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A2 · Practice questions · Principles of homeostasis

Stimulus, receptor, reverse.

Six original Cambridge-style questions on the principles of homeostasis in mammals, from defining the term to explaining a negative feedback loop.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Detect, coordinate, respond.

01
Recall
[2 marks]

Explain what is meant by homeostasis and name two factors that are controlled by homeostasis in mammals.

  • Homeostasis is the maintenance of a constant internal environment, keeping factors within narrow limits around a set point (despite changes inside or outside the body). ✓
  • Any two of: core body temperature, blood glucose concentration, water potential of the blood (also pH, carbon dioxide concentration). ✓
02
Explain
[3 marks]

Explain why it is important for a mammal to keep the water potential of its blood and tissue fluid constant.

  • If the tissue fluid has a lower water potential than the cells, cells lose water by osmosis and shrink / metabolism is disrupted. ✓
  • If the tissue fluid has a higher water potential, cells gain water by osmosis and swell (and may burst). ✓
  • Changes in water content alter the concentrations of solutes and enzymes in cells, so reactions do not run at a steady, efficient rate. ✓
03
Explain
[4 marks]

Using the example of a rise in core body temperature during exercise, explain the principle of negative feedback.

  • The rise above the set point (stimulus) is detected by thermoreceptors in the hypothalamus (and skin). ✓
  • The hypothalamus (coordinator) sends nerve impulses to effectors. ✓
  • Sweat glands secrete more sweat, which evaporates and removes heat; arterioles in the skin dilate so more blood flows near the surface and more heat is lost. ✓
  • Core temperature falls back towards the set point and the response then decreases: the response has reversed the original change. ✓
04
Recall
[2 marks]

Distinguish between an internal stimulus and an external stimulus, giving one example of each that could affect core temperature.

  • Internal: a change that originates inside the body, for example heat produced by respiration in contracting muscles / fever. ✓
  • External: a change in the surroundings, for example a fall in air temperature or swimming in cold water. ✓
05
Analysis
[3 marks]

A person's core temperature is recorded every minute. It rises from 37.0 °C to 37.6 °C over 10 minutes of hard exercise, then falls back to 37.1 °C over the next 15 minutes of rest. Describe and explain these results.

  • Temperature rises by 0.6 °C during exercise because heat is produced by respiration in muscles faster than it is lost. ✓
  • Receptors detect the rise and the hypothalamus increases sweating and vasodilation. ✓
  • During rest less heat is produced, so heat loss exceeds heat production and the temperature returns towards 37 °C (negative feedback); it does not return exactly, showing fluctuation around the set point. ✓
06
Explain
[3 marks]

Compare the ways in which the nervous system and the endocrine system coordinate homeostatic responses.

  • Nervous: electrical impulses along neurones (chemical at synapses); endocrine: hormones secreted into and carried by the blood. ✓
  • Nervous responses are rapid and short-lived; hormonal responses are slower to start and often last longer. ✓
  • Nervous signals reach specific effectors; hormones affect any target cells that have the specific receptors. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.