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IGCSE Biology Key Terms (0610)
IGCSE Biology Key Terms
Cambridge IGCSE Biology (0610) | Essential Definitions & Equations
Based on official Cambridge syllabus 2023-2025
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Diffusion
Net movement of particles...
Osmosis
Net movement of water molecules...
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1. Characteristics of Living Organisms (MRS GREN)
Movement An action by an organism causing a change of position or place
Respiration Chemical reactions in cells that break down nutrient molecules and release energy for metabolism
Sensitivity The ability to detect and respond to changes in the environment
Growth A permanent increase in size and dry mass
Reproduction The processes that make more of the same kind of organism
Excretion Removal from organisms of toxic materials and substances in excess of requirements
Nutrition Taking in of materials for energy, growth and development
2. Cell Structure
Cell membrane Controls what enters and leaves the cell; partially permeable
Nucleus Contains genetic material (DNA); controls cell activities
Cytoplasm Where chemical reactions take place
Mitochondria Site of aerobic respiration; releases energy
Ribosomes Site of protein synthesis
Plant cells only:
Cell wall Made of cellulose; provides support and prevents bursting
Chloroplasts Contain chlorophyll; site of photosynthesis
Vacuole Contains cell sap; maintains turgor pressure
3. Movement of Substances
Diffusion
The net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient
Osmosis
The net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution) through a partially permeable membrane
Active transport
Movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration
Key difference: Diffusion & osmosis = passive (no energy); Active transport = requires ATP
4. Enzymes
Enzyme: A protein that acts as a biological catalyst, speeding up reactions without being used up
Denaturation: Permanent change in enzyme shape due to high temperature or extreme pH; active site no longer fits substrate
Active site Part of enzyme where substrate binds (lock and key model)
Substrate The molecule that the enzyme acts upon
Optimum Temperature/pH at which enzyme works fastest (~37°C for human enzymes)
Tip: Enzymes are specific — each enzyme only catalyzes one reaction
5. Photosynthesis
Definition:
The process by which plants make glucose using light energy, carbon dioxide and water, releasing oxygen as a by-product
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
(requires light and chlorophyll)
Word equation:
carbon dioxide + water → glucose + oxygen
Requirements: Light, chlorophyll, CO₂, water
Limiting factors: Light intensity, CO₂ concentration, temperature
Uses of glucose: Respiration, starch storage, cellulose, proteins, fats
Limiting factors: Light intensity, CO₂ concentration, temperature
Uses of glucose: Respiration, starch storage, cellulose, proteins, fats
6. Respiration
Definition:
Chemical reactions in cells that break down nutrient molecules and release energy for metabolism
Aerobic Respiration (with oxygen):
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy
glucose + oxygen → carbon dioxide + water + energy
Anaerobic Respiration (without oxygen):
In muscles:
glucose → lactic acid
In yeast (fermentation):
glucose → ethanol + CO₂
Tip: Aerobic releases MORE energy; happens in mitochondria
7. Food Tests
| Nutrient | Reagent | Method | Positive Result |
|---|---|---|---|
| Starch | Iodine solution | Add drops | Blue-black |
| Reducing sugars | Benedict's solution | Heat in water bath | Orange/brick-red |
| Protein | Biuret reagent | Add and shake | Purple/lilac |
| Fats/oils | Ethanol + water | Shake, add water | White emulsion |
| Vitamin C | DCPIP | Add drops | Colourless |
8. Transport in Plants
Xylem
- Transports water & minerals
- From roots → leaves
- Dead, hollow tubes
- Lignified walls
Phloem
- Transports sucrose & amino acids
- Both directions
- Living cells
- Sieve tubes + companion cells
Transpiration: Loss of water vapour from leaves through stomata
Translocation: Movement of sucrose and amino acids in phloem from sources to sinks
Tip: Starch is NOT transported (insoluble) — converted to sucrose first
9. Circulatory System
Arteries
Away from heart
Thick walls
High pressure
Thick walls
High pressure
Veins
To heart
Thin walls
Have valves
Thin walls
Have valves
Capillaries
Exchange
One cell thick
Permeable
One cell thick
Permeable
Blood flow: Right atrium → Right ventricle → Lungs → Left atrium → Left ventricle → Body
Blood clotting: Fibrinogen (soluble) → Fibrin (insoluble threads) — traps red blood cells
Coronary arteries: Supply heart muscle with blood
Septum: Wall dividing left and right sides
10. Gas Exchange
Gas exchange: Oxygen diffuses into blood, carbon dioxide diffuses out, across the alveoli walls
Features of alveoli for efficient gas exchange:
- Large surface area — many alveoli
- Thin walls — one cell thick, short diffusion distance
- Good blood supply — maintains concentration gradient
- Moist lining — gases dissolve before diffusing
Pathway: Nose/mouth → Trachea → Bronchi → Bronchioles → Alveoli
11. Excretion & Homeostasis
Excretion: Removal of toxic waste products of metabolism from the body
Homeostasis: Maintaining a constant internal environment
Kidneys excrete: Urea, excess water, excess salts
Lungs excrete: CO₂, water vapour
Urea formation: Excess amino acids → deamination in liver → urea
Remember: Egestion (faeces) is NOT excretion — it's undigested food, not metabolic waste
12. Genetics & Inheritance
Gene A length of DNA that codes for a protein
Allele Different forms of the same gene
Genotype The alleles present (e.g., Bb, BB, bb)
Phenotype The observable characteristics
Dominant Allele that is expressed when present (capital letter)
Recessive Allele only expressed when homozygous (lowercase)
Homozygous Two identical alleles (BB or bb)
Heterozygous Two different alleles (Bb)
Mitosis: Cell division producing 2 identical diploid cells (growth/repair)
Meiosis: Cell division producing 4 different haploid gametes (sex cells)
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