Mixotrophs at Higher Level: The same statement as SL. HL questions ask you to spot a mixotroph in an energy-flow diagram and to explain the difference between obligate and facultative mixotrophs.
Practise this as you read
- Identify a mixotroph from its energy sources.
- Distinguish obligate and facultative mixotrophs.
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The big idea: A mixotroph uses both modes of nutrition: it is autotrophic (photosynthesis) and heterotrophic (feeding on organic matter or other organisms).
The points to remember
- Euglena, a freshwater protist, photosynthesises in the light and takes in food in the dark.
- Many mixotrophs live in oceanic plankton.
- Obligate mixotrophs must use both modes to grow.
- Facultative mixotrophs can survive by either mode alone.
Remember it as: Mixo = mixed: makes food and takes food.
Real example: ocean plankton. In the oceans, many dinoflagellates and other plankton protists photosynthesise and also eat bacteria: they are producers and consumers at the same time in plankton food webs.
Trap: Saying a mixotroph photosynthesises is only half the answer: name both modes, autotrophic and heterotrophic.
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How it is asked: Expect a protist described as using sunlight and other organisms, a reason for calling it a mixotroph, or a food-web diagram where one organism gets energy from the sun and from another organism.
IB-style questionExplain[2 marks]
Explain why Euglena is described as a mixotroph.
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