TOPIC 2C - CELLS AND THE IMMUNE SYSTEM

Question 1

Give the definition of antigens.

Answer 1

Antigens are molecules (usually proteins) that can generate an immune response when detected by the body.

They are usually found on the surface of cells and are used by the immune system to identify:

• Pathogens
• Abnormal body cells (E.g. cancer cells)
• Toxins and cells from other individuals of the same species (e.g. organ transplants)

Question 2

What are the 4 main stages in the immune response?

Describe each stage.

Answer 2

1. Phagocytes engulf pathogens
2. Phagocytes activate T-cells
3. T-cells activate B-cells, which divide into plasma cells
4. Plasma cells make more antibodies to a specific antigen.

(see page 44 in the revision guide)

Question 3

How are antibodies specific to an antigen?

Answer 3

Antibodies are proteins - they’re made up of chains of amino acids.
The specificity of the antibody depends on its variable regions, which form the antigen binding sites. Each antibody has a variable region with a unique tertiary structure (die to different amino acid sequences) that’s complementary to one specific antigen. All antibodies have the same constant region.

Question 4

Draw and label the structure of an antibody.

Answer 4

(see page 44 in the revision guide)

Question 5

What 2 responses can the immune response be split into?

Answer 5

• Cellular

- Humoral

Question 6

What is the cellular response in the immune response?

Answer 6

The T-cells and other immune system cells that they interact with, e.g. phagocytes, form the cellular response.

Question 7

What is the humoral response in the immune response?

Answer 7

B-cell, clonal selection and the production of monoclonal antibodies form the humoral response.

Question 8

Describe what happens in the primary immune response.

Answer 8

(see page 45 in the revision guide)

Question 9

Describe what happens in the secondary immune response.

Answer 9

(see page 45 in the revision guide)

Question 10

How do vaccinations protect individuals and populations against disease?

Answer 10

(see page 46 in the revision guide)

Question 11

What is a disadvantage of taking a vaccine orally?

Answer 11

It could be broken down by enzymes in the gut or the molecules of the vaccine may be too large to be absorbed into the blood.

Question 12

Why are booster vaccines sometimes given later on after the first vaccine (e.g. after several years)?

Answer 12

To make sure that memory cells are produced.

Question 13

How can antigenic variation help some pathogens evade the immune system?

Answer 13

(see page 46 in the revision guide)

Question 14

How does antigenic variation affect the production of vaccines?

Answer 14

(see page 46 in the revision guide, the blue box)

Question 15

What is active immunity?

Answer 15

The type of immunity you get when your immune system makes its own antibodies after being stimulate by an antigen.

1. Natural - this is when you become immune after catching a disease.
2. Artificial - this is when you become immune after you’ve been given a vaccination containing a harmless does of antigen.

Question 16

What is passive immunity?

Answer 16

The type of immunity you get from being given antibodies made by a different organism - your immune system doesn’t produce any antibodies of its own.

1. Natural - when a baby becomes immune due to the antibodies it receives from its mother, through the placenta and in breast milk.
2. Artificial - when you become immune after being injected with antibodies from someone else. e.g. if you contract tetanus you can be injected with antibodies against the tetanus toxin, collected from blood donations.

Question 17

Give 4 differences between active and passive immunity.

Answer 17

(see page 47 in the revision guide)

Question 18

What are monoclonal antibodies?

Answer 18

Monoclonal antibodies are antibodies produced from a single group of genetically identical B-cells (plasma cells). This means that they’re identical in structure.

You can make monoclonal antibodies that bind to anything you want, e.g. a cell antigens or other substances, and they will only bind to (target) this molecule.

Question 19

How can monoclonal antibodies be used to treat cancer?

Targeting drugs to a particular cell type

Answer 19

(see page 48 in the revision guide)

Question 20

How can monoclonal antibodies be used in pregnancy testing?

Targeting a particular substance for medical diagnosis

Answer 20

(see page 48 in the revision guide)

Question 21

What is an Elisa test?

Answer 21

The enzyme-linked immunosorbent assay.

Allows you to see if a patient has any antibodies to a certain antigen or any antigen to a certain antibody.

It can be used to test for pathogenic infections, for allegers and for just about anything you can make an antibody for.

Question 22

How does an Elisa test work?

Answer 22

(see page 49 in the revision guide)

Question 23

How does an Elisa test work as a HIV test?

Answer 23

(see page 49 in the revision guide)

Question 24

What happened with the MMR vaccine?

Answer 24

(see page 50 in the revision guide)

Question 25

What are 4 ethical issues surrounding vaccines?

Answer 25

(see page 51 in the revision guide)

Question 26

What is an ethical issue surrounding monoclonal antibodies?

Answer 26

(see page 51 in the revision guide)

Question 27

What is HIV?

Answer 27

HIV (human immunodeficiency) is a virus that affects the immune system and eventually causes AIDS (acquired immune deficiency syndrome).

(see page 52 in the revision guide)

Question 28

Draw and label the structure of HIV.

Answer 28

(see page 52 in the revision guide)

Question 29

Describe in 6 steps how HIV replicates inside its Host’s helper T-cells.

Answer 29

(see page 52 in the revision guide)

Question 30

What is are the initial symptoms fo AIDS?

Then as it progresses?

Then during the later stages?

Answer 30

(see page 53 in the revision guide)

Question 31

Why don’t antibiotics work against viruses?

Answer 31

(see page 53 in the revision guide)

Question 32

Is there a cure for HIV?

Answer 32

There is no cure for HIV.

Drugs can be used to slow down the progression of HIV infection and AIDS in an infected person.

The best way to control HIV infection in a population is by reducing its spread. HIV can be spread via unprotected sexual intercourse, through infected bodily fluids and from HIV-positive mother to her foetus.
Not all babies from HIV-positive mothers are born infected with HIV snd taking antiviral drugs during pregnancy can reduce the change of the baby being HIV-positive.