Overview
This lecture covers key CIE IGCSE Biology topics, focusing on the characteristics of living organisms, classification, cell structure, transport, biological molecules, plant and animal physiology, genetics, ecology, human impacts, and biotechnology.
Characteristics and Classification of Living Organisms
- All living things perform movement, respiration, sensitivity, nutrition, excretion, reproduction, and growth (MRS NERG).
- Classification groups organisms by shared features using the binomial system (Genus species).
- A species can breed to produce fertile offspring; hybrids like mules are sterile.
- Modern classification uses DNA and protein similarities.
- Dichotomous keys help identify organisms.
The Five Kingdoms and Key Features
- Five kingdoms: plants, animals, protists, bacteria, fungi.
- Vertebrates have a backbone; notable classes: mammals, birds, reptiles, fish, amphibians.
- Invertebrates include arthropods: insects, crustaceans, arachnids, myriapods.
Cell Structure and Functions
- Animal and plant cells share: cell membrane, cytoplasm, nucleus, ribosomes, mitochondria.
- Plant cells also have: cell wall (cellulose), vacuole, chloroplasts (photosynthesis).
- Prokaryotes (bacteria) lack membrane-bound organelles; possess plasmids and sometimes flagella.
- Viruses are non-living, made of a protein coat and DNA/RNA.
Specialized Cells and Organization
- Red blood cells transport oxygen (contain hemoglobin, lack nucleus).
- Muscle cells contract via protein fibers.
- Ciliated cells move mucus; motor neurons transmit impulses.
- Sperm has a tail for movement; ova contain nutrients and protective coat.
- Root hair cells absorb water/minerals (large surface area).
- Xylem transports water; phloem transports sugars.
- Biological organization: organelle → cell → tissue → organ → organ system → organism.
Biological Molecules
- Carbohydrates: energy (monosaccharides/polysaccharides: glucose, starch, glycogen, cellulose).
- Proteins: chains of amino acids, structure/function depend on sequence.
- DNA: double helix, base pairing (A-T, C-G), stores genetic info; genes code for proteins.
- Enzymes: biological catalysts; activity affected by temperature/pH.
Transport in Cells and Organisms
- Diffusion: net movement from high to low concentration (no energy).
- Osmosis: net movement of water across a partially permeable membrane.
- Active transport: movement from low to high concentration (requires energy, uses carrier proteins).
- Multicellular organisms require circulatory systems due to low surface area:volume ratios.
Nutrition and Digestion
- Balanced diet: proper proportions of carbs, proteins, fats, vitamins, minerals, water, fiber.
- Enzymes in digestion: amylase (starch), protease (proteins), lipase (fats).
- Bile emulsifies fats and neutralizes stomach acid.
- Small intestine adapted for absorption: villi, microvilli, blood supply, thin epithelium.
Transport in Plants
- Xylem: transports water/minerals upwards; made of dead, lignified cells.
- Phloem: transports sugars bidirectionally; consists of sieve tubes and companion cells.
- Water enters roots by osmosis; minerals by active transport.
- Transpiration: water loss from leaves, affected by humidity, temperature, wind, light.
Circulatory and Immune System in Animals
- Heart: four chambers (atria, ventricles); double circulation.
- Arteries carry blood away (thick walls); veins return blood (valves, thin walls); capillaries allow exchange (one-cell thick).
- Blood components: plasma (transports solutes), red cells (oxygen), white cells (immunity), platelets (clotting).
- Immunity: phagocytes ingest pathogens; lymphocytes produce antibodies; vaccines stimulate immunity.
Respiration and Excretion
- Aerobic respiration: glucose + O₂ → CO₂ + H₂O + energy.
- Anaerobic respiration: lactic acid (muscles) or ethanol + CO₂ (yeast).
- Kidneys filter blood, reabsorb useful substances, and regulate water via ADH.
Coordination and Homeostasis
- Nervous system uses electrical impulses (fast, short-lived, specific); hormones use chemicals (slower, longer, widespread).
- Reflex actions bypass conscious brain.
- Eye structure: cornea, lens, retina, optic nerve; accommodation and pupil reflex.
- Homeostasis maintains stable internal environment (temperature, blood sugar, water).
- Insulin lowers blood sugar; glucagon raises it; diabetes results from insulin issues.
Reproduction and Genetics
- Sexual reproduction: gametes, fertilization, genetic variation.
- Asexual: one parent, identical offspring.
- Plant reproduction: flower structure, pollination (insect vs. wind), fertilization, seed formation, conditions for germination.
- Human reproduction: male (testes, sperm), female (ovaries, eggs).
- Menstrual hormones: FSH, LH, estrogen, progesterone.
- STI prevention: condoms, testing, education.
Inheritance and Variation
- DNA organized in chromosomes; gene = DNA section coding for protein.
- Diploid (2 sets chromosomes); haploid (1 set).
- Mitosis (growth/repair, identical cells); meiosis (gametes, variation).
- Alleles: dominant (expressed), recessive (masked).
- Use Punnett squares for predicting inheritance.
- Sex determination: XX (female), XY (male); sex-linked traits (e.g., color blindness on X).
- Codominance: both alleles expressed (blood groups).
- Mutations: random DNA changes, sometimes caused by radiation/chemicals.
Evolution, Selection, and Biotechnology
- Natural selection: variation via mutation, best-adapted survive/reproduce.
- Selective breeding: humans breed for desired traits.
- Genetic engineering: transfer genes (e.g., human insulin in bacteria, GM crops).
- Microorganisms in biotechnology: yeast in bread/beer, fermenters optimize growth.
Ecology and Human Impact
- Ecosystem: interactions between organisms and environment.
- Food chains/webs: energy transfer, trophic levels, pyramids of number/biomass.
- Nitrogen/carbon cycles: recycling of elements.
- Population growth influenced by food, predation, disease.
- Human impacts: pollution, eutrophication, plastic waste, greenhouse effect, deforestation.
- Conservation: sustainable resources, endangered species, education, breeding programs.
Key Terms & Definitions
- Species — group producing fertile offspring.
- Diffusion — movement from high to low concentration.
- Osmosis — diffusion of water across partially permeable membrane.
- Active Transport — movement against concentration gradient, requires energy.
- Enzyme — biological catalyst that speeds reactions.
- Gene — DNA section coding for a protein.
- Allele — variant form of a gene.
- Transpiration — water loss from plant leaves.
- Homeostasis — maintenance of stable internal environment.
- Pathogen — microorganism causing disease.
- Vaccination — introduction of antigens to stimulate immunity.
- Mutation — random change in DNA.
- Natural Selection — process by which favorable traits increase in a population.
- Sustainable Resource — one produced as quickly as used.
Action Items / Next Steps
- Review diagrams for cell structure, heart, leaf, and flower anatomy.
- Practice using dichotomous keys and Punnett squares.
- Memorize key definitions and balanced equations for photosynthesis and respiration.
- Complete any assigned questions on genetic crosses, food webs, and cycles.
- Prepare for practicals by reviewing experiment steps (e.g., osmosis, enzyme activity).