Overview
This lecture provides a comprehensive overview of key topics in IGCSE Biology, including characteristics of living organisms, classification, cell biology, plant and animal physiology, genetics, ecology, and human impact on the environment.
Characteristics of Living Organisms & Classification
- All living organisms share movement, respiration, sensitivity, nutrition, excretion, reproduction, and growth (MRS GREN).
- Classification organizes organisms by shared features; the binomial system uses two names (genus and species).
- A species is a group of organisms able to produce fertile offspring.
- Modern classification uses DNA/protein similarities for greater accuracy.
Cells & Specialization
- Prokaryotes lack membrane-bound organelles; eukaryotes have them (nucleus, mitochondria, etc.).
- Specialized cells include red blood cells (oxygen transport), muscle cells (contraction), ciliated cells (mucus movement), nerve cells (impulse conduction), sperm (reproduction), and plant root hair cells (absorption).
Biological Molecules & Enzymes
- Organic molecules: carbohydrates (CH&O), proteins (CHON), lipids (CHO).
- Proteins are chains of amino acids; enzymes are biological catalysts with active sites.
- Enzyme activity is affected by temperature and pH; high temps or extreme pH denature enzymes.
Transport Mechanisms
- Diffusion: movement from high to low concentration, passive.
- Osmosis: movement of water from high to low water potential across a partially permeable membrane.
- Active transport: movement against concentration gradient, requires energy and carrier proteins.
Photosynthesis, Plant Structure & Transport
- Photosynthesis: carbon dioxide + water → glucose + oxygen (uses chlorophyll, occurs in chloroplasts).
- Limiting factors: light, CO₂, temperature.
- Xylem transports water/minerals up; phloem transports sugars in any direction.
Nutrition & Digestion
- A balanced diet includes carbohydrates, fats, proteins, vitamins, minerals, water, and fiber.
- Digestion: mechanical (teeth, stomach) and chemical (enzymes like amylase, protease, lipase).
- Small intestine adaptation: villi for absorption, microvilli for increased surface area.
Circulation & Respiration
- Double circulatory system: blood passes twice through heart per body circuit.
- Heart has four chambers; left ventricle wall is thickest.
- Arteries (high pressure, thick walls), veins (valves, low pressure), capillaries (one-cell thick).
- Aerobic respiration: glucose + oxygen → CO₂ + water + energy; anaerobic respiration produces lactate.
Immunity & Disease
- Pathogen entry prevented by skin, acid, tears.
- Phagocytes engulf pathogens; lymphocytes produce specific antibodies.
- Vaccination introduces antigens to stimulate antibody and memory cell production.
Genetics & Inheritance
- Genes code for proteins; alleles are different gene forms.
- Genotype: genetic makeup; phenotype: physical traits.
- Homozygous: same alleles; heterozygous: different alleles.
- Mitosis: growth/repair; meiosis: gamete formation.
- Sex determination: XX = female, XY = male.
Ecology & Environment
- Producers (plants) start food chains; energy lost at each trophic level (≈90%).
- Carbon and nitrogen cycles involve photosynthesis, respiration, decomposition, fixation, and denitrification.
- Eutrophication from excess fertilisers causes aquatic life death; plastics pollute land and water.
Human Impacts & Conservation
- Deforestation, greenhouse gases, and pollution cause habitat loss, global warming, and species extinction.
- Conservation methods: protected areas, education, captive breeding, sustainable resource management.
Key Terms & Definitions
- Species — Group able to produce fertile offspring.
- Osmosis — Movement of water across a partially permeable membrane.
- Genome — Entire DNA of an organism.
- Transpiration — Loss of water vapor from plant leaves.
- Pathogen — A microorganism causing disease.
- Allele — Different form of a gene.
- Haploid/Diploid — Single/double set of chromosomes.
- Biomass — Mass of living material at a trophic level.
Action Items / Next Steps
- Review diagrams of plant and animal cells, heart, leaf structure, and genetic crosses.
- Memorize key definitions and formulae (e.g., magnification, photosynthesis/respiration equations).
- Practice past exam questions on classification, cell structure, transport, inheritance, and ecological cycles.
- Prepare for practicals on osmosis, enzyme activity, and food testing.