gene.
• Dominant allele — expressed even if only one copy is present (shown with a capital letter, e.g. T for tall).
• Recessive allele — only expressed if TWO copies are present (lower case, e.g. t for short).
• Genotype — the alleles an organism has (e.g. TT, Tt, tt).
• Phenotype — the observable characteristic (e.g. tall or short).
• Homozygous — two identical alleles (TT or tt).
• Heterozygous — two different alleles (Tt).
• Punnett square (cross Tt × Tt):

	T	t
T	TT	Tt
t	Tt	tt

• Genotypes: 1 TT : 2 Tt : 1 tt. Phenotypes: 3 tall : 1 short (the classic 3:1 ratio).

WORKING OUT GENOTYPES — THE TEST CROSS (Biology only)

• If an organism shows the dominant phenotype (e.g. tall), its genotype could be TT or Tt — you can't tell.
• Test cross: cross it with a homozygous recessive (tt):
• If any offspring are short (tt) → the parent was Tt (heterozygous).
• If ALL offspring are tall → the parent was most likely TT (homozygous).

WAYS OF PRESENTING GENETIC INFORMATION (Biology only)

• Genetic diagram (showing parents' genotypes → gametes → Punnett square → offspring genotypes + phenotypes + ratio).
• Family pedigree charts — showing how a characteristic runs through a family (shaded = affected).

SEX DETERMINATION

• Humans have 23 pairs of chromosomes: 22 pairs of autosomes + 1 pair of sex chromosomes.
• Females: XX. Males: XY.
• The mother always contributes an X; the father contributes X or Y (sperm determines sex).
• Punnett square for sex:

	X	X
X	XX	XX
Y	XY	XY

• Result: 1 : 1 ratio of girls (XX) to boys (XY) — roughly 50:50.

POLYGENIC INHERITANCE

• Polygenic inheritance — characteristics controlled by many genes (each with a small effect), e.g. height, weight, skin colour, intelligence.
• These show continuous variation (a range — e.g. heights from short to tall, like a bell curve), unlike single-gene characteristics (discontinuous — e.g. blood group, tongue rolling).
• Environment also affects polygenic characteristics.

✅ Quick check

1. What did Mendel discover? (Characteristics are controlled by factors/genes in pairs, passed on unchanged; some dominant, some recessive.)
2. Define genotype, phenotype, homozygous, heterozygous. (Genotype = alleles present; phenotype = observable trait; homozygous = same alleles; heterozygous = different alleles.)
3. Draw the Punnett square for Tt × Tt and state the ratio. (1 TT : 2 Tt : 1 tt; 3 tall : 1 short.)
4. How is sex determined? (XX = female, XY = male; the father's sperm determines sex.)
5. What is polygenic inheritance? (A characteristic controlled by many genes — continuous variation, e.g. height.)

Chapter 19: Natural Selection and Evolution

Evolution is the gradual change in organisms over time. It happens by natural selection — individuals with characteristics best suited to their environment survive and reproduce, passing on their genes. This chapter covers Darwin's theory, how natural selection works, and evidence including antibiotic resistance in bacteria and selective breeding comparisons.

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WHAT IS EVOLUTION?

• Evolution — the gradual change in the characteristics of a species over many generations.
• The theory was developed by Charles Darwin (and Alfred Russel Wallace).

NATURAL SELECTION — HOW IT WORKS

1. Variation: individuals in a population vary (due to mutations and sexual reproduction — different alleles).
2. Overproduction: more offspring are produced than can survive (competition for food, space, mates).
3. Selection pressure: the environment (predators, disease, climate, food) kills the less well-adapted individuals — "survival of the fittest".
4. Survival and reproduction: the individuals with the advantageous characteristics survive and breed.
5. Inheritance: they pass on their advantageous alleles/genes to their offspring.
6. Over generations: the advantageous characteristic becomes more common in the population — the species evolves (becomes better adapted).

THE CLASSIC EXAMPLE — ANTIBIOTIC RESISTANCE IN BACTERIA

1. In a population of bacteria, a few have a mutation that makes them resistant to an antibiotic.
2. When the antibiotic is used, the resistant bacteria survive, the non-resistant ones die.
3. The resistant bacteria reproduce (asexually — fast), passing on the resistance gene.
4. Over time, the whole population becomes resistant — the antibiotic no longer works (e.g. MRSA). - KEY POINT — bacteria evolve resistance by natural selection. This is why antibiotics must be used sparingly and courses completed. - How to slow resistance: only use antibiotics when needed, finish the course, don't use them for viral infections, develop new antibiotics.

