Viruses

Question 1

What are viruses?

Answer 1

Tiny non-cellular structures that cannot be seen by a light microscope

Question 2

Virus structure

Answer 2

Outer protein coat called a capsid and inside the capsid nucleic acid [either DNA or RNA] never both

Question 3

Metabolic reactions

Answer 3

They do not carry any metabolic reactions on their own and require the organelles of a host to carry out limited number of reactions

Question 4

Living factors of viruses

Answer 4

Possess genetic material [DNA or RNA]
Posses a protein coat
Can replicate [inside a living cell]

Question 5

Non living features of viruses

Answer 5

Non-cellular
Cannot reproduce by themselves
Do not possess ribosomes, mitochondria etc
Only have one type of nucleic acid [living things have both DNA and RNA]

Question 6

What is a bacteriophage?

Answer 6

It is a virus that infects bacteria

Question 7

Stages in virus replication?

Answer 7

Attachment - proteins on virus match up with receptor sites on host wall/membrane
Entry - hole pushes nucleic acid
Synthesis - host nucleic acid is made inactive and uses organelles to produce new viral nucleic acid and proteins
Assembly - new viruses made
Release - cell bursts and releases

Question 8

Another way that viruses replicate

Answer 8

Won’t destroy host cell but join with host DNA and remain inactive so when host DNA is copied, the virus DNA is also copied

Question 9

Disadvantages of viruses

Answer 9

Human diseases - chickenpox, measles, polio
Plant diseases - potato mosaic disease
Animal diseases - cowpox, myxomatosis, rabies

Question 10

Benefits of viruses

Answer 10

Genetic engineering - used to transfer genes from one organism to the other
Control of infections - bacteriophages used to control bacterial infected and reduce infections by antibiotic resistant bacteria

Question 11

Distinguish between HIV and AIDS

Answer 11

HIV is the virus that enters the body and disables helper t-cells results in not being able to produce antibodies

Question 12

How can AIDS be prevented

Answer 12

Avoid sexual intercourse
Use protection during intercourse
Do not use shared needles

Question 13

Why can a person be HIV positive but not suffer from AIDS

Answer 13

Because AIDS is the advanced stage that occurs after HIV enters body

Question 14

Why do viruses not cause decay?

Answer 14

They are obligate parasites

Question 15

Control and immunity of viruses

Answer 15

• General defence system and specific defence system
• injections and vaccinations
• antibiotics do not affect viruses

Question 16

What is a retrovirus and give an example

Answer 16

They contain RNA and an enzyme that converts RNA to DNA

example is ; HIV

Question 17

What is the bursting of the host cell in virus multiplication known as?

Answer 17

Lysis

Question 18

What are obligate parasites?

Answer 18

Can only replicate using a cell

Question 19

Name one virus that causes disease in plants

Answer 19

Mosaic

Question 20

How do scientists distinguish between different viruses

Answer 20

Shape of protein coat
Type of nucleic acid
Antibody - antigen reaction

Question 21

Why are viruses difficult to classify into a kingdom?

Answer 21

Non-cellular

Question 22

Give one example of a beneficial virus

Answer 22

Bacteriophages - kill bacteria

Question 23

How does the genetic make up of the new yeast cell relate to that of the parent cell and why

Answer 23

Identical - asexual

Mitosis

Question 24

A virus has been described as a piece of genetic material that has escaped from a cell. Give one piece of evidence that supports this description

Answer 24

Composed of nucleic acid

Question 25

During 2009, swine flu spread through the population of many countries. Younger people were more at risk of becoming ill than older people. Using your knowledge of the immune system, suggest a reason for this

Answer 25

Older people have had previous exposure and therefore developed memory cells. They are able to produce the specific antibodies in large amounts if virus was to enter body again.

Question 26

What is the economic importance of viruses?

Answer 26

Damage crops - bad economically - viruses such as mosaic plant disease

Question 27

What is the medical importance of viruses?

Answer 27

Human diseases such as chicken pox

Question 28

-just over fifty years ago the myxoma virus was brought to Ireland. The disease for which it is responsible in rabbits, myxomatosis, quickly decimated the wild population. Now however, the disease is much less common and is responsible for far fewer deaths-

Why do you think the rabbit population was decimated when the virus was first brought to Ireland?

Answer 28

No immunity against virus - first time

Question 29

-just over fifty years ago the myxoma virus was brought to Ireland. The disease for which it is responsible in rabbits, myxomatosis, quickly decimated the wild population. Now however, the disease is much less common and is responsible for far fewer deaths-

Suggest a reason why myxomatosis is no longer a major threat to the Irish rabbit population?

Answer 29

Natural immunity - memory cells

Question 30

Suggest one advantage and one disadvantage of biological control

Answer 30

Advantage - environmentally friendly
May be inexpensive
Disadvantage - upsets balance of nature
Introduced species may become pest