General defence system

Question 1

Define general defence system

Answer 1

It acts as a barrier to all pathogens attempting to gain entry to the human body

Question 2

What does the first line of the general defence system consist of?

Answer 2

skin, mucous membranes that line the respiratory, digestive, urinary and reproductive tracts and secretions produced by the skin an mucous membranes

Question 3

What does the skin do in this system?

Answer 3

It provides a structural barrier to infection. It is a physical barrier that prevents pathogens from entering the body.

Question 4

What does clotting do in this system?

Answer 4

If the skin is broken, blood clotting prevents the entry of further pathogens (and prevents further blood loss)

Question 5

What is lysozyme? What does it do?

Answer 5

It is an enzyme found in sweat, tears and saliva.

It attacks and dissolves the cell walls of many bacteria.

Question 6

Where are the sebaceous glands and what do they produce?

Answer 6

They are found in the skin and produce sebum (oil).

Question 7

What does sebum contain?

Answer 7

It contains chemicals that kill bacteria

Question 8

What does mucus do?

Answer 8

Pathogens are trapped by this mucus and prevented from entering the body

Question 9

Give an example of beneficial bacteria and what they produce and do.

Answer 9

Bacteria in the vagina produce lactic acid.

This acid prevents the growth of pathogens

Question 10

What does the second line of the general defence system consist of?

Answer 10

It consists of the destruction by white blood cells of pathogens that have entered the body, the production of proteins that kill or prevent pathogens from reproducing and the inflammatory response

Question 11

What happens when cells are damaged by invading micro-organisms? (3)

Answer 11

They release a large number of chemicals.
These chemicals attract white blood cells from the bloodstream.
The white blood cells engulf and destroy any bacteria, viruses or other micro-organisms that they meet.

Question 12

What are the white blood cells that engulf and destroy micro-organisms known as?

Answer 12

phagocytes

Question 13

What are large phagocytes called?

Answer 13

Macrophages

Question 14

What do macrophages do? (2)

Answer 14

1. Some move around the body in body fluids and act as scavengers for pathogens.
2. Others remain mixed in places such as the spleen, lymph nodes and other lymphatic tissues. They filter out and destroy any pathogens that are present in lymph.

Question 15

What is complement

Answer 15

It is a set of about 20 proteins found in the blood plasma

Question 16

How are the proteins in complement activated? What do they then do?

Answer 16

activated by infection. The proteins then destroy viruses and other pathogens

Question 17

What are interferons

Answer 17

They are another set of defence proteins

Question 18

What do interferons do?

Answer 18

They prevent viral multiplication and help to limit the spread of virus infections (e.g. colds and influenza)

Question 19

When cells are infected, what do they release and what does this do?

Answer 19

They release a chemical that results in blood capillaries opening wider (dilating) and becoming more porous.
This causes localised swelling, redness, heat and pain.
It also brings more white blood cells to the area to fight infection.

Question 20

What does inflammation cause if all over the body?

Answer 20

increased body temperature (fever)

Question 21

When inflammation is widespread and fever occurs, how does this help the body?

Answer 21

The higher temperature interferes with the ability of some bacteria and viruses to reproduce