Name
Class
Date
21.1 Protist Classification—The
Saga Continues
Lesson Objectives
Explain what a “protist” is.
Describe how protists are related to other eukaryotes.
Lesson Summary
The First Eukaryotes Protists are eukaryotes that are not members of the plant, animal,
or fungi kingdoms. The first eukaryotes were protists.
Most protists are unicellular.
Protists are a very diverse group of species.
Many species of protists are more closely related to plants, fungi, or animals than they are
to other protists. Because of this, some scientists think the members of the kingdom
Protista should be reclassified.
Protists—Ancestors and Descendants All eukaryotes are descended from early
protists, but modern protists are very different from their ancestors. Like other eukaryotes,
they have been evolving over the last 2.5 billion years.
The First Eukaryotes
1. What is a protist?
2. Why are brown algae considered protists even though they are multicellular?
3. Why do scientists no longer use the categories of animal-like, plantlike, and fungus like
protists to classify protists?
For Questions 4–7, complete each statement by writing the correct word or words.
4. Most single-celled eukaryotes are currently classified as
.
5. Genetic analyses of protists indicate that they belong in six different
6. Protists were the first
.
.
7. Unlike most protists, which are unicellular, kelp has
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tissues.
Name
Class
Date
For Questions 8–11, use the diagram and legend below.
Six Major Groups
Excavates
Chromalveolates
Cercozoa,
Foraminifera,
and Radiolaria
Rhodophyta
(red algae)
Amoebozoa
Choanozoa
8. Plants are most closely related to which of the following groups?
A. Amoebozoa
B. Cercozoa
C. Rhodophyta
D. Choanozoa
9. Brown algae is a member of the clade Chromalveolates. Which of the
following is its closest relative?
A. slime mold, an Amoebozoan
C. Giardia, an Excavate
B. red algae, a Rhodophytan
D. Globigerina, a Foraminiferan
10. Which clade is most primitive?
A. Excavates
B. Choanozoa
C. Cercozoa
D. Chromalveolates
11. Which statement is true?
A. Plants, fungi, and animals all emerged from a common protist ancestor.
B. Only fungi and animals emerged from a common protist ancestor.
C. Only animals and plants emerged from a common protist ancestor.
D. Plants, fungi, and animals all emerged from different protist ancestors.
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Name
Class
Date
Protists—Ancestors and Descendants
For Questions 12–19, write True or False on the line provided.
12. The first eukaryotes were Archaea.
13. It is possible to find the earliest fungi by looking at modern protists.
14. Modern protists have evolved very little from their ancestral forms.
15. Today, there are as many as 300,000 known species of protists.
16. The oldest known eukaryotic fossils are around 1.5 billion years old.
17. The first protists most likely evolved 3.6 billion years ago.
18. Plants, animals, and fungi most likely evolved from multicellular
protists.
19. The protists are more diverse than any other eukaryotic kingdom.
20. Complete the concept map below.
Certain ancient
species of
Archaea
evolved into
which evolved Into
Many different
modern groups
of protists
Apply the Big idea
21. Euglena are photosynthetic protists that live in fresh water. How would their
photosynthetic properties help stabilize a pond ecosystem? Suppose they and all the other
photosynthetic organisms disappeared from the pond. How might their disappearance
affect other organisms that lived in the pond?
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