3.2.4 Cell recognition and the immune system

Question 1

What type of molecules on the surface of each cell help our immune system to identify it? (1)

Answer 1

Proteins

Question 2

What are examples of targets identified by the immune system using proteins on the surface of cells? (4)

Answer 2

• Pathogens
• Cells from organisms of the same species
• Abnormal body cells
• Toxins

Question 3

What are pathogens? (1)

Answer 3

Disease causing micro-organisms

Question 4

What are 4 examples of pathogens? (4)

Answer 4

• Bacteria
• Viruses
• Fungi
• Parasites

Question 5

What is meant by the term ‘antigens’? (1)

Answer 5

Proteins / glycoproteins that appear ‘foreign’ to the organism exposed to them

Question 6

Describe how antigen variation arises and why immunity to one strand does not confer immunity to new variants (3)

Answer 6

• Some organisms have a high mutation rate and therefore, lead to antigen variation
• Even though a person may become ‘immune’ to one strand
• This will not provide immunity to new forms as they wont be recognised by memory B cells and antibodies

Question 7

Describe the process of phagocytosis (3)

Answer 7

1. Phagocyte engulfs the pathogen
2. This forms a vesicle that fuses with lysosomes
3. Hydrolytic enzymes in lysosome digests the pathogen

Question 8

Describe the process of the cellular response (3)

Answer 8

1. Antigen is presented to helper T cell by antigen presenting cell (phagocyte)
2. Helper T cells with complementary protein receptor will bind to antigen
3. This stimulates the helper T cells to divide by mitosis to produce clones

Question 9

What are the three responses of the cloned helper T cells? (3)

Answer 9

• Activate cytotoxic T cells
• Develop into more helper T cells
• Develop into memory T cells

Question 10

What is the role of the activated cytotoxic T cells? (2)

Answer 10

• Attach to specific antigens on a pathogen
• Secrete chemicals to destroy the pathogen

Question 11

What is the role of the new helper T cells developed from the cloned helper T cells? (1)

Answer 11

Stimulate B lymphocytes to divide into plasma cells and secrete antibodies

Question 12

What is the role of the memory T cells? (2)

Answer 12

Remain in blood after an infection for a quicker secondary response

Question 13

What are antibodies? (1)

Answer 13

Proteins produced by B lymphocytes

Question 14

What are the structures on an antibody? (5)

Answer 14

• Antigen binding site
• Light chain
• Heavy chain
• Constant region
• Variable region

Question 15

Describe the pattern of amino acids in the constant region (1)

Answer 15

The sequence of amino acids is the same for all molecules of the same type of antibody

Question 16

Describe the pattern of the amino acids in the variable region (2)

Answer 16

• The amino acid sequence varies between different antibody molecules
• So specific to different antigens

Question 17

Describe the formation of antibody-antigen complexes (4)

Answer 17

1. Antigen binding sites on antibodies have a specific tertiary structure
2. That is complementary to the structure of the antigen to which they attach to
3. This forms an antibody-antigen complex
4. Which stimulates agglutination

Question 18

Describe the process of agglutination (3)

Answer 18

1. Antibody uses its two antigen-binding sites to attach to the same antigen present on two different cells
2. This joins the cells together to form a clump (agglutinated mass) of cells
3. Clump is then more easily destroyed eg. phagocytosis

Question 19

Describe how phagocytosis is activated in bacteria (3)

Answer 19

1. Antibody attaches to antigen on the surface of a bacteria and identifies it for destruction by the phagocyte
2. Receptors on the phagocyte recognise and bind to antibody
3. This enables phagocyte to form phagocytosis

Question 20

Describe the role of plasma cells in the primary response (3)

Answer 20

1. Produce antibodies and secrete them into the blood
2. Antibodies will bind specifically to antigens to form antibody-antigen complex
3. This will stimulate the processes that destroy the antigen/pathogen

Question 21

What is the difference between plasma cells and B cells? (2)

Answer 21

• Plasma cells are the effector form of B cells
• When a B cell is activated by its antigen, it can differentiate into a plasma cell

Question 22

How do memory B cells arise in the blood? (1)

Answer 22

Some B cells are stimulated to divide into memory B cells

Question 23

Describe the role of memory cells in the secondary response (3)

Answer 23

• If the same antigen is encountered by memory B cells again, they will divide and develop into plasma cells
• These plasma cells will secrete antibodies quicker and at a higher concentration than the primary response
• Therefore, provides immunity

