immunity

Question 1

student used sterilised pipette to transfer E.coli into each culture, suggest why number of E.coli cells in each culture might have been lower if student had not used a sterilised pipette (2)

Answer 1

• unknown bacteria introduced
• these bacteria use food and space

Question 2

explain how a fetus is protected against pathogens that infect it’s mother during pregnancy (3)

Answer 2

• antibodies from mother are complementary
• to pathogens crossing the placenta
• giving passive immunity in fetus

Question 3

suggest why there has been a recent increase in number of children catching measles (1)

Answer 3

reduced vaccination in children

Question 4

explain why giving children more than one tetanus vaccination develops good immunity against tetanus (2)

Answer 4

• more memory cells
• higher concentration of antibodies

Question 5

define immunity

Answer 5

the ability of an organism to resist infection

Question 6

give the 2 types of white blood cells and state if they are specific/non-specific

Answer 6

phagocytes- non-specific

lymphocytes- specific

Question 7

define self-cell and non-self cell

Answer 7

self- the body’s own cells and molecules

non-self- foreign cells

Question 8

give the 2 types of lymphocytes and where they mature and what they are involved in

Answer 8

B lymphocytes- mature in bone marrow, involved in humoral immunity

T lymphocytes- mature in thymus gland, involved in cell mediated response

Question 9

what is an antigen presenting cell and give 2 examples

Answer 9

a cell that presents a non-self antigen on it’s surface

e.g. infected body cell, transplanted organ cell

Question 10

what is the cell mediated response

Answer 10

T cells respond to antigens on the surface of cells

Question 11

how many polypeptides in an antibody and what bonds link them

Answer 11

4
disulfide bridges

Question 12

what is a monoclonal antibody (1)

Answer 12

Antibodies with the same tertiary structure
OR
Antibody produced from cloned plasma cells/B cells

Question 13

what is vaccination

Answer 13

introduction of disease antigens into the body

Question 14

what is a vaccine

Answer 14

small amount of weakened/dead pathogen or antigen introduced in mouth or by injection

Question 15

what is herd immunity

Answer 15

if a large proportion of population is vaccinated, it is difficult for pathogen to spread

Question 16

describe antigen variability

Answer 16

pathogen’s DNA can mutate frequently, antigen shape changes, memory cells store memory of old antigen shape so not effective anymore

Question 17

give 3 features of HIV

Answer 17

• lipid envelope
• reverse transcriptase
• RNA

Question 18

explain how HIV replicates (4)

Answer 18

1. Attachment proteins attach to receptors on helper T cell
2. RNA enters cell;
3. Reverse transcriptase converts RNA to DNA;
4. Viral proteins produced;
5. Virus particles assembled and released from cell;

Question 19

Describe how the human immunodeficiency virus (HIV) is replicated once
inside helper T cells (4)

Answer 19

1. RNA converted into DNA using reverse transcriptase;
2. DNA inserted into helper T cell’s DNA
3. DNA transcribed into HIV mRNA;
4. HIV mRNA translated into new HIV proteins for
   assembly into viral particles

Question 20

Describe how a phagocyte destroys a pathogen present in the blood (3)

Answer 20

1. phagocyte engulfs pathogen;
2. Forms phagosome and fuses with lysosome;
3. Enzymes hydrolyse pathogen;

Question 21

Give two types of cell, other than pathogens, that can stimulate an immune
response (2)

Answer 21

1. Cells from transplants;

2.Abnormal/cancer cells;

3. Cells infected by virus;

Question 22

give the role of the disulfide bridge in forming the quaternary structure
of an antibody (1)

Answer 22

Joins two different polypeptides;

Question 23

Explain how HIV affects the production of antibodies when AIDS develops
in a person (3)

Answer 23

1. no antibody produced;
2. Because HIV destroys helper T cells;
3. no B cells activated
   OR
   no B cells undergo mitosis to form plasma cells;

Question 24

viruses have infected a large number of frogs of different species. Previously, the viruses infected only 1 species of frog.
Suggest and explain how the viruses became able to infect other species
of frogs (3)

Answer 24

1. Mutation in the viral DNA/RNA/genome/genetic material;
2. Altered tertiary structure of viral attachment protein;
3. Attachment protein can bind to receptors of other
   species

Question 25

Determining the genome of the viruses could allow scientists to develop a
vaccine.
Explain how (2)

