Overview
This lecture reviews key concepts from AQA GCSE Biology Paper 2, focusing on homeostasis, the nervous and endocrine systems, kidneys, reproductive biology, and plant hormones.
Homeostasis and the Nervous System
- Homeostasis is maintaining a constant internal environment.
- A stimulus is a change in the environment needing a response.
- Receptors detect stimuli; effectors (muscles/glands) bring about a response.
- The central nervous system (CNS) consists of the brain and spinal cord.
- Sensory neurones carry information from receptors to CNS; relay neurones link sensory to motor neurones; motor neurones carry signals from CNS to effectors.
- Synapses are gaps between neurones where neurotransmitters transmit signals.
- Reflex arc: stimulus → receptor → sensory neurone → CNS (relay neurone) → motor neurone → effector → response.
- The brain has regions: cerebral cortex (consciousness/memory), medulla (unconscious activities), cerebellum (movement/balance), hypothalamus (homeostasis), pituitary gland (hormones).
Temperature and Blood Glucose Regulation
- The thermoregulatory centre near the hypothalamus monitors blood temperature.
- Responses to lower temperature: hairs stand up, shivering, vasoconstriction.
- Responses to higher temperature: hairs lie flat, sweating, vasodilation.
- Blood glucose is regulated by the pancreas with insulin (lowers glucose) and glucagon (raises glucose).
- Type I diabetes = little/no insulin; treated with insulin injections and diet.
- Type II diabetes = insulin resistance; treated with diet and exercise.
Kidneys and Osmoregulation
- Kidneys filter blood, removing urea, water, and ions; reabsorb glucose, water, and ions.
- Deamination in the liver produces ammonia (toxic), converted to urea.
- ADH controls water reabsorption in the kidneys: more ADH = more water reabsorbed.
- Dialysis and kidney transplants treat kidney failure.
Reproduction and Hormones
- Menstrual cycle has four stages: menstruation, lining builds up, ovulation, wall maintained/breakdown.
- FSH matures eggs; oestrogen rebuilds lining, stimulates LH, inhibits FSH; LH triggers ovulation; progesterone maintains lining, inhibits LH/FSH.
- Contraception methods include pills (oestrogen/progesterone), barrier methods (condoms, diaphragm), IUDs, and sterilisation.
- IVF uses FSH/LH to mature eggs, fertilisation in lab, embryo implanted in uterus.
Eye Structure and Function
- Sclera (support), cornea (refracts light), iris (controls pupil), retina (receptors), lens (focus), ciliary muscles/suspensory ligaments (lens shape), optic nerve (to brain).
- Bright light: circular muscles contract, pupil smaller; dim light: radial muscles contract, pupil widens.
- Accommodation: lens changes shape for focus.
- Hypermyopia (long-sightedness): can't focus near, treat with convex lens.
- Myopia (short-sightedness): can't focus far, treat with concave lens.
Plant Hormones
- Auxin promotes growth in shoots, inhibits in roots; controls phototropism and gravitropism.
- Ethene ripens fruit; gibberellin stimulates germination and growth.
- Selective weedkillers use auxin to kill broad-leafed plants.
Key Terms & Definitions
- Homeostasis — maintenance of stable internal conditions.
- Neuron — nerve cell carrying electrical impulses.
- Effector — muscle/gland acting in response to stimulus.
- Hormone — chemical messenger in blood.
- Insulin — hormone reducing blood glucose.
- Glucagon — hormone raising blood glucose.
- ADH — hormone controlling kidney water reabsorption.
- FSH/LH — hormones regulating menstrual cycle.
- Auxin — plant growth hormone.
- Phototropism — plant growth towards light.
Action Items / Next Steps
- Review diagrams of reflex arcs, kidney function, menstrual cycle, and eye anatomy.
- Practise applying homeostasis concepts to exam scenarios.
- Complete all assigned textbook/revision questions on today’s topics.