Infection and Immunty

Question 1

What are the differences between the genetic material of bacteria and viruses?

Answer 1

1. Bacteria have DNA - Viruses have DNA or RNA
2. Bacteria have circular genetic material - Viruses have linear/straight genetic material
3. Bacterial DNA is double stranded - Viral DNA/RNA is single or double stranded
4. Bacteria may have plasmids - Viruses do not have plasmids.

Question 2

Name some of the barriers that protect the body from infection?

Answer 2

• Skin
• Stomach acid
• Gut and skin flora

Question 3

How does the skin protect the body from infection?

Answer 3

• Keratin layer of skin prevents entry of microorganisms.
• Salty sweat, urea and fatty acids created by the skin create unfavourable conditions for some microorganisms.
• Skin flora prevent colonisation of other microorganisms.

Question 4

How does stomach acid prevent the body from infection?

Answer 4

The low pH of stomach acid (HCl) kills most bacteria.

Question 5

How does gut flora prevent the body from the infection?

Answer 5

1. They prevent colonisation of other microorganisms
2. By competing for space/nutrients/water/minerals
3. Bacteria also secrete chemicals, such as lactic acid, that are useful in the defence against pathogens.

Question 6

Explain the term infection.

Answer 6

An infection is where a microorganism/s has evaded the body’s barriers to infection and is now inside the tissues/cells of the body.