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Homeostasis: Question 1

Syllabus 14.1

Multiple choice A2 1 mark

A person exercises vigorously in a warm room, and their core body temperature rises above its normal set point of about 37°C. Within a few minutes, thermoreceptors detect this change, and a response is triggered that begins to lower the core body temperature back towards the set point.

Which statement correctly explains why this response is an example of negative feedback, and correctly identifies the receptors and effectors involved?

Choose an answer to check it, then compare with the worked solution below.
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Worked solution

Step 1: Recall what negative feedback means

Negative feedback is a control mechanism in which a change away from a set point triggers a response that acts in the opposite direction to the original change, correcting it and returning the system towards the set point. This is different from positive feedback, in which a response would amplify the original change and move the system further from the set point.

Step 2: Recall the roles of receptors, coordination and effectors

In any homeostatic control system:

  • Receptors detect the deviation from the set point (here, thermoreceptors in the skin and hypothalamus detecting the rise in temperature).
  • A coordination system (here, the hypothalamus acting as the coordination centre) processes this information and sends signals to the structures that will bring about a response.
  • Effectors are the structures that carry out the actual response (here, sweat glands, which increase sweat secretion and therefore evaporative cooling, and the smooth muscle in the walls of skin arterioles, which relaxes to cause vasodilation and so increases heat loss by radiation and convection from the skin surface).

Step 3: Apply this to the rise in core temperature

Because core temperature has risen above the set point, the correct response must increase heat loss so that temperature falls back towards 37°C. Increased sweating and vasodilation of skin blood vessels both increase heat loss from the body, so they act in the opposite direction to the original rise. This is exactly what negative feedback means, and it is the sweat glands and skin arteriole smooth muscle that are the effectors, not the hypothalamus (which coordinates) or the thermoreceptors (which detect the change).

Step 4: Evaluate each option

  • A: correct. Heat loss increases, opposing the original rise, and the effectors (sweat glands, skin arteriole smooth muscle) are correctly identified as distinct from the coordinating hypothalamus and the detecting thermoreceptors.
  • B: incorrect. Thermoreceptors are receptors, not effectors, and the hypothalamus does play an essential coordinating role; without it, the thermoreceptors could not bring about a coordinated response.
  • C: incorrect, increased heat loss reduces core temperature back towards the set point; it does not cause a further rise, so this is not positive feedback.
  • D: incorrect. This describes vasoconstriction and stopped sweating, which are the responses to a fall in temperature (heat conservation), not the responses needed when temperature has risen; the hypothalamus also coordinates rather than acting as an effector itself.

Final answer

  • The response is negative feedback because increased sweating and vasodilation increase heat loss, opposing the original rise in temperature and restoring the set point; the sweat glands and skin arteriole smooth muscle are the effectors, option A.