Defence Against Parasitic Attack

Question 1

Non-specific defences

Answer 1

• physical barriers
• chemical secretions
• inflammatory response
  -phagocytes
• natural killer cells destroying cells infected with viruses

Question 2

When parasites enter the body what are they destroyed by?

Answer 2

• bacterial cell walls are destroyed by hydrolytic enzymes in mucus, saliva and tears
• cellular proteins in pathogens are destroyed by the low pH environment (sweat glands, secretion of stomach and vagina)

Question 3

What blocks the entry of parasites?

Answer 3

Epithelial tissue

Question 4

How do injured cells defend themselves?

Answer 4

They release signalling molecules. This results in enhanced blood flow to the site, bringing antimicrobial proteins and phagocytes.

Question 5

Phagocytosis

Answer 5

1. Phagocytes arrive at the site of the protein
2. Phagocytes engulf parasite by enfolding their plasma membrane around the parasite
3. The parasite is then brought into the phagocytes in a vacuole. Lysosomes containing digestive enzymes fuse with the vacuole.
4. The enzymes digest the parasite and the digested products are absorbed into the cytoplasm of the phagocyte.

Question 6

How do natural killer cells work?

Answer 6

Natural killer cells can identify and attach to cells infected with viruses, releasing chemicals that lead to cell death by inducing, apoptosis.

Question 7

What monitors the tissues?

Answer 7

A range of white blood cells constantly circulates.

Question 8

Describe the sequence of events that occur if tissues become damaged or invaded

Answer 8

1. If tissues become damaged or invaded, cells release cytokines.
2. This increases blood flow resulting in non-specific and specific white blood cell accumulating at the site of infection/damage.

Question 9

Describe the events that follow an antigen binding to the receptor of a lymphocyte.

Answer 9

Binding of an antigen to a lymphocyte’s receptor selects that lymphocyte to then divide and produce a clonal population of this lymphocyte.

Question 10

Lymphocyte possible functions

Answer 10

• some will produce antibodies
• others can induce apoptosis in parasite-infected cells.

Question 11

How do antibodies have different specificity?

Answer 11

Antibodies possess regions where the amino acid sequence varies greatly between different antibodies.

Question 12

How do antibodies work?

Answer 12

When the antigen binds to the antigen binding site the antigen-antibody complex formed can result in inactivation of the parasite, rendering it susceptible to a phagocyte, or can stimulate a response that results in cell lysis.

Question 13

Memory lymphocyte cells purpose

Answer 13

They are also formed in order to produce a secondary immune response should the individual come in contact with the same antigen in the future. Initial antigen exposure produces memory lymphocytes specific for that antigen so that they can produce a secondary response when the same antigen enters the body in the future