IMMUNOLOGY (CELLS)

Question 1

Define an antigen.

Answer 1

A molecule on the surface of a pathogen that causes antibody production.

Question 2

Define a pathogen.

Answer 2

A microorganism that causes disease.

Question 3

Give two ways in which a pathogen may cause disease when it has entered the body.

Answer 3

Produces toxins.
Damages cells.

Question 4

What is immunity?

Answer 4

Protection against infectious diseases provided by the immune system.

Question 5

What is meant by a non-specific defence mechanism?

Answer 5

Doesn’t distinguish between pathogens/responds the same way to all pathogens
(e.g physical and chemical barriers)

Question 6

All red and white blood cells are produced in the bone marrow. What type of cell are they produced from?

Answer 6

Stem cells

Question 7

What type of white blood cell is non-specific?

Answer 7

Phagocytes

Question 8

When a pathogen enters the body it may be destroyed by phagocytosis. Describe how.

Answer 8

Phagocyte attracted by a chemical and binds to antigen
Engulfs pathogen
Into phagosome
Lysosome fuses with phagosome
And releases its hydrolytic enzymes (lysozymes)
Which hydrolyse the pathogen
Antigen is presented on the cell surface membrane of the phagocyte

Question 9

Describe how antibodies are produced in the body following a viral infection.

Answer 9

Virus contains antigen
Virus engulfed by phagocyte
Presents antigen to T-cells, T helper cells secrete cytokines
SPECIFIC B-cell becomes activated (sees antigen with help of T helper cells)
Divides by mitosis
To form clones (clonal selection)
Plasma cells produce and secrete antibodies
Which are specific to the antigen
Memory cells formed

Question 10

Give three types of cells, other than pathogens, that can stimulate a immune response.

Answer 10

Cells from other organisms/transplants
Abnormal cells
Cells infected by a virus

Question 11

Describe the role of memory cells in the secondary immune response.

Answer 11

Second exposure to antigen produces antibodies IN HIGHER CONCENTRATION and MORE QUICKLY

Question 12

Describe antibody structure.

Answer 12

Quaternary structure because it contains more than 1 polypeptide
Has variable and constant region- constant recognised by phagocytes causing them to engulf bacteria
Each have a different pair of binding sites

Question 13

What are monoclonal antibodies?

Answer 13

Antibodies produced from a single clone of B cells

Question 14

Vaccines protect people against disease. Explain how.

Answer 14

Vaccines contain dead pathogens
Memory cells made
On second exposure memory cells produce antibodies
Rapidly produce antibodies/produce more antibodies
Antibodies destroy pathogens

Question 15

Describe the difference between active and passive immunity.

Answer 15

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

Question 16

A high mutation rate makes it difficult to develop a vaccine. Explain why.

Answer 16

Antigens change/antigenic variability
Vaccine contains specific antigen
Antibodies not complementary to antigen

Question 17

Describe how HIV is replicated.

Answer 17

Attachment proteins attach to receptors on helper T cells
RNA enters cell
Reverse transcriptase
Enzyme uses HIV RNA to make DNA
DNA joined to host cell’s DNA
DNA transcribed into HIV RNA
HIV RNA translated into HIV proteins (for assembly into viral particles)

Question 18

The destruction of T cells by HIV leads to the death of an infected person. Explain how.

Answer 18

No T cells to activate B cells
Person unable to fight infections

Question 19

Why do antibodies only detect one antigen?

Answer 19

Antibody/variable region has specific amino acid sequence/primary structure
The tertiary structure of the antigen binding site
Is complementary with these antigens
Forms complex between antigen and antibody

Question 20

What is the role of antibodies?

Answer 20

Agglutination of cells (possible because antibodies have 2 binding sites)- makes it easier for phagocytes to locate
Act as markers that stimulate phagocytes to engulf the bacterial cells

Question 21

Describe and explain the role of antibodies in stimulating phagocytosis.

Answer 21

Bind to antigen
Cause agglutination/attracts phagocytes

Question 21

Give examples of using monoclonal antibodies in a medical treatment.

Answer 21

Carries drug to specific cells
Blocks antigens on cells

Question 21

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

Answer 21

Antibody binds to complementary antigen
Antibody with enzyme attached is added
Antibody attaches to antigen
Colour changes (once substrate added)