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Paper 2
Homeostasis and Response
Both
Insulin and glucagon work as a feedback loop.
Key Facts
- Homeostasis keeps internal conditions stable.
- Thermoregulation uses sweating, shivering, and blood flow changes.
- ADH release increases when the body is dehydrated.
- Auxin moves to the shaded side of a shoot.
Topics Covered
Nervous System
What you need to know
- •Reflexes are rapid, automatic responses.
- •A reflex arc: receptor -> sensory neuron -> relay -> motor -> effector.
Exam Tips
- List the order of the reflex arc in full for 4-6 marks.
Hormonal Control
What you need to know
- •Insulin lowers blood glucose; glucagon raises it.
- •Hormones are chemical messengers carried in the blood.
Exam Tips
- Use negative feedback in longer answers.
Kidneys and Osmoregulation
What you need to know
- •Kidneys filter the blood and reabsorb needed substances.
- •ADH controls how much water is reabsorbed.
Exam Tips
- Mention ADH and the collecting ducts for 4-6 mark answers.
Plant Hormones and Tropisms
What you need to know
- •Auxin controls growth responses to light and gravity.
- •Higher auxin concentration causes cells to elongate more.
Exam Tips
- Use phototropism and gravitropism terms.
Key Terms
Homeostasis
Regulation of internal conditions to maintain optimum function.
Negative feedback
Responses reduce the change and return to a set point.
ADH
A hormone that controls water reabsorption in kidneys.
Tropism
A growth response in plants to a stimulus.
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Common Exam Questions
Explain how the body cools down when temperature rises.
4 marksmediumPaper 2
Model Answer
Sweating increases evaporation to remove heat and blood vessels in the skin dilate to increase heat loss.
What examiners want to see
- ✓Mention sweating and evaporation.
- ✓Mention vasodilation.
Explain how ADH helps control water levels.
3 marksmediumPaper 2
Model Answer
ADH makes kidney tubules more permeable so more water is reabsorbed into the blood, reducing water loss in urine.
What examiners want to see
- ✓Mention ADH.
- ✓Link to increased water reabsorption.
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