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14.1: Introduction to Protists

Difficulty Level: At Grade Created by: CK-12
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Lesson 14.1: True or False

Name___________________ Class______________ Date________

Write true if the statement is true or false if the statement is false.

_____ 1. Protists are prokaryotes.

_____ 2. There is currently no scientific evidence supporting the endosymbiotic theory.

_____ 3. According to the endosymbiotic theory, eukaryotic cells evolved from prokaryotic cells.

_____ 4. According to the endosymbiotic theory, mitochondria evolved from small aerobic bacteria that were engulfed by a larger prokaryotic cell.

_____ 5. According to the endosymbiotic theory, chloroplasts evolved from small protists.

_____ 6. Chloroplasts, but not mitochondria, have DNA.

_____ 7. Chloroplasts and mitochondria are surrounded by membranes.

_____ 8. Protists contain organelles.

_____ 9. All protists are multicellular.

_____ 10. Most protists require a watery environment in which to live.

_____ 11. Protists have no way of moving on their own; they must hitch a ride with a motile organism.

_____ 12. Algae are protists.

_____ 13. Spores can be produced by some protists as a response to harsh conditions in their environment.

_____ 14. Some protists can carry out photosynthesis.

_____ 15. Protists cannot reproduce sexually.

Lesson 14.1: Critical Reading

Name___________________ Class______________ Date________

Read these passages from the text and answer the questions that follow.

Evolution of Protists

Scientists think that protists are the oldest eukaryotes. If so, they must have evolved from prokaryotic cells. How did this happen? The endosymbiotic theory provides the most widely accepted explanation. That’s because it is well supported by evidence.

The First Eukaryotic Cells

According to the endosymbiotic theory, the first eukaryotic cells evolved from a symbiotic relationship between two or more prokaryotic cells. Smaller prokaryotic cells were engulfed by (or invaded) larger prokaryotic cells. The small cells (now called endosymbionts) benefited from the relationship by getting a safe home and nutrients. The large cells (now called hosts) benefited by getting some of the organic molecules or energy released by the endosymbionts. Eventually, the endosymbionts evolved into organelles of the host cells. After that, neither could live without the other.

Some of the endosymbionts were aerobic bacteria. They were specialized to break down chemicals and release energy. They evolved into the mitochondria of eukaryotic cells. Some of the small cells were cyanobacteria. They were specialized for photosynthesis. They evolved into the chloroplasts of eukaryotic cells.

Evidence for Endosymbiotic Theory

Many pieces of evidence support the endosymbiotic theory. For example:

  • Mitochondria and chloroplasts contain DNA that is different from the DNA found in the cell nucleus. Instead, it is similar to the circular DNA of bacteria.
  • Mitochondria and chloroplasts are surrounded by their own plasma membranes, which are similar to bacterial membranes.
  • New mitochondria and chloroplasts are produced through a process similar to binary fission. Bacteria also reproduce through binary fission.
  • The internal structure and biochemistry of chloroplasts is very similar to that of cyanobacteria.


1. What does the endosymbiotic theory attempt to explain?

2. What benefits did the ancient endosymbionts get from their host cells?

3. What benefits did the host cells get from the endosymbionts?

4. Describe two examples of scientific evidence that support the endosymbiotic theory.

5. What does the “endo” part of endosymbiosis refer to? What does the “symbiosis” part refer to?

Lesson 14.1: Multiple Choice

Name___________________ Class______________ Date________

Circle the letter of the correct choice.

  1. Which of the following is not a principle of the endosymbiotic theory?
    1. Mitochondria evolved from aerobic bacteria that were engulfed by a larger prokaryotic cell.
    2. Chloroplasts evolved from endosymbiotic photosynthetic bacteria.
    3. Prokaryotic cells evolved from eukaryotic cells.
    4. The first eukaryotic cells evolved from a mutually beneficial relationship between two or more prokaryotic cells.
  2. How are mitochondria and chloroplasts similar?
    1. They are both organelles in eukaryotic cells.
    2. They are both surrounded by membranes.
    3. They divide by binary fission.
    4. all of the above
  3. Which location is least likely to have a population of protists?
    1. desert
    2. damp soil
    3. ocean
    4. lake
  4. Cilia
    1. are false feet.
    2. are short appendages that help some protists move.
    3. contain all of the DNA in a protist.
    4. all of the above
  5. The algae Spirogyra produces spores
    1. when conditions in their environment are ideal.
    2. to get rid of extra chloroplasts.
    3. when conditions in their environment become unfavorable.
    4. as a way to make food.
  6. The fusion of two Spirogyra spores to form a diploid zygote is an example of
    1. asexual reproduction.
    2. sexual reproduction.
    3. binary fission.
    4. triploid fission.
  7. Ingestive protists obtain food by
    1. photosynthesis.
    2. diffusion.
    3. osmosis.
    4. engulfing the food.
  8. Photosynthesis is
    1. the process of engulfing food particles.
    2. the process of transforming light energy, carbon dioxide, and water into chemical energy (food).
    3. a type of cell movement.
    4. none of the above.

Lesson 14.1: Vocabulary I

Name___________________ Class______________ Date________

Match the vocabulary word with the proper definition.


_____ 1. the simplest eukaryotes

_____ 2. a mutually beneficial relationship between a cell and the cell that engulfed it

_____ 3. longer, whip-like appendages that aid movement

_____ 4. an organelle that carries out photosynthesis

_____ 5. cell without a nucleus

_____ 6. cell with a nucleus

_____ 7. an organelle that carries out cellular respiration

_____ 8. short, whip-like appendages that aid movement

_____ 9. the ability to move

_____ 10. “false feet”

_____ 11. a reproductive cell produced by protists and other organisms

_____ 12. prokaryotes that use oxygen for cellular respiration


a. aerobic bacteria

b. chloroplast

c. cilia

d. endosymbiosis

e. eukaryote

f. flagella

g. mitochondria

h. motility

i. psuedopods

j. protists

k. prokaryote

l. spore

Lesson 14.1: Vocabulary II

Name___________________ Class______________ Date________

Fill in the blank with the appropriate term.

1. A term for the ability to move is ____________.

2. Whip-like cellular appendages some protists use to help them move are ____________.

3. Cells that live inside other cells in a mutually beneficial relationship are called ____________.

4. ____________ are the simplest eukaryotes.

5. A temporary, foot-like extension of the protist's cytoplasm that it can use for movement is a ____________.

6. Mitochondria are cellular ____________.

7. Photosynthesis in protists happens in the ____________.

8. Protists have a nucleus containing ____________.

9. ____________ are the haploid Spirogyra cells that can survive in harsh environments.

10. Haploid cells are produced from a diploid zygote by ____________.

11. Protists can be single celled or ____________.

12. Protists have get food by ____________, ____________, or ____________.

Lesson 14.1: Critical Writing

Name_________________________________ Class_________ Date____________

Thoroughly answer the question below. Use appropriate academic vocabulary and clear and complete sentences.

Many protists are capable of both asexual and sexual reproduction, including Spirogyra. How does Spirogyra benefit from being able to reproduce by both asexual and sexual reproduction?

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