2.3 Cell recognition and the immune system

Question 1

what two types of response involve lymphocytes?

Answer 1

cell mediated response (T lymphocytes)
humoral response (B lymphocytes)

Question 2

what is an antigen?

Answer 2

molecule usually found on surface of a cell that can trigger an immune response and production of antibodies

Question 3

what is a pathogen?

Answer 3

an organism that causes disease

Question 4

give three examples of types of pathogens

Answer 4

bacteria, viruses, fungi

Question 5

what are toxins?

Answer 5

harmful molecules released by some pathogens

Question 6

where are antigens usually found?

Answer 6

on the surface of cells

Question 7

what are the two types of defence mechanisms?

Answer 7

specific and non-specific

Question 8

define non-specific response

Answer 8

an immediate response that is the same for all pathogens

Question 9

define specific response

Answer 9

a slow response that is specific to each pathogen

Question 10

give two examples of non-specific response

Answer 10

physical barriers
phagocytosis

Question 11

give two examples of specific response

Answer 11

cell-mediated response
humoral response

Question 12

what is a phagocyte?

Answer 12

a white blood cell that carries out phagocytosis

Question 13

describe the process of phagocytosis [4-5]

Answer 13

• phagocyte recognises foreign antigen
• phagocyte engulfs pathogen
• pathogen is in phagosome
• phagosome fuses with lysosome, forming phagolysosome
• lysozyme enzymes in lysosome digest and hydrolyse pathogen
• phagocyte presents pathogen’s antigens on cell surface

Question 14

what is an antigen-presenting cell?

Answer 14

an immune system cell that processes and presents antigens on its surface to activate other immune system cells

Question 15

where do T-cells mature?

Answer 15

thymus gland

Question 16

where do B-cells mature?

Answer 16

bone marrow

Question 17

what are helper T-cells?

Answer 17

T-cells that release chemical signals to activate other immune system cells

Question 18

what are cytotoxic T-cells?

Answer 18

T-cells that kill abnormal or foreign cells

Question 19

how do cytotoxic T-cells kill abnormal or infected cells?

Answer 19

they produce perforin, which makes holes in the cell-surface membrane, causing it to become freely permeable to all substances

Question 20

describe the process of cell-mediated immunity [5-6]

Answer 20

• phagocyte presents pathogen antigens on its cell-surface membrane
• complimentary receptors on specific helper T-cell bind to these antigens
• this activates T-cell to divide rapidly by mitosis
• clone of genetically identical cells is produced
• cloned cells can develop into memory cells that enable a rapid response upon future infection by the same pathogen, stimulate phagocytes to engulf more pathogens by phagocytosis, stimulate B-cells to divide and secrete antibodies, or activate cytotoxic T-cells to produce perforin and kill infected cells.

Question 21

what is a clone?

Answer 21

a group of genetically identical cells or organisms formed from a single parent as a result of asexual reproduction or artificial means

Question 22

how does the function of cytotoxic T-cells illustrate the importance of cell-surface membranes in the survival of cells? [3-4]

Answer 22

cytotoxic T-cells produce perforin, which makes holes in the cell-surface membrane, causing it to become freely permeable to all substances, resulting in the cell’s death. this shows that cells membranes are vital in maintaining the integrity of cells, as they die without them.

Question 23

describe the process of humeral immunity

Answer 23

• B-cell engulfs pathogen and presents antigens on cell-surface
• helper T-cells bind to antigens on B-cell
• B-cell is now activated
• B-cell divides by mitosis to produce a clone of plasma cells
• cloned plasma cells produce and secrete antibodies specific to the pathogen’s antigens
• antibodies attach to antigens on pathogen and destroy them
• some B-cells develop into memory cells that enable rapid responses upon future infection

Question 24

what are antibodies?

Answer 24

proteins produced by B-cells and secreted by plasma cells that bind to complimentary antigens as part of the immune response

Question 25

describe the structure of an antibody [4-5]

Answer 25

• Y shaped protein
• quaternary structure made up of four polypeptide chains
• two heavy chains and two light chains held together with disulphide bridges
• constant region and variable region
• binding site on variable region is specific and complimentary to one antigen

Question 26

how do antibodies lead to the destruction of a pathogen? [3]

Answer 26

formation of antigen-antibody complex results in agglutination, making them easier to locate for phagocytes, and many pathogens can be phagocytoses at once

Question 27

what are monoclonal antibodies?

Answer 27

antibodies with the same tertiary structure produced from cloned plasma cells

Question 28

how are antibodies specific and complimentary to antigens? [2-3]

Answer 28

• variable region has specific primary structure
• tertiary structure of binding site is unique and complimentary to one antigen
• antigen-antibody complex only forms with complimentary antigen

Question 29

what are memory cells?

Answer 29

white blood cells produced by T and B-cells that remain in the body and remembers how to respond to infections

Question 30

what is the function of memory cells?

Answer 30

to remember a specific antigen and the antibodies it binds to so that a pathogen can be easily and quickly recognised upon future infection. when this happens, the memory cell divides rapidly by mitosis and develop into plasma cells and more memory cells.

Question 31

how does agglutination occur?

Answer 31

antibodies have two binding sites, so can bind to two pathogens at the same time, causing the pathogen to clump together

Question 32

what is the primary response?

Answer 32

when an antigen enters the body for the first time and activates the immune system

Question 33

what is the secondary response?

Answer 33

reinfection of a previous pathogen in the body that triggers a faster and stronger immune response

Question 34

why is the primary response slow? [1-2]

Answer 34

there aren’t many B-cells that make the antibody needed to bind to it, so it takes a long time to produce enough and overcome the infection

Question 35

why is the secondary response fast? [3]

Answer 35

memory cells recognise the antigen so clonal selection happens faster. memory T-cells are activated and divide to produce the correct type of T-cells to kill the antigen carrying cell. memory B-cells are activated and divide into plasma cells that produce antibodies complimentary to the antigen.

Question 36

is the concentration of complimentary antibodies higher during the primary or secondary response to a pathogen entering the body?

Answer 36

secondary, because antigen is recognised after by memory cells, so complimentary antibodies can be made faster and in higher quantities

Question 37

give two examples of how monoclonal antibodies are used in medical TREATMENT

Answer 37

• carries drugs to specific cells
• blocks antigens/receptors on cells

Question 38

how are monoclonal antibodies used in medical diagnosis?

Answer 38

• indicate the presence of a specific antigen
• antibodies are attached to a dye, fluorescent or radioactive marker
• when complementary antigen is present, it will bind the antibody and the marker will become visible
• monoclonal antibodies are used in this way in pregnancy tests

Question 39

explain one ethical issue surrounding the use of monoclonal antibodies [2-3]

Answer 39

production of monoclonal antibodies involves using mice to produce antibodies and tumour cells. production of tumour cells involves deliberately giving mice cancer. some people disagree with the use of animals in this way.

Question 40

describe the process of indirect monoclonal antibody therapy [3]

Answer 40

monoclonal antibodies are produced that are specific and complimentary to antigens on cancer cells. monoclonal antibody has radioactive or cytotoxic drug attached. when monoclonal antibody binds to complimentary receptor, cancer cells are killed.

Question 41

describe the process of direct monoclonal antibody therapy [3]

Answer 41

monoclonal antibodies are produced hat are specific and complimentary to antigen on cancer cells. they are given to patient and attach onto cancer cell receptors. this blocks chemical signals that stimulate the uncontrolled cell growth.