The big idea: Saprotrophs are heterotrophs that feed on dead organic matter. They digest it outside their bodies and absorb the products.
The points to remember
- Enzymes are secreted onto the dead matter: external digestion.
- The small, soluble products are absorbed.
- Many fungi and bacteria feed this way.
- They are decomposers: they release minerals for plants to reuse.
Holozoic
- Food ingested into a gut
- Digestion inside the body
- Most animals
Saprotrophic
- Enzymes secreted onto food
- Digestion outside the body
- Many fungi and bacteria
Remember it as: Saprotroph: digest outside, absorb, recycle.
Real example: bracket fungi. Bracket fungi grow on dead and dying trees: their hyphae spread through the wood, secrete enzymes that break down cellulose and lignin, and absorb the products, slowly rotting the trunk.
Trap: Both holozoic and saprotrophic nutrition use enzymes to digest food: the difference is where digestion happens.
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How it is asked: Expect a fungus or bacterium described as digesting dead matter, or a comparison of holozoic and saprotrophic nutrition.
IB-style questionCompare and contrast[3 marks]
Compare and contrast holozoic and saprotrophic nutrition.
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.