The Carbon and Water Cycles

All the elements that make up the bodies of living organisms are recycled. When organisms die, their bodies are broken down by decomposers and the elements are returned to the soil, water and atmosphere, ready to be used again. Two of the most important cycles are the carbon cycle and the water cycle. This lesson covers both in detail for AQA GCSE Biology.

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Why Are Nutrient Cycles Important?

Living organisms need a range of elements to build their bodies:

Element	What It Is Used For
Carbon	Found in all organic molecules: carbohydrates, lipids, proteins, DNA
Nitrogen	Essential for amino acids (proteins) and nucleic acids (DNA, RNA)
Hydrogen	Component of water and organic molecules
Oxygen	Used in respiration; component of water and organic molecules
Phosphorus	Found in DNA, RNA and ATP (adenosine triphosphate)

These elements are finite — there is a fixed amount on Earth. They must be constantly recycled between living organisms and the environment. Without this recycling, life would eventually run out of the raw materials it needs.