phagocytes T and b cells

Question 1

1. What is an antigen?

Answer 1

Foreign protein; that stimulates an immune response and production of antibody.

Question 2

2. Describe how bacteria are destroyed by phagocytes.

Answer 2

Phagocyte recognises the bacteria as foreign; Phagocyte engulfs the bacteria to form vesicle called a phagosome; Lysosome fuses with phagosome to form a phagolysosome, enzymes/lysozyme digest and hydrolyse bacteria, the antigens are displayed on the cell surface membrane of the phagocyte (it becomes an antigen presenting cell).

Question 3

3. Describe how phagocytosis of a virus leads to presentation of its antigens.

Answer 3

Phagosome fuses with lysosome; The Virus is destroyed by lysozymes ; antigens from the virus are displayed on the cell membrane;

Question 4

4. Phagocytes and lysosomes are involved in destroying microorganisms. Describe how.

Answer 4

Phagocytes engulf pathogens; Enclosed in a vesicle called a phagosome; Lysosomes have enzymes; That digest the microorganism by hydrolysing molecules such as proteins or lipids;

Question 5

5. Describe how presentation of a virus antigen leads to the secretion of an antibody against this virus antigen

Answer 5

Helper T cell binds to the antigen on the antigen-presenting cell; This helper T cell stimulates a specific B cell; B cell clones by mitosis; These form plasma cells that release antibodies;

Question 6

6. What is an antibody?

Answer 6

A quaternary protein specific to an antigen; Produced and secreted by B plasma cells;

Question 7

8. Explain why the antibody will only detect a specific antigen.

Answer 7

The variable region of the antibody has specific amino acid sequence; The tertiary structure of the binding site is complementary to, and binds with these antigens; This forms an antibody-antigen complex.

Question 8

9. Describe the cellular response

Answer 8

T-helper cell binds to specific antigen on the surface of an antigen presenting cell. T-helper cell divides by mitosis to form clones. The helper T-cells activate B-cells, activate cytotoxic T-cells and stimulate phagocytes. Some differentiate into T-memory cells.

Question 9

10. Describe the humoral response

Answer 9

B-cell binds to specific antigen AND is activated by T-helper cells. Activated B-cells divide by mitosis to form clones; they produce plasma cells; and the plasma cells make specific antibodies; B-cells also produce memory cells;

Question 10

11. How do antibodies lead to the destruction of antigens

Answer 10

As antibodies have 2 binding sites, they can cause the agglutination of bacterial cells so that it is easier for phagocytes to engulf them. The binding of an antibody to a pathogen can act as a chemical marker and attracts phagocytes. The binding of an antibody to a pathogen or toxin can neutralise them because they are unable to find to cells when they have antibody attached.