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IGCSE Biology - Extended > 10. Diseases & Immunity > Flashcards

10. Diseases & Immunity Flashcards

1
Q

What is a pathogen?

A

A pathogen is a disease-causing organism

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2
Q

What are diseases caused by pathogens called and why?

A

Pathogens are passed on from one host to another and therefore the diseases they cause are known as transmissible diseases

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3
Q

In what 2 ways can pathogens be passed from one host to another?

A

DIRECT or INDIRECT CONTACT

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4
Q

What is an explanation and example of direct contact?

A

The pathogen is passed directly from one host to another by transfer of body fluids such as blood or semen (eg HIV, gonorrhoea, hepatitis B & C)

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5
Q

What is an explanation of indirect contact?

A

the pathogen leaves the host and is carried in some way to another, uninfected individual

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6
Q

What 4 methods of transmission are there?

Give an example for a disease that can spread this way

A
  • droplets in air (common cold)
  • food or water (cholera)
  • touching contaminated surfaces (athlete’s foot)
  • insect bites (malaria)
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7
Q

In what 3 ways can the body defend itself from disease?

A
  • mechanical barriers
  • chemical barriers
  • cells
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8
Q

Mechanical barrier definition

A

structures that make it difficult for pathogens to get past them and into the body

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9
Q

Chemical barrier definition

A

substances produced by the body cells that trap / kill pathogens before they can get further into the body and cause disease

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10
Q

Cells (as a type of defence against disease) definition

A

different types of white blood cell work to prevent pathogens reaching areas of the body they can replicate in

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11
Q

What are two examples of mechanical barriers?

A
  • skin

- hairs in the nose

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12
Q

How is skin a mechanical barrier?

A

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.

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13
Q

How are hairs in the nose a mechanical barrier?

A

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

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14
Q

What are two examples of chemical barriers?

A
  • mucus

- stomach acid

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15
Q

How is mucus a chemical barrier?

A

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)

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16
Q

How is stomach acid a chemical barrier?

A

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

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17
Q

What are two examples of cells as barriers?

A
  • by phagocytosis

- by producing antibodies

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18
Q

How is phagocytosis a cell barrier?

A

engulfing and digesting pathogenic cells

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19
Q

How is the production of antibodies a cell barrier?

A

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

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20
Q

What do all cells have projecting from their cell membrane and what are these called? What is unique about them?

A

All cells have proteins and other substances projecting from their cell membrane

These are known as antigens and are specific to that type of cell

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21
Q

What ability do lymphocytes have which helps them detect pathogens?

A

Lymphocytes have the ability to ‘read’ the antigens on the surfaces of cells and recognise any that are foreign

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22
Q

How do lymphocytes respond when they detect foreign cells?

A

They then make antibodies which are a complementary shape to the antigens on the surface of the pathogenic cell

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23
Q

What do antibodies do?

A

The antibodies attach to the antigens and cause agglutination (clumping together)
This means the pathogenic cells cannot move very easily

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24
Q

What do antibodies release once they attach to antigens?

A

At the same time, chemicals are released that signal to phagocytes that there are cells present that need to be destroyed

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25
Q

What can cause a person to feel sick?

A

The initial response of a lymphocyte encountering a pathogen for the first time and making specific antibodies for its antigens can take a few days, during which time an individual may get sick

26
Q

What will lymphocytes do when they make specific antibodies for a pathogen for the first time?

A

Lymphocytes that have made antibodies for a specific pathogen for the first time will then make ‘memory cells’ that retain the instructions for making those specific antibodies for that type of pathogen

27
Q

Why are memory cells made?

A

This means that, in the case of reinfection by the same type of pathogen, antibodies can very quickly be made in greater quantities and the pathogens destroyed before they are able to multiply and cause illness

28
Q

What is the overall benefit of memory cells?

A

people can become immune to certain diseases after only having them once

29
Q

Why can a person become immune to some diseases but not some others?

A

It does not work with all disease-causing microorganisms as some of them mutate fairly quickly and change the antigens on their cell surfaces
Therefore, if they invade the body for a second time, the memory cells made in the first infection will not recall them as they now have slightly different antigens on their surfaces (e.g. the cold virus)

30
Q

What is active immunity?

A

Making antibodies and developing memory cells for future response to infection is known as active immunity

31
Q

What are the two ways in which an active immune response happens?

A
  • The body has become infected with a pathogen and so the lymphocytes go through the process of making antibodies specific to that pathogen
  • Vaccination
32
Q

How fast is active immunity and how long does it last?

A

Active immunity is slow acting and provides long-lasting immunity

33
Q

What is passive immunity?

