Chapter 10: Diseases and Immunity

Question 1

Define pathogen.

Answer 1

A disease-causing organism such as bacteria, viruses, fungi and protozoa.

Question 2

Define transmissible disease.

Answer 2

A disease in which the pathogen can be passed from one host to another.

Question 3

How do pathogenic bacteria cause diseases?

Answer 3

They damage host cells.
The produce poisonous waste products called toxins.

Question 4

What do toxins do?

Answer 4

They damage the cells in which the bacteria are growing.
They also upset some of the systems in the body.

Question 5

What do toxins cause?

Answer 5

A raised temperature
Headache
Tiredness
Weakness
Sometimes diarrhoea and vomitting.

Question 6

Name some human virus diseases.

Answer 6

Common cold
Poliomyelitis
Measles
Mumps
Chickenpox
Influenza
AIDS

Question 7

What does the tobacco mosaic virus affect?

Answer 7

Tomato plants as well as tobacco.
It causes mottling and discolouration of the leaves and eventually stunt the growth of the plant

Question 8

List the ways pathogens are transmitted.

Answer 8

Direct contact
Indirect contact

Question 9

How are pathogens transmitted by direct contact?

Answer 9

By transfer of body fluids (e.g. blood)

Examples of diseases: HIV, Hepatitis B & C

Question 10

How are pathogens transmitted by indirect contact?

Answer 10

When the pathogen leaves the host and is carried in some way or another to an uninfected individual (e.g. contaminated surfaces, water, air)

Question 11

List the types of defenses against pathogens.

Answer 11

Mechanical barriers
Chemical barriers
WBC

Question 12

Name some examples of mechanical barriers.

Answer 12

Skin - contains sweat glands that secrete oils to kill microbes

Hairs in the nose - acts as a filter and traps dust and larger microbes.

Question 13

Name some examples of chemical barriers against pathogens.

Answer 13

stomach acid - kills bacteria

mucus produced by lining of trachea and bronchi - is sticky, trapping the microbes.

Question 14

Name some examples of WBCs.

Answer 14

Phagocytes - engulfs microbes, performs phagocytosis

Lymphocytes - produces antibodies.

Question 15

What does vaccination do?

Answer 15

It enhances the body’s natural defences.

Question 16

How do you control the spread of disease?

Answer 16

1. Clean water supply:
   Ensure that untreated human sewage cannot reach water supply
   Treat water to make it safe (removes all microoragnisms that may cause disease)
2. Food Preparation
   Keep uncooked meats and vegetables separate
   Check expiry dates on food
   Refigerate leftovers
   Ensure food is covered if it is not eaten immediately
3. Personal hygiene
   Wash hands after using the toilet
   Cover your mouth when you cough/sneeze
   Regular bathing
   Not sharing drink bottles
4. Waste disposal
   Use a designated rubbish bin
   Change bin liners frequently
   Take out rubbish regularly
5. Sewage treatment
   Waste treatment plants use powerful microbial agents such as chlorine to kill pathogens.

Question 17

What are antigens?

Answer 17

Chemicals which the body recognises as foreign, found on the surface of the pathogen.

Question 18

What are antibodies.

Answer 18

Proteins produced by lymphocytes.
They are attracted to antigens on the outside of the pathogens and are able to attach to their surface to mark them
This makes it easier for phagocytes to find and ingest them.

Once marked, the antibodies clump the pathogens together.
Each pathogen has its own antigens which have specific shapes so specific antibodies which fit the specific shapes of the antigens are needed.

Question 19

Define active immunity.

Answer 19

Defence against a pathogen by antibody production.
It is slow acting and provides long-lasting immunity

Question 20

How is active immunity achieved?

Answer 20

By infection with the disease
From vaccination

Question 21

How does an organism gain active immunity by vaccination?

Answer 21

The person is injected with a harmless version of the pathogen, introducing the antigens to the body

The antigens trigger an immune response where lymphocytes produces antibodies

Memory (B-cells) are produced giving the person long term immunity.

Question 22

Define passive immunity.

Answer 22

Individuals are given antibodies in order to provide a short term defence against a pathogen.
No memory cells are formed.

Question 23

How does breast milk provide passive immunity?

Answer 23

Breast milk contains white blood cells and antibodies that gives infants temporary immunity from certain diseases.

This protects the baby until the immunisation programme can begin and active immunity can be acquired.

Question 24

What causes chloera.

Answer 24

The bacterium Vibrio cholerae which causes acute diarrhoea

Question 25

What happens if you get cholera.

Answer 25

The bacteria releases toxins that irritate the intestinal lining leading to secretion of large amounts of water and electrolytes including chloride ions.

The chloride ions decreases the osmotic potential of the gut contents, drawing more water from surrounding tissues and blood by osmosis.

This makes the undigested food more watery leading to acute diarrhoea and loss of body fluids and electrolytes leading to dehydration and kidney failure.