Cell Recognition and the Immune System

Question 1

Define a pathogen.

Answer 1

• A disease causing agent that disrupts the normal physiology of the infected organism.

Question 2

The first line of defence

Question 3

Define phagocytosis.

Answer 3

• A type of endocytosis where solid material such as bacteria are engulfed.
• The process is carried out by specialised white blood cells called phagocytes.

Question 4

Explain the process of phagocytosis and the subsequent destruction of infested pathogens.

Answer 4

• Phagocytes membrane surrounds the pathogen and engulfs it (phagocytosis).
• A vesicle called a phagosome is formed inside the cell.
• Lysosomes in the cytoplasm fuse with the phagosome releasing hydrolytic enzymes.
• A phagosome is formed. The enzymes inside hydrolyse the bacterium.

Question 5

What can stimulate an immune response?

Answer 5

• Pathogens
• Transplant cells
• Abnormal body cells
• Toxins in a solution

Question 6

Define lymphocytes.

Answer 6

Cells involved in the specific immune response.

Question 7

What do B cells do?

Answer 7

• Attack invaders outside the cells (humoral immunity)

Question 8

What do T cells do?

Answer 8

• Attack infected cells (cell mediated immunity)

Answer 9

• Each B cell has one type of antibody receptor attached to the cell-surface membrane.
• The antibody is specific for one type of antigen.

Question 10

Describe the structure of antibodies.

Question 11

How do antibodies lead to the destruction of an antigen?

Answer 11

• Agglutination
• Enhanced phagocytosis

Question 12

Define agglutination.

Answer 12

The clumping together of cells

Question 13

Define enhanced phagocytosis.

Answer 13

Antibodies coat the pathogen by binding to its surface antigens, making it more appetising for phagocytes to engulf.

Question 14

What are the two types of immunity?

Answer 14

• Active immunity
• Passive immunity

Question 15

Describe some features of active immunity.

Answer 15

• Requires exposure to antigens
• Antigens stimulate lymphocytes - takes time to develop (days)
• Memory cells are made
• Longer term protection

Answer 16

Natural: Infection
Artificial: Vaccine

Question 17

Describe some features of passive immunity.

Answer 17

• Doesn’t require exposure to antigen
• Immediate protection (just transfer of antibodies)
• No memory cells
• Short term protection (antibodies degrade over time)

Question 18

Give a natural and artificial example of passive immunity.

Answer 18

Natural: Maternal antibodies
Artificial: Monoclonal antibodies

Question 19

Define a vaccine.

Answer 19

A weakened (attenuated) form of the pathogen that contains antigens but is capable of triggering disease.

Question 20

How does a vaccine work?

Answer 20

• The body responds to an injected vaccine b6 initiating a primary immune response which results in memory cells being made.
• When exposed to the actual pathogen the memory cells trigger a more potent secondary immune response.
• As a consequence of this more potent immune response, disease symptoms do not develop.

Question 21

Define herd immunity.

Answer 21

• When individuals who are not immune to a pathogen are protected from exposure by the large amounts of immune individuals within the community.

Question 22

What are some ethical issues surrounding the use of vaccines?

Answer 22

• The risk of side effects vs the protection of the individual and community.
• Use of animals and animal products in producing vaccines.
• Human trials
• Should it be compulsory?
• Is it worth the cost?

Question 23

What are the features if a successful vaccination programme?

Answer 23

• Large enough amounts can be produced to vaccinate the most vulnerable at a reasonable cost.
• Side-effects are rare.
• Cold storage and transportation is manageable.
• Enough trained staff are available for administration.
• Possible to vaccine enough people to achieve herd immunity.

Question 24

Describe the effect if antigen variability on disease and disease prevention.