Answer 25

1. they could identify proteins that derive from the genetic code
2. They could then identify antigens to use in the vaccine

Question 26

Describe how the B lymphocytes of a frog would respond to vaccination
against the virus. (3)

Answer 26

1. B cell antibody binds to viral complementary
   antigen;
2. B cell clones
3. Plasma cells
   produce monoclonal antibodies against the
   virus
4. plasma cells produce memory cells;

Question 27

Give one example of using monoclonal antibodies in a medical treatment (1)

Answer 27

targets specific cells e.g. cancer cells
OR
Block antigens on cells;

Question 28

Describe the role of antibodies in producing a positive result in an ELISA
test (4)

Answer 28

1. First antibody binds to complementary antigen;
2. Second antibody with enzyme attached is added;
3. Second antibody attaches to antigen;
4. Substrate added and colour changes;

Question 29

Describe and explain the role of antibodies in stimulating phagocytosis (2)

Answer 29

1. bind to antigen
2. cause agglutination

Question 30

Antivenom contains
antibodies against snake toxin.Explain how treatment with antivenom works and why its essential to
use passive immunity, not active immunity. (2)

Answer 30

1. Antivenom antibodies bind to the
   antigen and destroy it
2. Active immunity would be too slow

Question 31

During vaccination, animal initially injected with small volume of
venom. 2 weeks later, its injected with larger volume of venom.
Use knowledge of humoral immune response to explain this
vaccination programme. (3)

Answer 31

1. B cells specific to the venom reproduce by mitosis;
2. B cells produce plasma cells and memory cells;
3. second dose produces antibodies in higher concentration and quickly

Question 32

Describe how phagocytosis of a virus leads to presentation of its antigens (3)

Answer 32

1. Phagosome fuses with lysosome;
2. Virus destroyed by lysozymes
3. antigen from virus are displayed on the cell
   membrane;

Question 33

Describe how presentation of a virus antigen leads to the secretion of an
antibody against this virus antigen (3)

Answer 33

1. Helper T cell binds to antigen on the antigen-presenting cell
2. This helper T cell stimulates a specific B cell;
3. B cell clones/ divides by mitosis
4. Forms plasma cells that release antibodies

Question 34

define antigen (2)

Answer 34

1. Foreign protein;
2. that stimulates an immune response

Question 35

define antibody (2)

Answer 35

1. A protein specific to an antigen;
2. Produced by B cells

Question 36

When a vaccine is given to a person, it leads to the production of
antibodies against a disease-causing organism. Describe how (5)

Answer 36

1. Vaccine contains antigen from pathogen;
2. Macrophage presents antigen on its surface;
3. T cell with complementary receptor protein binds to antigen;
4. T cell stimulates B cell;
5. With complementary antibody on its surface;
6. B cell secretes large amounts of antibody;
7. B cell divides to form clone all producing same
   antibody.

Question 37

Bacterial meningitis is a fatal disease affecting membranes around
the brain. Neisseria meningitidis (Nm) is a leading cause of it.

children are vaccinated against this disease. Describe how
vaccination can lead to protection against bacterial meningitis.
(6)

Answer 37

1. Antigen on surface of Nm bacterium binds to surface receptor on a specific B cell.
2. Activated B cell divides by mitosis
3. Division stimulated by by T cells;
4. B cells / plasma cells release antibodies;
5. Some B cells become memory cells;
6. Memory cells produce plasma cells / antibodies faster

Question 38

Describe the difference between active and passive immunity (5)

Answer 38

1. Active involves memory cells, passive does not;
2. Active involves production of antibody by plasma cells /
   memory cells;
3. Passive involves antibody introduced into body from outside source
4. Active is long term, because antibody produced in response to
   antigen;
5. Passive is short term, because antibody given is broken down;
6. Active takes time to work, passive is fast acting.

Question 39

vaccines protect people against disease. explain how (5)

Answer 39

1.vaccines contain antigens/ weakened pathogens

2. memory cells made
3. on second exposure memory cells recognise pathogens
4. they rapidly produce antibodies
5. antibodies destroy pathogens

Question 40

some white blood cells are phagocytic. describe how these destroy bacteria (4)

Answer 40

1. phagocyte attracted to bacteria by chemicals
2. engulf bacteria
3. bacteria in vesicle
4. lysosome fuses with vesicle
5. bacteria hydrolysed