Cell Recognition And The Immune System - Mark Scheme Answers (study Mind)

Question 1

Explain why antibody A attaches only to the protein found in species of Plasmodium.

Answer 1

1. Antibody has tertiary structure;
2. Complementary to binding site on protein.

Question 2

Explain why antibody B is important.

Answer 2

1. Prevents false negative results;
2. (Since) shows antibody A has moved up strip / has not bound to any Plasmodium protein.

Question 3

(a) HSV infects nerve cells in the face (line 1). Explain why it infects only nerve cells.

Answer 3

1. Outside of virus has antigens / proteins;
2. With complementary shape to receptor / protein in membrane of cells;
3. (Receptor / protein) found only on membrane of nerve cells.

Question 4

(b) HSV can remain inactive inside the body for years (lines 2–3). Explain why this virus can be described as inactive.

Answer 4

1. No more (nerve) cells infected / no more cold sores form;
2. (Because) virus is not replicating.

Question 5

(c) Suggest one advantage of programmed cell death (line 4).

Answer 5

Prevents replication of virus.

Question 6

The scientists concluded that production of this microRNA allows HSV to remain in
the body for years (lines 10–12).
Explain how this microRNA allows HSV to remain in the body for years.

Answer 6

1. (Binds) by specific base pairing;
2. (So) prevents mRNA being read by ribosomes;
3. (So) prevents translation / production of proteins;
4. (Proteins) that cause cell death.

Question 7

A mutation of a tumour suppressor gene can result in the formation of a tumour. Explain how

Answer 7

1. (Tumour suppressor) gene inactivated / not able to control / slow down cell division;
2. Rate of cell division too fast / out of control.

Question 8

(ii) Not all mutations result in a change to the amino acid sequence of the
encoded polypeptide.
Explain why.

Answer 8

1. (Genetic) code degenerate;
2. Mutation in intron.

Question 9

Some cancer cells have a receptor protein in their cell-surface membrane that binds
to a hormone called growth factor. This stimulates the cancer cells to divide.
Scientists have produced a monoclonal antibody that stops this stimulation.
Use your knowledge of monoclonal antibodies to

suggest how this antibody stops
the growth of a tumour.

Answer 9

1. Antibody has specific tertiary structure / binding site / variable region;
2. Complementary (shape / fit) to receptor protein / GF / binds to receptor protein / to GF;
3. Prevents GF binding (to receptor).

Question 10

(a) The scientists gave an injection to a mouse to make it produce the monoclonal
antibody used in this investigation (line 7).
What should this injection have contained?

Answer 10

Regulator protein.

Question 11

(b) LDL enters the liver cells (lines 3−4).
Using your knowledge of the structure of the cell-surface membrane, suggest how
LDL enters the cell.

Answer 11

1. Lipid soluble / hydrophobic
2. Enters through (phospholipid) bilayer

Question 12

(c) Explain how the monoclonal antibody would prevent the regulator protein from
working (lines 7−8).

Answer 12

1. (Monoclonal antibody) has a specific tertiary structure / variable region / is complementary to regulator protein
2. Binds to / forms complex with (regulator protein)

Question 13

(d) Describe how the control group should have been treated.

Answer 13

1. Injection with salt solution
2. Otherwise treated the same.

Question 14

(a) Suggest two reasons why the percentage of infants vaccinated decreased between
1973 and 1975.

Answer 14

1. (Decrease linked to) few(er) cases of whooping cough;
2. (Decrease linked to) risk of / fear of side effects;
3. Insufficient vaccine available / too expensive to produce / distribute.

Question 15

Between 1980 and 1990, there were three peaks in the number of reported cases of
whooping cough. After 1981, the number of cases of whooping cough in each peak
decreased.
Use the information from the graph to suggest why.

Answer 15

1. Vaccination rate increases;
2. Fewer people to spread the disease / whooping cough / more people immune / fewer susceptible.

Question 16

The percentage of the population vaccinated does not need to be 100% to be
effective in preventing the spread of whooping cough.
Suggest why.

Answer 16

1. More people are immune / fewer people carry the pathogen;
2. So susceptible / unvaccinated people less likely to contact infected
   people.

Question 17

(a) Give two ways in which pathogens can cause disease.

Answer 17

1. (Releases) toxins;
2. Kills cells / tissues.

Question 18

(b) Putting bee honey on a cut kills bacteria. Honey contains a high concentration of
sugar.
Use your knowledge of water potential to suggest how putting honey on a cut kills
bacteria.

