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13.1: Prokaryotes

Difficulty Level: At Grade Created by: CK-12
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Lesson 13.1: True or False

Name___________________ Class______________ Date________


_____ 1. Prokaryotes are single-celled organisms that lack a nucleus.

_____ 2. Since prokaryotes do not have organelles, they do not have ribosomes.

_____ 3. Cyanobacteria were probably the first organisms to photosynthesize.

_____ 4. Cyanobacteria contain the organelle chlorophyll.

_____ 5. The first Archaea discovered were the extremophiles.

_____ 6. The most common prokaryotic shapes are helices, polygons, spheres, and rods.

_____ 7. Prokaryotic DNA is usually one or two circular chromosomes.

_____ 8. Both Bacteria and Archaea have plasma membranes and cell walls.

_____ 9. Flagella help bacteria move.

_____ 10. Because they are simple single cells, prokaryotes do not need energy.

_____ 11. There are billions of bacteria inside the human intestines that help digest food.

_____ 12. Insects are common vectors for spreading bacterial diseases between humans.

_____ 13. Aerobic prokaryotes need oxygen, which they use for cellular respiration.

_____ 14. Bacteria provide vital ecosystem services - they are important producers and are needed for the carbon and nitrogen cycles.

_____ 15. Bacteria in food or water usually cannot be killed.

Lesson 13.1: Critical Reading

Name___________________ Class______________ Date________


Evolution and Classification of Prokaryotes

Prokaryotes are currently placed in two domains. A domain is the highest taxon, just above the kingdom. The prokaryote domains are Bacteria and Archaea. The third domain is Eukarya. It includes all eukaryotes. Unlike prokaryotes, eukaryotes have a nucleus in their cells.

Prokaryote Evolution

It’s not clear how the three domains are related. Archaea were once thought to be offshoots of Bacteria that were adapted to extreme environments. For their part, Bacteria were considered to be ancestors of Eukarya. Scientists now know that Archaea share several traits with Eukarya that Bacteria do not share (see Table below). In what ways are Archaea and Bacteria different? In what ways are Archaea and Eukarya alike? How can this be explained? One hypothesis is that Eukarya arose when an Archaean cell fused with a Bacterial cell. The two cells became the nucleus and cytoplasm of a new Eukaryan cell. How well does this hypothesis fit the evidence in Table below?

Characteristic Bacteria Archaea Eukarya
Flagella Unique to Bacteria Unique to Archaea Unique to Eukarya
Cell Membrane Unique to Bacteria Like Bacteria and Eukarya Unique to Eukarya
Protein Synthesis Unique to Bacteria Like Eukarya Like Archaea
Introns Absent in most Present Present
Peptidoglycan (in cell wall) Present Absent in most Absent

Domain Bacteria

Bacteria are the most diverse and abundant group of organisms on Earth. They live in almost all environments. They are found in the ocean, the soil, and the intestines of animals. They are even found in rocks deep below Earth’s surface. Any surface that has not been sterilized is likely to be covered with bacteria. The total number of bacteria in the world is amazing. It’s estimated to be 5 × 1030, or five million trillion trillion. You have more bacteria in and on your body than you have body cells!

Bacteria called cyanobacteria are very important. They are bluish green in color because they contain chlorophyll. They make food through photosynthesis and release oxygen into the air. These bacteria were probably responsible for adding oxygen to the air on early Earth. This changed the planet’s atmosphere. It also changed the direction of evolution. Ancient cyanobacteria also may have evolved into the chloroplasts of plant cells.

Domain Archaea

Archaea were first discovered in extreme environments. For example, some were found in hot springs. Others were found around deep sea vents. Such Archaea are called extremophiles, or “lovers of extremes.” The places where some of them live are thought to be similar to the environment on ancient Earth. This suggests that they may have evolved very early in Earth’s history.


1. What is a domain? What are the three domains of life?


2. List three main differences between Bacteria and Archaea.


3. Give three examples of places bacteria live.


4. What are cyanobacteria? What was their most significant contribution?


5. What is an extremophile?


Lesson 13.1: Multiple Choice

Name___________________ Class______________ Date________

Circle the letter of the correct choice.

