Overview
This lecture covers how the human body and plants use homeostasis, nervous and hormonal systems for internal regulation, response, and reproduction. Key biological processes and practical activities are discussed.
Homeostasis
- Homeostasis maintains stable internal conditions (temperature, pH, glucose, water) for optimal cell and enzyme function.
- Control systems use receptors (detect changes), coordination centres (process info), and effectors (restore balance).
The Human Nervous System
- The nervous system allows quick reactions and behavior coordination via electrical impulses along neurones.
- The CNS (brain and spinal cord) coordinates responses from effectors (muscles/glands).
- Reflex arcs provide automatic, rapid responses without conscious thought, involving sensory, relay, and motor neurones.
- Practical: Investigate how factors affect human reaction time.
The Brain (Biology Only)
- The brain controls complex behaviors using regions: cerebral cortex, cerebellum, and medulla, each with distinct functions.
- Brain investigation is challenging due to its complexity and potential risks (HT only).
The Eye (Biology Only)
- Eye structures (retina, optic nerve, sclera, cornea, iris, ciliary muscles, suspensory ligaments) relate to focusing and adaptation.
- Accommodation adjusts lens shape to focus on near or distant objects.
- Myopia and hyperopia are vision defects corrected with lenses, surgery, or contact lenses.
Control of Body Temperature (Biology Only)
- The thermoregulatory centre in the brain monitors blood temperature using receptors in the skin and brain.
- High temperature: vasodilation and sweating cool the body; low temperature: vasoconstriction, shivering, reduced sweating warm the body.
Hormonal Coordination in Humans
- The endocrine system uses glands to secrete hormones into the bloodstream for slower, longer-lasting effects.
- Major glands: pituitary, pancreas, thyroid, adrenal, ovaries, testes.
Control of Blood Glucose
- The pancreas uses insulin to lower blood glucose and glucagon (HT only) to raise it via negative feedback.
- Type 1 diabetes: lack of insulin, treated with injections; Type 2: insulin resistance, managed with diet/exercise; obesity increases risk.
Water and Nitrogen Balance (Biology Only)
- Water and ions lost through lungs, skin, and kidneys; kidneys control balance by filtering blood and producing urine.
- ADH hormone (HT only) increases kidney tubule permeability for water reabsorption.
- Kidney failure treated with dialysis or transplants.
Hormones in Human Reproduction
- Oestrogen (female) and testosterone (male) trigger puberty and gamete production.
- Menstrual cycle controlled by FSH (egg maturation), LH (egg release), oestrogen and progesterone (uterus lining).
Contraception
- Hormonal and non-hormonal methods include pills, injections, implants, patches, barriers, IUDs, spermicides, timing, sterilization.
- Ethical, social, and economic issues influence contraception choices.
Hormones for Treating Infertility (HT Only)
- Fertility drugs and IVF use FSH and LH to stimulate egg release and fertilization outside the body.
- IVF is stressful and has risks including multiple births.
Feedback Systems (HT Only)
- Adrenaline increases heart rate for "fight or flight"; thyroxine raises metabolic rate and is under negative feedback control.
Plant Hormones (Biology Only)
- Auxins control growth towards light (phototropism) and gravity (gravitropism).
- Gibberellins (HT only) start seed germination; ethene (HT only) controls fruit ripening.
- Practical: Investigate light/gravity effects on seedling growth.
Use of Plant Hormones (HT Only)
- Auxins used as weed killers, rooting powders, and in tissue culture.
- Ethene used for fruit ripening; gibberellins for seed dormancy, flowering, and fruit size.
Key Terms & Definitions
- Homeostasis — Regulation of internal conditions to maintain optimal cell function.
- CNS — Central Nervous System; includes brain and spinal cord.
- Reflex arc — Automatic neural pathway for rapid responses.
- Endocrine system — Glands secreting hormones for regulation.
- Insulin/Glucagon — Hormones regulating blood glucose.
- ADH — Antidiuretic hormone controlling water reabsorption in kidneys.
- FSH/LH — Hormones controlling reproductive cycles.
- Auxin — Plant hormone for growth response.
- IVF — In Vitro Fertilization; assisted reproductive technology.
Action Items / Next Steps
- Plan and conduct reaction time experiment (Required Practical 7).
- Investigate effect of light or gravity on seedling growth (Required Practical 8).
- Review diagrams of brain, eye, and hormone-producing glands.
- Prepare for data interpretation tasks (graphs, charts, tables) related to nervous and hormonal systems.