AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
Students should be able to explain the role of microorganisms in cycling…
Full specification wording
How materials are cycled: Students should be able to explain the role of microorganisms in cycling materials through an ecosystem by returning carbon to the atmosphere as carbon dioxide and mineral ions to the soil.
Microorganisms such as bacteria and fungi act as decomposers.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 5 of 5
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Microorganisms such as bacteria and fungi act as decomposers. They break down dead organisms, fallen leaves and animal waste, digesting the complex organic compounds and absorbing nutrients. During aerobic respiration, decomposers release carbon dioxide back to the atmosphere, so carbon is recycled for photosynthesis. As they break down material, mineral ions such as nitrate, phosphate and potassium ions are released into the soil. These ions are then taken up by plant roots and used to make proteins, DNA and other compounds, so they re-enter food chains. In this way microorganisms link dead material back to living plants and the atmosphere, preventing carbon and minerals from being locked up permanently in dead matter.
What earns the marks
- Microorganisms such as bacteria and fungi act as decomposers on dead organisms, waste and fallen leaves.
- Decomposers digest and absorb nutrients from dead material, breaking down complex organic compounds.
- Respiration by microorganisms releases carbon dioxide to the atmosphere, recycling carbon for photosynthesis.
- Decomposition releases mineral ions such as nitrate and phosphate into the soil, where plant roots can absorb them.
- The recycled carbon dioxide and mineral ions are reused by plants, so materials continue to cycle through the ecosystem.
Common mistakes and how to put them right
Saying microorganisms return carbon to the soil as carbon dioxide.
Put it right: Carbon dioxide is released to the atmosphere, while mineral ions remain in the soil.
Confusing decomposers with producers.
Put it right: Decomposers break down dead material, whereas producers make their own food by photosynthesis.
Stating that microorganisms create new mineral ions.
Put it right: They release mineral ions already present in dead material.
Exam tips
- Separate the two products clearly: carbon dioxide goes to the atmosphere, mineral ions go into the soil.
- Name at least one mineral ion, such as nitrate or phosphate, to show precise knowledge.
- Link decomposition to respiration so the carbon return is explained as a biological process, not just decay.
Try the lesson
The start of the How materials are cycled: Students should be able to explain the role of microorganisms in cycling materials through an ecosystem by returning carbon to the atmosphere as carbon dioxide and mineral ions to the soil. lesson, made from checked teaching notes for this specification point.
Have a go first
Which gas is released into the atmosphere by microorganisms as they aerobically break down dead plant material?
Listen
Microorganisms such as bacteria and fungi act as decomposers. They break down dead organisms, fallen leaves and animal waste, digesting the complex organic compounds and absorbing nutrients. During aerobic respiration, decomposers release carbon dioxide back to the atmosphere, so carbon is recycled for photosynthesis. As they break down material, mineral ions such as nitrate, phosphate and potassium ions are released into the soil. These ions are then taken up by plant roots and used to make proteins, DNA and other compounds, so they re-enter food chains. In this way microorganisms link dead material back to living plants and the atmosphere, preventing carbon and minerals from being locked up permanently in dead matter. A strong answer earns marks for these points. Microorganisms such as bacteria and fungi act as decomposers on dead organisms, waste and fallen leaves. Decomposers digest and absorb nutrients from dead material, breaking down complex organic compounds. Respiration by microorganisms releases carbon dioxide to the atmosphere, recycling carbon for photosynthesis. Decomposition releases mineral ions such as nitrate and phosphate into the soil, where plant roots can absorb them. A common slip: Saying microorganisms return carbon to the soil as carbon dioxide. Instead, carbon dioxide is released to the atmosphere, while mineral ions remain in the soil. Exam tip: Separate the two products clearly: carbon dioxide goes to the atmosphere, mineral ions go into the soil.
Key words
Say what each word means before you turn the card.
Decomposition
Try answering aloud or in your head before turning the card.
Microorganisms and nutrient cycling
Try answering aloud or in your head before turning the card.
Respiration and carbon return
Try answering aloud or in your head before turning the card.
Mineral ions and plant nutrition
Try answering aloud or in your head before turning the card.
See every definition
- Decomposition
- The breaking down of dead organisms, fallen leaves and animal waste by microorganisms such as bacteria and fungi, which digest complex organic compounds and absorb nutrients.
- Microorganisms and nutrient cycling
- Bacteria and fungi act as decomposers, releasing carbon dioxide to the atmosphere and mineral ions to the soil so that materials continue to cycle through the ecosystem.
- Respiration and carbon return
- During aerobic respiration, decomposers release carbon dioxide back to the atmosphere, so carbon is recycled for photosynthesis.
- Mineral ions and plant nutrition
- Mineral ions such as nitrate, phosphate and potassium ions are released into the soil and taken up by plant roots to make proteins, DNA and other compounds.
There is more to this lesson
The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Test your understanding of How materials are cycled: Students should be able to explain the role of microorganisms in cycling materials through an ecosystem by returning carbon to the atmosphere as carbon dioxide and mineral ions to the soil.
Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge