Diseases and immunity

Question 1

What is a pathogen?

Answer 1

Disease causing organism

Question 2

What is a transmissible disease?

Answer 2

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

Question 3

What are the two ways pathogens can be transferred?

Answer 3

1. Direct contact
   The pathogen is passed directly from one host to another by transfer of body fluids including through blood and other fluids
2. Indirect contact
   The pathogen leaves the host and is carried in some way to another, uninfected individual including from contaminated surfaces, food, animals and air

Question 4

What are the three body defense systems?

Answer 4

1. Mechanical barriers (structures that make it difficult for pathogens to get past them and into the body)
2. Chemical barriers (substances produced by the body cells that trap / kill pathogens before they can get further into the body and cause disease)
3. Cellular barriers (different types of white blood cells work to prevent pathogens reaching areas of the body they can replicate in)

Question 5

What are the mechanical barriers in the body?

Answer 5

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

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

Question 6

What are the chemical barriers in the body?

Answer 6

Mucus- 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, swallowing etc)

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 consumed in food or water

Antibacterial tears

Question 7

What are the cellular barriers in the body?

Answer 7

Byphagocytosis- engulfing and digesting pathogenic cells

By producingantibodies- which clump pathogenic cells together so they can’t move as easily and releasing chemicals that signal to other cells that they must be destroyed

Question 8

What are the five ways to control the spread of diseases?

Answer 8

1. Hygienic food preparation
2. Good personal hygiene
3. Waste disposal
4. Sewage treatment
5. A clean water supply

Question 9

How does hygienic food preparation control the spread of disease?

Answer 9

• Prepare food hygienically to avoid contamination of pathogens by washing hands well with soap and cleaning work surfaces with products like bleach to kill pathogens
• Cook food well (long enough at a high temperature) to kill bacteria and fungi
• Keep food cold so that bacteria and fungi reproduce slower
• Use separate chopping boards and utensils for cutting uncooked meat
• Cover food to prevent flies from landing on it before eating

Question 10

How does good personal hygiene control the spread of disease?

Answer 10

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

Question 11

How does waste disposal control the spread of disease?

Answer 11

• Waste food is a food source for flies that can act as vectors for transmissible diseases so should be disposed of in a sealed container
• Rubbish bins should be covered and removed to the landfill for disposal regularly

Question 12

How does sewage treatment control the spread of disease?

Answer 12

• 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 released into the environment
• Properly treated sewage protects water bodies from contamination, thus preventing water-borne diseases

Question 13

How does a clean water supply control the spread of disease?

Answer 13

• Contaminated water serves as a medium for pathogens causing diseases such as cholera, dysentery, and typhoid.
• Effective methods to purify water, including boiling, filtration, and chlorination, are vital in ensuring water safety.
• Regular testing and treatment of water supplies help in the early detection and elimination of contaminants.

Question 14

What is active immunity?

Answer 14

Active immunity is defence against a pathogen by antibody production in the body

Question 15

How is active immunity gained?

Answer 15

Active immunity is gained after an infection by a pathogen (so the lymphocytes go through the process of making antibodies specific to that pathogen) or by vaccination. Produces memory cells

Question 16

What are lymphocytes?

Answer 16

Cells that tag foreign material (known as the antigen) with antibodies, targeting the material for destruction

Question 17

What are antigens?

Answer 17

Antigens are structures that can be identified by the immune system (usually proteins) and each pathogen has its own antigens, which have specific shapes

Question 18

What are phagocytes?

Answer 18

Eat/engulf foreign material through phagocytosis

Question 19

What do lymphocytes do when they encounter an antigen?

Answer 19

• Lymphocytes can recogniseforeign antigens, e.g. the antigens of a pathogen inside the body
• In response to foreign antigens lymphocytes makeantibodieswhich arecomplementaryin shape to the antigens on the surface of the pathogenic

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.
Specific antibodies have complementary shapes which fit specific antigens (like the lock and key model for enzymes)

Question 21

How do antibodies work?

Answer 21

The shape of the antigen is complementary to the binding groove on the antibody. Once the antibody-antigen complex is formed it marks the foreign material for destruction by phagocytes. Each pathogen has its own unique antigens, so our bodies need to create an antibody that firs the antigen for an adaptive immune response to occur. These antibodies cause clumping of pathogens and enhance the activity of phagocytes.

