Unit 2- Immunity =)

Question 1

Older people are more likely to suffer from infectious diseases.
Sugest how this may be linked to the decrease in the mean concentration of protein in the blood as people get older. (1)

Answer 1

↓ antibodies

Question 2

If a sheep is injected with the box jellyfish venom on more than one occasion a higher yield of antivenom is obtained.
Explain why. (2)

Answer 2

• stimulates prod of memory cells
• secondary response
• quicker antibody prod

Question 3

Injecting antivenom does not give a person lasting protection against the venom of box jellyfish.
Explain why. (2)

Answer 3

• passive immunity
• x memory cells produced
• antivenom breaks down (after treatment)

Question 4

Suggest one possible problem in injecting people with antivenom made in sheep. (1)

Answer 4

• antibodies from an animal would trigger an immune response

Question 5

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

Answer 5

• attracted by/ recognises antigen
• engulfs
• enclosed in vesicle + fuses w/ lysosome
• hydrolysed by enzymes

Question 6

What is the role of the disulfide bridge in forming the quaternary structure of an antibody? (1)

Answer 6

Joins 2 polypeptides

Question 7

In Europe, viruses have infected a large number of frogs of different species. The viruses are closely related and all belong to the Ranavirus group.
Previously, the viruses infected only one species of frog.
Suggest and explain how the viruses became able to infect other species of frog. (2)

Answer 7

• mutation in viral DNA
• tertairy structure of attachment protein changed
• ✔️ bind to recptors of other species

Question 8

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

Answer 8

• ✔️ identify proteins from genetic code
• ✔️ identify potential antigens

Question 9

Describe how the B lymphocytes of a frog would respond to vaccination against Ranavirus.
You can assume that the B lymphocytes of a frog respond in the same way as B lymphocytes of a human. (3)

Answer 9

• B cells bind to complementary antigen
• divide by mitosis
• Plasma cells produce antibodies
• memory cells

Question 10

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

Answer 10

• RNA converted into DNA by reverse transcriptase
• DNA incorporated into TH cell’s DNA in nucleus
• transcribed into HIV mRNA
• translated into new HIV proteins
• assembled into viral particles

Question 11

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

Answer 11

• ❌antibodies produced
• ∵ HIV destroys TH cells
• ❌stimulate B-cells –>❌divide by mitosis to produce plasma cells

Question 11

Describe and explain the role of antibodies in stimulating phagocytosis.
Do not include details about the process of phagocytosis. (2)

Answer 11

• bind to antigens
• agglutination

Question 12

Explain how the treatment with antivenom works and why it is essential to use passive immunity, rather than active immunity. (2)

Answer 12

• antibodies destroy antigens by binding
• active- too slow

Question 13

A mixture of venoms from several snakes of the same species is used to produce antivenom.
Suggest why. (2)

Answer 13

• snakes within one species may have diff. forms of antigen
• diff. antibodies (so complementary to several antigens)

Question 14

During vaccination, each animal is initially injected with a small volume of venom. Two weeks later, it is injected with a larger volume of venom.
Use your knowledge of the humoral immune response to explain this
vaccination programme. (3)

Answer 14

• B cells specific to venom- divide by mitosis
• produce plama cells + memory cells
• 2nd dose stimulates faster antibody production + in ↑ conc.

Question 15

Azidothymidine (AZT) is a drug used to treat people infected with human immunodeficiency virus (HIV). It inhibits the enzyme that synthesises
DNA from HIV RNA.
Suggest why this does not destroy HIV in the body but stops or slows the development of AIDS. (4)

Answer 15

• infected person already has HIV DNA in their DNA
• new HIV still made
• reverse transcriptase inhibited
• stops new HIV from forming new HIV DNA
• stops destruction of ↑ infected T cells
• immune system can still work (∴ AIDS ❌develop)

Question 16

Give two ways in which pathogens can cause disease. (2)

Answer 16

• release toxins
• kill cells

Question 17

Honey contains a high concentration of
sugar.
Use your knowledge of water potential to suggest how putting honey on a cut kills
bacteria. (3)

Answer 17

• Ψ in bacterial cells > honey
• leaves cells by osmosis
• metabolic reactions stop–> dies

Question 18

What is an antigen? (2)

Answer 18

• foreign protein
• stimulates an immune response

Question 19

What is an antibody? (2)

Answer 19

• protein specific to an antigen
• produced by B cells

Question 20

Describe how vaccination can lead to protection against bacterial meningitis. (6)

Answer 20

1. antigens on surface of bacterium bind to surface receptors on specific B cell
2. B cells divide by mitosis to produce plasma cells
3. ∵ stimulated by T cells
4. plasma cells release antibodies
5. some B cells form memory cells
6. produce (↑) antibodies + quicker

Question 21

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

Answer 21

1. vaccine contains antigen of pathogen
2. macrophage present antigens on its surface
3. T cells w/ complementary receptor protein binds to antigen
4. stimulates B cells
5. w/ complementary antibody on its surface
6. releases large amounts of antibody
7. B cell divides to form clones- all producing same antibody

Question 22

Explain why the number of HIV particles in blood rises during the first few months after infection. (2)

Answer 22

• HIV invading cells–> make new HIV particles
• cells release viruses into blood

Question 23

Explain why the number of HIV particles in the blood remains low between 1 and 7 years after infection. (1)

Answer 23

• virus remains dormant (exists as DNA in host DNA)

