3.2.4 Immunology

Question 1

What is a pathogen?

Answer 1

• Microorganism (bacteria, virus, fungi)
• That causes disease

Question 2

What is a non specific defense mechanism?

Answer 2

Doesn’t distinguish between pathogens/ responds the same way to all pathogens

Question 3

How does a pathogen cause disease after entering the body?

Answer 3

• Produces toxins
• Damages cells

Question 4

Describe how antibodies are produced in the body following an infection

Answer 4

• Virus contains antigen
• Virus engulfed by phagocyte
• Presents antigen to T cells / T helper cells which secrete cytokines
• Specific B cell becomes activated
• Divides to form clones
• By mitosis (in clonal selection and expansion)
• Plasma cells produce and secrete antibodies
• Which are specific to the antigen
• Memory cells formed

Question 5

Describe how a pathogen is destroyed by phagocytosis

Answer 5

• Phagocyte attracted by a substance or chemical/ binds to antigen
• Engulfs pathogen
• Into vesicle/phagosome
• Lysosome fuses with phagosome
• And releases hydrolytic enzyme (eg lysozyme)
• Which hydrolyses the pathogen
• Antigen is presented on the cell surface membrane of the cell - it is an antigen presenting cell

Question 6

Antigen definition

Answer 6

Foreign protein
which triggers an immune response - production of antibodies

Question 7

Description of active immunity

Answer 7

• Immunity gained from antibodies produced by the immune response (after a pathogen / antigen enters the body)
• Memory cells made

Question 8

Description of passive immunity

Answer 8

• Immunity gained without an immune response (body is given the antibodies)
• No memory cells

Question 9

Natural immunity description

Answer 9

Immunity gained by being infected (active) or receiving antibodies from the mother across the placenta or breast milk (passive)

Question 10

Description of artificial immunity

Answer 10

Immunity gained either by vaccination (active) or injecting antibodies (passive)

Question 11

Aside from pathogens what types of cell stimulate an immune response?

Answer 11

• Transplanted cells/cells from other organisms
• Virus infected cells
• Cancerous cells

Question 12

Describe the difference between active and passive immunity (6)

Answer 12

• Active involves memory cells, passive doesn’t
• Active involves production of antibody by plasma cells/ memory cells
• Passive involves antibody introduced into body from outside/ named source
• 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 fast acting

Question 13

Uses of monoclonal antibodies in medical treatments (*2)

Answer 13

• Targets/carries/binds drug to specific cells/antigens/receptors
• Block antigens/receptors on cells

Question 14

How do antibodies stimulate phagocytosis?

Answer 14

Bind to antigen (are markers) and cause agglutination (clumping) /attract phagocytes

Question 15

Role of antibodies (*2)

Answer 15

• Agglutination of cells - easier for phagocytes to locate
• Act as markers that stimulate phagocytes to engulf the bacterial cells

Question 16

How are antibodies specific to an antigen?

Answer 16

• Antibody variable region has specific amino acid sequence/primary structure
• Shape/tertiary structure of the binding site
• Is complementary to these antigens
• (Binds and) forms antigen-antibody complex

Question 17

What is the difference between cellular and humoural immune response?

Answer 17

Humoural immunity produces antigen-specific antibodies, cellular doesn’t.
Antibodies, T cells, B cells = humoural
Phagocytes = cellular

Question 18

What are the 2 types of white blood cells?

Answer 18

• phagocytes (non-specific)
• lymphocytes (B cells/B lymphocytes, T cells, memory B cells7)

Question 19

Antibody definition, monoclonal antibody definition

Answer 19

• A protein specific to an antigen produced by B cells/ secreted and released by plasma cells
• antibodies produced from a single clone of B cells/plasma cells or the same B/plasma cell

Question 20

Description of secondary immune response

Answer 20

• higher concentration of antibodies
• produced more quickly
• due to memory cells

Question 21

How do vaccines protect people from disease?

Answer 21

• vaccine contains antigens
• dead/weakened pathogens
• memory cells produced
• on second exposure more antibodies are produced more rapidly
• antibodies destroy pathogens
• herd immunity/ fewer people to pass on the disease

Question 22

Describe how a positive result is produced in an ELISA test

Answer 22

• antibodies attached to plate
• first antibody binds to antigen to form antigen - antibody complex because they’re complementary
• plate washed to remove unbound antibodies
• second antibody with enzyme attached is added
• second antibody attaches to antigen
• plate washed to remove unbound antibodies
• substrate added to cause colour change due to enzyme

Question 23

Describe how HIV causes the symptoms of AIDs

Answer 23

• HIV destroys T helper cells
• more viruses produced leads to fall in T cells
• so fewer T cells to activate B cells
• reduced antibody production
• immune system not working properly - person more prone to opportunistic infections/cancer
• eg cancer, TB, pneumonia

Question 24

Why are antibiotics ineffective against viruses?

Answer 24

• antibiotics stop metabolism, viruses don’t have metabolism
• some antibiotics work against (eg ribosomes) which viruses don’t have
• viruses hide in cells were antibiotics can’t reaxg

Question 25

What does attenuated mean?

Answer 25

• microorganism alive
• but does not cause symptoms of a disease