Viruses

Question 1

Why are viruses known as obligate parasites?

Answer 1

They need a host to reproduce/replicate
They can’t replicate by themselves

Question 2

two types of immunity

Answer 2

active
passive

Question 3

explain active immunity

Answer 3

body produces antibodies

Question 4

explain passive immunity

Answer 4

body receives antibodies

Question 5

Virus structure

Answer 5

Viruses are tiny, non-cellular structures.
° They have an outer layer of protein called a capsid.
° They contain either RNA or DNA but never both.
° They have no organelles of their own.
° Viruses are non-living structures as they are non-cellular, have no organelles and are unable to reproduce themselves.

Question 6

Stages of replication

Answer 6

The steps of viral replication are:
1. Attachment
2. Entry
3. Synthesis
4. Assembly
5. Release

Question 7

replication : attachment

Answer 7

• Viruses attach to a living host cell by means of receptor sites.

Question 8

replication: entry

Answer 8

Viruses then make a hole in the host cell and push their own DNA or RNA into it.

Question 9

replication: synthesis

Answer 9

The host DNA is inactivated, and the viral DNA/ RNA is used to make new viral nucleic acid/ protein.

Question 10

replication: assembly

Answer 10

New viruses are made in the host cells.

Question 11

replication: release

Answer 11

The host cell bursts to release new viruses

Question 12

Human diseases:

Answer 12

• HIV
• Influenza
• Warts
• Polio

Question 13

Animal diseases:

Answer 13

• Rabies
• Cowpox
• Foot and mouth disease

Question 14

Plant diseases

Answer 14

• Tobacco mosaic disease
• Potato mosaic disease
• Tomato mosaic disease

Question 15

viruses: living argument

Answer 15

contain nucleus acid
have protein cost
can replicate

Question 16

viruses non living

Answer 16

non cellular - lack plasma membrane and organelles
One type of nucleus acid
Cant reproduce on its own -> obligate parasites
Not killed by antibiotics - a substance produced by micro organisms that kill other micro organisms

no means of nutrition
dont respire

Question 17

Shapes of viruses

Answer 17

round
rod
complex

Question 18

bacteriophage

Answer 18

a virus that infects bacteria

Question 19

medical and economic impact - disadvantages of viruses

Answer 19

Human disease - cold , flu , cold sore, measles , mumps

Plant disease - tobacco mosaic disease

Animal disease - rabies, foot and mouth

Question 20

medical and economic importance of viruses - benefits of viruses

Answer 20

Generic Engineering - transfer genes from one organism to another (vectors)

Control of infections (bacterial infections) may reduce infections by antibiotic resistant bacteria

Question 21

Control and immunity of viruses

Answer 21

Viruses are controlled by the body’s general defence system (e.Q. skin, mucus, stomach acid and phagocytes) and the specific defence system (i.e. antibodies are produced to disable viruses).
Vaccine - immunity to many virus infections can be produced artificially by
vaccination or by injecting antibodies.
Antibiotics kill bacteria but do not affect viruses.**
**Interferons are a range of substances produced by virus-infected cells to protect healthy cells. They can be made artificially and can help to treat colds and other virus infections.
Antiviral drugs are used to treat virus infections. These drugs interfere with viruses without affecting the host

Question 22

Viruses may be controlled by

Answer 22

the general body defences
production of antibodies
vaccination
drugs (partially)

Question 23

During 2009 swine flu spread through the
population of many countries. Younger
people were more at risk of becoming ill
with swine flu than older people. Using
your knowledge of the immune system,
suggest a reason for this.
(2010 HL’Q6)

Answer 23

previous exposure: antibodies, active immunity, memory T cells