Question 24

A person developed a large number of infections about 9 years after he first becaome infected with HIV. Explain why. (4)

Answer 24

1. HIV **destroys** T-cells 2. ↑ viruses produced ∴ ↓ T-cells 3. ↓ T-cells **activate B-cells** 4. ↓ antibody prod. 5. compromised immune system--> inability to fight infections 6. **opportunistic infections**

Question 25

What is an *attenuated* microorganism? (2)

Answer 25

- **alive** - but **x cause symptoms** of disease (avirulent)

Question 26

It took more than a week for antibodies to appear in the child's blood after the first vaccination. Explain why. (2)

Answer 26

Takes time for: 1. **antigens to be recognised** 2. **T-cells to be activated** 3. B-cells to be activated/ plasma cells to release antibodies

Question 27

Explain why this ELISA test would detect vCJD protein, but not other antigens in the urine. (2)

Answer 27

- antibodies are **specific** - other antigens **diff. shape** --> x bind to antibodies

Question 28

Explain why the antibodies used in an ELISA test must be monoclonal antibodies. (1)

Answer 28

- all have **same shape** - only bind to **specific antigen**

Question 29

Why is it important to wash the plate after a second antibody is added in an ELISA test? (2)

Answer 29

- **second** antibody would remain - enzyme still **react** w/ substrate when x antigens present

Question 30

When a pathogen causes an infection, plasma cells secrete sntibodies which destroy this pathogen. Explain why these antibodies are only effective agasint a specific pathogen. (2)

Answer 30

- **antibodies- specific TERTIARY STRUCTURE** - complementary to antigen (bind --> antibody-antigen complex)

Question 31

Ebola is a rare disease in humans, passed onto humans from wild animals. Suggest, using your knowledge of the immune system, why the disease spreads faster once it is presnt in one human in an urban area. (4) ## Footnote dk if it's a real one

Answer 31

1. rare- x prev. immunity 2. takes time to recognise antigen, clone B cells, release antibodies 3. **infectious while immune system still fighting pathogen** 4. contagious- eg. contact w/ body fluids/ contaminated clothing

Question 32

The vaccine is made from HPV types 16 and 18. Explain why this vaccine may not protect against other types of this virus. (2)

Answer 32

1. diff. antigens 2. **x memory cells for those antigens** 3. antibodies x bind

Question 33

3 injections of the HPV vaccine are given. Suggest why. (2)

Answer 33

- ↑ antigens - **↑ memory cells** - ↑ + quicker antibodies

Question 34

People given whole-cell vaccines produced a greater range of antibodies against the bacterium than the people given the vaccines containing parts of the bacterial cells. Explain why. (2)

Answer 34

- many diff. antigens - **each antigen stimulates its own immune response**

Question 35

The scientists concluded from their test that 4% of patients with long-term coughs actually had whooping cough. Explain how they used the results of their test to reach this conclusion. (3)

Answer 35

- only patient who had whooping cough have **toxins** - toxin = **antigen only prodiced by this bacterium** - **∴ presence of specific antibody**

Question 36

What is a monoclonal antibody? (1)

Answer 36

- antibodies produced from **identical plasma cells** - w/ **same tertiary structure**

Question 37

After a disease is diagnosed, monoclonal antibodies are used in some medical treatments. Give one example of using monoclonal antibodies in a medical treatment. (1)

Answer 37

- targets specific cells - block antigens on cells

Question 38

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

Answer 38

1. 1st antibody binds to comp. antiigen 2. **2nd antibody** added- w/ **enzyme attached** 3. 2nd antibody **attaches to antigen** 4. colourless substrate added --> colour changed

Question 39

Give two factors, other than cost, that should be considered when selecting an antibiotic to treat a bacterial disease. (2)

Answer 39

1. side effects/ toxicity to cells 2. interaction w/ other drugs 3. how much resistance the bacteria have built up 4. should only act on problem bacteria

Question 40

Suggest how one antibody can be specific to tick protein and to alpha-gel. (2)

Answer 40

- similar shape - antibody complimentary to both

Question 41

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

Answer 41

1. cells from **other organisms** 2. tumour/ abnormal cells 3. cells **infected by virus**

Question 42

In Europe, viruses have infected a large number of frogs of different species. The viruses are closely related and all belong to the Ranavirus group. Previously, the viruses infected only one species of frog. Suggest and explain how the viruses became able to infect other species of frog. (2)

Answer 42

- mutation in viral DNA - altered 3' struc of viral **attachment protein** - ✔ bind to receptors of other species

Question 43

Stem cell growth factor receptor protein (SCFR) is on the surface membrane of a stem cell. After it has differentiated, SCFR is enclosed within a vesicle and destroyed by a lysosome. Suggest how SCFR is destroyed by a lysosome. (2)

Answer 43

1. vesicle **fuses** w/ lysosome 2. lysosome **hydrolyses** SCFRA

Question 44

Give two types of cell that can stimulate an immune response. (2)

Answer 44

1. pathogens 2. **abnormal** body cells 3. cells from an individual of same species 4. antigen-presenting cell ## Footnote 2. - x dead/ damaged!

Question 45

As humans age, there is a decrease in body protein. Give the name of one body protein that could have resulted in reduced immunity. (1)

Answer 45

antibodies

Question 46

A mother who was infected with HIV gave birth to a baby. The baby tested positive using this test. This does not prove the baby is infected with HIV. Explain why. (2)

Answer 46

- received from mother - solution will always turn blue (before 18 months)