3.2.4 - CELL IMMUNITY

Question 1

explain how HIV affects the production of antibodies when AIDS develops in a person. (4)

Answer 1

1. less antibodies are produced
2. because HIV reduces number of helper T cells
3. so fewer B cells are stimulated to differentiate into plasma cells which produce antibodies

Question 2

explain in detail how HIV is replicated (6)

Answer 2

1. attachment proteins on the surface of HIV attach to receptors on helper T cells
2. viral RNA is released into the cytoplasm of the cell
3. the enzyme reverse transcriptase converts the RNA into DNA
4. this DNA is then inserted into the helper T cell nucleus
5. the DNA is then transcribed into HIV mRNA
6. HIV mRNA is then translated into new viral proteins to be assembled into viral particles
7. then it is released from the cell

Question 3

describe how a phagocyte destroys a pathogen (3)

Answer 3

1. engulfs the pathogen
2. forms a phagosome and then fuses with lysosomes
3. enzymes (lysozyme) digest the pathogen

Question 4

give three types of cells, other than pathogens, that can stimulate an immune response (3)

Answer 4

1. cells from other organisms
2. cancer cells
3. cells infected by the virus

Question 5

what is the role of the disulfide bridge in forming the quaternary structure of an antibody? (1)

Answer 5

it joins two different polypeptides together

Question 6

suggest and explain how a virus became able to infect other species of an organism (2)

Answer 6

1. there was a mutation in the viral genetic material
2. this altered the tertiary structure of the viral protein (causes antigen variability)
3. allows the attachment proteins to bind to the receptors of other species

Question 7

explain how determining the genome of a virus could allow scientists to develop a vaccine (2)

Answer 7

1. scientists can identify certain proteins that derive from the genetic code
2. they could then identify potential antigens to use in the vaccine (to stimulate production of antibodies)

Question 8

describe how B cells would respond to a vaccination (3)

Answer 8

1. antibodies on the B cell will bind to complementary antigen
2. B cell then divides and differentiates into plasma and memory cells
3. plasma cells will release antibodies against this virus
4. memory cells will also be produced

Question 9

what is a monoclonal antibody? (1)

Answer 9

antibodies with the same tertiary structure

OR

antibody is produced from identical plasma cells

Question 10

give one example of using monoclonal antibodies in a medical treatment (1)

Answer 10

binds to specific antigens
OR
blocks receptors on cells

Question 11

describe the role of antibodies in producing a positive result in an ELISA test (4)

Answer 11

1. the first antibody binds to complementary antigen
2. a second antibody with enzyme attached to it is added
3. the second antibody attaches to the antigen
4. substrate solution is added and colour change takes place to show a positive result

Question 12

describe and explain the role of antibodies in stimulating phagocytosis (2)

Answer 12

1. antibodies bind to antigen (acts as markers)
2. this causes agglutination

Question 13

when a person is bitten by a venomous snake, the snake injects a toxin into the person. antivenom is injected as treatment, which contains antibodies against the snake toxin, this is an example of passive immunity.

explain how this treatment works and why it is essential to use passive immunity rather than active immunity. (2)

Answer 13

1. antivenom antibodies bind to the toxin and cause its destruction
2. passive immunity because active immunity would be too slow.

Question 14

describe how phagocytosis of a virus leads to presentation of its antigens (3)

Answer 14

1. the phagosomes fuses with lysosomes
2. the virus is destroyed by lysozymes
3. antigens from the virus are displayed on the cell membrane

Question 15

describe how presentation of a virus antigen leads to the secretion of an antibody against this virus antigen (3)

Answer 15

1. helper T cell binds to the antigen on an antigen-presenting cell
2. this helper T cell stimulates a specific B cell
3. B cell divides by mitosis
4. forms plasma cells that release antibodies

Question 16

what is an antigen? (2)

Answer 16

1. a foreign protein
2. that stimulates an immune response

Question 17

what is an antibody (2)

Answer 17

1. a protein specific to an antigen
2. produced by B cells

Question 18

describe how vaccination can lead to protection against ______ (6)

Answer 18

1. antigen on surface of pathogen binds to receptor on a specific B cell
2. this B cell divides by mitosis
3. the division is stimulated by T cells
4. B cells release antibodies
5. some B cells become memory cells
6. memory cells lead to fast production of antibodies

Question 19

describe how a vaccine leads to the production of antibodies against a disease causing organism (5)

Answer 19

1. vaccine contains antigens from the pathogen
2. phagocytes present these antigens on it surfaces after phagocytosis
3. T cell with complementary receptor protein binds to the antigen
4. T cell stimulates B cell with complementary antibodies on its surface
5. B cell secretes large amounts of antibody
6. B cell divides to form clones that all produce the same antibody

Question 20

describe the difference between passive and active immunity (5)

Answer 20

1. active involves memory cells, passive does not
2. active involves production of antibodies by plasma cells
3. passive involves antibody introduced into the body from the outside
4. active provides long term immunity because antibody is produced in response to antigen
5. passive provides short-term immunity because antibody is broken down
6. active can take time to develop but passive acts quickly

Question 21

give two ways in which pathogens cause disease (2)

Answer 21

1. by releasing toxins
2. by killing cells/tissue

Question 22

explain why the % of the population vaccinated does not need to be 100% to be effective in preventing the spread of a disease (2)

Answer 22

1. most people no longer carry the pathogen/most are immune to it
2. so unvaccinated people are less likely to contact infected people/come to face the pathogen

Question 23

describe how a control group should be treated (2)

Answer 23

1. inject with placebo
2. otherwise treated the same

Question 24

suggest why a mixture of venoms from several snakes of the SAME species is used to produce antivenom (2)

Answer 24

1. the snakes me have different mutations
2. so there will be several antibodies complementary to several different antigens

Question 25

suggest one reason why animals involved in the creation of antivenom are undergoing observation by a vet (1)

Answer 25

so that the animal does not suffer from the venom

Question 26

some cancer cells have a receptor protein in their cell-surface membrane that binds to a hormone called growth factor. this stimulates cancer cells to divide.

scientists have produced a monoclonal antibody that stops this stimulation.

explain how this antibody stops the growth of a tumour. (3)

Answer 26

1. antibody has a specific tertiary structure
2. with a complementary shape to the receptor protein
3. prevents growth factor binding to the receptor (preventing tumour growing)