Covers stimulus-response pathways, negative and positive feedback, thermoregulation, glucose regulation, water balance, and plant homeostasis.
Focus on how organisms maintain internal balance through receptors, control centres and effectors. Key ideas include tolerance ranges, endotherm and ectotherm adaptations, insulin and glucagon, ADH and aldosterone, nephron water reabsorption, and plant stomatal responses.
1. Which sequence correctly represents the stimulus-response model in homeostasis?
2. Negative feedback is best described as:
3. Which adaptation directly increases heat loss in an endotherm?
4. When blood glucose falls, which hormone-response pair is correct?
5. Increased blood osmolarity is most likely to lead to:
6. Which plant feature is most useful for reducing transpiration in a dry environment?
MC Answers: 1-B, 2-C, 3-A, 4-D, 5-B, 6-C
SA1: After a meal, rising blood glucose is detected by beta cells in the pancreas. These cells act as receptors and the control centre, releasing insulin. Insulin increases glucose uptake by body cells and stimulates the liver and muscles to convert glucose to glycogen. As blood glucose falls back toward the normal range, insulin secretion decreases, showing negative feedback.
SA2: A negative feedback example is blood glucose regulation, where a rise in glucose triggers insulin release to lower the variable back toward normal. A positive feedback example is labour, where cervical stretching triggers oxytocin release, increasing uterine contractions and causing more stretching. Negative feedback opposes change, while positive feedback amplifies it until the event is complete.
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