Explain how the structural and behavioural adaptations of a named desert mammal help it to maintain water balance.

IB DP Biology Standard Level (2023 syllabus) — B4.1 Adaptation to environment · Explain · 4 marks · View as Markdown

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

Desert mammals face extreme heat and scarce water, yet many species thrive in arid environments through a suite of integrated adaptations.

Model answer (4 marks)

The kangaroo rat is a desert rodent that survives on very little water.
1. It has highly efficient kidneys that produce very concentrated urine, so only a small amount of water is lost in excretion.
2. It is nocturnal, being active at night when temperatures are lower and humidity is higher.
3. The reduced daytime activity means it avoids the hot, dry air that would otherwise cause evaporative loss through panting and sweating.
4. Together, the concentrated urine and nocturnal behaviour minimise water loss, allowing the kangaroo rat to maintain its water balance in an arid environment.

Examiner tips

State the animal first, then give one structural and one behavioural adaptation, linking each to water conservation.
Explain how the two adaptations complement each other – e.g. less activity reduces evaporative loss.
Use specific terms: ‘highly efficient kidneys’, ‘concentrated urine’, ‘nocturnal’, ‘evaporative loss’.
Keep answer to 4 points – one per mark.

Common mistakes

Failing to name a specific desert mammal; using a generic term like ‘desert animal’. Not linking the adaptation to water balance – e.g. saying ‘nocturnal’ without explaining reduced evaporative loss. Using vague language such as ‘good at saving water’ instead of specific mechanisms like ‘concentrated urine’.

Mark scheme (4 marks)

Named desert mammal stated (e.g. kangaroo rat, fennec fox, camel, jerboa)
Structural adaptation identified AND linked to reducing water loss or conserving water — e.g. highly efficient kidneys produce concentrated urine, reducing water lost in excretion; or nasal countercurrent cooling recovers water vapour from exhaled air
Behavioural adaptation identified AND linked to reducing water loss or conserving water — e.g. nocturnal/crepuscular activity avoids peak heat, reducing evaporative water loss through sweating and panting
Explanation of how the two adaptations work together / are complementary to maintain water balance, or a mechanistic explanation of why reduced activity reduces evaporative loss (e.g. lower body temperature means less sweating / panting, so less water lost through evaporation from skin and respiratory surfaces)

Key terms in this question

water balance · behavioural adaptation