Decomposers & nutrient cycling
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Question
What is a decomposer?
Answer
An organism that feeds on **dead organic matter** and breaks it down, **releasing nutrients** back to the environment.
Question
Name the two kinds of decomposer.
Answer
**Detritivores** and **saprotrophs**.
Question
What is a saprotroph, and how does it feed?
Answer
A decomposer (mostly **bacteria and fungi**) that **secretes enzymes onto** dead matter and **absorbs** the soluble products — it digests **externally**.
Question
What is a detritivore, and how does it feed?
Answer
An **animal** (e.g. earthworm, woodlouse) that **ingests** pieces of dead matter and digests them **internally**, in a gut.
Question
Give the key difference between a detritivore and a saprotroph.
Answer
**Where digestion happens**: a detritivore digests **internally** (it ingests); a saprotroph digests **externally** (it secretes enzymes and absorbs).
Question
What do detritivores and saprotrophs have in common?
Answer
Both are **decomposers** — they feed on **dead organic matter** and **recycle nutrients** back to the environment.
Question
What is the role of decomposers in an ecosystem? (2 marks)
Answer
They **break down dead organic matter** AND **release/recycle inorganic nutrients** to the soil for producers to reuse.
Question
What is nutrient cycling?
Answer
The repeated movement of nutrients (carbon, nitrogen, phosphorus) **between living organisms and the environment**, so the same atoms are **reused**.
Question
Why are decomposers essential to an ecosystem?
Answer
They **unlock the nutrients** trapped in dead matter; without them, nutrients would stay locked away and **producers would run out of raw materials**.
Question
On a nutrient-cycle diagram, what do the BOXES and ARROWS represent?
Answer
**Boxes = stores** of nutrients (soil, litter, biomass); **arrows = transfers** of nutrients between the stores.
Question
Name two processes that REDUCE the soil nutrient store.
Answer
**Uptake by plant roots** and **leaching** (nutrients washed out by water); also runoff/erosion.
Question
Why is the litter-to-soil nutrient flow large in a tropical rainforest?
Answer
It is **warm and wet**, so **decomposers are very active** and break litter down **quickly**, releasing nutrients fast.
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Full study notes for Decomposers & nutrient cycling
Topic 3.9 hub
Transfers of energy and matter
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