AQA Biology Paper 2

Topics Covered

1. Homeostasis and Response
2. Inheritance, Variation, and Evolution
3. Ecology

Homeostasis and Response

Regulation of Internal Conditions

• Homeostasis: Maintains optimal conditions for enzyme actions and cell functions.
• Regulated Factors: Blood glucose concentration, body temperature, water levels.

Nervous System

• CNS: Central Nervous System (brain and spinal cord).
• PNS: Peripheral Nervous System (nerves throughout the body).
• Reflex Arc: Faster responses bypass the brain and travel from sensory to motor neurons.
• Neurotransmitters: Chemicals that transmit signals across synapses.

Reaction Time Investigation

• Experiment: Dropping a ruler to measure reaction times.
• Variables: Stimulants (like coffee) and depressants to test reaction time changes.

Brain Structure and Function

• Cerebral Cortex: Memory, speech, problem-solving.
• Cerebellum: Motor skills, balance, and coordination.
• Medulla Oblongata: Unconscious actions like heart and breathing rates.

Eye Function

• Accommodation: Eye adjusts lens shape to focus light on the retina.
• Parts of the Eye: Pupil, Cornea, Iris, Retina, Rod and Cone Cells, Optic Nerve.
• Vision Issues: Myopia (short-sightedness) and Hyperopia (long-sightedness).

Thermoregulation

• Body Temperature Control: Sweating, vasodilation, and vasoconstriction.
• Adaptive Reactions: Shivering to produce heat.

Endocrine System

• Hormones: Chemical messengers in the body, slower than nervous signals.
• Key Glands & Hormones:
  • Pituitary Gland (Master gland)
  • Pancreas (Insulin and Glucagon)
  • Adrenal Glands (Adrenaline)
  • Thyroid Gland (Thyroxin)
  • Ovaries/Testes (Sex hormones)

Hormonal Control of Blood Glucose

• Insulin: Lowers blood glucose by converting glucose to glycogen.
• Glucagon: Raises blood glucose by converting glycogen back to glucose.
• Diabetes Types:
  • Type 1: No insulin production, requires injections.
  • Type 2: Cells resistant to insulin, managed by diet.

Reproduction

• Menstruation:
  • FSH: Matures eggs.
  • Estrogen: Thickens uterine lining, inhibits FSH, stimulates LH.
  • LH: Causes egg release.
  • Progesterone: Maintains uterine lining.
• Contraception: Pills, injections, implants, barriers, IUDs, timing, surgical methods.
• IVF: Fertilization in lab, insertion of embryos, low success rate, risk of multiple births.

Negative Feedback

• Concept: Body's mechanism to maintain homeostasis.
• Examples: Thyroxin regulation, ADH for water balance.

Inheritance, Variation, and Evolution

Genetic Basics

• Genome: All genetic material in an organism.
• DNA: Two-stranded polymer in a double helix shape.
• Genes: Code for specific proteins.
• Human Genome Project: Mapped out all human genes.

Meiosis vs. Mitosis

• Meiosis: Produces genetically diverse sex cells (gametes).
• Mitosis: Produces identical daughter cells for growth and repair.

Dominant and Recessive Alleles

• Alleles: Different versions of a gene.
• Dominant Alleles: Expressed if present.
• Recessive Alleles: Expressed only if both alleles are recessive.
• Punnett Squares: Used to predict inheritance patterns.

Inherited Disorders

• Examples: Polydactyly (dominant), Cystic Fibrosis (recessive).
• Sex Chromosomes: XX (female), XY (male).

Evolution

• Theory of Evolution: Random variations, survival of the fittest.
• Epigenetics: Gene expression influenced by the environment.
• Evidence: Bacterial resistance to antibiotics.

Selective Breeding and Genetic Engineering

• Selective Breeding: Breeding for desired traits.
• Genetic Engineering:
  • Process: Gene extraction, insertion into vectors, organism modification.
  • Examples: GM crops like golden rice, insulin-producing bacteria.

Cloning

• Plant Cloning: Cuttings or tissue culture.
• Animal Cloning: Embryo splitting, nucleus transfer.

Ecology

Ecosystem Interactions

• Competition: For resources like food, water, space.
• Interdependence: Organisms relying on each other.

Factors Influencing Ecosystems

• Abiotic Factors: Non-living (light, temperature, soil pH).
• Biotic Factors: Living (predators, pathogens).

Sampling Techniques

• Quadrats and Transects: Estimate population sizes and distributions.

Food Chains and Trophic Levels

• Producers: Create biomass from sunlight.
• Consumers: Herbivores, omnivores, carnivores.
• Apex Predators: Top of the food chain, no natural predators.

Nutrient Cycles

• Carbon Cycle: Recycles carbon through respiration, photosynthesis, decomposition.
• Water Cycle: Precipitation, runoff, evaporation.

Human Impact on Biodiversity

• Deforestation and Land Use: Reduces biodiversity.
• Waste and Pollution: Affects ecosystems and climate.
• Conservation Efforts: Sustainable farming and fishing practices.

Food Security

• Challenges: Increasing population, diet changes, conflict.
• Solutions: Sustainable agriculture, reducing biomass loss.