GENES AND ENVIRONMENT (recap from Ch 17)

• Variation comes from genes (alleles/mutations) and environment.
• Natural selection acts on this variation.

EVOLUTION BY NATURAL SELECTION vs SELECTIVE BREEDING

• Natural selection: the environment does the selecting, over thousands/millions of years, naturally.
• Selective breeding (Ch 20): HUMANS do the selecting, over much shorter periods, for characteristics we want.
• Both work by changing the frequency of alleles in a population.

EXTENSION: OTHER EVIDENCE

• Fossils show gradual change over time; homologous structures; antibiotic/pesticide resistance observed today.

SOME EXAMPLES OF HOW NATURAL SELECTION WORKS (case studies)

• Polar bears: Arctic ancestors varied in fur thickness, fat stores and swimming ability; bears with thicker fur/fat survived the cold better, bred, and passed on their genes — over many generations the population became adapted to the Arctic.
• Peppered moths (classic example): before the Industrial Revolution, most peppered moths were light-coloured (camouflaged against pale tree bark — birds ate the dark ones). As soot darkened the trees, the dark (melanic) form became better camouflaged and survived to breed — the dark form became common. When air pollution was cleaned up, light moths became common again.
• Darwin's finches: on the Galápagos Islands, finches with beaks suited to the available food (seeds, insects) survived and passed on their beak genes — different islands produced different beak shapes.
• The work of Charles Darwin: Darwin (and Wallace) gathered evidence from fossils, breeding and nature; he proposed that evolution happens by natural selection and published On the Origin of Species (1859).

✅ Quick check

1. Define evolution. (Gradual change in the characteristics of a species over generations.)
2. List the five steps of natural selection. (Variation → overproduction → selection pressure → survival of the fittest → inheritance of advantageous alleles.)
3. Explain how bacteria become resistant to antibiotics. (A resistant mutation survives the antibiotic and reproduces; resistance spreads through the population.)
4. Who developed the theory of natural selection? (Charles Darwin.)
5. Why is it important not to overuse antibiotics? (It speeds up the evolution of resistant bacteria.)

Chapter 20: Selective Breeding

Selective breeding (artificial selection) is when humans choose which animals or plants to breed from, to get offspring with desirable characteristics. This chapter covers traditional selective breeding, modern techniques, and cloning of plants and animals (Biology only).

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TRADITIONAL SELECTIVE BREEDING

• Selective breeding — choosing parents with desirable characteristics to breed together, over many generations, until the offspring reliably show those characteristics.
• Steps: 1. Choose individuals with the desired characteristic (e.g. high milk yield, fast growth, disease resistance, bigger fruit). 2. Breed them together. 3. Select the best offspring and breed them again. 4. Repeat over many generations.
• Examples: cows with high milk yields, dogs bred for specific traits, wheat with disease resistance, hens that lay more eggs, ornamental plants.
• Advantages: predictable improvement in useful traits; faster than waiting for natural selection.
• Disadvantages: reduces the gene pool (all individuals closely related) → less variation → vulnerable to new diseases; can cause health problems (inbreeding); harmful recessive alleles may be passed on.

MODERN SELECTIVE BREEDING (Biology only)

• Uses modern knowledge of genetics (and marker-assisted selection) to speed up choosing the best animals/plants — but the principle is the same as traditional breeding.

CLONING PLANTS (Biology only)

• Clone — a genetically identical copy of an organism.
• Methods:
• Cuttings — cut a stem, plant it, it grows roots (quick, cheap).
• Tissue culture (micropropagation) — grow many identical plants from tiny pieces of tissue (explants) on sterile nutrient medium with hormones. Produces many clones rapidly, disease-free, all year round.
• Uses: preserving rare plants, producing identical high-quality crops.

CLONING ANIMALS (Biology only)

• Embryo splitting: a developing embryo is split into several cells, each grows into a separate identical embryo, implanted into surrogate mothers → identical offspring.
• Somatic cell nuclear transfer (the "Dolly the sheep" method): 1. Take an egg cell and remove its nucleus. 2. Take a body (somatic) cell from the adult to be cloned and remove its nucleus. 3. Insert the adult nucleus into the empty egg cell. 4. Stimulate it to divide (by mitosis) → embryo. 5. Implant the embryo into a surrogate mother → the offspring is a genetic clone of the adult.

