QCE Biology — Unit 3
Homeostasis — Flashcards & Quiz
Homeostasis is the maintenance of a relatively stable internal environment and underpins QCE Biology Unit 3. You need to describe negative feedback loops using the stimulus-receptor-control centre-effector-response model, and apply the framework to specific examples such as thermoregulation, osmoregulation and glucose regulation. Strong responses name the hormones and organs involved and explain how they correct disturbances back toward the set point.
Key Points
- Homeostasis = relatively stable internal environment despite external change; "relatively" matters because variables oscillate around a set point.
- Negative feedback loop structure: stimulus → receptor → control centre → effector → response → return to set point.
- Thermoregulation: hypothalamus detects temperature change; effectors include sweat glands, vasodilation/constriction, and shivering.
- Glucose regulation: pancreatic β-cells release insulin when glucose is high; α-cells release glucagon when low.
- Osmoregulation: the hypothalamus triggers ADH release from the pituitary, which increases water reabsorption in kidney collecting ducts.
- Positive feedback is rare but exists — childbirth oxytocin, blood clotting; it amplifies the change rather than correcting it.
Common Mistakes to Avoid
- Saying homeostasis maintains a "constant" internal environment — it's RELATIVELY stable, not fixed.
- Confusing receptors (detect stimuli) with effectors (produce responses).
- Forgetting positive feedback exists — it's rare but examinable.
- Missing the role of the hypothalamus as the main integrator of thermoregulation and osmoregulation.
- Applying the same feedback loop diagram without adapting to the specific variable being regulated.
Exam Strategy
QCAA Unit 3 homeostasis questions give a disturbance (cold, dehydration, hyperglycaemia) and ask you to describe the corrective response. Structure your answer around the feedback loop: identify the stimulus, name the receptor, trace the signal to the control centre, list the effectors and their responses, and explain how the response returns the variable to the set point. Always use specific hormone and organ names — "the pancreas responds" scores less than "pancreatic β-cells secrete insulin, which binds receptors on liver and muscle cells to promote glucose uptake".
Revision Tip
Feedback loop diagrams are classic flashcard material — build a Revizi deck with one loop per variable (temperature, glucose, water, blood pressure) and practise filling in the receptor, effector and hormone fields from memory.
Last updated: March 2026