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 a pathogen (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 in cases of secondary infection

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 may 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)

Question 27

when HIV infects a human cell, the following events occur.
- a single-stranded length of HIV DNA is made
- the human cell then makes a complementary strand to the HIV DNA
the complementary strand is made in the same way as a new complementary strand is made during semi-conservative replication of human DNA.

describe how the complementary strand of HIV DNA is made (3)

Answer 27

1. complementary nucleotides base pair
2. DNA polymerase
3. nucleotides join together to form new strand/phosphodiester bonds form

Question 28

explain why the anti-AQP4 antibody only damages nerve cells (4)

Answer 28

1. antibody has a specific tertiary structure
2. has a binding site/variable region that is only complementary to one antigen
3. the antigen complementary to this antibody is only found on nerve cells
4. so antibody only forms antigen-antibody complex with nerve cells

Question 29

the structure of the variable region of this monoclonal antibody is identical to the variable region on an anti-AQP4 antibody, but the rest of the structure is different.

suggest how this monoclonal antibody prevents anti-AQP4 damaging nerve cells (2)

Answer 29

1. monoclonal antibody binds to nerve cell antigen so less anti-AQP4 can bind
2. when monoclonal antibody binds it does not damage the nerve cell

Question 30

explain how HIV affects the production of antibodies when AIDs develops in a person (3)

Answer 30

1. less antibody produced
2. because HIV reduces number of t helper cells
3. so fewer B cells stimulated

Question 31

the protein ZO-1 is found on the surface of ileum cells.

a scientist used an anti-ZO-1 monoclonal antibody to identify ileum cells in a sample of intestine observed using an optical microscope.

suggest how the monoclonal antibody helped the scientist to identify the ileum cells (3)

Answer 31

1. ZO-1 located in cell membrane
2. antibody is complementary to ZO-1
3. so binds to it
4. cells are identified with stain linked to antibody

Question 32

suggest how one antibody can be specific to both protein A and protein B (2)

Answer 32

1. part of protein A and B have similar shape
2. antibody is complementary to both

Question 32

describe viral replication (3)

Answer 32

1. attachment proteins attach to receptors
2. viral nucleic acid enters cell
3. nucleic acid replicated in cell OR reverse transcriptase makes DNA from RNA
4. cell produces viral protein
5. virus assembled and released from cell

Question 33

human papilloma virus (HPV) is the main cause of cervical cancer. a vaccine has been developed to protect girls and women from HPV.

describe how giving this vaccine leads to production of antibody against HPV (4)

Answer 33

1. vaccine contains antigens from HPV
2. displayed on antigen-presenting cells/phagocyte
3. specific helper T cell detects the antigen and stimulates a specific B cell
4. B cell divides by mitosis to give plasma cells
5. plasma cell produces antibody

Question 34

some strains of Streptococcus bacteria are more likely to cause lung disease than other strains.

strains that do not cause lung disease are quickly destroyed by phagocytes. phagocytes are stimulated when they bind to murein on the bacteria.

each strain of the bacteria has a capsule of different thickness from the others.

suggest how the bacteria with a thicker capsule are more likely to survive and so cause lung disease (2)

Answer 34

1. thicker capsule so phagocytes less likely to bind to murein
2. reduced phagocytosis so more binary fission can occur

Question 35

the human papilloma virus (HPV) contains a double-stranded DNA genome. which components are found in a HPV?

1. capsid and attachment protein
2. capsid, attachment protein and reverse transcriptase
3. capsule and attachment protein
4. cell-surface membrane and attachment protein

Answer 35

1

Question 36

state one role of a helper T cell (1)

Answer 36

1. stimulating cytotoxic T cells
2. stimulating B cells
3. stimulating phagocytes

Question 37

HPV infects cells that are no longer dividing. the HPV genome contains genes that code for proteins that cause human cells to restart their cell cycles.

HPV infection can cause cancer. explain why (1)

Answer 37

uncontrolled cell division/mitosis

Question 38

HSV infects nerve cells in the face. explain why it infects only nerve cells (3)

Answer 38

1. virus has antigens (attachment proteins) on its surface
2. with complementary shape to receptor on the membrane of nerve cells
3. this receptor is found only on nerve cells

Question 39

describe how mice injected with the human EPO produce anti-human EPO antibody (3)

Answer 39

1. human EPO antigens presented on antigen-presenting cells
2. specific T helper cell stimulates B cell to clone
3. plasma cell produces antibody

Question 40

suggest why there has been a recent increase in the number of children catching measles (1)

Answer 40

the virus has mutated

Question 41

explain why giving children more than one tetanus vaccination develops good immunity against tetanus (2)

Answer 41

1. production of more memory cells
2. so there will be a higher concentration of antibodies in the blood

Question 43

give one reasons why antibiotics are not effective against viruses (1)

Answer 43

do not have bacterial structures OR do not have metabolic processes OR do not have a cell wall/murein

Question 44

explain how the use of antibiotics has led to antibiotic-resistant strains of bacteria becoming a common cause of infection acquired when in hospital (3)

Answer 44

1. some bacteria have alleles for resistance
2. resistant bacteria will survive and reproduce
3. more antibiotics used in hospital than elsewhere OR patients have weakened immune systems