Cambridge International GCSE Biology Overview

Cells

• All life consists of cells.
• Light microscopes can see cells and nucleus but not sub-cellular structures.
• Electron microscopes: finer details, higher resolution; can see organelles.
• Magnification calculation: Image size / Object size.
  • Calculate actual size by dividing image size by magnification.

Cell Types

• Eukaryotic Cells: Have nucleus (e.g., plant and animal cells).
• Prokaryotic Cells: No nucleus; DNA in a plasmid ring.
• Organelles
  • Cell membrane: semi-permeable, keeps cell structure.
  • Cell wall: made of cellulose in plants and bacteria.
  • Cytoplasm: liquid medium for chemical reactions.
  • Mitochondria: site of respiration.
  • Ribosomes: protein synthesis.
  • Chloroplasts: photosynthesis in plants.
  • Permanent vacuole: stores sap in plants.

Transport Mechanisms

• Diffusion: Movement from high to low concentration, passive.
• Osmosis: Diffusion of water across semi-permeable membrane.
• Active Transport: Uses energy to move substances against concentration gradient.

Organisation in Organisms

• Tissues: Similar cells connected.
• Organs: Tissues working together (e.g., heart).
• Organ Systems: Organs working together (e.g., digestive system).
  • Various components and roles (e.g., bile digestion, enzymes).

Enzymes

• Specific biological catalysts.
• Lock and Key: Specific substrate fits enzyme's active site.
• Factors affecting enzyme activity: Temperature (optimum and denaturation), pH.

Practical: Enzyme Activity

• Measure time for starch breakdown with iodine indicator.
• Plot time against temperature or pH to find optimum.

Food Tests

• Iodine: Starch turns black.
• Benedict's solution: Sugars turn orange.
• Biuret reagent: Proteins turn purple.
• Ethanol: Lipids turn cloudy.

Balanced Diet

• Carbohydrates: Energy (bread, cereal).
• Fats and Oils: Energy (butter, nuts).
• Proteins: Growth/repair (meat, eggs).
• Vitamins: Health (fruit, veg), e.g., Vitamin C (scurvy); Vitamin D (rickets).
• Minerals: Health, e.g., Calcium (bones), Iron (blood).
• Fiber: Digestive health.

Respiratory System

• Breathing vs. Respiration: Air passage (trachea, bronchi, alveoli); gas exchange in alveoli.
• Oxygen transport: Hemoglobin in red blood cells.
• Double circulatory system: Blood enters twice in one cycle (heart, lungs).
• Heart Structure: Chambers, valves, and blood flow pattern.

Blood Vessels

• Arteries: Away from heart, thick walls.
• Veins: Toward heart, thin walls, valves.
• Capillaries: One cell thick, fast diffusion.

Plants

• Photosynthesis: Chloroplasts, production of food.
• Water Transport: Transpiration in xylem.
• Nutrient Transport: Translocation in phloem.

Disease

• Non-communicable: e.g., Cancer, obesity.
• Communicable: Pathogens (virus, bacteria, fungi, protists).
  • Viruses: Need host cell (e.g., Measles, HIV).
  • Bacteria: Toxins (e.g., Salmonella, Gonorrhoea).
  • Fungi: Infections like athlete's foot.
  • Protists: e.g., Malaria.

Body’s Defense

• Physical barriers, mucus, acid.
• Immune response: White blood cells (lymphocytes, phagocytes).
  • Vaccinations: Expose immune system to pathogen for immunity.
  • Antibiotics: Target bacteria, not viruses.

Homeostasis

• Internal Regulation: Blood glucose, temperature, water levels.
• Nervous System: CNS (brain/spine), PNS (body nerves).
  • Reflex Arc: Fast, bypasses brain.
  • Glands and Hormones: Chemical responses to stimuli.

Human Reproduction

• Menstruation cycle: Hormones (FSH, LH, Estrogen, Progesterone).
• Hormones: Roles and regulation.

Plant Hormones

• Auxins: Shoot/root growth.
• Gibberellins: Seed germination, flowering.
• Ethylene: Fruit ripening.

Genetics and Evolution

• Gene and DNA: Basic unit of heredity.
• Human Genome Project: Mapping genetic code.
• Chromosomes: 23 pairs in humans.
• Mutations: Changes in genetic code.
• Selective Breeding and GM: Enhancing desired traits.
• Evolution: Natural selection, adaptation.

Microorganisms

• Pathogens: Disease causing microbes.
• Useful Microorganisms: e.g., Bacteria producing insulin.

Ecosystem

• Interdependence: Community of organisms.
• Abiotic/Biotic Factors.
• Quadrat Sampling: Population estimation.
• Food Chains and Webs: Energy transfer.

Environmental Impact

• Deforestation: Biodiversity loss.
• Pollution: CO2, methane.
• Sustainable Practices: Fishing, farming.

Practical Skills

• Microscopy, Enzyme reactions, Food tests, Photosynthesis rates, Respiration experiments, Reaction times.

Remember, this is an overview, so ensure to dive deep into each topic during study sessions. Good luck!