A

This is when ready-made antibodies, from another source, are introduced to the body

34
Q

How fast is passive immunity and how long does it last?

A

Passive immunity is a fast-acting, short-term defence against a pathogen by antibodies acquired from another individual,

35
Q

What are two examples of passive immunity?

A

From mother to infant via breast milk – 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

Injected antibodies for certain diseases where the individual is already infected and a fast response is required, like rabies or tetanus

36
Q

Why is passive immunity called that?

A

The body does not make its own antibodies or memory cells in passive immunity, hence the name

37
Q

How may a disease caused by the immune system start?

A

Occasionally, the cells of the immune system start to attack the body’s own cells

38
Q

Why is a disease caused by the immune system rare?

A

This is rare as lymphocytes usually recognise their own body cells by the antigens on the cell surfaces and do not respond to them

39
Q

What happens in a disease caused by the immune system?

A

In this situation, specific body cells are targeted by lymphocytes and antibodies are made against them, destroying them

40
Q

What is an example of a disease caused by the immune system

A

Type 1 diabetes

41
Q

What happens to people with Type 1 diabetes?

A

People who suffer from this disease no longer make their own insulin and so are unable to regulate their blood glucose levels

42
Q

What causes type 1 diabetes?

A

This is because their immune system is targeting and destroying the pancreatic cells which are responsible for making the insulin, eventually leading to dangerously high glucose levels in the blood

43
Q

Antibiotic definition

A

An antibiotic is a drug that slows down or stops the growth of bacteria.

44
Q

Antibody definition

A

An antibody is a chemical made by lymphocytes that is complementary to an antigen and, when attached, clumps them together and signals the cells they are on for destruction.

45
Q

Vaccination definition

A

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

46
Q

What does the level of protection from a vaccination depend on?

A

The level of protection in a population depends on the proportion of people vaccinated

47
Q
  1. What do vaccinations allow to enter the body?
A

Vaccines allow a dead or altered form of the disease-causing pathogen, which contains specific antigens, to be introduced into the body

48
Q
  1. Why is the pathogen weakened and what does this allow the body to do?
    (vaccination)
A

In this weakened state, the pathogen cannot cause illness but can provoke an immune response

49
Q
  1. How does the body respond to the vaccine?
A

Lymphocytes produce complementary antibodies for the antigens
The antibodies target the antigen and attach themselves to it in order to create memory cells

50
Q
  1. What allows the vaccination be effective and helps the body fight an infection?
A

The memory cells remain in the blood and will quickly respond to the antigen if it is encountered again in an infection by a ‘live’ pathogen

51
Q

How long is the immunity from the vaccine and why?

A

As memory cells have been produced, this immunity is long-lasting

52
Q

What is herd immunity?

A

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 – it can only do so if it enters the body of an unvaccinated person
This is known as herd immunity

53
Q

What happens if the number of people vaccinated for a specific disease drops?

A

If the number of people vaccinated against a specific disease drops in a population, it leaves the rest of the population at risk of mass infection, as they are more likely to come across people who are infected and contagious

This increases the number of infections, as well as the number of people who could die from a specific infectious disease

54
Q

Why is herd immunity important?

A

Herd immunity prevents epidemics and pandemics from occurring in populations

55
Q

Why are many vaccinations given to children?

A

This is the reason that many vaccinations are given to children, as they are regularly seen by medical practitioners and can be vaccinated early to ensure the entire vaccinated population remains at a high level

56
Q

What is an example of a disease which has been eradicated by vaccination?

A

An example of a disease which has been eradicated as a result of a successful vaccination programme is smallpox, which was officially eradicated in 1980 after a vaccination programme run by the World Health Organisation since the mid-1950s

57
Q

What is the simplest way to prevent disease?

A

The simplest way to prevent disease is to stop pathogens from spreading

58
Q

What are ways in which can stop pathogens from spreading?

A
  • hygienic food preparation
  • personal hygiene
  • waste disposal
  • sanitation
59
Q

How does hygienic food preparation help prevent the spread of disease?

A
  • keep food cold so bacteria and fungi reproduce more slowly
  • prepare food hygienically to avoid contamination from pathogens by washing hands well 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/utensils for cutting uncooked meat
  • wash hands after using the bathroom before handling food
60
Q

How does personal hygiene help prevent the spread of disease?

A

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

61
Q

How does waste disposal help prevent the spread of disease?

A

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 the landfill for disposal or burning regularly all rubbish should be stored before collection away from human habitation

62
Q

How does sanitation help prevent the spread of disease?

A
  • 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

IGCSE Biology - Extended (22 decks)

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