Overview
The lecture reviews all core topics for AQA GCSE Biology Paper 1, including cells, organization, infection and response, and bioenergetics, providing essential concepts, definitions, and practical techniques.
Cells & Microscopy
- All life is made of cells, visible with light microscopes; electron microscopes show finer cell structures (organelles).
- Magnification = image size ÷ object size; rearrange to find actual size.
- Eukaryotic cells have a nucleus (plants, animals); prokaryotic cells (bacteria) do not.
- Cell membrane is semi-permeable; plant and bacterial cells have rigid cell walls (cellulose).
- Key organelles: mitochondria (respiration), ribosomes (protein synthesis), chloroplasts (photosynthesis in plants), vacuole (storage in plants).
- Bacteria multiply by binary fission (Triple only); aseptic techniques are used in microbial cultures.
- Eukaryotic cell nuclei contain DNA in chromosomes; humans have 23 pairs in somatic (diploid) cells, 23 single in gametes (haploid).
- Mitosis produces two identical cells for growth and repair.
Cell Specialization, Stem Cells, & Cloning
- Cells specialize for specific functions (nerve, muscle, root hair, xylem, phloem).
- Stem cells are unspecialized, found in embryos and adult bone marrow (only make blood cells).
- Stem cells treat conditions like diabetes, paralysis; ethical arguments exist.
- Plant cloning preserves species or desired traits.
Transport in Cells
- Diffusion: passive movement from high to low concentration.
- Osmosis: diffusion of water across a membrane.
- Active transport: moves substances against a concentration gradient using energy (e.g., minerals into root hair cells).
- Surface area, temperature, and concentration difference affect diffusion/osmosis rates.
Organization: Tissues, Organs & Systems
- Cells form tissues, tissues form organs, organs form organ systems.
- Digestive system breaks down food using acid, enzymes, and bile.
- Bile neutralizes stomach acid and emulsifies fats.
- Enzymes are biological catalysts; specific to substrates (lock and key model).
- Rate of enzyme activity depends on temperature and pH; enzymes can denature.
- Food tests: iodine (starch), Benedict’s (sugars), Biuret (proteins), ethanol (lipids).
Circulatory & Respiratory Systems
- Gas exchange: air enters alveoli, oxygen diffuses into blood, CO₂ diffuses out.
- Heart pumps blood in a double circulatory system: right (deoxygenated) to lungs, left (oxygenated) to body.
- Arteries (away from heart, thick walls), veins (to heart, valves), capillaries (one-cell thick).
- Coronary heart disease caused by blocked arteries; treated with stents and statins.
- Blood contains plasma, red/white blood cells, platelets (clotting).
Disease: Non-Communicable & Communicable
- Non-communicable: not infectious (e.g., heart disease, diabetes, cancer).
- Cancer: uncontrolled cell division; benign (localized), malignant (spreads).
- Communicable: caused by pathogens (virus, bacteria, fungi, protist).
- Viruses hijack cells to reproduce; bacteria release toxins; fungi and protists can also cause disease.
- Plants: diseases like rose black spot (fungus), tobacco mosaic virus affect growth/photosynthesis.
Defence Mechanisms & Immunity
- Barriers: skin, mucus, stomach acid, enzymes.
- White blood cells: lymphocytes make antibodies/antitoxins, phagocytes ingest pathogens.
- Immunity arises after antibody production and memory cell formation.
- Vaccines contain inactive pathogens to stimulate immunity.
Antibiotics & Drug Development
- Antibiotics kill bacteria, not viruses; resistance develops with overuse.
- Drug discovery: natural sources, now mostly synthesized; trialled in labs, animals, humans.
- Placebo, blind and double-blind trials prevent bias.
Monoclonal Antibodies (Triple Only)
- Made by cloning cells to produce specific antibodies; used in treatment and diagnostics.
- Produced by combining lymphocytes and tumor cells (hybridoma); potential side effects.
Plant Biology & Transport
- Leaves: photosynthesis (in chloroplasts), transpiration (water loss).
- Roots absorb water/minerals; xylem (water, one way), phloem (food, both ways).
- Rate of transpiration increases with temperature, air movement, and low humidity.
- Deficiency: lack of nitrates (stunted growth), magnesium (chlorosis/yellowing).
Photosynthesis & Respiration
- Photosynthesis: endothermic reaction in chloroplasts; uses CO₂, water, light to make glucose and O₂.
- Rate limited by temperature, light, or CO₂ concentration.
- Respiration: releases energy (aerobic with O₂, anaerobic forms lactic acid or ethanol/CO₂).
- Anaerobic respiration less efficient, causes oxygen debt; fermentation used in baking/brewing.
Metabolism
- Metabolism: sum of all chemical reactions in organisms.
- Includes respiration, synthesis/breakdown of carbohydrates, proteins, and lipids.
Key Terms & Definitions
- Eukaryotic cell — cell with a nucleus.
- Prokaryotic cell — cell without nucleus.
- Mitosis — cell division producing identical cells.
- Diffusion — passive movement from high to low concentration.
- Osmosis — diffusion of water across a membrane.
- Active transport — movement against a concentration gradient using energy.
- Enzyme — biological catalyst speeding up reactions.
- Antibody — protein produced by lymphocytes to combat pathogens.
- Vaccine — inactive pathogen to stimulate immunity.
- Transpiration — loss of water from plant leaves.
- Photosynthesis — process using light to make glucose in plants.
- Respiration — energy-releasing process in cells.
Action Items / Next Steps
- Review food tests and practical methods (osmosis, enzyme activity, photosynthesis).
- Practice calculating magnification and cell sizes.
- Learn and practice drawing/labeling cell and heart diagrams.
- Review key definitions and processes for each topic.