Topic 2C - Cells And The Immune System

Question 1

What is a pathogen?

Answer 1

A harmful microorganism that can cause disease

Question 2

What do antigens allow the immune system to identify? (3)

Answer 2

Pathogens
Abnormal body cells
Toxins

Question 3

What are antigens?

Answer 3

Molecules that can generate an immune response when detected by the body

Question 4

What are the 4 main stages of the immune response?

Answer 4

Phagocytosis
T-cells
B-cells
Antibody production

Question 5

What is a phagocyte?

Answer 5

A type of WBC that carries out phagocytosis

Question 6

How does phagocytosis occur? (5 steps)

Answer 6

1. Pathogen secretes chemicals which is detected by the pathogen
2. Cytoplasm of the phagocyte moves around the pathogen and engulfs it
3. The pathogen is now in the phagocytosis vesicle in the cytoplasm of the phagocyte
4. A lysosome fuses with the vesicle and releases lysozymes. The lysozymes digest the pathogen
5. Phagocyte then presents the pathogens antigens on its surface - this activates other immune cells. Phagocyte acts as an APC (antigen presenting cell)

Question 7

What are T cells?

Answer 7

Another WBC - has receptor proteins on surface which bind to complimentary antigens presented by phagocytes. This activates the b cell.

Question 8

What do helper T cells do?

Answer 8

Release chemical signals that activate and stimulate phagocytes, cytotoxic T cells and activate b cells

Question 9

What do cytotoxic T cells do?

Answer 9

Kill abnormal and foreign cells

Question 10

What do b cells do?

Answer 10

Secrete antibodies

Question 11

What is on b cells?

Answer 11

Covered in antibodies - proteins that bind to antigens to form an antibody-antigen complex

Question 12

What happens in clonal selection?

Answer 12

When a b cell meets a complimentary antigen it binds together
This, aswell as substances released from t helper cells activates the b cell
Activated b cells will divide into plasma cells

Question 13

What are monoclonal antibodies?

Answer 13

Antibodies which are specific to the antigen - bind to the antigen on the surface of the pathogen to form lots of antigen-antibody complexes

Question 14

What is agglutination?

Answer 14

An antibody has 2 binding sites, meaning 2 pathogens can bind at the same time and they become clumped together

Question 15

State the different parts of an antibody? (6)

Answer 15

Variable regions
Light chain
Hinge region
Disulfide bridge
Heavy chain
Constant region

Question 16

What are the 2 responses the immune response is split into?

Answer 16

Cellular
Humoural

Question 17

What is the cellular response?

Answer 17

T cells and other immune cells that they interact with

Question 18

What is the humoural response?

Answer 18

B cells, colonal selection and the production of monoclonal antibodies

Question 19

Describe what happens in the primary response? (5)

Answer 19

Antigen enters the body for the first time
Response is slow as there aren’t many b-cells that can make the antibody needed to bind to it
Eventually body will make enough right antibody to overcome the infection
After exposure, t-cells and b-cells make memory cells
These remain for a long time in the body

Question 20

What would memory t-cells do? What will memory b-cells do?

Answer 20

Remember the specific antigen for next time
Secrete the specific antibodies needed to bind to the antigen

Question 21

What happens during the secondary response? (3)

Answer 21

If same pathogen enters again, response happens much quicker
Clonal selection happens faster
Memory b cells and T cells are activated

Question 22

What are the the 2 types of active immunity? How do they work?

Answer 22

Natural - when you become immune after catching the disease
Artificial - when you become immune after receiving a vaccination

Question 23

What are the 2 types of passive immunity? How do they work?

Answer 23

Natural - when a baby becomes immune due to the antibodies it receives from the mother
Artificial - when you become immune after being injected with antibodies from someone else

Question 24

What are the differences between active immunity and passive immunity? (4)

Answer 24

Active:
Requires exposure to antigen
Takes a while for protection to be developed
Memory cells are produced
Protection is long term

Passive:
Doesn’t require exposure to antigen
Protection isn’t immediate
Memory cells aren’t produced
Protection short term as antibodies given are broken down

Question 25

What is a vaccination?

