Overview
This lecture covers key topics from GCSE Biology Paper 1, including cell biology, organization, infection and response, and bioenergetics, with a focus on definitions, processes, and exam-relevant content.
Cell Biology & Microscopy
- Light microscopes use light, can view living specimens, magnify up to 2,000x, but have lower resolution (200 nm).
- Electron microscopes use electrons, require dead specimens, magnify up to 2,000,000x, with very high resolution (0.2 nm).
- Animal cells have nucleus, cytoplasm, cell membrane, mitochondria (aerobic respiration), and ribosomes (protein synthesis).
- Plant cells also have chloroplasts (photosynthesis), permanent vacuole (cell rigidity), and cell wall (cellulose, support).
- Eukaryotic cells (plants, animals) have nucleus, prokaryotic cells (bacteria) have DNA in loops/plasmids, no nucleus.
Specialized Cells & Cell Processes
- Specialized animal cells: sperm (tail, mitochondria), muscle (mitochondria, protein for contraction), nerve (axon, dendrites).
- Specialized plant cells: root hair (large surface, vacuole, mitochondria), xylem (hollow, lignin), phloem (sieve plates, companion cells).
- Diffusion: movement from high to low concentration, passive process.
- Osmosis: movement of water across partially permeable membrane from dilute to concentrated solution.
- Active transport: moves substances from low to high concentration, requires energy from respiration (mitochondria).
Cell Division & Stem Cells
- Mitosis is cell division resulting in two identical cells (growth, repair).
- Stem cells: undifferentiated, can become specialized cells; embryonic stem cells are more versatile than adult stem cells.
- Plant meristems provide stem cells for growth, cloning, and crop improvement.
Culturing Microorganisms
- Bacteria divide by binary fission; population after n divisions: 2ⁿ.
- Key aseptic techniques: sterilize equipment, secure lids, incubate at ≤25°C in schools.
Organization in Living Things
- Biological hierarchy: cells → tissues → organs → organ systems → organism.
- Digestive system: mechanical breakdown (mouth), chemical digestion (enzymes: amylase, protease, lipase), absorption (villi, microvilli in small intestine).
- Enzymes: biological catalysts; lock-and-key model; affected by temperature and pH.
Blood, Circulation & Gas Exchange
- Blood: plasma (transports substances), red cells (carry oxygen), white cells (immune), platelets (clotting).
- Blood vessels: arteries (thick walls, high pressure), capillaries (thin walls, diffusion), veins (valves, low pressure).
- Heart: double circulatory system; right pumps to lungs (deoxygenated), left pumps to body (oxygenated).
- Gas exchange in lungs: alveoli (large surface, thin walls, good blood supply); similar principles in fish gills.
Non-Communicable Diseases & Cancer
- Non-communicable diseases: not infectious; risk factors include diet, smoking, alcohol, lack of exercise.
- Cancer: uncontrolled cell division; benign tumors don't spread, malignant do; treated with radiotherapy or chemotherapy.
Plant Structure, Transport & Transpiration
- Leaf structure: upper/lower epidermis, palisade (photosynthesis), spongy mesophyll (gas exchange), stomata (gas/water control).
- Xylem transports water/minerals up; phloem transports food in both directions.
- Transpiration: water loss via stomata; affected by light, temperature, humidity, wind.
Infection and Immunity
- Pathogens: bacteria (toxins), viruses (invade cells), protists, fungi.
- Disease spread: direct contact, water, air.
- Body defenses: skin, mucus, stomach acid, white blood cells (phagocytosis, antibodies, antitoxins).
- Vaccination: introduces inactive pathogens, triggers antibody production, leads to immunity (herd immunity).
Medicines & Drug Development
- Antibiotics treat bacteria, not viruses; antibiotic resistance is a concern.
- Drug development: extracted from plants/microbes; tested for toxicity, efficacy, dosage (TED).
- Clinical trials: double-blind, placebo-controlled.
Bioenergetics (Photosynthesis & Respiration)
- Photosynthesis: CO₂ + H₂O + light → glucose + O₂; endothermic process in chloroplasts.
- Limiting factors: light, CO₂, temperature, chlorophyll.
- Glucose uses: fats/oils, starch, respiration, amino acids, cellulose (mnemonic: "FOSRAC").
- Respiration: aerobic (glucose + O₂ → CO₂ + H₂O, more energy), anaerobic (glucose → lactic acid or ethanol + CO₂, less energy).
- Exercise increases heart/breathing rate to supply muscles with oxygen; lactic acid causes muscle fatigue, leads to oxygen debt.
Key Terms & Definitions
- Microscope — instrument for viewing small objects.
- Osmosis — movement of water through a partially permeable membrane from dilute to concentrated solution.
- Active Transport — movement of substances against concentration gradient, using energy.
- Enzyme — biological catalyst, specific to substrates.
- Transpiration — evaporation of water from plant leaves.
- Pathogen — microorganism causing disease.
- Vaccination — introduction of harmless pathogen to stimulate immunity.
- Antibiotic — drug that kills bacteria.
- Photosynthesis — process by which plants make glucose using CO₂, water, and light.
- Respiration — process cells use to release energy from glucose.
Action Items / Next Steps
- Review diagrams of plant/animal cells, heart, and lungs.
- Practice calculations for bacterial growth and transpiration rate.
- Memorize enzyme types, functions, and optimal conditions.
- Practice interpreting data and graphs related to limiting factors and disease incidence.
- Complete assigned revision workbooks and mind maps as suggested.