5.1 Cell Recognition and the Immune System

Question 1

What is an infection?

Answer 1

An interaction between a pathogen and the body’s various defence mechanisms

Question 2

What is immunity?

Answer 2

The means by which the body protects itself from infection

Question 3

Give examples of non specific defence mechanisms

Answer 3

• physical barriers such as the skin

- phagocytosis

Question 4

Give examples of specific defence mechanisms

Answer 4

• cell mediated t lymphocyte response

- humoral b lymphocyte response

Question 5

What is a non specific defence mechanism?

Answer 5

A response which is immediate and the same for all pathogens

Question 6

What is a specific defence mechanism?

Answer 6

A response which is slower and specific to each pathogen

Question 7

What is a lymphocyte?

Answer 7

A type of white blood cell

Question 8

Which lymphocytes carry out cell-mediated responses?

Answer 8

T lymphocytes

Question 9

Which lymphocytes carry out humoral responses?

Answer 9

B lymphoctes

Question 10

Why do lymphocytes need to be able to distinguish between self and non-self material?

Answer 10

Because if lymphocytes cannot distinguish then they would destroy the organisms own tissues

Question 11

What do all cells have on their surface?

Answer 11

Specific molecules on its surface that all it to be identified, made of proteins

Question 12

Why are the cell identifiers on the cell surface membrane proteins?

Answer 12

Because proteins have enourmous variety and highly specific tertiary structures allowing them to be distinguished from one another

Question 13

What is the immune system trying to identify?

Answer 13

• pathogens such as HIV
• non-self material such as cells from other organisms of the same species
• toxins such as the ones produced by certain pathogens
• abnormal body cells such as cancer cells

Question 14

How can the immune system identifying non-self material be a disadvantage?

Answer 14

In humans who have had organ transplants, the immune system will attack the transplanted organ as it cannot be identified as self material. This response can be suppressed using immunosuppressant drugs which can open the body up to other infections or he response can be minimised by using donor tissues from genetically close relatives

Question 15

How do specific lymphocytes come about during an infection?

Answer 15

They are already present in the body therefore when a pathogen is located it is likely that a present lymphocyte will have a complementary protein to the pathogen which can be stimulated to divide and build up its numbers to a point where it can effectively destroy the pathogen

Question 16

What is the process of a specific lymphocyte replicating in the presence of its complimentary pathogen called?

Answer 16

Clonal selection

Question 17

What does clonal selection explain?

Answer 17

The time lag between exposure to the pathogen and the body’s defences bringing it under control

Question 18

What happens to lymphocytes in the fetus?

Answer 18

They are constantly colliding with other cells

Question 19

Why is fetus infection rare?

Answer 19

Because the fetus is protected from the outside world by the mother and the placenta

Question 20

What material will fetus lymphocytes most commonly collide with?

Answer 20

The body’s self material

Question 21

How are lymphocytes with an anti-self antigen dealt with in the fetus?

Answer 21

The lymphocytes that have receptors that fit body cells will either die or be suppressed leaving only the lymphocytes that might fit foreign material

Question 22

How are lymphocytes with an anti-self antigen dealt with in adults?

Answer 22

The lymphocytes produced in the bone marrow will initially only encounter self antigens and any lymphocytes that show an immune response to self material will undergo apoptosis before they can differentiate into mature lymphocytes therefore no clones of these lymphocytes will appear in the blood, leaving only the lymphocytes that might respond to non-self antigens

Question 23

State two differences between a specific and a non specific defence mechanism

Answer 23

A specific defence mechanism responds slower because it differentiates between different pathogens
Non-specific defence mechanisms respond to all pathogens in the same way

Question 24

After a pathogen gain entry to the body it often takes a number of days for the body’s immune system to begin to control it, suggest why

Answer 24

The lymphocytes that will finally control the pathogen need to build up their numbers, which takes time

Question 25

Why would it be inaccurate to say it taken the body days to ‘respond’ to a pathogen?

Answer 25

The body responds immediately by recognising the pathogen (and phagocytosis) delay is building up lymphocyte numbers and controlling the pathogen