Viruses(Complete)

Question 1

What is a virus?

Answer 1

A virus is a non cellular infectious agent that is composed of protein and one nucleic acid( DNA or RNA).

Question 2

Describe the structure of a virus.

Answer 2

It contains the a protein coat/ capsid.

It has one nucleic acid (DNA or RNA).

Question 3

Why are viruses often referred to as obligate parasites?

Answer 3

They require to be inside of a living host cell to replicate.
They have no organelles.
They need to be inside a living host cell to carry out metabolic reactions.

Question 4

What is an inactive form of a virus called?

Answer 4

A virion.

Question 5

What is a virion?

Answer 5

An inactive virus outside the living host cell.

Question 6

Compare the size of a virus to the size of bacteria.

Answer 6

Bacteria are 500 times larger than viruses.

Question 7

How do scientists distinguish between viruses?

Answer 7

By shape.
By nucleic acid.
By host.

Question 8

Name the three shapes of viruses and give an example for each one.

Answer 8

Spherical- flu virus.
Rod- mosaic virus.
Complex- bacteriophage- harms and kills bacteria.

Question 9

Comment briefly on the difficulty in classifying viruses as living organisms.

Answer 9

They have no organelles.
They are obligate parasites.
They only have one nucleic acid.

Question 10

What are the features that support a virus as being living?

Answer 10

They have genetic material- DNA/RNA.
They have the biomolecule protein.
They replicate.

Question 11

Describe how a virus replicates.

Describe how viruses reproduce.

Answer 11

The virus attaches itself to the body cell.
The nucleic acid is injected into the host.
The hosts DNA becomes inactive.
The virus uses the DNAs structures to replicate the nucleic acid and protein coat.
The protein coats and nucleic acids are assembled to form viruses.
The host cell bursts releasing the newly formed viruses and the host cell dies.

Question 12

What are the disadvantages of viruses in reference to:
Animals.
Plants.
Humans.

Answer 12

Animals:
They cause foot in mouth disease in cattle which is is of great economic importance.

Plants:
They cause mosaic diseases in plants e.g, potato mosaic virus.

In humans:
They cause many diseases such as:
Cold sores, polio, measles, mumps and AIDS.

Question 13

What are the benefits of viruses?

Answer 13

They are used to make vaccines.

Bacteriophages are used to control bacterial infections.

Question 14

What features of the general and specific defence system control viruses?

Answer 14

The skin.
Mucous membranes.
HCL in stomach.
Phagocytes.
B lymphocytes produce antibodies which help fight off infection.

Question 15

What vaccines are used to control viruses?

Answer 15

MMR- used to treat measles, mumps and rubella.
Flu vaccine- taken yearly to prevent infection from influenza.
HPV- taken by women aged 16-25 to prevent the risk of cervical cancer.

Question 16

What antiviral drugs are used to control viruses?

Answer 16

Interferon- to treat hepatitis B.

Acyclovir- to treat cold sores.

Question 17

Why should antibiotics not be prescribed to treat influenza?

Answer 17

Because the flu may be viral.

Antibiotics have no effect on viruses.

Question 18

Give a biological explanation for why active immunity results in long term immunity.

Answer 18

Antibodies are produced by the b lymphocytes in the body after an infection or vaccination.
Long term immunity as memory B cells are formed.

Question 19

Name two locations in eukaryotic cells where RNA but no DNA is found.

Answer 19

Cytosol.

Ribosome.

Question 20

What is AIDS?

Answer 20

HIV/ Human immunodeficiency virus causes AIDS.
It attacks the immune system and prevents the person from producing antibodies.
It is a retrovirus as it has RNA that it uses to make DNA once in the host cell.

Question 21

How is AIDS transmitted?

Answer 21

Through sexual fluids like semen during sexual intercourse.
In blood plasma, using used needles, in infected blood products.
May be given to babies through the maternal placenta or in breastmilk.

Question 22

Who are the high risk groups of contracting AIDS?

Answer 22

People with multiple sexual partners.
People receiving blood transfusions.
Intravenous drug users.
Haemophiliacs.

Question 23

Describe how AIDS attacks the immune system.

Answer 23

AIDS attacks the helper T cells which stimulate the b lymphocytes to produce antibodies to fight infection. As a result the person cannot produce the necessary antibodies to recover.

Question 24

Why is there no vaccine to prevent AIDS?

Answer 24

HIV constantly mutates which makes the production difficult.

Question 25

What are methods of preventing AIDS.

Answer 25

Avoid multiple sexual partners.
Used screened blood products.
Sterilise wounds and equipment.
Use condoms.