Immunity

Question 1

what are the roles of B-lymphocytes and T-lymphocytes in the defence of the body against
a virus infection.

Answer 1

• B cells are involved in humoral response.
• MACROPHAGES present antigens
• b cells bind to antigen;
• increase in numbers by mitosis
• produce plasma cells(which make antibodies)
• antibodies bind to and AGGLUTINATE pathogen
• memory cells produced by 1st exposure then cloned on 2nd exposure
• T cells involved in cell mediated immunity.
• t helper cells produce chemicals which aid B cells cloning
• encourages phagocytes to engulf agglutinated viruses
• killer T cells kill virus infected cells

Question 2

suggest how the drug kills only cancer cells.

Answer 2

• Antibody binds only to cancer cells;
• because of antibody-antigen binding.
• Enzyme activated the drug
• at cancer cells only

Question 3

Immunisation programmes may use either attenuated or dead microorganisms. Suggest
why there might be problems for the patient when using these vaccines.

Answer 3

• Process of killing organisms might not be 100% efficient;
• live organisms might give rise to full-blown disease;
• attenuated organisms are non-virulent;•but might mutate to virulent forms;•immunity can decline - booster injections required;
• named side effects, eg allergies;•less effective due to changed antigens;

Question 4

Describe what is happening during Stage 1.

Answer 4

Formation of vesicle / phagocytosis; Derived from plasma membrane

Question 5

Name Organelle A.

Answer 5

Lysosome

Question 6

Describe the role of Organelle A in the defence against disease.

Answer 6

Contain hydrolytic enzymes;To break down / digest bacterium;

Question 7

Describe how memory cells protect the body from disease

Answer 7

On further exposure to same microorganism;
Antigen recognised;
Faster response;
Greater production of antibodies;

Question 8

HSV can remain inactive inside the body for years (lines 2–3). Explain why this virus can be described as inactive.

Answer 8

1. No more (nerve) cells infected/no more cold sores form;
2. (Because) virus is not replicating;

Question 9

Suggest one advantage of programmed cell death (line 4).
[1 mark]

Answer 9

Prevents replication of virus;

Question 10

The scientists concluded that production of this microRNA allows HSV to remain in the body for years (lines 10–12).
Explain how this microRNA allows HSV to remain in the body for years.
[4 marks]

Answer 10

MicroRNA binds to cell’s mRNA (no mark)
1. (Binds) by specific base pairing;
2. (So) prevents mRNA being read by ribosomes;
3. (So) prevents translation/production of proteins;
4. (Proteins) that cause cell death;

Question 11

Describe how bacteria are destroyed by phagocytes. [3 marks]

Answer 11

1.(Phagocyte engulfs) to form vacuole / vesicle / phagosome;
2. Lysosome empties contents into vacuole / vesicle / phagosome;
3. (Releasing) enzymes that digest / hydrolyse bacteria;

Question 12

What is a poliomyelitis antigen?

Answer 12

Protein / glycoprotein / molecule on surface of virus;

Stimulates immune response / antibody production;

Question 13

Explain why this antibody binds only to an

antigen on a myeloid leukaemia cell.

Answer 13

These antigens/antibodies have complementary/particular shape;
[Reject: Active site]
Allow fitting/binding with (relevant) antibody/antigen;

Question 14

Explain why it was necessary to have a control group.

Answer 14

Results could be compared with control group

Question 15

Explain how B-lymphocytes, plasma cells and memory cells help to protect the body
from disease.

Answer 15

B-lymphocytes respond to specific antigen;
divide rapidly/clone produced;
form plasma cells;
plasma cells secrete antibodies;
some form memory cells which become active on second exposure to antigen;
produce antibodies faster

Question 16

Antibodies are protein molecules. Explain why protein molecules are particularly well
suited to carry out the role of antibodies.

Answer 16

tertiary shape;

complements specific antigen;

Question 17

Give two factors which affect the ability of bacteria to cause a disease

Answer 17

pathogenicity / toxicity of products;
site of infection;
invasiveness;

Question 18

in an antibody, each heavy and light chain is made up from one type of monomer. Name the type of
monomer in each chain.

Answer 18

amino acid

Question 19

Each antibody can form a complex with only one type of antigen. Explain why.

Answer 19

shape of antigen complementary to (shape of)

antibody;

Question 20

The hinge region of the antibody allows both ends to pivot and rotate in relation to one
another. Suggest how this action assists the role of antibodies in agglutination.

Answer 20

allows antibody to lock onto / (easily) make contact with antigen;
more likely / able to make contact
with 2 / more than 1 (identical) antigens;

Question 21

Explain why HIV rapidly entering host cells means that a vaccine might not be effective against
HIV.

Answer 21

1. HIV enters cells before antibodies can destroy it;
2. Antibodies cannot enter cells
   to destroy HIV

Question 22

Describe other ways than, simple diffusion, by which substances cross this membrane.

Answer 22

By osmosis (no mark)

1. Down a water potential gradient;
2. Through water channels;

By facilitated diffusion (no mark)

3. Channel protein;
4. Down concentration gradient;

By active transport (no mark)

5. Carrier protein
6. Against concentration gradient;
7. Using ATP

By phagocytosis (nomark)
8. Engulfing by cell surface membrane to form vesicle

By exocytosis of Golgi vesicles (no mark)
9. Fusion of vesicle with cell
surface membrane;

Question 23

Atheroma formation increases a person’s risk of dying.

Explain how

Answer 23

1. Atheroma is cholesterol depositition;
2. In the wall of artery;
3. (Higher risk of)
   aneurysm/described;
4. (Higher risk of) thrombus
   formation/blood clot;
5. Blocks coronary artery;
6. Less oxygen/glucose to heart
   muscle/cells/tissue;
7. Reduces/prevents respiration;
8. Causing myocardial
   infarction/heart attack;
9. Blocks artery to brain;
10. Causes stroke/stroke described;