Explain why homeostasis is important for the body and describe two processes that the kidneys carry out as part of homeostasis.

Eduqas A-Level Biology — 3.7 Homeostasis and the kidney · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Homeostasis is the maintenance of a constant internal environment. The kidneys play a central role in homeostasis in humans.

Model answer (5 marks)

Homeostasis keeps the internal environment of the body within narrow, constant limits, so that cells and enzymes can function correctly and metabolic reactions occur at the proper rate.

The kidneys maintain homeostasis by 1) filtering the blood and removing waste products such as urea, and 2) regulating the water and ion content of the blood, for example by controlling the concentration of sodium and other salts.

Examiner tips

Use the exact phrases ‘keeps the internal environment within narrow limits’ and ‘so that cells and enzymes can function correctly’.
Show the two kidney functions as separate points and include examples (urea, sodium).

Common mistakes

Writing that homeostasis is ‘good for health’ without linking to cellular function; "keeping the body healthy" is too vague. "Kidneys produce urine" is acceptable but missing the specific processes of filtration and osmoregulation.

Mark scheme (5 marks)

Homeostasis keeps internal conditions within narrow/constant limits (accept: keeps conditions stable/balanced)
So that cells/enzymes function correctly / optimally (accept: so metabolic reactions can occur at the correct rate)
The kidneys filter the blood / remove waste products (e.g. urea) from the blood
The kidneys regulate/control the water content of the blood (osmoregulation)
The kidneys regulate ion/salt concentration of the blood (accept: control levels of ions such as sodium in the blood)

Key terms in this question

homeostasis