Overview
This lecture covers the key topics from AQA GCSE Biology Paper 1, including cell biology, biological organization, transport systems, health and disease, photosynthesis, respiration, and practical methods essential for the exam.
Cell Structure and Types
- Animal cells have a cell membrane, cytoplasm, ribosomes (protein synthesis), nucleus (controls activities), and mitochondria (aerobic respiration).
- Plant cells include all animal cell parts plus a cell wall (cellulose), chloroplasts (photosynthesis), and a permanent vacuole (support).
- Prokaryotic (bacterial) cells lack a nucleus; DNA floats in cytoplasm, may have plasmids (extra DNA), flagellum (movement), and a distinct cell wall.
- Eukaryotic cells have a nucleus containing DNA.
Specialized Cells & Cell Differentiation
- Examples: root hair cells (absorb water/minerals), xylem and phloem (transport), sperm, nerve, and muscle cells (various functions).
- Differentiation: process by which cells become specialized; animal cells mostly differentiate early, plant cells throughout life.
- Stem cells are undifferentiated cells that can become various cell types.
Microscopy and Culturing Microorganisms
- Light microscopes magnify up to 1,500x; electron microscopes offer greater magnification/resolution.
- Prepare slides by staining and focusing at low to high power.
- Bacteria grow via binary fission; aseptic techniques prevent contamination in cultures.
Transport in Cells
- Diffusion: net movement from high to low concentration, passive process.
- Osmosis: movement of water from dilute to concentrated solution across a semi-permeable membrane.
- Active transport: movement from low to high concentration using energy (e.g., mineral uptake in roots).
- Surface area to volume ratio affects exchange—smaller ratio in larger organisms needs specialized surfaces.
Biological Organization
- Cells → Tissues → Organs → Organ Systems → Organism.
- Digestive system: mouth (amylase for carbohydrates), stomach (protease for proteins), small intestine (lipase for lipids).
Enzymes and Digestion
- Enzymes are biological catalysts, work by the lock-and-key mechanism, denatured by extreme temperatures or pH.
- Bile (from liver) neutralizes stomach acid, emulsifies fats.
- Food tests: iodine for starch (blue-black), biuret for protein (purple), Benedict's for glucose (brick red), ethanol for lipids (cloudy emulsion).
Circulation and Blood
- Arteries (thick walls, narrow lumen), veins (valves, wide lumen), capillaries (thin walls for diffusion).
- Blood: plasma (liquid), red cells (oxygen), white cells (immunity), platelets (clotting).
- Heart: right pumps to lungs, left to body; double circulatory system; heart disease treated by statins, stents, or transplants.
Health, Disease, and Immunity
- Communicable diseases (pathogens—virus, bacteria, fungi, protists); spread via air, direct contact, vectors.
- Vaccines stimulate antibody production, create immunity (memory cells).
- Antibiotic resistance results from overuse and incomplete courses.
Photosynthesis and Respiration
- Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (in chloroplasts, needs light).
- Limiting factors: light intensity, CO₂ concentration, temperature.
- Respiration: aerobic (with O₂, more energy), anaerobic (less energy, produces lactic acid or ethanol/CO₂ in yeast).
- Exercise increases demand for energy, leads to oxygen debt.
Key Terms & Definitions
- Eukaryotic — cells with a nucleus.
- Prokaryotic — cells without a nucleus (e.g., bacteria).
- Diffusion — net movement of particles from high to low concentration.
- Osmosis — movement of water from dilute to concentrated solution through a semi-permeable membrane.
- Active Transport — movement of substances against a concentration gradient using energy.
- Enzyme — biological catalyst speeding up reactions.
- Photosynthesis — process in plants converting light, CO₂, and water into glucose and oxygen.
- Antibiotic Resistance — ability of bacteria to survive antibiotic treatment.
Action Items / Next Steps
- Review labeled diagrams of animal, plant, and bacterial cells.
- Memorize definitions and functions for diffusion, osmosis, and active transport.
- Practice enzyme reactions and calculation graphs.
- Complete any assigned practical write-ups (e.g., osmosis, photosynthesis).
- Study disease examples and prevention methods outlined above.