B5. Cell Recognition and The Immune System

Question 1

What is an infection?

Answer 1

Interaction between pathogen and the body’s various defence mechanisms

Question 2

What are the types of specific defence mechanisms ?

Answer 2

Cell mediated - T lymphocytes; Humoral response - B lymphocytes

Question 3

Describe the specific defence mechanism.

Answer 3

Response is slower and specific to each pathogen

Question 4

Describe the non specific defence mechanism.

Answer 4

Response is immediate and the same for all pathogens

Question 5

Give 2 examples of non specific defence mechanisms.

Answer 5

Physical barrier - skin, phagocytosis

Question 6

What are the types of white blood cells?

Answer 6

Phagocytes and lymphocytes

Question 7

Explain the process of phagocytosis.

Answer 7

Phagocyte recognises the antigens on a pathogen
Cytoplasm of the phagocyte moves round the pathogen, engulfing it.
Pathogen is now contained in a vesicle, phagosome, in cytoplasm.
Lysosome fuses with the phagosome and the lysozymes hydrolyse the pathogen
Phagocyte presents the pathogens antigens, it presents the antigens on its surface to activate other immune system cells.

Question 8

What are antigens?

Answer 8

Any part of of an organism or substance that is recognised as foreign by the immune system and stimulates an immune response

Question 9

Describe B lymphocytes.

Answer 9

B cells, mature in bone marrow; Associated with humoral immunity, involving antibodies present in body fluids

Question 10

Describe T lymphocyte.

Answer 10

T cells, mature in thymus glads; Associated with cell mediated immunity, involving body cells

Question 11

What do T clone cells do?

Answer 11

Develop into memory cells, enabling rapid response into future infections from same pathogen; Stimulate phagocytes to engulf pathogens by phagocytosis; Stimulate B cells to divide and secrete their antibodies; Activate cytotoxic T cells

Question 12

Explain the T lymphocyte response to infection.

Answer 12

Pathogen invades body cells or are taken in by phagocytes; Phagocytes places antigens from pathogen on its cell surface membrane; Receptors on a specific helper T cell fit exactly onto these antigens; Attachment activates T cell to divide rapidly by mitosis and form clones of genetically identical cells, cloned T cells

Question 13

Describe how cytotoxic T cells kill infected cells.

Answer 13

Produces proteins, perforin, that make holes in the cell surface membrane; Cells die due to becoming freely permeable

Question 14

Why are cytotoxic T cells effective against viruse?

Answer 14

Viruses replicate inside cells; Viruses use living cells, sacrificing body cells prevent viruses multiplying

Question 15

Describe the primary immune response.

Answer 15

Plasma cells (survive for a few days) secrete antibodies into blood plasma, destroying of antigens; Production of antibodies and memory cells

Question 16

Describe the secondary immune response.

Answer 16

Memory cells (live for decades) circulate blood and tissue fluids; Contact with known antigen results in rapid division and development into plasma cells and more memory cells; Plasma cells produce antibodies needed to destroy pathogen; New memory cells circulate for future infections; Long term immunity formed

Question 17

Explain the role of B cells in humoral immunity.

Answer 17

Surface antigens of invading pathogens are taken up by a B cell; B cell processes the antigens and presents them on its surface; Helper T cells attach to processed antigens on B cells, activating B cells; B cell activated to divide by mitosis to give clone of plasma cells; Cloned plasma cells produce and secrete specific antibody that exactly fits the antigen on the pathogens surface; Antibody attaches to antigens on pathogen and destroys them; B cells develop into memory cells

Question 18

What are monoclonal antibodies?

Answer 18

Antibodies produced by a clone cell and consisting of identical antibody molecules

Question 19

What is clonal selection?

Answer 19

process of matching the antigens on an antigen presenting cells with antigen receptors on B and T lymphocytes.

Question 20

What is clonal expansion?

Answer 20

Production of many genetically identical daughter cells through cell division of the activated B or T lymphocyte after clonal selection.