Immunity

Question 1

What is an antigen?

Answer 1

A molecule that triggers an immune response when detected by the body.

Question 2

What are pathogens?

Answer 2

Microorganisms that cause diseases.

Question 3

What are antibodies?

Answer 3

Proteins produced by B-cells that bind to complementary antigens.

Question 4

Draw the general shape of an antibody.

Question 5

Why can antibodies only bind to a specific antigen?

Answer 5

The variable region of the antibody has a specific tertiary structure, which is only complementary to one specific antigen.

Question 6

Why is phagocytosis a part of the non-specific immune response?

Answer 6

It reacts with all pathogens in the same way.

Question 7

Describe what happens in phagocytosis.

Answer 7

1. The pathogens release toxins that attract the phagocyte towards it.
2. The phagocyte engulfs the pathogen. This forms a vesicle called a phagosome.
3. The phagosome fuses with a lysosome.
4. The lysosome releases its lysosymes into the phagosome.
5. These kill the pathogen by hydrolysis of their cell walls.

Question 8

What are the two processes that are part of the specific immune response?

Answer 8

1. Cellular response.
2. Humoral response.

Question 9

What is the cellular response?

Answer 9

The response of T-cells to foreign antigens.

Question 10

What are T-cells?

Answer 10

Lymphocytes that are produced in the thymus gland.

Question 11

Describe the cellular response.

Answer 11

1. The phagocytes engulf the pathogen and display their antigen on its cell surface membrane.
2. The T-cells have receptors on their cell membrane, that are complementary to that antigen.
3. The antigen binds to the receptors and the T-cells replicate rapidly by mitosis.
4. It produces cytotoxic cells and helper T-cells.

Question 12

What is the role of the cytotoxic cells produced in the cellular response?

Answer 12

They kill abnormal body cells like tumour cells.

Question 13

What is the role of the helper T-cells produced in the cellular response?

Answer 13

1. They activate the phagocytosis of pathogens.
2. They release chemicals that activate B-cells.

Question 14

What is the humoral response?

Answer 14

The response of B-cells to foreign antigens. This involves the production of antibodies.

Question 15

Where are B-cells produced?

Answer 15

The bone marrow.

Question 16

Describe the humoral response.

Answer 16

1. The B-cells have antibodies on their cell membrane that are complementary to a specific antigen.
2. They also have receptors on their cell membrane that are complementary to the chemicals released by the T-cells.
3. When the antibodies bind to the antigens and the chemicals bind to the receptors on the B-cells, they are activated.
4. They divide and differentiate rapidly to form memory cells and plasma cells.

Question 17

What is the role of the plasma cells?

Answer 17

They release antibodies which bind to antigens and cause them to stick together. This makes it easier for the pathogens to be engulfed and killed by phagocytes.

Question 18

What is the role of the memory cells?

Answer 18

They stay in the blood for a long time. When they come across the pathogen again they divide and differentiate rapidly into plasma cells. The plasma cells then release antibodies.

Question 19

Why is the secondary response faster than the primary response to infection?

Answer 19

The primary response involves the production of helper T-cells, the activation of B-cells and the B-cells binding to an antigen before plasma cells can be produced. The secondary response only needs the antigen to bind to the memory cells they then divide rapidly to form plasma cells that release antibodies.

Question 20

What is passive immunity?

Answer 20

Antibodies are introduced into the body from an outside source.

Question 21

Give an example of natural and artificial passive immunity.

Answer 21

Natural: antibodies received by a baby from its mother’s breast milk.
Artificial: monoclonal antibodies

Question 22

What is active immunity?

Answer 22

Your immune system makes antibodies.

Question 23

Give an example of natural and artificial active immunity.

Answer 23

Natural: exposure to diseases
Artificial: vaccines

Question 24

What are vaccines?

Answer 24

Dead or inactive pathogens are injected into a patient to trigger an immune response

Question 25

What is herd immunity?

Answer 25

If a sufficient number of people are vaccinated diseases are less likely to spread. This protects people who can't get vaccinated

Question 26

What are the ethical issues with vaccines?

Answer 26

1. The vaccines must be tested on animals first. 2. There may be side effects. 3. Volunteers may put themselves at unnecessary risk if the vaccine does not work.

Question 27

What is antigenic variation?

Answer 27

The antigens on pathogens are constantly changing due to genetic mutations.

