Overview
This lecture rapidly covers all key topics for AQA Biology Paper 2, including homeostasis, inheritance, evolution, and ecology, highlighting both core and triple content.
Homeostasis and Response
- Homeostasis is the regulation of internal body conditions to maintain enzyme activity and survival.
- The nervous system includes the CNS (brain and spinal cord) and PNS (nerves throughout the body).
- Receptors detect stimuli, sending signals via sensory, relay, and motor neurons to effectors (muscles/glands).
- Reflex arcs bypass the brain for faster responses.
- Glands act as effectors by releasing necessary chemicals.
- Reaction time can be investigated using ruler drop tests, with mean averages calculated.
Brain, Eye, and Thermoregulation (Triple)
- Cerebral cortex: memory, speech, problem-solving; cerebellum: movement/balance; medulla: heart/breathing.
- MRI scans show brain activity safely.
- Eye accommodates by changing lens shape to focus light on the retina; myopia and hyperopia corrected with lenses or surgery.
- Thermoregulation: Vaso-dilation/cooling by sweating; vaso-constriction/shivering for warmth.
Hormones and Endocrine System
- Endocrine system controls body functions via glands and hormones in the blood.
- Pituitary gland is the master gland; pancreas regulates blood glucose with insulin (lowers) and glucagon (raises).
- Type 1 diabetes: insufficient insulin; Type 2: cells resist glucose uptake.
Water and Nitrogen Balance (Triple)
- Kidneys regulate water balance, filter blood, reabsorb useful substances, and remove urea (from ammonia).
- ADH hormone controls water reabsorption; dialysis is needed if kidneys fail.
- Negative feedback maintains internal balance.
Reproduction and Menstrual Cycle
- FSH matures eggs; estrogen thickens uterus and inhibits FSH; LH triggers ovulation; progesterone maintains lining.
- Contraception methods: pills, injections, implants, barriers, IUD, abstinence, surgical intervention.
- IVF uses eggs and sperm fertilized outside and implanted into uterus for pregnancy.
Plant Hormones (Triple)
- Gibberellins trigger germination; ethene induces fruit ripening; auxins control growth direction (phototropism/geotropism).
Inheritance and Evolution
- Meiosis creates gametes with genetic variation; asexual reproduction makes clones.
- Genome: all DNA in an organism; gene: DNA coding for a protein; genotype: genetic code; phenotype: expressed traits.
- Dominant/recessive alleles determine traits; Punnett squares predict inheritance.
- Sex determined by XX (female) or XY (male) chromosomes.
- Natural selection and variation explained by Darwin; bacterial resistance as evidence.
- Genetic engineering modifies organisms for desired traits; selective breeding enhances features.
Ecology
- Abiotic factors: non-living (light, temp, soil); biotic: living (food, predators).
- Quadrats and transects sample populations/distribution.
- Food chains show energy/biomass flow; trophic levels: producers, consumers, apex predators.
- Carbon, water, and decay cycles recycle materials.
- Biodiversity increases stability; human activities (deforestation, pollution) reduce biodiversity.
- Biomass pyramids show energy loss at each trophic level.
- Food security needs efficient farming, sustainable fishing.
Key Terms & Definitions
- Homeostasis — regulation of internal conditions.
- Neuron — nerve cell transmitting electrical signals.
- Hormone — chemical messenger in the blood.
- Negative Feedback — system returns conditions to normal.
- Allele — different forms of a gene.
- Genotype — genetic makeup.
- Phenotype — physical expression of genes.
- Ecosystem — community of organisms and their environment.
- Biodiversity — variety of life in an ecosystem.
Action Items / Next Steps
- Review and practice drawing Punnett squares and biomass pyramids.
- Ensure understanding of hormone roles and feedback mechanisms.
- Prepare example answers for reflex arcs, inheritance, and food chains.
- Triple students: revisit plant hormones, kidney function, and cloning methods.