Answer 18

1. Water potential in (bacterial) cells higher (than in honey) / water

potential in honey lower (than in bacterial cells);

2. Water leaves bacteria / cells by osmosis;
3. (Loss of water) stops (metabolic) reactions.

Question 19

Describe how HIV is replicated.

Answer 19

1. Attachment proteins attach to receptors on helper T cell/lymphocyte;
2. Nucleic acid/RNA enters cell;
3. Reverse transcriptase converts RNA to DNA;
4. Viral protein/capsid/enzymes produced;
5. Virus (particles) assembled and released (from cell);

Question 20

Use your knowledge of phagocytosis to describe how an ADC enters and
kills the tumour cell.

Answer 20

1. Cell ingests/engulfs the antibody/ADC
2. Lysosomes fuse with vesicle/phagosome (containing ADC);
3. Lysozymes breakdown/digest the antibody/ADC to release the drug;

Question 21

(b) Some of the antigens found on the surface of tumour cells are also found
on the surface of healthy human cells.
Use this information to explain why treatment with an ADC often causes
side effects.

Answer 21

1. ADC will bind to non-tumour/healthy cells;
2. Cause death/damage of non-tumour/healthy cells

Question 22

Suggest and explain two further investigations that should be done before
this ADC is tested on human breast cancer patients.

Answer 22

1. Tested on other mammals to check for safety/side effects;
2. Tested on (healthy) humans to check for safety/side effects;

Question 23

Describe how the human immunodeficiency virus (HIV) is replicated once inside helper T cells (TH cells).

Answer 23

1. RNA converted into DNA using reverse transcriptase;
2. DNA incorporated/inserted into (helper T cell)
   DNA/chromosome/genome/nucleus;
3. DNA transcribed into (HIV m)RNA;
4. (HIV mRNA) translated into (new) HIV/viral proteins (for assembly into viral particles);

Question 24

Use the information given to evaluate the use of BSCT to treat HIV infections.

Answer 24

For
1. (There appears to be) no virus/ HIV(-1)/RNA/DNA, so could be a cure/effective;
2. No CCR5/receptor, so not get HIV(-1) in the future 3. Only one transplant/BSCT needed (shown by patient Q)

Against
1. Don’t know if chemotherapy/radiotherapy is needed
2. Do not know if BSCT alone would be effective;
Do not know which ones having an effect.
3.Could be due to chemotherapy/radiotherapy;

Question 25

Describe how a phagocyte destroys a pathogen present in the blood.

Answer 25

1. Engulfs 2. Forming vesicle/phagosome and fuses with lysosome 3. Enzymes digest/hydrolyse

Question 26

Give two types of cell, other than pathogens, that can stimulate an immune response.

Answer 26

1. (Cells from) other organisms/transplants 2. Abnormal/cancer/tumour (cells) 3. (Cells) infected by virus

Question 27

What is the role of the disulfide bridge in forming the quaternary structure of an antibody?

Answer 27

Joins two (different) polypeptides;

Question 28

Explain how HIV affects the production of antibodies when AIDS develops in a person.

Answer 28

1. Less/no antibody produced; 2. (Because HIV) destroys helper T cells; 3. (So) few/no B cells activated / stimulated

Question 29

Use all of this information to evaluate the effectiveness of the drug in treating AIDS.

Answer 29

Not effective in treating AIDS because 1. Number of T cells < 200 at 4 months; 2. (So) drug is not effective 3. Does not remove (all) HIV (particles) Effective in treating AIDS because Number of T cells > 200 after 5 months So drug is effective AIDS symptoms relieved/removed;

Question 30

In Europe, viruses have infected a large number of frogs of different species. The viruses are closely related and all belong to the Ranavirus group. Previously, the viruses infected only one species of frog. (a) Suggest and explain how the viruses became able to infect other species of frog.

Answer 30

1. Mutation in the viral DNA/RNA/genome/genetic material; 2. Altered (tertiary structure of the) viral attachment protein; 3. Allows it/attachment protein/virus to bind (to receptors of other species);

Question 31

Determining the genome of the viruses could allow scientists to develop a vaccine.

Answer 31

(The scientists) could identify proteins (that derive from the genetic code) (They) could (then) identify potential antigens (to use in the vaccine);

Question 32

Describe how the B lymphocytes of a frog would respond to vaccination against Ranavirus. You can assume that the B lymphocytes of a frog respond in the same way as B lymphocytes of a human.