Question 22

How does immunity occur?

Answer 22

• Theinitial responseof a lymphocyte encountering a pathogen for the first time can takea few days, during which time an individual may get sick
• After an initial encounter with a pathogen, lymphocytes can give rise tomemory cellsthat retain the instructions for making specific antibodies
• This means that in the case of reinfection by the same type of pathogen,antibodies can be made very quicklyand ingreater quantities; the pathogens are destroyed before they multiply and cause illness. This is how people becomeimmuneto certain diseases after only having them once
• Note that this does not work with all disease-causing microorganisms as some of themmutatequickly and change the antigens on their cell surface. Therefore, if they invade the body for a second time the memory cells made in the first infection will not produce antibodies that match the new antigens

Question 23

What does vaccination do?

Answer 23

Vaccines allow adead or altered formof the disease-causing pathogen, which contains specificantigens, to be introduced into the body. In this weakened state, the pathogencannot cause illnessbut canprovoke an immune response

Question 24

How do vaccinations help?

Answer 24

Vaccinations giveprotection against specific diseasesandboost the body’s defence against infectionfrom pathogens without the need to be exposed to dangerous diseases that can lead to death. The level of protection in a population depends on theproportion of people vaccinated

Question 25

Process of vaccination

Answer 25

1. Weakened pathogens or their antigens are put into the body
2. The antigens stimulate an immune response by lymphocytes which produce antibodies
3. Memory cells are produced that give long-term immunity (allows antibody to be produced rapidly in the future)

Question 26

How vaccinations prevent spread of disease

Answer 26

• Ifa large enough percentageof the population is vaccinated, itprovides protection for the entire populationbecause there arevery few places for the pathogen to breed- it can only do so if it enters the body of an unvaccinated person. This is known asherd immunity
• If the number of people vaccinated against a specific diseasedropsin a population, it leaves the rest of the population at risk ofmass infection, as they are more likely to come across people who are infected and contagious Thisincreases 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. This is the reason that many vaccinations are given tochildren, as they are regularly seen by medical practitioners and can be vaccinated early to ensure the entire vaccinated population remains at a high level. In certain instances, vaccination programmes are run with the aim oferadicatingcertain dangerous diseases, as opposed to controlling them at low levels like in smallpox which became officially eradicated

Question 27

What is passive immunity?

Answer 27

A short-term defence against a pathogen by antibodies acquired from another individual
- It doesn’t make memory cells and examples are from mother to baby across the placenta and in breast milk

Question 28

Why is passive immunity important for newborns?

Answer 28

Passive immunity is important for newborns as antibodies pass frommother to infantviabreast milk- this is important as it helps the very young to fight off infections until they areolder and strongerand their immune system is more responsive. They get all their antibodies from their mother

Question 29

What is cholera?

Answer 29

Cholera is a disease caused by a bacterium which is transmitted in contaminated water. You can get cholera by ingested Vibrio cholerae viainfected water or food. Symptom is diarrhoea

Question 30

What is diarrhoea?

Answer 30

The loss of watery faeces from the anus

Question 31

What can severe diarrhoea cause?

Answer 31

If it is severe and continues for a long time, itcan lead to death. Severe diarrhoea can cause theloss of significant amounts of water and ionsfrom the body, causing the tissues and organs to stop working properly

Question 32

How can diarrhoea be treated?

Answer 32

It can be effectively treated byoral rehydration therapy. This is adrink with a small amount of salt and sugardissolved in it

Question 33

How does Vibrio choleraecause diarrhoea?

Answer 33

1. Bacteria attach to the wall of thesmall intestine
2. They produce atoxin. The toxin stimulates the cells lining the intestine torelease chloride ionsfrom inside the cells into the lumen of the intestine
3. The chloride ions accumulate in the lumen of the small intestine andlower the water potentialthere
4. Once the water potential is lower than that of the cells lining the intestine,water starts to move out of the cellsinto the intestine (byosmosis)
5. Large quantities of water are lost from the body inwatery faeces
6. The blood containstoo little chloride ions and water causing loss of ions from the blood and dehydration