USING CLONED ANIMALS TO MAKE PROTEINS (Biology only)

• Transgenic animals (see Ch 22) can be cloned so that herds of identical animals produce human proteins (e.g. human insulin, clotting factors) in their milk — used as medicines.
• Arguments for cloning: guaranteed quality, production of medicines, preserving rare breeds.
• Arguments against: reduces genetic variation, ethical concerns, animal welfare, high cost and low success rate.

✅ Quick check

1. What is selective breeding? (Humans choosing parents with desirable traits to breed, over generations.)
2. Give two advantages and two disadvantages. (Adv: improved traits, predictable. Disadv: reduced gene pool, inbreeding, disease vulnerability.)
3. Name two ways of cloning plants. (Cuttings; tissue culture/micropropagation.)
4. Describe the Dolly method of cloning animals. (Transfer an adult body-cell nucleus into an enucleated egg cell → divide → implant into surrogate.)
5. Why might cloning reduce variation? (All clones are genetically identical — a single disease could wipe them out.)

Chapter 21: Using Microorganisms (Biotechnology)

Humans have used microorganisms for thousands of years to make food and drink — this is biotechnology. Yeast anaerobically respires to make alcohol and carbon dioxide (bread, beer, wine); bacteria make yoghurt. Modern industry uses large-scale fermenters to grow microorganisms efficiently.

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FERMENTATION AND BIOTECHNOLOGY

• Fermentation — the anaerobic respiration of microorganisms (especially yeast) that produces useful products.
• Biotechnology — the use of living organisms (or their products) to make useful things.
• Yeast is a single-celled fungus.
• Anaerobic respiration in yeast: glucose → ethanol (alcohol) + carbon dioxide (+ energy)

TRADITIONAL BIOTECHNOLOGY — MAKING FOOD AND DRINKS

MAKING DRINKS (beer, wine)

• Yeast + sugar solution (from grapes/malt) → ethanol + CO₂.
• Beer: yeast ferments sugars from malted barley; hops add flavour.
• Wine: yeast ferments grape juice sugars.
• Conditions needed: warm temperature (optimum for yeast enzymes ~30–40 °C), no oxygen (anaerobic — so alcohol is made instead of CO₂+water), food (sugar), time.

MAKING BREAD

• Yeast is mixed into dough; it respires (aerobically first, then anaerobically) producing carbon dioxide.
• The CO₂ bubbles make the dough rise.
• Baking kills the yeast and evaporates the alcohol → bread.

🔬 Practical: INVESTIGATING THE RATE OF ANAEROBIC RESPIRATION IN YEAST

• Set up yeast + sugar solution in a flask with a delivery tube into limewater (or measure gas volume).
• Measure the volume of CO₂ produced over time at different temperatures.
• Rate = volume of CO₂ ÷ time. Rate increases with temperature up to the optimum, then falls as enzymes denature.

MAKING YOGHURT

• Yoghurt is made using bacteria (Lactobacillus): 1. Pasteurise (heat) the milk to kill unwanted bacteria. 2. Cool to ~40 °C (optimum for the bacteria). 3. Add the starter culture (Lactobacillus). 4. Keep warm for several hours — the bacteria ferment the milk sugar (lactose) to lactic acid. 5. The lactic acid makes the milk thicken and turn sour (yoghurt). 6. Cool and flavour.

INDUSTRIAL FERMENTERS (large-scale biotechnology)

• Fermenter — a large vessel where microorganisms are grown under controlled conditions to make products in bulk (e.g. antibiotics like penicillin from the fungus Penicillium, insulin from genetically modified bacteria, enzymes).
• KEY POINT — conditions controlled in a fermenter:
• Nutrients/food for the microorganisms (sugar, nitrogen source).
• Temperature (kept at the optimum — excess heat from respiration is removed by a water-cooled jacket; thermostats control it).
• pH (controlled by adding acid/alkali — buffers).
• Oxygen (supplied by sterile air pumped in, if aerobic; stirred by paddles to keep it mixed and aerated).
• Sterile conditions (steam-sterilised before use; filtered air — to stop competing microorganisms contaminating the culture).
• 📊 Diagram: label the fermenter — paddles/stirrer, air inlet, nutrient inlet, cooling jacket, sterile conditions, product outlet.

✅ Quick check

1. What is fermentation? (Anaerobic respiration of yeast — glucose → ethanol + CO₂.)
2. Why does dough rise? (Yeast produces CO₂ bubbles that make it expand.)
3. How is yoghurt made? (Milk pasteurised, cooled, Lactobacillus added; bacteria turn lactose into lactic acid → milk thickens and sours.)
4. Give four conditions controlled in a fermenter. (Nutrients, temperature, pH, oxygen, sterility.)
5. Why must a fermenter be sterile? (To stop competing microorganisms ruining the culture.)