Answer 32

1. B cell (antibody) binds to (viral) specific/complementary receptor/antigen; 2. B cell clones 3. Plasma cells release/produce (monoclonal) antibodies (against the virus); 4. (B/plasma cells produce/develop) memory cells;

Question 33

What is a monoclonal antibody?

Answer 33

(Antibodies with the) same tertiary structure

Question 34

After a disease is diagnosed, monoclonal antibodies are used in some medical treatments. Give one example of using monoclonal antibodies in a medical treatment.

Answer 34

carries drug to specific cells/antigens/receptors

Question 35

Describe the role of antibodies in producing a positive result in an ELISA test.

Answer 35

1. (First) antibody binds/attaches /complementary (in shape) to antigen; 2. (Second) antibody with enzyme attached is added; 3. (Second) antibody attaches to antigen; 4. (Substrate/solution added) and colour changes;

Question 36

Describe and explain the role of antibodies in stimulating phagocytosis. Do not include details about the process of phagocytosis.

Answer 36

1. Bind to antigen 2. (Antibodies) cause clumping/agglutination

Question 37

When a person is bitten by a venomous snake, the snake injects a toxin into the person. Antivenom is injected as treatment. Antivenom contains antibodies against the snake toxin. This treatment is an example of passive immunity. Explain how the treatment with antivenom works and why it is essential to use passive immunity, rather than active immunity.

Answer 37

1. (Antivenom/Passive immunity) antibodies bind to the toxin/venom/antigen and (causes) its destruction; 2. Active immunity would be too slow/slower;

Question 38

Describe how phagocytosis of a virus leads to presentation of its antigens.

Answer 38

1. Phagosome / vesicle fuses with lysosome; 2. (Virus) destroyed by lysozymes / hydrolytic enzymes; 3. Peptides / antigen (from virus) are displayed on the cell membrane;

Question 39

Describe how presentation of a virus antigen leads to the secretion of an antibody against this virus antigen.

Answer 39

1. Helper T cell / TH cell binds to the antigen (on the antigen- presenting cell / phagocyte); 2. This helper T / TH cell stimulates a specific B cell; 3. B cell clones

Question 40

Collagen is a protein produced by cells in joints, such as the knee. Rheumatoid arthritis (RA) is an auto-immune disease. In an auto-immune disease, a person’s immune system attacks their own cells. RA causes pain, swelling and stiffness in the joints. Scientists have found a virus that produces a protein very similar to human collagen. Suggest how the immune response to this viral protein can result in the development of RA.

Answer 40

1. The antibody against virus (antigen) will bind to collagen; 2. This results in the destruction of the (human) cells / collagen;

Question 41

What is an antigen?

Answer 41

1. Foreign protein 2. (that) stimulates an immune response / production of antibody;

Question 42

What is an antibody?

Answer 42

1. A protein / immunoglobulin specific to an antigen; 2. Produced by B cells

Question 43

Bacterial meningitis is a potentially fatal disease affecting the membranes around the brain. Neisseria meningitidis (Nm) is a leading cause of bacterial meningitis. (a) In the UK, children are vaccinated against this disease. Describe how vaccination can lead to protection against bacterial meningitis.

Answer 43

1. Antigen / epitope on surface of N. meninigitidis / bacterium binds to surface protein / surface receptor on a (specific single) B cell. 2. (Activated) B cell divides by mitosis / produces clone; 3. (Division) stimulated by cytokines / by T cells; 4. B cells / plasma cells release antibodies; 5. (Some) B cells become memory cells; 6. Memory cells produce plasma / antibodies faster

Question 44

When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how.

Answer 44

1. Vaccine contains antigen from pathogen; 2. Macrophage presents antigen on its surface; 3. T cell with complementary receptor protein binds to antigen; 4. T cell stimulates B cell; 5. (With) complementary antibody on its surface; 6. B cell secretes large amounts of antibody; 7. B cell divides to form clone all secreting /producing same antibody.

Question 45

Describe the difference between active and passive immunity.

Answer 45

1. Active involves memory cells, passive does not; 2. Active involves production of antibody by plasma cells /memory cells; 3. Passive involves antibody introduced into body from outside /named source; 4. Active long term, because antibody produced in response toantigen; 5. Passive short term, because antibody (given) is broken down; 6. Active (can) take time to develop / work, passive fast acting.