What is a nutrient cycle?
Unlike energy, which flows one way and is lost as heat, nutrients are recycled. A nutrient cycle is the movement of materials such as carbon, oxygen and water between living things and the environment. These materials are used over and over, keeping the ecosystem in balance.
The carbon cycle
Carbon moves between the air, living things and the soil.
- Plants take in carbon dioxide from the air during photosynthesis.
- Animals and plants release carbon dioxide during respiration.
- Burning fuels and the action of decomposers also release carbon dioxide.
Key idea
Photosynthesis removes carbon dioxide from the air, while respiration, decay and burning add it back. This keeps the amount of carbon dioxide balanced.
The water cycle
Water also moves in a cycle. The Sun heats water in oceans and rivers, turning it into vapour by evaporation. The vapour rises, cools and forms clouds by condensation, then falls again as rain during precipitation. This water returns to rivers and seas, and the cycle repeats.
Example
Rain that falls on a hill flows into a river, evaporates from the sea, forms clouds and falls again — the same water is reused many times.
Remember
- Energy flows one way; nutrients are recycled.
- Photosynthesis removes CO₂; respiration and decay add it.
- Water cycle: evaporation → condensation → precipitation.