The immune system

Question 1

What is an antigen?

Answer 1

Molecules that generate an immune response when detected by the body. The are normally found on the surface of cells and used by the immune system to identify foreign cells.

Question 2

What four things do antigens help the immune system to identify?

Answer 2

Pathogens
Abnormal body cells
Toxins
Cells from other individuals of the same species

Question 3

What is a phagocyte?

Answer 3

A type of white blood cell that carries put phagocytosis. They are the first cells to respond to an immune system trigger inside the body

Question 4

Explain the process of phagocytosis

Answer 4

1. Phagocyte recognises the foreign antigen on the pathogen
2. The cytoplasm of the phagocyte moves round the pathogen and engulfs it
3. The pathogen is contained in a phagocytic vacuole in the cytoplasm of the phagocyte
4. A lysosome fuses with phagocytic vacuole. Lysozymes break down pathogen
5. Phagocyte presents the pathogen’s antigens on its cell surface membrane to activate other immune responses

Question 5

What are T cells?

Answer 5

A white blood cell. They have receptor proteins on their surface which binds to complementary antigens presented to it by phagocytes which activates the T cell

Question 6

What do helper T cells do?

Answer 6

Release chemical signals that activate and stimulate phagocytes and T cells. They also activate B cells

Question 7

What do cytotoxic T cells do?

Answer 7

Kill abnormal and foreign cells

Question 8

What are B cells?

Answer 8

White blood cell that is covered with antibodies. Each B cell has a different shaped antibody on its membrane so binds to different shaped antigens

Question 9

When do B cells become activated?

Answer 9

1. When the antibody on the surface of a B-cell meets a complementary shaped antigen it binds to it.
2. This (along with help from helper T cells) activates the B cell (clonal selection).
3. B cell is now activated to divide by mitosis into plasma cells.

Question 10

What are plasma cells and what do they do?

Answer 10

Identical to B cells (clones)
Secrete loads of antibodies specific to antigens (monoclonal antibodies)
Bind to antigen to form an antigen antibody complex

Question 11

What are antibodies?

Answer 11

Chains of amino acids that have a constant region and a variable region (unique tertiary structure). The specificity of antibodies depends on the variable regions (binding sites). Antibodies have 2 binding sites which means that pathogens become clumped together (agglutination).

Question 12

Name the 2 types of immune response

Answer 12

Cellular
Humoral

Question 13

What is involved in the cellular immune response?

Answer 13

T cells and other immune system cells that they interact with

Question 14

What is involved in the humoral immune response?

Answer 14

B cells, clonal selection and production of monoclonal antibodies from humoral response

Question 15

Describe the primary immune response

Answer 15

Slow response as there aren’t many B cells that make the antibody
Symptoms of disease will show
Eventually body will produce enough antibodies
After being exposed to antigen that T cells and B cells will produce memory cells which stay in the body for a long time
Person is now immune

Question 16

Describe the secondary immune response

Answer 16

Quicker and stronger response
Clonal selection happens quicker
Gets rid of the pathogen before any symptoms show

Question 17

What do memory T cells do?

Answer 17

Remember specific antigens

Question 18

What do memory B cells do?

Answer 18

Record the specific antibodies needed to bind the antigen