Chapter 22: Genetic Modification (Genetic Engineering)

Genetic modification moves a gene from one organism into another (which may be a different species) so the recipient produces a new protein or shows a new characteristic. This chapter covers recombinant DNA, genetically modified bacteria (making human insulin), modified plants and animals, and cloning transgenic animals (Biology only).

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WHAT IS GENETIC MODIFICATION?

• Genetic modification (genetic engineering) — changing the genetic material (DNA) of an organism by transferring a gene from one organism into another.
• The organism that receives a foreign gene is transgenic.
• The inserted gene is called a recombinant gene; the DNA is recombinant DNA (DNA made by joining pieces from different organisms).

RECOMBINANT DNA — THE STAGES (Biology only)

1. Extract the required gene from the donor organism's DNA (using enzymes that cut DNA at specific points — restriction enzymes).
2. Cut the plasmid (a small loop of DNA in bacteria) with the same enzymes (so the ends match).
3. Insert the gene into the plasmid (using ligase enzymes to join the DNA).
4. The plasmid now contains recombinant DNA — insert it into the host bacterium.
5. The bacterium divides (mitosis/asexual) — every new bacterium contains the gene and produces the protein.

PRODUCING GENETICALLY MODIFIED (TRANSGENIC) BACTERIA

• Classic example — making human insulin: 1. The human insulin gene is inserted into a bacterial plasmid. 2. The modified bacteria are grown in a fermenter. 3. The bacteria produce human insulin, which is extracted and purified. 4. Used to treat diabetes.
• Advantages over animal insulin: identical to human insulin (fewer allergic reactions), produced in huge quantities cheaply, no animal suffering.
• Other products: human growth hormone, clotting factors, vaccines, enzymes.

MAKING USE OF GENETICALLY MODIFIED BACTERIA

• GM bacteria can also be engineered to break down oil spills (clean-up), make biofuels, and produce medicines and food additives (e.g. rennet for cheese).

PRODUCING GENETICALLY MODIFIED PLANTS

• A gene is inserted into plant cells (often using a bacterial carrier or a gene gun); the cells grow into whole plants (tissue culture).
• Examples:
• Herbicide-resistant crops (weeds die, crop survives → higher yields).
• Pest-resistant crops (make their own insecticide — e.g. Bt corn — fewer pesticides needed).
• Drought/salt-resistant crops.
• Golden rice — contains extra vitamin A (helps prevent blindness in developing countries).

PRODUCING GENETICALLY MODIFIED ANIMALS

• A gene (e.g. the human gene for a blood-clotting factor or insulin) is inserted into an animal embryo; the animal (e.g. a goat or sheep) produces the human protein in its milk, which is collected and purified.
• Cloning transgenic animals: the transgenic animal can be cloned (Chapter 20) so a whole herd produces the medicine.

ARGUMENTS FOR AND AGAINST GM (evaluation)

For: - Medicines (insulin, clotting factors) — cheap, safe, unlimited supply. - Crop yields up — feeds a growing population; less pesticide needed (environmental benefit). - Crops with added nutrients (golden rice) improve health.

Against: - Unknown long-term effects on human health (allergies, toxins). - Gene flow: GM pollen can spread to wild plants (superweeds); GM crops reduce biodiversity. - Monopoly: big companies own GM seeds — farmers depend on them. - Ethical concerns about modifying organisms (especially animals) — "playing God".

LOOKING AHEAD (Biology only)

• Polymerase chain reaction (PCR) — a technique to make millions of copies of a piece of DNA quickly (used in forensics, diagnosis, and to amplify genes for GM).

✅ Quick check

1. What is genetic modification? (Transferring a gene from one organism into another — creating recombinant DNA/transgenic organisms.)
2. Describe how human insulin is made by bacteria. (Human insulin gene cut out, inserted into a bacterial plasmid, plasmid put into bacteria, bacteria grown in a fermenter produce insulin.)
3. Give two uses of GM crops. (Herbicide/pest resistance, drought resistance, golden rice nutrients.)
4. Give two arguments for and two against GM. (For: medicines, yields, nutrients. Against: health risks, gene flow, ethics, monopoly.)
5. What is PCR? (Making millions of copies of a piece of DNA.)