1. Chapter
20
Protists
Protists

2. What is a Protist?
• The kingdom Protista is a diverse
group that may include more than
200,000 species
• Biologists have argued for years over
the best way to classify protists, and
the issue may never be settled
• In fact, protists are defined less by
what they are and more by what they
are not

3. Protist
• Eukaryotes that are not members
of the kingdoms Plantae, Animal,
or Fungi
• Most protists are unicellular, but
some are multicellular

4. Endosymbiotic theory
• Theory that eukaryotic cells
formed from a symbiosis among
several different prokaryotic
organisms

5. Evolution of Protists
• The kingdom “Protista” means
“the very first” which is
appropriate because they were
the first eukaryotic organism on
Earth
• It is hypothesized that the first
Protists evolved from a symbiosis
of several prokaryotic cells

6. Endosymbiotic theory

7. Endosymbiotic theory

8. Endosymbiotic theory

9. Classification of Protists
• Protists are so diverse that biologists
suggest that they should be broken
up into several kingdoms
• Currently biologists don’t agree how
this should be done
• Therefore we will look at Protists as if
they belong in the same kingdom and
classify them by how they obtain
nutrition

10. Heterotrophs
• Can’t make their own food
• Many are capable of locomotion
(moving)

11. Animal-like Protists

12. Flagellates

13. Cilliates

14. Sarcodines

15. Sporozoans

16. Malaria

17. Plant-like Protists
• Many protists contain the green
pigment chlorophyll and carry out
photosynthesis
• Autotrophic
• However, they are not classified
as plants, they are algae

18. Euglena

19. Volvox

20. Diatoms

21. Dinoflagellates

22. Ecology of Unicellular Algae
• Plant-like protists play a major
ecological role on earth
• They make up a large part of the
phytoplankton

23. Phytoplankton
• The population of small
photosynthetic organisms near
the surface of the ocean
• About 1/2 of photosynthesis on
earth occurs in phytoplankton

24. Phytoplankton

25. Green algae

26. Red Algae

27. Algal Blooms
• Sometimes populations of algae
grows in enormous masses called
blooms
• These algal blooms deplete the
water of nutrients and can release
toxins into the water
• Ex.) Red tide

28. Red tide

31. Fungus-like Protist
• Like fungi, the fungus-like protist
are heterotrophs that absorb
nutrients from dead or decaying
organic matter
• But unlike true fungi, fungus-like
protists have centrioles
• They also lack the chitin cell walls
of true fungi

32. Slime molds
• Slime molds are fungus-like
protists that play a key role in
recycling organic material
• Found in places that are damp
and rich in organic matter

34. Water Molds
• Fungus-like protists that thrive on
dead decaying organic matter in
water and some are plant
parasites on land

35. Ecology of Fungus-like Protists
• They are important as
recyclers or organic material
• They can cause diseases
however
–Mildews and blights
–Potato famine 1845 and 1851