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All 14 Flashcards — The carbon cycle
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Question
What is the carbon cycle?
Answer
The continuous **recycling of carbon** between the atmosphere, living organisms, the oceans and rocks — carbon is never made or destroyed.
Question
Which single process REMOVES CO₂ from the air?
Answer
**Photosynthesis** — producers fix CO₂ into organic carbon (glucose).
Question
Which three processes ADD CO₂ back to the air?
Answer
**Respiration, decomposition and combustion.**
Question
How does carbon move from producers to animals?
Answer
By **feeding** — organic carbon passes along the **food chain**.
Question
Which organisms carry out respiration?
Answer
**All living things** — producers, consumers and decomposers — releasing CO₂.
Question
What happens to carbon during decomposition?
Answer
Decomposers (bacteria, fungi) break down dead matter and **respire**, releasing the stored carbon as **CO₂**.
Question
What is combustion in the carbon cycle?
Answer
The **burning** of wood and fossil fuels, which releases their stored carbon as **CO₂**.
Question
How do aquatic autotrophs obtain their carbon?
Answer
From **dissolved CO₂ and hydrogencarbonate (HCO₃⁻) ions** in the water around them.
Question
How do land plants obtain their carbon?
Answer
As **CO₂ gas** taken directly from the air.
Question
What is a carbon sink? Give examples.
Answer
A store that **takes carbon out of the air** — e.g. forests, peat bogs, limestone, fossil fuels, the deep ocean.
Question
What is a carbon source? Give examples.
Answer
Something that **releases CO₂ into the air** — respiration, decomposition and combustion.
Question
What conditions lock carbon away in peat?
Answer
**Waterlogged, anaerobic (low-oxygen) and acidic** conditions slow decomposition, so carbon-rich material builds up.
Question
Why might atmospheric CO₂ rise?
Answer
When **combustion of fossil fuels** (a source) adds CO₂ **faster than photosynthesis** (the sink) can remove it.
Question
On a carbon-cycle diagram, which arrow removes CO₂?
Answer
The **photosynthesis** arrow — running from CO₂ in the air into living things.
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Full study notes for The carbon cycle
Topic 3.9 hub
Transfers of energy and matter
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