  1. The prokaryotic domains are
    1. Bacteria and Eukarya.
    2. Bacteria and Archaea.
    3. Archaea and Eukarya.
    4. Prokarya and Bacteria.
  2. One significant difference between Bacteria and Archaea is that
    1. genes in Bacteria have introns.
    2. peptidoglycan is found in the cell wall of most Archaea.
    3. genes in Archaea have introns.
    4. two of the above
  3. Cyanobacteria
    1. contain chlorophyll.
    2. make food through photosynthesis.
    3. were probably responsible for adding oxygen to the air on early Earth.
    4. all of the above
  4. Hyperthermophiles
    1. live in very hot water.
    2. live in very acidic environments.
    3. live in very salty water.
    4. are an early member of the domain Bacteria.
  5. The most common prokaryotic shapes include
    1. rod, square, and helix.
    2. helix, sphere, and rod.
    3. sphere, rod, and double helix.
    4. helical, icosahedral, and complex.
  6. Prokaryotic DNA
    1. is usually circular and located in the cytoplasm.
    2. is usually circular and located in the nucleus.
    3. consists of numerous chromosomes and is located in the cytoplasm.
    4. consists of numerous chromosomes and is located in the nucleus.
  7. Ways humans use bacteria include
    1. killing plant pests.
    2. transferring normal genes to human cells in gene therapy.
    3. cleaning up oil spills and toxic wastes.
    4. all of the above.
  8. Genetic transfer refers to
    1. how Archaea dissolve in extreme environments and transfer their DNA to other prokaryotes.
    2. how Bacteria evolve new genes through spontaneous mutations.
    3. how prokaryotes increase genetic variation.
    4. all of the above.

Lesson 13.1: Vocabulary I

Name___________________ Class______________ Date________

Match the vocabulary word with the proper definition.


_____ 1. bacteria that were responsible for adding oxygen to the air on early Earth

_____ 2. prokaryotes that are specialized to live in extreme environments

_____ 3. small, circular pieces of DNA

_____ 4. used by prokaryotes to increase genetic variation

_____ 5. first discovered in extreme environments

_____ 6. the most diverse and abundant group of organisms on Earth

_____ 7. results from misuse and over-use of the drugs

_____ 8. a colony of prokaryotes that is stuck to a surface

_____ 9. help prokaryotes move

_____ 10. enclose the DNA and help it survive under conditions that may kill the cell

_____ 11. bacteria with a thin cell wall

_____ 12. bacteria with a thick cell wall


a. antibiotic resistance

b. Archaea

c. Bacteria

d. biofilm

e. cyanobacteria

f. endospore

g. extremophile

h. flagella

i. genetic transfer

j. Gram-negative bacteria

k. Gram-positive bacteria

l. plasmid

Lesson 13.1: Vocabulary II

Name___________________ Class______________ Date________

Fill in the blank with the appropriate term.

1. The prokaryote domains are ____________ and ____________.

2. The common prokaryotic shapes include helices, ____________, and rods.

3. The DNA of a prokaryotic cell is in the cytoplasm because the cell lacks a ____________.

4. Under ideal conditions, bacterial populations can double every ____________20 minutes.

5. Bacteria called ____________ make food through photosynthesis and release oxygen into the air.

6. Genetic ____________ increases genetic variation in prokaryotes.

7. A ____________ is a colony of prokaryotes that is stuck to a surface such as a host’s tissues.

8. Bacterial infections in people can be treated with ____________ drugs.

9. Prokaryotes reproduce through binary fission, a type of ____________ reproduction.

10. A plasmid is an extra-chromosomal piece of ____________.

11. Cellular respiration and photosynthesis take place in the ____________ of prokaryotes.

12. Prokaryotes have a ____________ outside their plasma membrane, usually to give strength and rigidity to the cell.

13. ____________ live everywhere on Earth, including extreme environments such as deep sea vents.

14. There are ____________ of bacteria inside the human intestines that help digest food.

Lesson 13.1: Critical Writing

Name___________________ Class______________ Date________


What are cyanobacteria? Discuss the importance of this prokaryote.

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