Defence mechanisms

Question 1

Define pathogen and give examples

Answer 1

A pathogen is a microorganism that causes disease. Examples include bacteria, viruses, fungi and protists.

Question 2

Define antigen

Answer 2

Any part of cell surface membrane (usually a protein) that can be recognised by the immune system and can stimulate an immune response.

Question 3

Describe the first line of defence

Answer 3

Physical and chemical barriers

Question 4

Describe the second line of defence

Answer 4

Phagocytosis

Question 5

Describe what is meant by immunity

Answer 5

Immunity is where an organism is no longer susceptible to a
particular disease

Question 6

What are the 2 types of immunity called

Answer 6

• Active immunity
• Passive immunity

Question 7

Describe what is meant by active immunity

Answer 7

Active immunity is where the resistance to disease is caused by the activities of a person’s own immune system.

Question 8

Pros and cons of active immunity

Answer 8

Pros - Long lasting protection, the body has produced memory cells
Cons - Takes longer as the body has to produce memory cells and antibodies in response to a foreign antigen

Question 9

Describe how active immunity can be naturally acquired

Answer 9

An encounter with the pathogen

Question 10

Describe how active immunity can be artificially acquired

Answer 10

Through the use of a vaccination

Question 11

Describe what is meant by passive immunity

Answer 11

Passive immunity is when resistance to the disease is acquired from the introduction of antibodies from another individual, rather than an individual’s own immune system

Question 12

Pros and cons of passive immunity

Answer 12

Pros - Immediate protection
Cons - Short-lived, the body is unable to produce its own antibodies

Question 13

Describe how passive immunity can be naturally acquired

Answer 13

Through the mother’s milk/across the placenta,

Question 14

Describe how passive immunity can be artificially acquired

Answer 14

Through injections with the necessary antibodies and is usually used to treat diseases that are difficult to build an immune response to.

Question 15

What cells are used by the specific part of the immune system

Answer 15

Lymphocytes

Question 16

State the 2 types of lymphocytes and their function

Answer 16

• T lymphocytes are involved in the ‘cell mediated response’
• B lymphocytes are involved in the ‘humoral reponses’

Question 17

Describe what lymphocytes are and explain their uses

Answer 17

• lymphocytes use a structure called
  ‘antigens’ to identify between their own cells and molecules (referred to as ‘self) versus those that are foreign (or, ‘non-self’). If it wasn’t for these antigens, the body would destroy its own tissues.
• Each type of cell has specific molecules on its surface that identify it, but it is the proteins that are most important. This is due to its highly specific 3D tertiary structure
  They help us to identify: pathogens, non-self material from other organisms of the same species, toxins and abnormal cells e.g. cancer cells.

Question 18

Why do people who need organ transplants have to take immunosuppressant drugs?

Answer 18

• When somebody has an organ transplant, they are accepting foreign material from another organism. This means that they antigens present will be different to their own, even if this organism is of the same species, and their body will recognise this as ‘non-self’. Their immune system will begin to attack and causes tissue rejection.
  In order to minimise this, donors are usually relatives who have closely matched DNA. However, this still isn’t enough, so immunosuppressant drugs are given (Immuno
  immune system, suppressant - stop/prevent/weaken)
  This reduces the level of immune response that occurs.