Question 28

What is the problem with antigenic variation?

Answer 28

The memory cells produced in the primary response won't be able to recognise the antigen on a specific antigen. This is because the antigen will no longer be complementary to the shape of the receptors on the memory cell. This means that plasma cells won't be produced from the memory cells. The primary response has to happen again. The patient may get very ill during this time.

Question 29

How do antibiotics kill bacteria?

Answer 29

They interfere with their metabolic processes.

Question 30

Why do antibiotics not work with viruses?

Answer 30

Antibiotics kill pathogens by interfering with their metabolic processes. Viruses don't have their metabolic processes and use the ones from their host cell. The antibiotics can't interfere with these without harming the host cell.

Question 31

What is used to kill viruses?

Answer 31

Antiviral drugs.

Question 32

What is AIDS?

Answer 32

When the immune system deteriorates and falls apart, this means that a person with AIDS is more susceptible to infections.

Question 33

How does HIV lead to the development of AIDS?

Answer 33

HIV infect and kills helper T-cells. Helper T-cells are needed to trigger an immune response as they activate B-cells, phagocytosis and cytotoxic T-cells. If the body does not have enough T-cells the immune system will not be able to bring about a response to infections.

Question 34

Draw the structure of an HIV.

Question 35

How does HIV replicate?

Answer 35

1. The attachment proteins on the virus bind to receptors on the cell membrane of the helper T-cell. 2. The capsid is released into the host cell. 3. The capsid opens inside the host cell, which releases the viral RNA and reverse transcriptase into the host cell. 4. The reverse transcriptase turns viral RNA into viral DNA. 5. The viral DNA is inserted into the helper T-cell's DNA. 6. The cell starts making viral components to make new viruses.

Question 36

What are monoclonal antibodies?

Answer 36

These are antibodies produced from a single group of genetically identical plasma cells.

Question 37

How can monoclonal antibodies be used to bring anti-cancer drugs to cancerous cells?

Answer 37

1. The antibodies can be complementary to tumour markers on cancer cells. 2. Anti-cancer drugs can be attached to these monoclonal antibodies. The antibodies bind to the tumour markers and release that drug. 3. This drug can then kill the cancerous cells.

Question 38

How can monoclonal antibodies be used in pregnancy tests?

Answer 38

1. The application area contains antibodies bound to coloured beads complementary to the hCG hormone. 2. When urine is applied to the application area, any hCG present will bind to the antibodies on the beads, forming an antigen-antibody complex. 3. The urine will move up the test strip, carrying the beads. 4. Further up, the test strip contains immobilised antibodies complementary to the hCG antibody complex. 5. The immobilised antibody binds to any hCG, concentrating the hCG antibody complex with the blue beads attached. 6. The test strip will turn blue if hCG is present.

Question 39

What is an ELISA test?

Answer 39

It allows you to see if a patient has antibodies that bind to a specific antigen or antigens that bind to a specific antibody.

Question 40

What is a direct ELISA test?

Answer 40

It is used to see if a patient possesses antigens that bind to a specific antibody.

Question 41

Describe how a direct ELISA test is carried out.

Answer 41

1. Antigens from a patient are added to a well in a plate. 2. An antibody with an enzyme attached to it that is complementary to the antigen of interest is added. 3 If the antigen of interest is present, it will bind to the antibody. 4. The well is washed out to remove any unbound anybody. 5. If the antigen of interest is present, the bound detection antibody will remain. 6. A substrate is added. If the detection antibody is present, the enzyme attached to it will react with the substrate to give a color change.

Question 42

What is an indirect ELISA test?

Answer 42

It is used to see if a patient possesses antibodies that bind to a specific antigen.

Question 43

Describe how an indirect ELISA test is carried out.

Answer 43

1. Antigens from HIV are bound to the inside of a well in a plate. 2. A sample of the patient's plasma, which contains many different antibodies, is added to the well. 3. If any antibodies are complementary to the HIV antigen, they will bind to the HIV antigens. 4. A second antibody with a specific enzyme attached is added to the well. This binds to the primary antibody present. 5. The well is washed out to remove any unbound antibodies. 6. If the primary antibody is present, the secondary antibody will remain. 7. A substrate solution is added. 8. If the secondary antibody is present, then the substrate will react with the enzyme to produce a colour change.