Explain how water is cycled between the environment and living organisms.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Water evaporates from oceans, lakes, rivers and land surfaces, forming water vapour.
The vapour rises, cools and condenses into cloud droplets, which fall back to the Earth as precipitation (rain or snow).
Plants absorb water from the soil through their roots and transport it to leaves.
Through stomata in leaves, plants release water vapour to the atmosphere by transpiration.
Animals obtain water by drinking or eating food, and return water to the environment via respiration, excretion and sweating.
The vapour rises, cools and condenses into cloud droplets, which fall back to the Earth as precipitation (rain or snow).
Plants absorb water from the soil through their roots and transport it to leaves.
Through stomata in leaves, plants release water vapour to the atmosphere by transpiration.
Animals obtain water by drinking or eating food, and return water to the environment via respiration, excretion and sweating.
Examiner tips
- Use the sequence: evaporation → condensation → precipitation → uptake by plants → transpiration → animal water intake and loss
- Mention key organs/structures: roots, stomata, lungs, kidneys
Common mistakes
- Confusing evaporation with transpiration, or omitting the role of plants
- Failing to mention the return of water to the atmosphere by animals
Mark scheme (5 marks)
- Water evaporates from the surface of oceans / lakes / rivers / land (evaporation)
- Water vapour condenses to form clouds and falls as precipitation / rain / snow
- Plants absorb water from the soil through their roots
- Plants lose water vapour to the atmosphere by transpiration (through stomata / leaves)
- Animals obtain water by drinking / eating food, and return water to the atmosphere / environment through respiration / excretion / sweating
Related
- All AQA A-Level Biology (7402) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →