Section 2: Chapter 5: Immunity

Question 1

Explain the process of Phagocytosis.

Answer 1

1) Phagocyte recognises chemicals released by pathogen as foreign.
2) Phagocyte’s receptors binds to pathogen’s antigen.
3) Phagocyte engulfs pathogen, creating a phagosome.
4) Phagosome and lysosome fuse and the enzyme lysozyme hydrolyses/digests the pathogen.
4) Phagocyte presents some of the pathogens antigens on it’s cell surface membrane.

Question 2

Where do B-cells mature?

Answer 2

Bone marrow.

Question 3

Where do T-cells mature?

Answer 3

Thymus gland.

Question 4

What type of lymphocyte is used in cell-mediated immunity?

Answer 4

T-cells.

Question 5

What type of lymphocyte is used in humoral immunity?

Answer 5

B-cells.

Question 6

Explain the process of cell mediated immunity.

Answer 6

1) Pathogens invade body cells or are digested by phagocytes, both leading to their antigens being presented.
2) Receptors on a helper T cell bind to the antigen.
3) T cell divides by mitosis and do one of 4 things:
- Develop into memory cells.
- Stimulate phagocytes.
- Stimulate B cells.
- Activate cytotoxic T cells.

Question 7

What 4 things can T cells divide by mitosis / clone to do?

Answer 7

1) Develop into memory cells.
2) Stimulate phagocytes.
3) Stimulate B cells.
4) Activate cytotoxic T cells.

Question 8

How do cytotoxic T cells kill infected body cells?

Answer 8

• Release perforin.

- Creates pores/holes in cell so their cell surface membrane is open to all substances.

Question 9

Explain the process of humoral immunity.

Answer 9

1) B cells take up a pathogens antigen and present them on it’s surface.
2) Helper T cells bind to the antigen and activate the B cell.
3) B cells divide by mitosis into either plasma or memory cells.
4) Plasma cells secrete antibody specific to antigen, so it can attach to, and destroy pathogen.

Question 10

What are the 6 structures on an antibody?

Answer 10

• Light chain.
• Heavy chain.
• Variable region.
• Constant region.
• Receptor binding site.
• Antigen binding sites.

Question 11

What 2 ways do antibodies help to destroy a pathogen?

Answer 11

• Cause agglutination - clumps bacteria together so phagocyte can locate them easier.
• Markers to stimulate phagocytes.

Question 12

What are monoclonal antibodies?

Answer 12

A type of antibody that can be isolated and cloned outside the body.

Question 13

Example of monoclonal antibody uses.

Answer 13

• Cancer treatment.
• Medical diagnosis.
• Pregnancy tests.

Question 14

How are monoclonal antibodies used in pregnancy tests?

Answer 14

• AB’s ( that are linked to coloured particles) bind to hormone found in pregnant women.
• AB-colour-hormone complex formed and trapped by a second AB to show coloured line on test.

Question 15

What are some ethical issues with using monoclonal antibodies?

Answer 15

• Mice delibrately given cancer so they can produce ABs.
• Have caused death in patient before.
• Testing new monoclonal ABs can be dangerous.

Question 16

What is passive immunity?

Answer 16

Injected directly with antibodies. Short-term, no memory cells produced.

Question 17

What is active immunity?

Answer 17

Immune system comes in contact with pathogen so your own body produces ABs. Long lasting as produce memory cells.

Question 18

What is natural active immunity?

Answer 18

Infected with disease under normal circumstances.

Question 19

What is artificial active immunity?

Answer 19

Injected with pathogen - vaccination.

Question 20

What is herd immunity?

Answer 20

Large amount of population is vaccinated so hard for pathogen to spread.
- Important in protecting people who can’t be vaccinated (babies, ill people).

Question 21

Why don’t vaccinations always work?

Answer 21

• Some people have defective immune systems.
• Could catch disease immediately after vaccination, before it’s had time to work.
• Pathogens can mutate.

Question 22

What are 6 structural features of the HIV virus?

Answer 22

• Attachment protein.
• Matrix.
• Capsid.
• Reverse transcriptase enzyme.
• RNA.
• Lipid envelope.

Question 23

Why is HIV called a retrovirus?

Answer 23

• Contains reverse transcriptase.

- Can turn RNA to DNA.

Question 24

Explain how HIV is replicated.

Answer 24

1) HIV enters bloodstream and attaches to protein found in helper T cells.
2) Protein capsid fuses with cell surface membrane, RNA and enzymes enter cell.
3) Reverse transcriptase converts HIV’s RNA to DNA.
4) This DNA moves into the cells nucleus and inserted into cells DNA.
5) HIV DNA in nucleas makes mRNA that contains instructions for making HIV.
6) mRNA leaves nucleas and protein synthesises new HIV particles.
7) HIV particles leave, taking a bit of cell-surface membrane with them for lipid envelope.

Question 25

What does the ELISA test test for?

Answer 25

Quantity of a protein.

Question 26

Explain the procedure of an ELISA test.

Answer 26

1) Apply sample to a surface so antigens can attach to it.
2) Wash any unattached antigens off.
3) Add specific AB and leave to bind.
4) Wash off excess AB.
5) Add second AB that has enzyme attached.
6) Add enzymes substrate (substrate will bind to enzyme and change colour).
Amount of protein depends on intensity of colour.