Immune System

Question 1

Define pathogen

Answer 1

A foreign microorganism that causes a disease and stimulates an immune response

Question 2

What are the two types of defence mechanisms?

Answer 2

Non-specific and Specific

Question 3

What is a non-specific Defense mechanism?

Answer 3

• immediate response to any pathogen
• E.g physical barriers and phagocytosis

Question 4

What is a specific defence mechanism?

Answer 4

• slower response which is specific to each pathogen
• E.g B lymphocytes and cell mediated responses

Question 5

What does hydrochloric acid in the stomach do to protect again pathogens?

Answer 5

Destroys pathogens by denaturing proteins, changing their tertiary structure

Question 6

What does epithelial mucus do to protect against pathogens?

Answer 6

Traps pathogens, then ciliated epithelial cells waft them up trachea to be swallowed so they can be destroyed by stomach acid

Question 7

What does the skin do to protect against pathogens?

Answer 7

Provides a waterproof barrier so pathogens cannot enter the body

Question 8

Describe phagocytosis

Answer 8

1. Phagocytes move to the site of infection, attracted by chemical products from the pathogen
2. Phagocyte binds to pathogen via receptors and engulfs pathogen
3. Pathogen enclosed in a phagosome
4. Lysozymes fuse with phagosome, releasing enzymes (lysozymes) which digest the pathogen. Soluble products are absorbed into cytoplasm of the phagocyte
5. Once the pathogen has been digested, the phagocyte displays the antigen from the pathogen on its cell surface membrane - it becomes an antigen presenting cell

Question 9

Describe T cells

Answer 9

• formed in bone marrow
• travel to and mature in the thymus
• cell mediated response
• respond only to antigen presenting cells, not pathogen directly
• do not produce antibodies

Question 10

Describe B cells

Answer 10

• formed in bone marrow
• mature in bone marrow
  -humoral response
• can respond to pathogen directly
• produce antibodies

Question 11

Describe a cell mediated response

Answer 11

• pathogens and infected body cells present antigens on their surface
• A T cell with specific complementary receptors will bind to the antigen on the antigen presenting cell
• this T cell then divides by mitosis to form clones
• these clones then can differentiates into 3 different cells
  helper T cells
  memory T cells
  killer T cells

Question 12

Describe what helper T cells, killer T cells and memory T cells do

Answer 12

-helper T cells stimulate phagocytosis, stimulate cytotoxic T cells and activate specific B cells
-memory T cells are used in the secondary immune response
-killer T cells punctures holes in a protein using perforin to kill infected body cells

Question 13

Describe the humoural response

Answer 13

• a pathogen enters the blood
• a specific B cell with complementary antibodies will bind to the antigens the display them on their cell surface
• a T-helper cell attached to the processed antigens and stimulates the B cell to divide
• the B cell then divides by mitosis to form clones
• the B cells clones can differentiate into either B plasma cells or memory B cells

Question 14

Describe what B plasma and memory cells do.

Answer 14

-memory B cells remain in the blood for years
-plasma B cells produce antibodies which are specific to antigens, the antibodies destroy the pathogen by causing agglutination, which clumps together pathogens to makes it easier for phagocytosis

Question 15

Describe and explain 2 differences between the primary and secondary immune response

Answer 15

• more rapid production of antibodies because memory cells do not need to wait to be activated (like T and B cells do)
• greater concentration of antibodies produced, because there are more specific memory cells in the blood than there were inactive B or T cells before activation. So more plasma cells produced

Question 16

Describe antibodies structure

Answer 16

• have four polypeptide chains, two heavy and two light
• have a variable region with two antigen binding sites
• fit precisely into the specific antigen to form an antigen-antibody complex
• different antibodies have different antigen binding sites
• they also have a constant region which has receptor binding site which binds with receptors on B cells.

Question 17

What is a monoclonal antibody

Answer 17

Antibodies produced from the same plasma cell (B) do they will all have the same shaped variable region and be complementary and specific to the same antigen

Question 18

What can monoclonal antibodies be used for?

Answer 18

-medical diagnosis levels of a particular molecule can be detected with monoclonal antibodies specific to that particular molecule
-pregnancy testing women produce a protein called hCG when pregnant, monoclonal antibodies can detect this

Question 19

Ethical problems against monoclonal antibodies

Answer 19

• involves the use of mice, deliberately inducing cancer
• deaths have been associated with their use
• testing the safety of new drugs poses dangers

Question 20

Contrast passive vs active immunity

Answer 20

• passive short term immunity because antibodies get broken down and no memory cells produced. active long term immunity because memory cells produced.
  -passive immediate immunity. active takes a while for T and B cells to be activated so immunity takes longer.
  -passive antibodies supplied from external source. active body produced antibodies.

Question 21

Describe passive and active immunity

Answer 21

-passive immunity is produced by introducing antibodies from an outside source. The immunity is short lived.
-active immunity is produced by stimulating the body to produce its own antibodies, this is long lasting.

Question 22

What is vaccination

Answer 22

Vaccination involves the introduction of a weakened pathogen or toxin. The antigens are detected and an immune response occurs. Memory cells are produced and a secondary response can occur quicker if the body comes into contact with the same pathogen again.

Question 23

What is herd immunity?

Answer 23

When a sufficiently large proportion of the population has been vaccinated to make it difficult for a pathogen to spread

Question 24

Why can’t vaccination eliminate a disease?

Answer 24

• the pathogen may mutate frequently changing the antigens on the surface meaning it’s no longer compatible to the memory cells in the body
• certain pathogens can hide from the immune system
• some people object to vaccination

Question 25

What are the ethical issues when using vaccines?

Answer 25

• use of animals
• side affects of vaccines
• who are they tested on
• can a vaccination be compulsory? Or can people opt out