4.3.1.6 Human Defence System

Question 1

What are humans’ first line of defence against pathogens?

Answer 1

non-specific defence systems against pathogens

Question 2

How do bacteria and viruses cause illnesses?

Answer 2

• bacteria and viruses may reproduce rapidly inside the body
• bacteria may produce poisons (toxins) that damage tissues and make us feel ill
• viruses live and reproduce inside cells, causing cell damage

Question 3

Human non-specific defence systems agains pathogens:

Answer 3

• skin
• nose
• trachea and bronchi
• stomach

Question 4

How is skin a non-specific defence system?

Answer 4

• tough/dry/dead outer layer difficult to penetrate
• acts as a physical barrier against pathogens
• it produces antimicrobial secretions (sweat and fatty acids) to kill bacteria
• sebum / oil on surface of skin - repels the pathogens
• good microorganisms known as skin flora compete with the bad microorganisms for space and nutrient
• produces sweat and fatty acids
• scabs form over cuts or scabs form a barrier - platelets are involved in forming clots/scabs

Question 5

How is the nose a non-specific human defence system?

Answer 5

• trachea/bronchi/nose has hairs and produce mucus (sticky substance) which prevent particles from entering the lungs
• mucus is sticky + traps bacteria
• mucus is carried away by cilia
• removal of inhaled particles through e.g. sneezing

Question 6

How is the trachea and bronchi a non-specific human defence system?

Answer 6

• secrete mucus in order to trap pathogens
• muscle and cilia (hair-like structures) beat to waft mucus upwards so it can be swallowed

Question 7

How is the stomach a non-specific human defence system?

Answer 7

• produces hydrochloric acid that kills any ingested bacteria (e.g. bacteria) from mucus, food or drink
• kills pathogens as hydrochloric acid has a low pH and denatures the pathogens

Question 8

How are the large and small intestines non-specific human defence systems?

Answer 8

• rapid pH change from stomach to upper intestine
• normal flora in large intestine

Question 9

How is the vagina a non-specific defence system?

Answer 9

• pH (slightly acidic) and normal flora of vagina
• flushing of urinary tract

Question 10

What is the role of the immune system in the defence against diseases?

Answer 10

• if a pathogen enter the body the immune system tries to destroy the pathogen
• the specific immune system acts to destroy any pathogens which pass through the non-specific immune system to the body
• a large part of the specific immune system is white blood cells, which can act in 3 different ways: phagocytosis, producing antibodies, producing antitoxins

Question 11

What are humans’ second line of defence against pathogens?

Answer 11

• non-specific defence systems
• involves white blood cell - phagocyte
• phagocytosis takes place

Question 12

Process of phagocytosis:

Answer 12

1. Phagocytes are attracted to any area of the body in which an infection is present
2. Phagocyte (type of white blood cell) moves towards a bacterium
3. The phagocyte begins to engulf the bacterium
4. When the phagocyte comes into contact with pathogen, it binds to it
5. The membrane of the phagocyte then surrounds the pathogen and engulfs it with the cytoplasm of the phagocyte wrapping around the bacterium - the bacterium is engulfed into the vacuole
6. The bacterium is now enclosed in a vacuole inside the phagocyte
7. Digestive enzymes enter the vacuole and it is killed and digested

Question 13

Diagram for process of phagocytosis:

Answer 13

Question 14

What is the third line of defence against pathogens (the immune response)?

Answer 14

• the third line of defence against infection is specific
• a specific white blood cell ( a lymphocyte) is activated to prevent further disease

Question 15

How is producing antibodies used to defend against pathogens?

Answer 15

• each pathogen has an antigen on their surface, which is a structure with a specific complementary antibody which can bind to it when they come in close proximity
• lymphocytes only recognise one type of antigen
• when the lymphocyte binds to the antigen, antibodies are produced in huge quantities
• these proteins clump the pathogens together, preventing them from entering body cells and making it easier for white blood cells to find them, leaving them more vulnerable to phagocytosis
• if you become infected again with the same pathogen, the specific complementary antibodies will be produced at a faster rate
• the individual will not feel the symptoms of the illness - said to be immune

Question 16

How is producing antitoxins used to defend against pathogens?

Answer 16

• neutralise the toxins released by the pathogen binding to them

Question 17

Diagram to show how antibodies work:

Answer 17

Question 18

Diagram to show the specificity of lymphocytes to antigens:

Answer 18

Question 19

Order of events for how antibodies are used to defend body from pathogens:

Answer 19

1. Bacterium entering body has molecules on its surface
   
   1. each pathogen has a different antigen on its surface
   2. the antigen activates a specific lymphocyte
2. white blood cells release antibodies
   
   1. a specific lymphocyte makes a specific antibody
   2. the antibody is secreted by the lymphocyte
3. antibodies lock onto the microorganisms
   
   1. the antibody is complementary to the antigen
4. bacteria are clumped together - pathogen is clumped together
5. white blood cells surround clumped bacteria and engulf them
   
   1. bacteria being clumped together makes it easier for white blood cells to engulf the pathogen
   2. this process is called phagocytosis

Question 20

Which type of pathogen causes small pox?

Answer 20

Virus

Question 21

How was James Phipps given immunity to smallpox?

Answer 21

• Edward Jenner took pus from cowpox and put it on a cut on Phipp to make him catch cow pox
• this made him immune to small pox

Question 22

Why were people not keen to use Jenner’s cure for small pox?

Answer 22

didn’t want to have period of being unwell from cowpox

Question 23

Use ideas about antibodies to suggest why James Phipps became immune to smallpox:

Answer 23

• cow pox is similar virus to small pox so have same antigen on pathogen
• means specific complementary antibodies were already produced when Phipps had cowpox so the antibodies are now produced at a faster rate so Phipp’s doesn’t feel the symptoms of smallpox and is said to be immune

Question 24

Non-specific defence:

Answer 24

general physical and chemical barriers that defend the body against lots of different types of pathogens

Question 25

How do white blood cells help to defend against pathogens?

Answer 25

• Phagocytosis
• Antibody production - which destroys particular bacterias or viruses
• Antitoxin production - which counteract the toxins released by the pathogens

Question 26

How do eyes defend against pathogens?

Answer 26

• produce tears which contain enzymes to kill bacteria
• tears are anti-septic