CELL RECOGNITION + THE IMMUNE SYSTEM

Question 1

What vaccines are

Answer 1

Vaccines provide protection against disease. What is a vaccine?
Explain this

Contains antigen / proteins / dead / weakened microorganism / pathogen / virus / bacteria; Stimulates production of antibodies / plasma cells / memory cells;

Question 2

How they work

Answer 2

A vaccine stimulates the primary immune response, and produces memory cells against a specific antigen. It assumes that if there is a second infection, then the same antigen will be present on the pathogen.

Question 3

What is meant by herd immunity

Answer 3

Herd immunity arises when a sufficiently large proportion of the population has been vaccinated (and are therefore immune) which makes it difficult for a pathogen to spread within that population
Those who are not immunised are protected and unlikely to contract it as the levels of the disease are so low
It is very important as it allows for the individuals who are unable to be vaccinated (e.g. children and those with weak immune systems) to be protected from the disease
The proportion of the population that needs to be vaccinated in order to achieve herd immunity is different for each disease
If vaccination rates fall below the required level then herd immunity can break down
There was an outbreak of Measles in Swansea in 2012 due to a lack of vaccine uptake

Question 4

External defenses

Answer 4

: Known as the first line of defense, external defenses work to protect an organism from pathogen exposure and include things like the skin, tears and stomach acid.

Question 5

Passive immunity

Answer 5

• Passive involves antibody introduced into body from outside
• Passive short term, because antibody (given) is broken down;
• Passive is fast

Question 6

Active immunity

Answer 6

• Active involves memory cells, passive does not;
• Active involves production of antibodies by plasma cells / memory cells;
• Active long term, because antibodies produced in response to antigen;
• Active (can) take time to develop / work

Question 7

Describe how vaccines produce antibodies against a disease-causing organism?

Answer 7

• phagocytes engulf and become antigen presenting cells
• T-cells with complimentary receptor binds
• T-helper cell stimulates B memory cells
• B cells secrete antibodies, undergo clonal expansion

Question 8

Innate immunity

Answer 8

• natural or genetic immunity, is something an organism is born with, encoded in their genes and protects them throughout their life.

Question 9

Immunity is made up of …

Answer 9

both innate and adaptive arms.

Question 10

Antigens?

Answer 10

Foreign protein presented on the cell-surface mem that stimulates an immune response

Question 11

Phagocytosis

Answer 11

• Engulfment of pathogen by phacyte
  1- Attracted to pathogen and binds to pathogen via receptors
  2- Pathogen engulfed by phagocyte by endocytosis- vesicle is formed (phagosome)
  3- Lysosomes (break down unwanted material) fuse with pathogen and lysozymes (proteolytic enzymes that are present on lytozome)break down pathogen into soluble material
  4- Antigens on the pathogen are presented on the surface of the phagocyte - antigen presenting cell

Question 12

B - cell and t CELLS

Answer 12

• B cells mature in the bone marrow (humoral response)
• T cells mature in thymus gland (cell-mediated response)
• Helper T-cells stimulate B-cell to replicate producing antibodies by plasma cells
  1) Carried memory of specific antigen
  2) Greater rapid production of antibodies

Question 13

Explain the role of B-lymphocytes and T-lymphocytes against virus infection 6 marks

Answer 13

1) B lymphocytes recognise antigen
2) Produce plasma cells which make antibodies
3) Antibodies agglutinate virus
4) T lymphocytes helpers produce chemicals
5) Encourages phagocytes to engulf clumped virus
6) Killer T cells kill infected cells

Question 13

What is an antibody?

Answer 13

Glycoprotein a molecule that stimulates an immune response

Question 14

Suggest why a person may have influenza several times but usually has measles only once 3 marks

Answer 14

1) Influenza has several antigens changing
2) Several types of antibodies needed
3) Measles only one type of antibodies needed

Question 15

People who do not have the specific receptor protein in their cell-surface membranes may be infected with the Ebola virus but do not develop the disease
Explain why they do not develop the disease.

