AQA Biology (8464) 4.7.2.2
Decomposition
Dead things rot away. Where do their carbon and their minerals go?
Combined Science · Higher tier
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A compost heap steams on a frosty morning.
The air is below 0 °C, but a thermometer pushed into the middle of the heap of garden waste reads over 50 °C. Nothing is on fire, and there is no heater.
If you had to guess, is the heat coming from sunshine soaked up in the day, or from living things inside the heap?
Dead leaves, dead animals and their waste are broken down by microorganisms, mainly bacteria and fungi, called decomposers. Nothing is lost in the process: every atom in a dead leaf ends up somewhere. Follow one fallen leaf, and predict each step before you watch it.
Follow the leaf
The leaf is digested
Step 1 of 3
Bacteria and fungi digest the leaf and respire. Where does most of its carbon go?
Think again · eating is not the answer
“Decomposers eat dead leaves. That is how the carbon gets back into the air.”
Spot the flaw
ExplainWhat is missing from this answer?
Where does it end up?
Air, soil, or locked away?
Each one starts in a living thing.
Tap a card, then tap the box it belongs in. Tap a placed card to take it back.
Command words in this lesson
- Explain
- Link each step to the next: break down, respire, carbon dioxide out, mineral ions into the soil.
- Identify
- Pick out the right answer from what you are given. No reason needed.
Key fact
Microorganisms break down dead material. They respire, returning carbon to the atmosphere as carbon dioxide, and they return mineral ions to the soil.
Key note · AQA 4.7.2.2 (8464)
Decomposition
- Microorganisms respire, returning carbon to the atmosphere as carbon dioxide.
- Breaking down dead material returns mineral ions, such as nitrate, to the soil for plant roots to absorb.
Photograph this card. Tomorrow, cover it and say each line first.
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Not sure where the carbon from a dead leaf goes?
The leaf scene is a model: carbon dioxide and mineral ions are drawn as labelled particles, and the soil animals that also feed on dead material are left out.