Immunity

Question 1

Define an antigen

Answer 1

A cell surface protein which can trigger an immune response.

Question 2

An antigen is ________ to each organism

Answer 2

Specific

Question 3

4 ways in which we get antigens in our bodies?

Answer 3

Pathogens
Abnormal body cells (e.g cancers)
Organ transplants, unless donor is genetically identical
Toxins produced from bacteria

Question 4

Name the two types of Phagocytes

Answer 4

Neutrophils
Macrophages

Question 5

Name the two types of Lymphocytes.

Answer 5

T- Lymphocytes
B- Lymphocytes

Question 6

Describe the process of phagocytosis.

Answer 6

Attraction - mast cells release histamines at the site of infection to attract phagocytes to the site.
Phagocytes “mark” antigens with opsonins, so they can target them to engulf them.
The opsonin with the antigen attached binds to the receptor on the phagocyte, triggering the engulfing of the antigen.
After being engulfed, the foreign antigen is trapped in a phagosome.
A lysosome fuses with the phagosome.
Lysozymes are released into the phagosome.
Pathogen is digested/hydrolysed
Nutrients from the pathogen reabsorbed.
Neutrophil dies forming pus.

Question 7

Structure of an antibody

Answer 7

-Type of glycoprotein called an immunoglobulin.
-It is made of 2 heavy and 2 light polypeptide chains, held together by disulphide bridges.
-Variable region is an antigen binding site which is specific to one antigen.
-Hinge region gives flexibility to bind.

Question 8

3 Actions of Antibodies

Answer 8

-Combine with viruses and bacterial toxins to prevent them from entering cells.
-Attach to the flagellum of bacteria, making them less active and easier for phagocytes to engulf.
-Agglutination of bacteria, reducing chances of spread throughout the body.

Question 9

Role of phagocytes in the immune response

Answer 9

-Pathogens enter the body and are detected by phagocytes
-Pathogens are engulfed and digested (phagocytosis)
-Antigens are presented on the surface of phagocyte

Question 10

Role of T-Lymphocytes in the immune response

Answer 10

T-Helper cell binds to the complementary, presented antigen
T Helper cell is activated to further activate B- Lymphocytes

T- Cytotoxic cells are activated by infected body cells displaying antigens on their surface and kill them by inducing apoptosis.

Question 11

Role of B- Lymphocytes in the immune response

Answer 11

B- Lymphocytes are activated by T cells.
Once the correct B-Lymphocyte has bound to the displayed antigen (clonal selection), it rapidly divides into plasma cells and memory cells (clonal expansion).
Plasma cells produce up to 2000 antibodies per second.
These antibodies are specific to the foreign antigens.
They bind to antigens on the pathogen surfaces to clump pathogens together, or neutralise antigens directly (antitoxins).

Question 12

What is the final step of the immune response?

Answer 12

Pathogen is destroyed/removed from the body.
Memory T and B cells remain in the blood, enabling a faster and stronger response if the same pathogen invades again.

Question 13

What is a pathogen?

Answer 13

An organism which causes disease.

Question 14

What is the cellular response?

Answer 14

T Cells and Phagocytes form this response

Question 15

What is the humoral response?

Answer 15

Formed from B-cells, clonal selection and production of monoclonal antibodies.

Question 16

Features of lymphocytes

Answer 16

Smaller than phagocytes
Large nucleus
Produced in bone marrow
Approximately 10 million in the bloodstream at any one time.