Answer 15

1) Ebola antigen doesn’t bind with receptor
2) Can’t enter cell and reproduce

Question 16

Explain how a blood (plasma) transfusion from a patient recently recovered from Ebola may be an effective treatment

Answer 16

1) Blood transfusion contains antibodies
2) Antibodies specific to Ebola antigen so will bind, antibody-antigen complex formed
3) Virus destroyed

Question 17

A high mutation rate makes it difficult to develop a vaccine

Answer 17

1) Vaccine contains specific antigen
2) Mutation causes antigens to change
3) Antibodies can’t bind to antigen, no antibody-antigen formed

Answer 18

A mouse is injected with an antigen.
This triggers an immune response in the mouse and its lymphocytes will begin producing antibodies specific to the injected antigen.
These lymphocytes do not divide easily so are fused with tumour cells that divide rapidly. These new cells are called hybridomas.
Hybridomas divide rapidly and create lots of cells that all create the same antibody. These antibodies can be collected, purified and used.

Question 19

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

Answer 19

-water potential in bacterial cells is higher than in honey
-water leaves the bacterial cells by osmosis
-loss of water stops metabolic reactions

Question 20

scientists use this antibody to detect an antigen on the bacterium that causes stomach ulcers. explain why the antibody will only detect this antigen

Answer 20

-variable region has a specific amino acid sequence - primary structure
-the tertiary structure of the binding site is complementary to these antigens
-forms a complex between an antigen and and antibody

Question 21

Describe how B-lymphocytes respond when they are stimulated by antigens.

Answer 21

-divide by mitosis
-produce plasma cells
-plasma cells make antibodies
-plasma cells produce memory cells

Question 22

suggest how this antibody stops the growth of a tumor

Answer 22

-antibodies have a specific tertiary structure
-which is complementary to the receptor protein
-prevents growth factor binding to the receptor

Question 23

describe the difference between the primary and secondary response

Answer 23

-primary response is when an antigen enters the body for the first time it activates the immune system. it is a slow response
-secondary response is where the same pathogen enters the body again but the immune response is much faster and stronger

Question 24

explain the structure of an antibody molecule and how this relates to their function

Answer 24

-specific variable region
-creates antigen antibody complexes
-two binding sites - agglutination
-constant region for signalling to immune cells
-hinge region - flexibility

Question 25

explain the role of B cells in the immune response

Answer 25

-specific
-able to divide by mitosis
-differentiate into plasma cells and memory cells
-plasma cells produce antibodies which stimulate phagocytes and carry out agglutination or neutralise toxins
-memory cells involved in secondary response

Question 26

explain the structure of an antibody molecule and how this relates to their function

Answer 26

-specific variable region
-creates antigen antibody complexes
-two binding sites - agglutination
-constant region for signalling to immune cells
-hinge region - flexibility

Question 27

explain the difference between the primary and secondary response

Answer 27

-primary response is slow because there arent many B cells that can make the antibody needed to bind to it. eventually enough will be made and both T cells and B cells will make memory cells
-secondary response- clonal selection happens faster as memory B cells are activated and divide into plasma cells that produce the correct antibody. memory T cells are activated and divide into the correct Tc cell to kill the cell carrying the antigen much faster and before symptoms appear.

Question 28

briefly describe how an antibody leads to the destruction of an antigen

Answer 28

-antigen antibody complexes form and can neutralise the pathogen as follows:
-they bind to the pathogen as foreign-leading to phagocytosis
-they coat the pathogen so that it cannot invade a host cell
-they make pathogens stick together (agglutination) preventing invasion of host cells (easier for phagocytes to identify)
-neutralise the toxins

Question 29

HIV/AIDS is a human disease which is transmitted sexually by blood to blood contact
a. name the cells which HIV infects (1 mark)
b. name the laboratory test which is carried out to determine if someone is HIV positive (1 mark)
c. explain why antibiotics are not effective against HIV (2 marks)

Answer 29

a. T helper cells
b. ELISA test
c. antibiotics do not affect viruses. antibiotics inhibit bacterial enzymes. biological processes affected by antibiotics do not occur in viruses