Unit 5: Homeostasis and response
AQA GCSE Biology Unit 5 common mistakes: homeostasis without the waffle
Unit 5 is where students often understand the idea, then lose marks because the exam wants precise biological wording. Annoying, yes. Fixable, also yes.
Quick takeaways
- Homeostasis answers need a stimulus (change), a receptor, a coordination centre, an effector, and a response.
- Do not mix up nervous and hormonal control. AQA notices.
- Diabetes, kidneys, and menstrual hormones reward sequence and precision.
- Plant hormone questions often test exact wording around auxin, light, gravity, and growth.
Mistake 1: saying "the body keeps it the same"
Homeostasis is the maintenance of a constant internal environment, but exam answers need more than a definition. A strong answer explains how a change is detected and corrected.
- Weak: the body cools down.
- Better: receptors detect increased temperature, the thermoregulatory centre coordinates a response, sweat glands produce more sweat, and evaporation transfers energy from the skin.
- Best: add vasodilation if the question is about blood vessels near the skin.
AQA evidence
AQA mark schemes reward the sequence of detection, coordination and response. Vague effect words are not enough: name the receptor, coordination centre, effector and specific response.
Mistake 2: treating reflex arcs like a loose sequence
The reflex arc has a sequence. Stimulus, receptor, sensory neurone, relay neurone, motor neurone, effector, response. If those words are in the wrong order, the answer becomes much harder to credit.
Quick fix
Practise explaining why reflexes are useful: they are rapid, automatic responses that reduce damage because they do not require conscious thought before the response happens.
Mistake 3: mixing up insulin, glucagon, and glycogen
This is a classic. Insulin and glucagon are hormones. Glycogen is the storage carbohydrate in liver and muscle cells. One is a message. One is a stored substance.
- High blood glucose: pancreas releases insulin, cells take in glucose, liver and muscle cells convert glucose to glycogen.
- Low blood glucose: pancreas releases glucagon, liver cells convert glycogen back to glucose, glucose is released into the blood.
- Type 1 diabetes: the pancreas produces little or no insulin, so blood glucose is controlled with insulin injections plus diet and exercise.
Mistake 4: writing kidney answers as if more detail must be better
AQA GCSE Biology does not need A-level kidney anatomy. The useful GCSE model is filtration, selective reabsorption, urea removal, and water control by ADH. Keep it sharp.
- Urea is made from excess amino acids in the liver, then removed by the kidneys.
- Useful substances such as glucose are selectively reabsorbed back into the blood.
- ADH controls how much water is reabsorbed, which changes the volume and concentration of urine.
Mistake 5: learning menstrual hormones as a list, not a sequence
For menstrual cycle questions, learn each hormone by job. FSH matures the egg and stimulates oestrogen. Oestrogen rebuilds the uterus lining and stimulates LH. LH triggers ovulation. Progesterone maintains the uterus lining.
Exam habit
If a question gives a graph, describe the hormone pattern with data first, then explain the biological effect. The graph is there to be used.
Mistake 6: plant hormones without direction
Auxin questions often ask about light or gravity. Say where auxin moves, how it affects cell elongation, and what that does to the direction of growth. "The plant bends towards the light" is a start, not a full answer.
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