Chemical Coordination, Homeostasis and Animal Behaviour
What the exam tests
Chemical coordination, homeostasis, and animal behaviour test endocrine glands, hormone actions, feedback loops, thermoregulation, osmoregulation, blood glucose regulation, and types of behaviour.
Core rules
- The hypothalamus controls the pituitary; the anterior pituitary secretes FSH, LH, TSH, ACTH, GH, and prolactin. The posterior pituitary releases ADH and oxytocin.
- Thyroid hormones regulate metabolism; parathyroid hormone raises blood Ca2+; calcitonin lowers it. Adrenal medulla secretes adrenaline; adrenal cortex secretes cortisol and aldosterone. Pancreatic islets secrete insulin (beta cells) and glucagon (alpha cells).
- Negative feedback maintains homeostasis; positive feedback amplifies a change (e.g., oxytocin during childbirth).
- Behaviour includes innate (instinct, taxis, kinesis) and learned (habituation, conditioning, imprinting) types. Communication can be visual, auditory, chemical, or tactile.
Worked example
After a carbohydrate-rich meal, blood glucose rises. Beta cells of the pancreas secrete insulin, which promotes glucose uptake by cells and glycogen synthesis in the liver. Blood glucose falls toward the set point. If blood glucose falls too low, alpha cells secrete glucagon, which promotes glycogen breakdown and gluconeogenesis. Reasoning: this is negative feedback because the response reverses the initial change.
Traps
Do not confuse insulin (lowers glucose) with glucagon (raises glucose). ADH is released from the posterior pituitary but made in the hypothalamus. Thyroid hormone is not the same as TSH. Taxis is directed movement toward or away from a stimulus; kinesis is nondirectional. Imprinting occurs during a critical period.