Overview
This lecture summarizes all core concepts required for AQA Biology Paper 2, covering homeostasis, inheritance and evolution, and ecology for both combined and triple science.
Homeostasis and Response
- Homeostasis regulates internal conditions (e.g., glucose, temperature, water) for optimal enzyme activity.
- The nervous system includes CNS (brain, spinal cord) and PNS (body nerves), transmits signals via neurons and synapses.
- Reflex arcs bypass the brain for fast automatic responses.
- Reaction times can be measured using a ruler-drop experiment with variables like caffeine as stimulants.
- The endocrine system uses glands to release hormones into blood, acting slower than nerves.
- The pituitary gland controls other glands (e.g., pancreas for insulin, adrenal glands for adrenaline).
- Blood glucose too high: insulin causes cells to absorb glucose, storing excess as glycogen in liver.
- Blood glucose too low: glucagon prompts liver/muscles to release glucose.
- Type 1 diabetes: lack of insulin production; requires injections.
- Type 2 diabetes: resistance to insulin; managed by diet and weight.
Triple Only: The Brain, Eye, and Thermoregulation
- Brain areas: cerebral cortex (thought), cerebellum (movement), medulla (automatic actions).
- Eye accommodation: lens shape changes for focus; myopia = short sight, hyperopia = long sight.
- Pupil size adjusts to light intensity; rods detect light, cones detect color.
- Thermoregulation: sweat cools body, vasodilation increases heat loss, vasoconstriction reduces it, shivering generates heat.
- ADH hormone regulates kidney water absorption; negative feedback restores water balance.
- Dialysis replaces kidney function if failed.
Reproduction and Hormones
- Menstrual cycle: FSH matures egg, estrogen thickens uterus lining, LH releases egg, progesterone maintains lining.
- Contraception options: pills, injections, implants, condoms, IUDs, surgical methods, timing intercourse.
- Infertility treatments: hormone injections, IVF (in vitro fertilization).
- Adrenaline prepares body for action; thyroxin controls metabolism via negative feedback.
- Plant hormones (triple): gibberellins (germination), ethene (ripening), auxins (growth/phototropism/geotropism).
Inheritance, Variation, and Evolution
- Sexual reproduction uses meiosis to produce varied gametes; asexual creates clones via mitosis.
- Genome = all DNA; gene = DNA section coding for protein.
- Genotype = genetic code; phenotype = observable traits.
- Mutations alter proteins; some DNA regulates other genes (epigenetics).
- Alleles: dominant shows even if only one copy, recessive only if both copies.
- Homozygous = same alleles, heterozygous = different.
- Punnett squares predict inheritance probabilities.
- Sex determination: XX = female, XY = male.
- Variation results from genes and environment; Darwin's theory = survival of the fittest.
- Antibiotic resistance in bacteria is evidence of evolution.
Genetic Engineering and Cloning (Triple Only)
- Selective breeding enhances traits; genetic engineering inserts genes for desired traits (e.g., insulin production in bacteria).
- Genetic engineering process: cut desired gene, insert into vector, transfer to organism early in development.
- Cloning plants via cuttings/tissue culture; animals by embryo splitting or nuclear transfer.
Ecology
- Ecology studies organism interactions in ecosystems; competition for resources is common.
- Abiotic factors: non-living (light, moisture, temp); biotic: living (food, predators).
- Quadrats and transects estimate population size/distribution.
- Food chains show energy flow: producers → consumers → apex predators; these are trophic levels.
- Biomass pyramids visualize energy loss at each level; calculate efficiency (percentage = part/whole × 100).
- Decomposition, carbon, and water cycles recycle materials; farmers use decomposition for fertilizer and methane (triple).
- Biodiversity = variety of life; high biodiversity = stable ecosystems, but human activity reduces it.
- Environmental issues: pollution, deforestation, peat destruction, global warming (COâ‚‚ and methane).
- Food security challenges: population growth, farm costs, supply chain, conflicts.
- Sustainable fishing uses net sizes to allow young fish to escape.
Key Terms & Definitions
- Homeostasis — maintaining stable internal conditions.
- Reflex Arc — fast nerve pathway that skips the brain.
- Synapse — gap between neurons where signals pass via chemicals.
- Hormone — chemical messenger in blood.
- Negative Feedback — process that returns a condition to normal.
- Genome — all genetic material of an organism.
- Allele — different versions of a gene.
- Genotype — genetic makeup.
- Phenotype — observable traits.
- Mutation — change in DNA sequence.
- Selective Breeding — mating for desired traits.
- Genetic Engineering — modifying an organism's DNA directly.
- Quadrat — square used to sample populations.
- Trophic Level — position in a food chain.
- Biodiversity — variety of life in an ecosystem.
Action Items / Next Steps
- Review menstrual cycle hormones, inheritance patterns, and food chain calculations.
- Practice drawing and interpreting biomass pyramids.
- Prepare Punnett square problems for genotype/phenotype predictions.
- Read textbook sections on genetic engineering and ecosystems.