Response to Pathogens

Question 1

What is phagocytosis?

Answer 1

The defence mechanism we produced once the body’s 1st line of defence has been crossed. A non specific mechanism that destroys any pathogen the cell encounters.

Question 2

What is a phagocyte?

Answer 2

A cell that has the ability to engulf others.

Question 3

Where are phagocytes most often found?

Answer 3

Circulating in the blood.

Question 4

1. In phagocytosis, how does the phagocyte draw to the pathogen?

Answer 4

Phagocyte attracts to the pathogen by responding to chemicals released by the pathogen. Therefore, the phagocyte moves towards it along a concentration gradient.

Question 5

2. In phagocytosis, how do the phagocyte and the cell attach to eachother?

Answer 5

Receptors on the phagocytes cell surface surface attach to chemicals on the pathogen’s surface.

Question 6

3. In phagocytosis, which organelle moves close to where the pathogen has started to bind and become and engulfed?

Answer 6

Lysosomes.

Question 7

4. In phagocytosis, what do lysosomes do once the pathogen has fully engulfed?
   What is the name of the region where the pathogen has been engulfed?

Answer 7

Lysosomes secrete lysozymes into the phagosome, which are hydrolytic enzymes. These can hydrolyse the bacterial cell wall, so the cell breaks and bursts open.

Question 8

5. In phagocytosis, what happens to the remaining products from the pathogen?

Answer 8

Any remaining products from the hydrolysed pathogen are absorbed by the phagocyte.

Question 9

What does the cell mediated response aim to target?

Answer 9

Any pathogen that invades a cell or has been engulfed by the cell.

Question 10

What is a T lymphocyte?

Answer 10

A type of white blood cell which is able to destroy pathogens.

Question 11

Name 4 different types of reason why antigens are displayed on a cell surface and can be recognised.

Answer 11

They recognise APCs created in phagocytosis.
They recognise antigens on cells invaded by viruses
Transplanted cells have different antigens
Cancer cells have different antigens

Question 12

Describe Th cell receptors.

Answer 12

Highly specific to one type of antigen only.

Question 13

What do T lymphocytes respond to?

Answer 13

Antigen presenting cells.

Question 14

1. In cell mediated immunity, how does the invaded cell become recognisable by T lymphocytes?

Answer 14

The cell uses the antigens from the pathogen and displays it on its cell surface, producing an APC.

Question 15

2. In cell mediated immunity, what do T lymphocytes bind to?

Answer 15

Antigens that have been displayed on the cell surface.

Question 16

3. In cell mediated immunity, what happens once T lymphocytes have bound to the cell?

Answer 16

Attachment between the T lymphocyte and the APC stimulates the Th cell to divide rapidly by mitosis into clones of the Th cell.

Question 17

4. In cell mediated immunity, once the T cells have been cloned, what 4 things could they potentially develop into or do?

Answer 17

Memory cells
Activate Tc cells
Stimulate B cells to divide
Stimulate phagocytosis.

Question 18

What is a memory cell?
What do these cells prevent?

Answer 18

A cell that circulates in the blood after infection so a rapid response can be produced should you encounter the same pathogen again.
They prevent symptoms from being produced, as the pathogen is often destroyed before it can cause harm.

Question 19

What is a cytotoxic T cell?

Answer 19

A type of T cell that can destroy pathogens by making holes in their cell surface membrane using the perforin protein.

Question 20

What is a B lymphocyte?

Answer 20

A type of lymphocyte that can produce antibodies.

Question 21

What are plasma cells?

Answer 21

Cells with a short lifespan that can rapidly produce antibodies.

Question 22

What are effector B cells?

Answer 22

Cells that can give rise to plasma cells when activated by Th cells.

Question 23

What is a humoral response?

Answer 23

A response to pathogens using antibodies.

Question 24

1. In a humoral response, what happens once a pathogen has been taken up by a cell?

Answer 24

Antigens are displayed on the cell surface.

Question 25

2. Th cells, activated in cell mediated immunity, attach to what?
   What does this do?

Answer 25

Th cells attach to processed antigens on the antigen presenting B cell. This activates the B cell.

Question 26

3. In humoral immunity, by what type of cell division do B cells divide by? Clones of what type of cell are produced?

Answer 26

Mitosis. This produces a clone of plasma cells.

Question 27

4. In humoral immunity, what do plasma cells produce?

Answer 27

Antibodies

Question 28

5. In humoral immunity, how are the pathogens destroyed?

Answer 28

Antibodies produced by the plasma cells bind to the pathogen and destroy it.

Question 29

6. In humoral immunity, B cells can then develop into what type of cell?

Answer 29

Memory cells