5. Viruses that attack only bacteria are known as … .

1. DNA viruses b. RNA viruses

c. retroviruses d. bacteriophages

e. all of the above.

6. Some viruses infect a host cell by

1. attaching to the host’s protein coat while injecting the viral DNA or RNA into the host

2. entering the host intact

3. injecting viral genetic information into a host’s cells

4. all of the above e. none of the above.

7. It is possible that viruses may be moving genetic material from

1. plants to animals b. animals to plants

c. plants to plants d. animals to animals

5. all of the above.

8. Viruses may prove, in some cases, to be the simplest of

1. all simbionts b. all parasites

c. all living things d. all of the above

5. none of the above.

9. Prions have been said to be

1. the smallest infectious agents known

2. the largest infectious agents known

3. 100 times smaller than viruses to almost as large as mitochondria and bacteria

4. the cause of certain diseases e. a, c, and d.

10. Prions

1. have been found to contain nucleic acids

2. have not been found to contain nucleic acids

3. are viruses d. are not viruses

5. b and d.

11. Recent work has shown that prions may be

1. proteins produced somewhat abnormally by “infected” genes that somehow go awry

2. bacteria c. viruses

4. protists e. mitochondria.

2. Questions to think about.

1. Describe viruses. Are they considered living?

2. What might account for the origin of viruses?

3. How do viruses increase in number? Describe the different mechanisms.

4. What are five diseases affecting humans that are caused by viruses?

5. Describe similarities and differences between viruses and subviruses.

3. Think of 5-7 statements that would contradict the contents of the text. Language focus

1. Match the words that are: a) similar and b) opposite in meaning:

a)		b)
lysing	to make	terminally	useless
to promote	way	inside	inability
conventional	dissolving	normally	continuously
mode	structure	beneficial	inner
to induce	regular, normal	capacity	abnormally
machinery	to contribute	outer	outside

2. Form the derivatives of the words given in the table (where possible):

Noun	Verb	Adjective
	to interfere
	to revise
virus
infection
		befeficial
	to succeed
		sore
theory
	to elucidate
	to transfer

3. Define the following terms:

virus	prions	retroviruses
rhinovirus - ["raInqV'vaI(q)rqs]	influenza viruses - ["InflV'enzq] ['vaI(q)rqsi:z]	bacteriophage - [bxk'tI(q)rIqfeIdZ]
subvirus	AIDS	viral capsid

4. Match the first half of a sentence in column a with the appropriate second half in column b:

A	B
1. Viruses are from 10 to 100 times smaller	a) than to one another.
2. Viruses contain nucleic acids	b) which would explain their small and uncertain molecular weights.
3. Viruses are more closely related to their hosts	c) than the typical bacterium.
4. The mode of prion reproduction might involve fracture and continued growth,	d) that would identify it as living.
5. A virus is inert, incapable of reproduction, or of any metabolic functions	e) which are enclosed in a protective coat of protein.