# Explain how phosphorus from the bodies of dead organisms is returned to the soil and then absorbed by living plants.

> AQA A-Level Biology (7402) — 3.5.4 Nutrient Cycles · Explain · 5 marks

> Phosphorus is an essential element for living organisms. It is found in biological molecules such as DNA and cell membranes. Unlike carbon, phosphorus does not have a gaseous phase in its cycle.

## Mark scheme (5 marks)

1. Decomposers (bacteria / fungi) break down the bodies of dead organisms
2. Decomposers release phosphorus (as phosphate ions / minerals) into the soil
3. Plants absorb (dissolved) mineral ions / phosphate ions through their roots
4. Active transport is used to absorb mineral ions against the concentration gradient
5. Phosphorus is used to make biological molecules / DNA / phospholipids (cell membranes)

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