Overview
This lecture provides a comprehensive review of key topics in AQA Biology Paper 2, covering homeostasis, the nervous and endocrine systems, reproduction, genetics, evolution, and ecology, with exam-focused explanations and examples.
Homeostasis and Control Systems
- Homeostasis maintains optimal internal conditions (temperature, glucose, water) via the nervous and endocrine systems.
- Receptors detect stimuli, coordinators (brain/spinal cord/pancreas) process signals, and effectors (muscles/glands) trigger responses.
- The nervous system includes the CNS (brain and spinal cord) and peripheral nerves; transmits electrical impulses for rapid responses.
- Reflex actions are quick, involuntary responses involving sensory, relay, and motor neurons; synapses use chemicals to transmit signals.
- Reaction time can be measured using the ruler drop test; variables like sleep, caffeine, and distractions affect results.
Hormonal Coordination and Endocrine System
- The endocrine system uses glands to secrete hormones into the blood for slower, longer-lasting responses.
- Major glands: pituitary (master gland), adrenal (adrenaline), pancreas (insulin, glucagon), ovaries (estrogen, progesterone), testes (testosterone), thyroid (thyroxine).
- Insulin lowers high blood glucose by promoting glucose uptake/storage; glucagon raises low glucose by stimulating glycogen breakdown.
- Diabetes results from insulin production/reception problems; treated with insulin (Type 1) or diet/exercise/medication (Type 2).
- Water balance is controlled by ADH from the pituitary; kidneys filter blood and regulate urine via selective reabsorption and excretion.
- Kidney failure is treated with dialysis or transplantation.
Reproduction and Genetics
- Sexual reproduction (meiosis) produces genetically diverse gametes; asexual reproduction (mitosis) makes identical offspring.
- DNA is a double helix polymer; genes code for proteins; chromosomes carry genetic information.
- Alleles are gene variants; genotype is the allele combination; phenotype is the physical trait.
- Punnett squares predict inheritance; some disorders (cystic fibrosis, polydactyly) follow dominant/recessive patterns.
- Sex determination is by XX (female) or XY (male) chromosomes; 50% chance of either at fertilization.
Evolution, Variation, and Selective Breeding
- Evolution is the change in inherited traits over time via natural selection.
- Variation comes from mutations and gene-environment interaction.
- Selective breeding enhances desired traits but reduces genetic diversity and increases disease risk.
- Genetic engineering transfers genes between organisms for useful traits; GM crops and animals have benefits and risks.
Ecology and Ecosystems
- An ecosystem consists of living (biotic) and non-living (abiotic) components; populations, communities, and habitats interact.
- Competition for resources drives adaptation; abiotic and biotic factors affect organism distribution and population sizes.
- Adaptations can be structural, behavioral, or functional for survival in specific environments (e.g., extremophiles).
- Food chains/webs show energy transfer; only about 10% biomass passes up each trophic level.
- Sampling methods like quadrats and transects estimate population sizes and species distribution.
Human Impact and Biodiversity
- Pollution, habitat destruction, deforestation, and climate change reduce biodiversity and ecosystem stability.
- Sustainable practices include conservation, breeding programs, habitat protection, recycling, and reducing emissions.
- Intensive farming, overfishing, and use of biotechnological solutions (GMOs, microprotein) impact food security and environment.
Key Terms & Definitions
- Homeostasis — regulation of internal environment for optimal conditions.
- Reflex Arc — neural pathway for automatic responses.
- Hormone — chemical messenger transported in the blood.
- Insulin/Glucagon — hormones controlling blood glucose.
- Meiosis — cell division producing gametes with half chromosome number.
- Genotype/Phenotype — genetic makeup/observable characteristic.
- Natural Selection — process where best-adapted organisms survive and reproduce.
- Adaptation — feature enhancing survival in an environment.
- Biodiversity — variety of species in an ecosystem.
Action Items / Next Steps
- Make flashcards for key hormones, organs, genetic terms, and cycles.
- Review example questions on the provided website.
- Practice drawing and labeling diagrams (nervous system, eye, food webs).
- Complete predicted papers and detailed walkthroughs for exam preparation.