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13.2: Viruses

Difficulty Level: At Grade Created by: CK-12

Lesson 13.2: True or False

Name___________________ Class______________ Date________

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

_____ 1. An individual virus is a virion.

_____ 2. Viruses lack cell membranes, cytoplasm, ribosomes, but they do have genetic material.

_____ 3. Because they evolve, viruses are living organisms.

_____ 4. A virus is essentially DNA or RNA and a protective protein coat.

_____ 5. Populations of viruses still divide like cells even though they are not cells.

_____ 6. Virus can remain latent in within the body for many years.

_____ 7. Antibiotics only kill certain on viruses.

_____ 8. Viruses can be used as vectors in gene therapy treatments.

_____ 9. Viruses are small particles, smaller than eukaryotic cells but larger than prokaryotic cells.

_____ 10. Scientists did not know about viruses until they were first seen with an electron microscope in the 1930s.

_____ 11. A virus can only replicate inside a host cell.

_____ 12. Some viruses can cause cancer.

_____ 13. The protective protein coat around the virus is called a capsid.

_____ 14. Viruses cause AIDS, the flu, chicken pox, the common cold, and food poisoning.

Lesson 13.2: Critical Reading

Name___________________ Class______________ Date________

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

Characteristics of Viruses

An individual virus is called a virion. It is a tiny particle much smaller than a prokaryotic cell. Because viruses do not consist of cells, they also lack cell membranes, cytoplasm, ribosomes, and other cell organelles. Without these structures, they are unable to make proteins or even reproduce on their own. Instead, they must depend on a host cell to synthesize their proteins and to make copies of themselves. Viruses infect and live inside the cells of living organisms. When viruses infect the cells of their host, they may cause disease. For example, viruses cause AIDS, influenza (flu), chicken pox, and the common cold.

Although viruses are not classified as living things, they share two important traits with living things. They have genetic material, and they can evolve. This is why the classification of viruses has been controversial. It calls into question just what it means to be alive. What do you think? How would you classify viruses?

Structure and Classification of Viruses

Viruses vary in their structure. The structure of a virus determines how it is classified.

Structure of Viruses

A virus particle consists of DNA or RNA within a protective protein coat called a capsid. The shape of the capsid may vary from one type of virus to another.

Some viruses have an envelope of phospholipids and proteins. The envelope is made from portions of the host’s cell membrane. It surrounds the capsid and helps protect the virus from the host’s immune system. The envelope may also have receptor molecules that can bind with host cells. They make it easier for the virus to infect the cells.

Classification of Viruses

Viruses are classified on the basis of several traits. For example, they may be classified by capsid shape, presence or absence of an envelope, and type of nucleic acid. Table below gives examples of virus families and their traits. Most systems of classifying viruses identify at least 20 virus families, but only 4 are shown in the table. Have any of these viruses made you sick?

Virus Family Capsid Shape Envelope Present? Type of Nucleic Acid Disease Caused by a Virus in this Family
Adenovirus icosahedral no DNA acute respiratory disease
Herpesviruses icosahedral yes DNA chicken pox
Orthomyxoviruses helical yes RNA influenza
Coronaviruses complex yes RNA common cold


1. Describe a virion.

2. Why are viruses not able to make their own proteins?

3. Describe the structure of a virus.

4. What are the traits used to classify a virus?

5. Do you think viruses should be classified as “living organisms”? Why or why not?

Lesson 13.2: Multiple Choice

Name_________________________________ Class_________ Date____________

Circle the letter of the correct choice.

  1. Viruses are in which domain of life?
    1. Archaea
    2. Bacteria
    3. Eukarya
    4. none of the above
  2. Which of the following structures do viruses lack? (1) genetic material, (2) cell membrane, (3) cytoplasm, (4) ribosomes.
    1. 1 only
    2. 1, 2, and 3
    3. 2, 3, and 4
    4. 1, 2, 3, and 4
  3. Which statement best describes a capsid?
    1. A capsid defines the shape of the virus.
    2. A capsid is the outside coat of the virus.
    3. A capsid is a protein coat that protects the genetic material of the virus.
    4. A capsid is either helical, icosahedral, or complex.
  4. Which traits describe the virus that causes the common cold?
    1. It is an RNA virus with a complex capsid surrounded by an envelope.
    2. It is a DNA virus with a complex capsid surrounded by an envelope.
    3. It is an RNA virus with a helical capsid surrounded by an envelope.
    4. It is a DNA virus with an icosahedral capsid surrounded by an envelope.
  5. To replicate, a virus must
    1. infect a host cell and use the cell’s ribosomes, enzymes, DNA, and other components.
    2. infect a host cell and use the cell’s ribosomes, enzymes, ATP, and other components.
    3. infect a host cell and use the viral enzymes, ATP, and other components.
    4. infect a host cell and use the viral DNA and ribosomes, but the cell's enzymes, ATP and other components.
  6. Latency refers to
    1. the process of viral disease formation inside a host.
    2. the process of making a viral envelope from portions of the host’s cell membrane.
    3. a dormant state of the virus inside a host's body.
    4. the process of viral replication inside a host.
  7. A vaccine
    1. can be harmful because it contains pathogens such as viruses.
    2. contains a changed pathogen, so the pathogen is no longer harmful.
    3. provokes a response from the viral immune system.
    4. all of the above
  8. Which of the following statements is true? (1) HPV causes cancer of the cervix in females. (2) Hepatitis B virus causes cancer of the liver. (3) Many viral diseases can be prevented with proper vaccination. (4) Antibiotics have no effect on viruses.
    1. 1 and 2
    2. 3 and 4
    3. 1, 2, and 3
    4. 1, 2, 3, and 4

Lesson 13.2: Vocabulary I

Name___________________ Class______________ Date________

Match the vocabulary word with the proper definition.


_____ 1. surrounds the capsid and helps protect the virus

_____ 2. the ability to resist a pathogen

_____ 3. a dormant state inside the body

_____ 4. a protective protein coat

_____ 5. usually considered to be nonliving

_____ 6. a substance that contains harmless pathogens

_____ 7. 20-sided

_____ 8. spiral

_____ 9. an individual virus


a. capsid

b. envelope

c. helical

d. icosahedral

e. immunity

f. latency

g. vaccine

h. virion

i. virus

Lesson 13.2: Vocabulary II

Name___________________ Class______________ Date________

Fill in the blank with the appropriate term.

1. Many viral diseases can be prevented by giving people ____________.

2. Viruses do not meet most of the criteria of ____________.

3. The three shapes of viral capsids are helical, icosahedral, and ____________.

4. Viruses are so small that they can be seen only with an ____________ microscope.

5. Viruses must use the cell’s ____________, enzymes, ATP, and other components to replicate.

6. A virus particle consists of DNA or RNA within a ____________ coat.

7. Viruses may cause illness by disrupting ____________ in host cells.

8. Viruses are used as vectors in gene ____________.

9. The virus that causes chicken pox may remain ____________ within the body for decades.

10. Though some antiviral drugs are available, the more common ____________ have no effect on viruses.

11. One way viruses cause ____________ is by causing host cells to burst open and die.

12. Viruses cause diseases such as ____________, influenza, chicken pox, and the common cold.

Lesson 13.2: Critical Writing

Name___________________ Class______________ Date________

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

Are viruses living organisms? Discuss why or why not.

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