Immune system 2

People with AIDS die because they are unable to produce an immune response to pathogens (lines 2-4).

Explain why this leads to death. (3)

Pathogens cause disease (1)

and damage cells and tissues (1)

by releasing toxins (1)

Explain why each of the following means that a vaccine might not be effective against HIV.

(i) HIV rapidly enters host cells (lines 6-7) (2)

HIV enters cells before antibodies can bind to/ destroy it (1)

Antibodies cannot enter cells to destroy HIV (1)

Explain why each of the following means that a vaccine

might not be effective against HIV.

(ii) HIV shows a lot of antigenic variability. (2)

Antigen on HIV changes/mutates (1)

Specific antibody no longer binds to new antigen (1)

What is an antigen? (2)

a molecule that triggers an immune response (2)

Describe how B-lymphocytes respond when they are stimulated by antigens (4)

Divide by mitosis (1)

Produces plasma cells (1)

Plasma cells make antibodies (1)

Plasma cells produce memory cells (1)

Suggest which labelled component of the virus is most likely to act as an antigen.

Give a reason for your answer. (2)

Glycoprotein (1)

Different shape to body of proteins (1)

A cell that HIV infects is 15 μm in diameter.

Calculate how many times larger in diameter this cell is than an HIV particle. Show your working. (2)

HIV - 80nm (1)

187.5 (1)

Suggest which component of an intact red blood cell is most likely to act as an antigen during a blood transfusion.

Explain your answer. (2)

Glycoprotein (1)

Different shape to body of proteins (1)

This test only detects the presence of HIV antibodies. Give two reasons why it cannot be used to find out if a person has AIDS. (2)

To diagnose AIDS need to look for AID-related symptoms (1)

and number of helper T cells (1)

A mother who was infected with HIV gave birth to a baby. The baby tested positive using this test. This does not prove the baby is infected with HIV. Explain why.

Children receive (HIV) antibodies from their mothers antibodies (1)

So solution will always turn blue/will always test positive (1)

A control well is set up every time this test is used. This is treated in exactly the same way as the test wells, except that blood plasma is replaced by a salt solution.

Use information from the figure above to suggest two purposes of the control well. (2)

1. Only the enzyme / nothing else is causing a colour change (1)

2. Washing is effective / all unbound antibody is washed away (1)

The data obtained in this investigation have been plotted on a graph. How would you join the points? Give a reason for your answer. (1)

Straight lines point to point as not possible to predict intermediate values (1)

Use the graph to describe the effect of MCP on mean antibody production (2)

increases then levels / falls (1)

Maximum antibody production 180 units (1)

The dose of MCP given to the mice was calculated in g per kg body mass. Explain why the dose was calculated per unit mass. (1)

Takes into account different masses of mice / allows comparison (1)

Explain how antibodies were produced when the mice were injected with sheep red blood cells. (3)

Sheep red blood cells have antigens on their surface (1)

Antigens are foreign to mice (1)

And stimulate B cells to produce antibodies (1)

A newspaper suggested that these data show that taking MCP will give people increased resistance to disease.

With reference to the data give two reasons why this conclusion may not be valid. (2)

Response only observed in mice (1)

Disease organisms not investigated (1)

Not all disease caused by pathogens / cured by antibodies (1)

The scientists also grafted skin from one area to another on the same animal. These grafts were not rejected. (1)

To show weather immune response occurred. (1)

They also grafted skin from one area to another on the same animal. Explain why. (1)

To show that rejection did not normally occur (1)

Give three conclusions that you can make from the data in the table above about the time taken for rejection (3)

Rapid rejection between unrelated (domestic) cats (1)

Rapid rejection between (domestic) cat and cheetah (1)

Slow / no rejection in cheetahs / cheetahs are genetically similar (1)

There are proteins on the skin of cheetahs that act as antigens. What do the data inthe table suggest about these cheetah antigens? (1)

Similar antigens on all cheetahs (1)

Antigens are proteins. Explain why a knowledge of antigens can show that animals are genetically similar. (2)

Protein / antigen production determined by alleles (1)

The more similar the proteins the more similar their alleles (1)

HPV vaccine is offered to girls aged 12 to 13 (line 5). Suggest why it is offered to this age group. (1)

- unlikely to be sexually active so you are preventing them getting the virus (1)

The vaccine is made from HPV types 16 and 18 (line 5). Explain why this vaccine may not protect against other types of this virus. (2)

Other (HPV) types have different antigens (1)

No memory cells for other types (1)

Three injections of the vaccine are given (lines 5 to 6). Use your knowledge of immunity to suggest why. (3)

More antigen (1)

more memory cells (1)

more antibodies produced (1)

will be many years before it can be shown that this vaccination programme has reduced cases of cervical cancer (lines 7 to 9).

Suggest two reasons why. (2)

Few people / only teenagers vaccinated (1)

Cervical cancer takes long to develop (1)

Smear tests will continue to be offered to women, even if they have been vaccinated (lines 9 to 10).

Suggest why women who have been vaccinated still need to be offered smear tests. (1)

a different strain of HPV could have caused them to get cervical cancer (1)

Suggest one reason why vaccinating a large number of people would reduce significantly the spread of HPV through the population (lines 14 to 16). (2)

Virus cannot replicate (1)

Non-vaccinated people more likely to contact vaccinated people (1)

What is an antibody? (1)

a blood protein produced in response to a specific antigen (1)