Question 24

Describe how a vaccine works (5)

Answer 24

1. Vaccine contains antigens from a dead/weakened pathogen
2. T helper cell with a complementary receptor protein binds to the antigen
3. T cell stimulates B cell
4. B cell secretes large amounts of antibody
5. B cell divides to form clones that all produce the same antibody

Question 25

Describe the term 'herd immunity' (2)

Answer 25

- The higher the percentage of people in a population that are vaccinated against a particular antigen/pathogen, the smaller the chance of infection - This is because the probability of encountering an unprotected individual with that particular pathogen will be lower

Question 26

What are the differences between active and passive immunity? (6)

Answer 26

- Active immunity involves memory cells, passive immunity does not - Active immunity involves production of antibodies by plasma cells. Passive immunity involves antibodies introduced into the body from the outside - Active immunity is long term, because antibody is produced in response to antigen. Passive immunity is short term, because antibodies that are given are broken down - Active immunity can take time to develop or work. Passive immunity is fast acting

Question 27

Why are antibiotics ineffective against viruses? (2)

Answer 27

Antibodies affect cellular structures either by inhibiting their division or destroying them Viruses do not contain cellular structures

Question 28

What are the structures in HIV? (5)

Answer 28

- Capsid - Glycoprotein - Viral envelope - RNA - Reverse transcriptase

Question 29

Describe the process of HIV replication (5)

Answer 29

1. Attachment proteins on surface of HIV are used to attach to receptors on helper T cell 2. RNA is injected into the host cell 3. Reverse transcriptase converts RNA to DNA 4. Viral proteins are produced 5. Virus particles assembled and are released from the cell to infect others

Question 30

Describe how HIV is replicated once it is inside helper T cells (4)

Answer 30

1. RNA is converted to DNA using reverse transcriptase 2. DNA is incorporated into helper T cell's DNA 3. DNA is transcribed into HIV mRNA 4. HIV mRNA is then translated into HIV proteins for assembly into new viral particles

Question 31

Describe phase 1 in the symptoms of AIDS (1)

Answer 31

The body produces HIV antibodies and there may be a short flu-like illness

Question 32

Describe phase 2 in the symptoms of AIDS (2)

Answer 32

- HIV positive phase - Period between infection and the onset of clinical signs

Question 33

Describe phase 3 in the symptoms of AIDS (2)

Answer 33

- AIDS-related complex (ARC) - Resulting from variety of infections as number of helper T cells decrease

Question 34

Describe phase 4 in the symptoms of AIDS (3)

Answer 34

- Infection of body organs - Possible development of cancers - Death stage

Question 35

Describe the uses of monoclonal antibodies in targeting medication (2)

Answer 35

- You can attach therapeutic drugs to a monoclonal antibody - E.g. cancer cells display a different antigen to healthy cells so can be targeted by attaching a toxic drug to a monoclonal antibody

Question 36

Describe how monoclonal antibodies are used in medical diagnosis (2)

Answer 36

- To detect presence of specific antigens in body fluids to diagnose if a person is infected with a particular disease - To detect presence of specific antibodies produced by a person against an antigen

Question 37

What are some brief ethical issues associated with the use of monoclonal antibodies? (2)

Answer 37

- Monoclonal antibodies are often expensive, raising concerns about who can afford or access these treatments - Development of monoclonal antibodies requires research which is usually done on animals

Question 38

What is the difference between direct and indirect ELISA test? (2)

Answer 38

- Direct = used to detect antigens - Indirect = used to detect antibodies

Question 39

Explain what happens in each step of the direct ELISA test (4)

Answer 39

1. Well is coated with monoclonal antibodies 2. Antigen is added which binds to antibody 3. A second monoclonal antibody binds to antigen 4. Substrate is added and converted by enzyme into coloured product

Question 40

Explain what happens in each step of the indirect ELISA test (4)

Answer 40

1. Well is coated with antigen 2. Specific antibody is added which binds to antigen 3. Enzyme linked antibody binds to specific antibody 4. Substrate is added and converted by enzyme into coloured product

Question 41

What is the rate of colour formation in direct ELISA test proportional to? (1)

Answer 41

The amount of antigen

Question 42

What are some brief ethical issues associated with the use of vaccines? (2)

Answer 42

- There is a lack of information provided about possible side effects - Policies requiring vaccination may conflict with personal freedom and autonomy