Concept preview

What you will be able to do

1. 01Explain why protists are grouped together and what they have in common.
2. 02Describe the three informal groups of protists (animal-like, plant-like, fungus-like).
3. 03Use Euglena to explain why protists are hard to classify.
4. 04Explain why protists are important despite being a 'leftover' group.

After you have sorted living things into plants, animals and fungi, a huge and bewildering assortment of eukaryotes is left over — and biologists sweep them all into the protists. This makes protists less a natural family than a 'junk drawer': they are grouped together mostly by what they are not. What unites them is that they are eukaryotes (true nucleus and organelles) that are not plants, animals or fungi. Most are single-celled and microscopic, most live in water or moist places, and among them lies some of the most spectacular diversity in all of biology.