Learning focus
Use precise biological vocabulary, interpret diagrams and data, explain mechanisms as linked sequences, and evaluate biological applications and environmental decisions.
External digestion
Fungi and bacteria secrete enzymes onto dead organic material and waste. The enzymes hydrolyse large molecules into small soluble products, which are absorbed. This is decomposition.
Nutrient recycling
Decomposition releases mineral ions and returns elements to soil and atmosphere. Plants reuse these nutrients, preventing them remaining locked in dead matter. Decomposers therefore support future productivity.
Respiration
Decomposers use absorbed organic substances in respiration and release carbon dioxide. Their aerobic respiration also consumes oxygen, which is important in eutrophication.
Factors affecting rate
Warm, moist and oxygenated conditions often speed decomposition because they support enzyme activity and microbial growth. Very dry, cold or anaerobic conditions slow the process and can preserve organic material.
Practical or data skill
Investigate decomposition using identical plant material under different temperature or moisture conditions, using mass change or visible decay.
Examination tip
Decomposers are organisms; decomposition is the process they carry out.
Review questions and suggested answers
Question 1
How do fungi obtain nutrients from dead material?
Suggested answer
They secrete enzymes and absorb soluble products.
Question 2
Why are decomposers important?
Suggested answer
They recycle nutrients.
Question 3
Why can decomposition lower oxygen in water?
Suggested answer
Decomposers use oxygen in aerobic respiration.