Answer 25

Dead or weakened pathogen that are injected into a person to trigger an immune response

Question 26

What is herd immunity?

Answer 26

Indirect protection from an infectious disease that happens when a population is immune either through vaccination or immunity developed through previous infection

Question 27

What are the ethical issues surrounding the use of vaccines? (4)

Answer 27

Vaccines are tested on animals beforehand - people may disagree with animal testing Testing vaccine on humans can be risky Some people dont take vaccine dune to fear of side effects, however they can still be protected via herd immunity - some people deem this as unfair If there was a new epidemic then there would be conflict for who should get the vaccine first

Question 28

What is antigenic variation?

Answer 28

When some pathogens change the antigens on the surface of their cell membrane

Question 29

How does antigenic variation affect the production of vaccines?

Answer 29

Pathogen will change the antigens on its surface This means the antibodies in the vaccine will be ineffective so it won’t stop the infection This means new antibodies and vaccines will have to be created

Question 30

What is the ELISA test?

Answer 30

ELISA allows you to see if a patient has any antibodies to a certain antigen or any antigen to a certain antibody

Question 31

How does an ELISA test work?

Answer 31

An antibody is used which has an enzyme attached to it This enzyme can react with a substrate to produce a coloured product This causes the solution in the reaction vessel to change colour If a colour change is present, it shows the antigen or antibody is present in the sample being tested

Question 32

What is the direct ELISA test?

Answer 32

Uses a single antibody that is complimentary to the antigen your testing for Antigens from sample are bound to the inside of a well A detection antibody (with an attached enzyme) that is complimentary to the antigen of interest is added If the antigen of interest is present, it will be immobilised on the inside of the surface of the well and the detection antibody will bind to it The well is then washed out to remove any unbound antibody and a substrate solution is added If the detection antibody is present, the enzyme reacts with the substrate to give a colour change This is a positive result

Question 33

What is the indirect ELISA test

Answer 33

Uses 2 different antibodies Antigen bound to well Sample is added Antibody in sample will stick to antigen Well washed to remove unbound antibodies Secondary antibody with enzyme attached is added Secondary antibody binds to primary antibody Well is washed to remove secondary antibody Substrate added - if reacts colour change will be observed

Question 34

What are the ethical issues surrounding the use of monoclonal antibodies?

Answer 34

Often involve animal rights issues - animals used to produce the cells from which monoclonal antibodies are produced

Question 35

What is HIV?

Answer 35

A virus that affects the human immune system

Question 36

What does HIV do?

Answer 36

Infect and kill helper t-cell, these act as hosts Helper T cells send signals which activate phagocytosis, b-cells and cytotoxic T cells Without enough T cells the immune system is unable to deliver an effective response When helper T cells get critically low

Question 37

What are the symptoms of AIDS?

Answer 37

Initial symptoms include minor infections of mucous membranes As aids progresses, more serious infections occur such as chronic diarrhoea, severe bacterial infections and Tb During late stages, parasite infections and a fungal infection

Question 38

Label the structure of HIV and explain each

Answer 38

Capsid Nuclear envelope - made of membrane from cell membrane of previous host cell Attachment protein - attach to host t-helper cell RNA Reverse transcriptase - needed for viral replication

Question 39

Explain the process of HIV replication (6)

Answer 39

1. The attachment protein attaches to a receptor on the cell membrane on the host helper T cell 2. Capsid is released into the cell, where it uncoats and releases the genetic material into the cells cytoplasm 3. Inside the cell, reverse transcriptase is used to make a complimentary strand of DNA 4. From this, double stranded DNA is made and inserted into human DNA 5. Host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA 6. The viral proteins are assembled into new viruses, which go and infect other cells