Chapter 10 - Diseases and immunity

Question 1

What is a pathogen?

Answer 1

A pathogen is a disease-causing organism.

Question 2

What is a transmissible disease?

Answer 2

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

Question 3

How can pathogens be transmitted?

Answer 3

Pathogens can be transmitted through direct contact of bodily fluids such as blood or semen (e.g. HIV, gonorrhoea, hepatitis B and hepatitis C). Pathogens can also be transmitted through indirect contact including contaminated surfaces, food, animals and air.

Question 4

What are some examples of diseases spread by certain methods of transmission?

Answer 4

Question 5

What are mechanical barriers?

Answer 5

Mechanical barriers are structures that make it difficult for pathogens to get past them and into the body. Skin and hairs in the nose are examples of mechanical barriers.

Question 6

How does skin act as a mechanical barrier?

Answer 6

Skin covers almost all parts of your body to prevent infection from pathogens. If it is cut or grazed, it immediately begins to heal itself, often by forming a scab.

Question 7

How do hairs in the nose act as a mechanical barrier?

Answer 7

Hairs in the nose make it difficult for pathogens to get past them further up the nose so they are not inhaled into the lungs.

Question 8

What are chemical barriers?

Answer 8

Chemical barriers are substances produced by the body cells that trap or kill pathogens before they can get further into the body and cause disease. Mucus and stomach acid are examples of chemical barriers.

Question 9

How does mucus act as a chemical barrier?

Answer 9

Mucus is made in various places in the body, pathogens get trapped in the mucus and can then be removed from the body (by coughing, blowing the nose or swallowing).

Question 10

How does stomach acid act as a chemical barrier?

Answer 10

Stomach acid contains hydrochloric acid which is strong enough to kill any pathogens that have been caught in mucus in the airways and then swallowed or have been consumer in food or water.

Question 11

How can different cells prevent pathogens from reaching the body?

Answer 11

Cells are different types of white blood cells that work to prevent pathogens reaching areas of the body they can replicate in. By phagocytosis which is when phagocytes engulf and digest pathogenic cells. By producing antibodies which clump pathogenic cells together so they can’t move as easily (known as agglutination) and releasing chemicals that signal to other cells that they must be destroyed.

Question 12

How can people prevent the spread of disease?

Answer 12

The simplest way to prevent the spread of disease is to stop pathogens from spreading. This can be done by using a clean water supply, having hygienic food preparation, good personal hygiene, proper waste disposal or sewage treatment.

Question 13

What are some examples of hygienic food preparation?

Answer 13

Keep food cold so bacteria and fungi can’t reproduce.
Prepare food hygienically to avoid contamination from pathogens by washing hands with soap and cleaning work surfaces with products such as bleach to kill pathogens.
Cook food well (long enough at high temperature to kill bacteria and fungi.
Cover food to prevent flies landing on it before eating.
Use separate chopping boards and utensils for cutting uncooked meat,
Wash hands after using the bathroom before handling food.

Question 14

What are some examples of good personal hygiene?

Answer 14

Washing with soap removes substances which trap pathogens as well as pathogens themselves from the skin.
Use tissues to catch sneezes and coughs.
Dispose of used tissues as soon as possible as pathogens can still be alive.
Wash hands after using the bathroom.

Question 15

What are some examples of waste disposal?

Answer 15

Waste food is a food source for flies that can act as vectors for transmissible diseases and so should be disposed of in a sealed container.
Rubbish bins should be covered and removed to landfill for disposal or burning regularly.
All rubbish should be stored before collection away from human habitation.

Question 16

What are some examples of a clean water supply?

Answer 16

Homes and public places should have plumbing and drains to safely remove faeces and waste which can carry pathogens.
Raw sewage should be treated to remove solid waste and kill pathogens before being releasing into the environment.

Question 17

What is active immunity?

Answer 17

Active immunity is a defence against a pathogen by antibody production in the body. Active immunity is gained after an infection by a pathogen or by vaccination.

Question 18

What is an antigen?

Answer 18

An antigen is a unique chemical present on the surface of a cell that induces an immune response. Antigens are found on pathogens

Question 19

How do antigens and antibodies bind?

Answer 19

Each pathogen has its own antigens which gave specific shapes that bind to antibodies. Specific antibodies have complementary shapes to fit specific antigens.

Question 20

What are antibodies?

Answer 20

Antibodies are proteins that bind to antigens leading to direct destruction of pathogens or marking of pathogens for destruction by phagocytes.

Question 21

What are vaccinations?

Answer 21

Vaccinations give protection against specific diseases and boost the body’s defence against infection from pathogens without the need to be exposed to dangerous diseases that can lead to death.

Question 22

What is the process of vaccinations?

Answer 22

Weakened pathogens or their antigens are put into the body which cannot cause illness but can provoke an immune response, these antigens stimulate an immune response by lymphocytes which produce complementary antibodies for the antigens and memory cells are produced that give long term immunity.

Question 23

What are memory cells?

Answer 23

The memory cells are types of white blood cells remain in the blood and will quickly produce lots of antibodies respond to the antigen if it is encountered again in an infection by a ‘live’ pathogen. As memory cells have been produced, this immunity is long-lasting.

Question 24

What is herd immunity?

Answer 24

If a large enough percentage of the population is vaccinated, it provides protection for the entire population because there are very few places for the pathogen to breed. This is known as herd immunity. If the number of people vaccinated against a specific disease drops in a population, it leaves the population at risk of mass infection as they are more likely to come across infected and contagious people. This increases the number of infections as well as the number of people who could die from a specific infectious disease. Herd immunity prevents epidemics and pandemics from occurring in populations.

Question 25

What is passive immunity?

Answer 25

Passive immunity is a fast-acting, short-term defence against a pathogen by antibodies acquired from another individual, including across the placenta in breast milk. The body does not make its own antibodies or memory cells in passive immunity. Antibodies pass from the mother to the infant via breast milk and this is important as it helps the very young to fight off infections until they are older and stronger, and their immune system is more responsive. The body does not make its own antibodies or memory cells in passive immunity.

Question 26

What is cholera?

Answer 26

Cholera is a disease caused by a bacterium which is transmitted in contaminated water.

Question 27

How does cholera lead to diarrhoea?

Answer 27

1. Bacteria attach to the wall of the small intestine.
2. The cholera bacterium produces a toxin.
3. The toxin stimulates the cells lining the small intestine to secrete chloride ions into the lumen of the small intestine.
4. The chloride ions accumulate in the lumen of the small intestine and lower the water potential.
5. Once the water potential is lower than that of the cells lining of the intestine, water starts to move out of the cells into the intestine by osmosis
6. Large quantities of water are lost from the body in watery faeces (diarrhoea).
7. The blood contains too little chloride ions and water which leads to dehydration and the loss of ions from the blood.