2.4 - The immune system

Question 1

What do specific molecules (proteins) on the cell surface enable the immune system to identify?

Answer 1

Pathogens
Cells from other organisms of the same species
Abnormal body cells
Toxins

Question 2

Define antigen

Answer 2

Foreign protein that stimulates an immune response

Question 3

How does antigen variability affect disease and disease prevention?

Answer 3

Increases the spread of disease as vaccines target specific antigens, so if an antigen changes shape vaccine does not work for new strain

Question 4

Describe the process of phagocytosis

Answer 4

Phagosome fuses with lysosome
Virus digested by lysozymes
Antigen from virus displayed on cell-surface membrane

Question 5

Describe the cellular response (T-lymphocytes)

Answer 5

Foreign antigens presented by phagocytes bind to specific receptors on cell surface of T cells, which activates them

Question 6

What do helper T cells stimulate?

Answer 6

Cytotoxic T cells, more helper T cells, B cells, phagocytes

Question 7

Describe the response of B lymphocytes to a foreign antigen in the humoral response

Answer 7

B cell binds to complementary receptor (clonal selection)
B cell divides by mitosis (clonal expansion)
Plasma cells produce monoclonal antibodies
Plasma cells produce memory cells

Question 8

What is an antibody?

Answer 8

A protein specific to an antigen produced by B cells

Question 9

Draw a labelled diagram of the structure of an antibody

Question 10

How is an antigen destroyed?

Answer 10

Formation of antigen-antibody complex which leads to agglutination and phagocytosis of bacterial cells

Question 11

Describe the role of plasma cells

Answer 11

Primary immune response

Question 12

Describe the role of memory cells

Answer 12

Secondary immune response

Question 13

What is herd immunity?

Answer 13

When a large proportion of a population are vaccinated against a disease which prevents the disease spreading to unvaccinated individuals

Question 14

What are vaccines?

Answer 14

Introducing small quantities of dead/inactive pathogen into the body to stimulate a primary immune response

Question 15

Describe the differences between active and passive immunity

Answer 15

Active involves memory cells, passive doesn’t
Active involves production of antibody by plasma cells
Passive involves antibody introduced into body from outside source
Active is long term because antibody produced is in response to antigen
Passive is short term as antibody is broken down
Active can take time to develop, passive is fast acting

Question 16

Draw the structure of the human immunodeficiency virus (HIV)

Question 17

How does HIV cause the symptoms of AIDS?

Answer 17

After infection of T helper cell, T helper cell is killed. HIV spreads so more are killed, which weakens the immune system

Question 18

Why are antibiotics ineffective against viruses?

Answer 18

Antibiotics target the cell wall and viruses have a capsid coating as they are a acellular

Question 19

Define monoclonal antibody

Answer 19

Antibody produced from identical B plasma cell

Question 20

Name two things monoclonal antibodies are used for

Answer 20

Medical diagnosis
Targeting medication to specific cell types by attaching a therapeutic drug to an antibody

Question 21

Explain the ethical issues associated with the use of vaccines and monoclonal antibodies

Answer 21

Some thing animal testing is unethical

Question 22

Describe the ELISA test

Answer 22

First antibody binds to antigen
Second antibody with enzyme attached is added
Second antibody binds to antigen
Substrate added and colour changes

Question 23

Give two ways in which pathogens can cause disease

Answer 23

Bacteria release toxins
Kill tissues/cells

Question 24

Describe how a virus is replicated

Answer 24

Attachment proteins attach to receptors on helper T cell
RNA enters cell
Reverse transcriptase converts RNA to DNA
DNA inserted into helper T cell DNA
DNA transcribed into HIV mRNA
Translated into new viral proteins
Viral particles assembled and released