2C - Cells and the Immune System

Question 1

What are the the four main stages of the immune response?

Answer 1

• phagocytes engulf pathogens
• phagocytes activate T-cells
• T-cells activate B-cells, divide into plasma cells
• plasma cells make more antibodies to specific antigen

Question 2

How does a phagocyte engulf a pathogen?

Answer 2

• foreign antigens are recognised
• cytoplasm moves round the pathogen
• pathogen is now contained in a phagocytic vacuole
• lysosome fuses with the vacuole, breaks down pathogen
• antigens are presented by sticking to phagocytes’ surface to activate other immune system cells

Question 3

How do phagocytes activate T-cells?

Answer 3

• it’s receptor proteins bind to complementary antigens presented to it
• helper T-cells release chemical signals
• cytotoxic T-cells kill abnormal and foreign cells

Question 4

How do T-cells activate B-cells?

Answer 4

• antibodies on a B-cell binds to a complementary shaped antigen
• clonal selection
• B-cell divides into plasma cells

Question 5

What is the primary immune response?

Answer 5

• antigen enters the body for this 1st time
• slow response
• memory cells are produced

Question 6

What is the secondary immune response?

Answer 6

• same pathogen enters the body again
• quicker, stronger response
• clonal selection is faster

Question 7

What are vaccines?

Answer 7

• contain dead or inactive antigens that cause the body to produce memory cells

Question 8

What is meant by ‘antigenic variation’?

Answer 8

• pathogens change their surface antigens
• memory cells will not recognise the different antigens
• immune system has to have primary immune response

Question 9

What is meant by ‘active immunity’?

Answer 9

• immune system makes its own antibodies after being stimulated
• natural (becoming immune after catching the disease)
• artificial (vaccinations)

Question 10

What is meant by ‘passive immunity’?

Answer 10

• immune system doesn’t produce any antibodies on its own
• natural (baby becomes immune due to antibodies from its mother)
• artificial (injected antibodies from someone else)

Question 11

What are the differences between active and passive immunity?

Answer 11

• active requires exposure to antigens, passive doesn’t
• passive had immediate protection, active takes a while
• active produces memory cells, passive doesn’t.
• passive is short term, active is long term

Question 12

What are ‘monoclonal antibodies’?

Answer 12

• produced from a single group of genetically identical B-cells
• used to target specific substances or cells

Question 13

What are the stages in an ELISA test?

Answer 13

• antibody with an enzyme attached is used.
• enzyme reacts with a substrate to produce a coloured product
• colour change means antigen or antibody is present

Question 14

What are the ethical issues surrounding vaccines?

Answer 14

• tested on animals before humans
• animal based substances are used
• tricky, risky
• people don’t want to do it due to side effects, but still protected because of herd immunity
• new epidemic means increased demand for vaccinations

Question 15

What is the ethical issue surrounding monoclonal antibody therapy?

Answer 15

• animals are used to produce cells so monoclonal antibodies can be produced

Question 16

What is HIV / AIDS?

Answer 16

• virus that affects the immune system
• immune system deteriorates and eventually fails
• people become more susceptible to infections
• kill helper T-cells

Question 17

What is the structure of HIV?

Answer 17

• a core that contains RNA and proteins
• outer coating of protein (capsid)
• extra outer layer (envelope) made of membrane
• many copies of attachment proteins sticking out

Question 18

How does HIV replicate inside a helper T-cell?

Answer 18

• attachment protein attaches to receptor molecule on cell membrane of T-cell
• capsid is released, uncoats and releases RNA into cells cytoplasm
• reverse transcriptase makes complementary strand of DNA from viral RNA template
• double stranded DNA is made and inserted into DNA
• host cell enzymes make viral proteins from viral DNA
• viral proteins are assembled into new viruses which leave the cell and infect other cells

Question 19

What are the symptoms of AIDS?

Answer 19

• initial symptoms include minor infections of mucous membranes and respiratory infections.
• no. of immune system cells decrease
• late stages mean very low number of immune system cells and serious infections of the brain and respiratory system occur

Question 20

Why can’t antibiotics work against viruses?

Answer 20

• antibiotics do not target human processes
• they attack bacterial enzymes and ribosomes
• viruses don’t have enzymes or ribosomes, they use the host cells
• antibiotics can’t inhibit them