Defence Mechanisms

Question 1

Define immune system.

Answer 1

A group of cells, tissues, organs etc that defend the body against pathogens and foreign substances.

Question 2

What is a pathogen?

Answer 2

A disease causing organism

Question 3

What is an immune response?

Answer 3

A reaction to pathogens from the body. A complex series of specific and non specific processes involving a range of cells and chemicals, triggering symptoms.

Question 4

What is a physical barrier to infection?
What are these defence mechanisms also known as?

Answer 4

Anything that stops pathogens from entering the body.
Also known as primary defence mechanisms.

Question 5

Describe how the skin acts as a physical barrier to infection.

Answer 5

Secretes antimicrobial substances that can kill pathogens on the skin surface.
Also acts as a barrier by protecting components inside the body.

Question 5

Describe the barriers to infection in the digestive system.

Answer 5

The stomach contains hydrochloric acid which can kill some pathogens that may have been swallowed.

Question 6

Describe barriers to infection in the respiratory system.

Answer 6

The nose contains hairs to trap particles and stop them from entering.
The trachea contains mucus which inhaled pathogens can stick to. The cilia lining the trachea waft the mucus out of the respiratory system, so it can be swallowed and destroyed by the digestive system.

Question 7

What is an antigen?

Answer 7

A protien present on a pathogen or cell, that is specific to that type of pathogen or cell only

Question 8

How does detection of antigens lead to an immune response?

Answer 8

Antigens are recognised as foreign, ‘non self’ material, so the immune system processes a response to try and destroy it.

Question 9

Name 2 types of non specific immune response.

Answer 9

Phagocytosis
Lysozymes

Question 10

Name 2 types of specific immune response.

Answer 10

Cell mediated
Humoral

Question 11

Name 3 things that antigens can detect.

Answer 11

Other cells, including cancerous cells
Transplant material
Pathogens

Question 12

Why are transplant organs often taken from relatives?

Answer 12

Because your antigens are most similar to your relatives, and therefore are less likely to cause an immune response.

Question 13

Why do we need to be able to recognise our own cells?

Answer 13

So the attacking of healthy, ‘self’ material can be prevented.

Question 14

Why is the immune system able to differentiate between different cells?

Answer 14

Antigens are highly specific to each type of cell.

Question 15

Name 4 types of pathogen.

Answer 15

Virus
Bacteria
Protist
Fungi

Question 16

How do foetuses develop lymphocytes that will only attack foreign cells rather than their own body cells?

Answer 16

Lymphocytes collide with cells, including own body cells.
The lymphocytes that have receptors which fit exactly onto the own body cells are killed or suppressed.
The lymphocytes that remain are those that fit non self material.

Question 17

In adults, how is it ensured that any lymphocytes produced will only respond to foreign material?

Answer 17

Lymphocytes are produced in the bone marrow so initially only encounter self antigens.
Any cells that show an immune response to self antigens undergo programmed cell death before they specialise into lymphocytes.
Only cells that can respond to foreign material remain.