Immunity

Question 1

Phagocytes and lysosomes are involved in destroying microorganisms. Describe how.

Answer 1

Phagocytes engulf pathogens/microorganisms;
Enclosed in a vacuole / vesicle/ phagosome;
Fuses with lysomsome to for a phagolysosome
Lysosomes have enzymes;
That digest/hydrolyse molecules/proteins/lipids/microorganism;

Question 2

What is an antigen?

Answer 2

Molecule/part of molecule/protein/glycoprotein;

Stimulates immune response;

Question 3

What is an antibody?(2)

Answer 3

Protein/immunoglobulin;
specific to antigen;
idea of “fit’/complementary shape;

Question 4

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

Answer 4

Large variety of different molecules;
range of shapes;
Tertiary shape;
locks onto / complements specific antigen;

Question 5

Vaccines protect people against disease. Explain how.(5)

Answer 5

1. Vaccines contain antigens / antigens are injected;
2. Dead pathogens / weakened pathogens;
3. Memory cells made;
4. On second exposure memory cells produce antibodies / become active / recognise pathogens;
5. Rapidly produce antibodies / produces more antibodies;
6. Antibodies destroy pathogens;
7. Herd effect / fewer people to pass on disease;

Question 6

What is vaccination?

Answer 6

Injection of antigens/toxoids;
(Antigen from) attenuated microorganism/non-virulent microorganisms/dead
Microorganisms/isolated from microorganism;
Stimulates the formation of memory cells;

Question 7

Give two other methods used to prepare vaccines.

Answer 7

Killed microorganism;
modified toxin;
attenuated/heat treated/UV treated microorganism;
genetically engineered antigens;
isolated antigen;

Question 8

Vaccines protect against disease by stimulating the production of memory cells. Describe how memory cells protect the body from disease.

Answer 8

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

Question 9

What is a monoclonal antibody? (2)

Answer 9

Reference to hybrid cell from tumour / cancer and
B-lymphocyte/hybridoma;
antibodies all the same / from one type of plasma cell;
specific to / complementary to / fits only one antigen;

Question 10

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

Answer 10

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 11

Suggest two reasons why parents may decide against vaccination for their children.

Answer 11

consider vaccines to be unsafe / have side effects / damage immune system;
consider natural immunity to be more effective; allow in (a) if not here
religious / ethical objections qualified e.g. objections to use of fetal /
animal tissue;
consider low risk of disease when high percentage of population already
vaccinated/Ref. to ‘Head Effect’

Question 12

Explain how the defence mechanisms of the body reduce the chance of entry by a pathogen.

Answer 12

Epidermis of skin is dead / keratinised so pathogens cannot penetrate;
mucus in respiratory system is trapping sticky pathogens;
cilia move fluid / mucus removing pathogens;
tears / saliva / mucus contain lysozyme breaking down bacterial cell wall;
stomach contains hydrochloric acid which destroys bacteria;
blood clot prevents entry;
fluid nature of tears wash away bacteria;
vaginal acid destroys bacteria;
commensal bacteria on skin compete with pathogen;
sebum (fatty acid) inhibits bacterial growth;

Question 13

Explain how the body responds both generally and specifically to pathogens that enter the blood.

Answer 13

action of phagocytes;
Interferon production;
body temperature increased;
ref to B or T lymphocytes;
activated by non-self-antigen;
either clone / divide by mitosis;
T helper cells role;
B plasma cells produced;
which produces antibodies;
any specific effect (e.g. immobilise /agglutinate / lysis /coat for recognition /
neutralise toxins);
T killer / cytotoxic cell;
perform produced;
memory cell produced;

Question 14

Explain the role of B-lymphocytes and T-lymphocytes in the defence of the body against a virus infection.

Answer 14

B lymphocytes produce antibodies/involved in humoral response;
T lymphocytes involved in cell mediated immunity;
Macrophages present antigens;
(specific) B lymphocytes recognise/bind to antigen;
increase in numbers by mitosis;
produce plasma cells (which make antibodies);
antibodies bind to and clump/ agglutinate virus;
memory cells produced by 1st exposure/cloned on 2nd exposure;
T lymphocytes(helpers) produce lymphokines/chemicals;
which aid B lymphocyte cloning;
encourages phagocytes to engulf clumped virus;
killer T cells kill virus infected cells;