Infections And Immunity

Question 1

Immune response by animals

Answer 1

1. First line of defense is the skin, it prevents the entry of germs
2. Second line of defense involves two responses if the germs do get into the body:
   - the primary response tries to destroy the germs and prevent them from spreading. This can be brought about by: inflammation and fever.
   - the secondary response, if germs start spreading, is to activate the immune system

Question 2

Immune system - secondary response to infection

Answer 2

Immunity is the body’s active response to an infection.
The response involves two main measures:
- destruction of the invading germs
- holding a memory of this response
The immune process involves two main groups of white blood cells:
1. Lymphocytes
2. Phagocytes

Question 3

How do B lymphocytes destroy germs

Answer 3

• Germs have molecules called antigens on their surface
• the antigen tells the B lymphocyte that the germ is “non-human” and is dangerous
• this will cause the B lymphocyte to replicate itself rapidly producing lots of identical cells
• the B lymphocytes are then stimulated to produce proteins called antibodies which are secreted into the plasma which they circulate
• the antibodies will combine with the antigens on the germs surface. This will destroy or neutralise the germs
• some of these B lymphocytes stay in the lymph glands as memory cells

Question 4

Natural immunity

Answer 4

Occurs when a person has an attack of a disease so that antibodies are produces and give protection against a future attack

Question 5

Antigen

Answer 5

A protection or large polysaccharide molecule in the coating of a virus or a bacterium which cause B lymphocytes to make antibodies

Question 6

Antibody

Answer 6

A protein made by B lymphocytes that destroys or neutralises a germ

Question 7

How do antibodies destroy the germs

Answer 7

The antibodies work in a variety of ways, some:

• cause bacterial cells to burst
• make it easier for phagocytes to ingest the germs by labelling the germs for phagocytosis
• make the germs clump together which weakens them
• neutralise bacterial toxins

Question 8

T lymphocytes

Answer 8

These are lymphocytes that matured in a gland in the chest (thymus)

Question 9

Role of T lymphocytes in immune system

Answer 9

1. CD4 cells (helper T cells)
   CD4 cells start the immune response to infections. They do this by helping B lymphocytes, killer T cells and phagocytes to do their work. Without these cells the other cells will not start doing anything.
2. Killer T cells
   Killer T cells destroy body cells infected by viruses and some parasites. Killer cells play a role in destroying cancer cells and transplanted organs
3. Suppressor cells
   Act as breaks stopping the immune system once an infection is over

Question 10

Phagocytes

Answer 10

Are large lymphocytes that can change their shape. They are produced in the red bone marrow. The major role of phagocytes in immunity is to engulf germs by phagocytosis

Question 11

How do phagocytes destroy germs

Answer 11

• Phagocytes move around the body looking for germs
• they van squeeze through gaps in capillary walls and reach almost any part of the body
• when a phagocyte comes into contact with a germ it engulfs it taking it into the cell forming a phagosome
• hydrolytic enzymes in the phagosome digest and thus destroy the germ, the resultant organic molecules are absorbed into the cytoplasm to be used by the cell