Viruses

Question 1

Features of viruses

Answer 1

• Non-cellular structures
• 50 times smaller than bacteria( can be seen using an electron microscope

Question 2

Viruses structure

Answer 2

Protein coat and Nucleic acid( DNA or RNA)

Question 3

What are the main chemical components of a virus

Answer 3

• Have an outer protein coat
• Inside the protein coat is a nucleic acid(DNA or RNA)

Question 4

Other things to note about viruses

Answer 4

• Viruses do not contain ribosomes, mitochondria or any other cell organelles( non cellular)
• Viruses require other organelles on a host cell to carry out their metabolic functions.

Question 5

Reasons for classifying viruses as living

Answer 5

• Posses genetic material (DNA or RNA)
• Have a protein coat
• Can replicate

Question 6

Reasons for classifying viruses as non-living

Answer 6

• Are non cellular
• Only have DNA or RNA (not both
• Cannot reproduce by themselves
• Do not have mitochondria or chloroplasts

Question 7

How to distinguish between different viruses

Answer 7

• Shape( Round, rod shape, complex)
• Type of nucleic acid

Question 8

Medical and economic advantages of viruses

Answer 8

• Control of infection: Bacteriophages are viruses that infect bacteria
• Manufacturing of vaccines

Question 9

Medical and economic disadvantages of viruses

Answer 9

• Human diseases: common colds, flu, chicken pox, rabies, AIDS
• Plant diseases: tobacco mosaic disease, potato mosaic disease

Question 10

Replication

Answer 10

Viruses need another cell to replicate (obligate parasites)

Question 11

What is a bacteriophage

Answer 11

A bacteriophage is a virus that infects bacteria

Question 12

Stages in virus replication

Answer 12

1. Attachment: Virus attaches itself to the host cell
2. Entry: Nucleic acid in the virus is pushed in(enters) the host cell
3. Synthesis: Host’s organelles are used to produce more viral nucleic acid and proteins
4. Assembly: Virus assemble occurs resulting in new viruses being made inside the host cell
5. Release: Host cell bursts releasing new viruses (lysis)

Question 13

How does the human body control viral infections

Answer 13

• The general defence system(skin or mucous in trachea) prevent the virus entering body
• Viruses are destroyed by the body’s specific defence system (lymphocytes make antibodies which inactivate antigens that belong to the virus)
• Vaccinations encourage the body to form antibodies
• Anti viral drugs help fight the viral infection
• Antibodies have no effect on viruses

Question 14

HIV and AIDS

Answer 14

HIV(Human Immunodeficiency Virus)
AIDS(Acquired Immune Deficiency Syndrome)
Transmission: HIV enters the body through semen or blood(sexual intercourse or sharing of needles)
Effects: Enters the white blood cell where it may remain dormant and produce no effects OR disable the white blood cells( preventing white blood cells from making antibodies)
Control and Prevention: Always use condoms and avoid sexual intercourse