Chapter 11 Causes of disease

Question 1

11.1 What are micro-organisms?

Answer 1

It is a general term for organisms that are too small to be seen without a microscope.

Question 2

11.1 Do all micro-organisms cause disease?

Answer 2

No, some micro-organisms are beneficial to us and other micro-organisms cause disease; known as pathogens.

Question 3

11.1 What are pathogens? (include examples)

Answer 3

Pathogens refer to micro-organisms which cause disease. Such as, protists, fungi, viruses and bacteria

Question 4

11.1 What is disease?

Answer 4

Disease suggests a malfunction of the body or mind that has an adverse effect on good health . It has mental, physical and social aspects

Question 5

11.1 What are the characteristics that micro-organisms must have to be considered pathogens?

Answer 5

They must;
- gain entry to the host
- colonise the host tissues
- resist the host’s defences
- cause damage to the host tissues

Question 6

11.1 What is infection?

Answer 6

Infection refers to when a pathogen gains entry to the host and colonises its tissues

Question 7

11.1 What is transmission?

Answer 7

Transmission refers to when a pathogen is transferred from one individual to another

Question 8

11.1 How do pathogens enter the body?

Answer 8

Pathogens enter the body by penentrating one of the organism’s interfaces with the environment.

Question 9

11.1 What is an interface?

Answer 9

An interface is a boundary linking both the external environment and the internal environment of the body.

Question 10

11.1 Why are some interfaces considered easy entry sites for pathogens?

Answer 10

Some interfaces have evolved to allow exchange of material between the internal and external environments.
So, the body linings at this point are moist (therefore sticky), thin, have a large SA and are well supplied with blood vessels.
Just as these features allow for easy entry of molecules, they also allow for easy entry of pathogenic micro-organisms.

Question 11

11.1 What are the 3 main interfaces of the body? (include what pathogens use each of the 3 routes)

Answer 11

• Gas-exchange system-many pathogens enter the body through the gas-exchange surfaces. E.g. the pathogens that cause tuberculosis, bronchitis and influenza enter the body this way.
• Reproductive system- many pathogens can be transmitted through intimate sexual contact. E.g. the bacterium which causes syphilis and viruses such as herpes virus can be transmitted in this way.
• Digestive system- food and water may carry pathogens into the stomach and intestines from the mouth. E.g. the bacteria that causes cholera and typhoid enter the body this way

Question 12

11.1 How does the body prevent entry of pathogens?

Answer 12

• A mucus layer that covers exchange surfaces and forms a thick sticky barrier that is difficult to penetrate (traps pathogens)
• The production of enzymes that break down pathogens
• The production of stomach acid that kills micro-organisms

Question 13

11.1 How do pathogens cause disease?

Answer 13

• By producing toxins- Most bacterial pathogens produce toxins. E.g. cholera bacterium produce toxins that leads to excessive water loss from the small intestine’s linings
• By damaging host tissues- Many pathogens break down the membranes of the host cells (V and B) Also, the sheer number of pathogens can cause damage by preventing tissues from functioning properly for instance (V and B). E.g. viruses inhibit the synthesis of DNA, RNA and proteins as well as, diverts the cell’s resources towards making new virus particles

Question 14

11.1 What determines how quickly a pathogen causes damage to the body?

Answer 14

The speed at which a pathogen divides determines how quickly a pathogen causes damage to the body. However some pathogens cause harm in small numbers (typhoid) and others when numbers are large (gastroenteritis)

Question 15

11.1 What can cause disease?

Answer 15

1. Pathogens
2. Lifestyle factors
3. Genetic factors

Question 16

11.1 Important note:

Answer 16

It is the pathogen that causes the symptoms, not the disease. E.g. The bacterium which causes Cholera enters the body and causes diarrhoea.

Question 17

11.2 What is epidemiology?

Answer 17

Epidemiology refers to the study of the incidence and pattern of a disease with a view to finding means of preventing and controlling it

Question 18

11.2 How do epidemiologists do this?

Answer 18

They collect data on diseases and look for patterns and relationships between these diseases and various factors in the lives of the people who have them

Question 19

11.2 What is a correlation?

Answer 19

Refers to when a change in one of the two variable is reflected by a change in the other variable

Question 20

11.2 When interpreting/analysing data on diseases, what can you and can’t do (and why)?

Answer 20

Using the data provided, it can be suggested that there is a correlation between the factor and the disease.
However, what you can’t do is conclude that the factor is the cause of the disease. This is because, there is not enough evidence to prove that there is a casual link between the two. Also, another factor may be the cause of the disease other than the factor suggested by the data.

Question 21

11.2 How is a casual link established?

Answer 21

A casual link is established between a factor and a disease when there is experimental evidence which proves that some aspect of the factor directly causes the disease. For example, to establish a casual link between smoking cigarettes and lung cancer, there must be experimental evidence showing that some component of the tobacco smoke led directly to people developing lung cancer.

Question 22

11.2 What should you consider when deciding how reliable the data is?

Answer 22

• Has the right factor been measured and have the correct questions been asked?
• How were the data gathered, were the methods reliable, and the right apparatus used?
• Do those collecting the data have a vested interest in the outcome of the research?
• Has the study been repeated, with the same results and conclusions by other people?
• Are there still unanswered questions?

Question 23

11.2 What does the statement ‘relative risk of lung cancer’ mean when investiagting the effect of smoking on developing lung cancer?

Answer 23

The risk of getting lung cancer when compared to a non-smoker

Question 24

11.2 How can you identify the correlation between two variables graphically?

Answer 24

By using a scatter diagram

Question 25

11.2 What are the two types of correlations?

Answer 25

• Positive- as one variable increases, the other also increases
• Negative- as one variable increases, the other decreases

Question 26

11.2 What are meant by the terms; valid, precise, reliable and data?

Answer 26

• Valid- suitability of the investigative procedure to answer the question being asked
• Precise- measurements with little difference between them
• Relaible- the investigation is repeatable by other scientists who get similar results
• Data- information that has been collected (can be qualitative or quantitative)

Question 27

11.2 Important note

Answer 27

Correlation doesn’t mean causation/ casual link has been established

Question 28

11.3 What is risk?

Answer 28

It is the probability that damage to health will occur as a result of a given hazard

Question 29

11.3 What are the two elements of risk?

Answer 29

1. The probability that a hazardous event will occur
2. The consequences of that hazardous event

Question 30

11.3 How is risk measured?

Answer 30

Measured as a value that ranges from 0% (no harm will occur) to 100 % (harm will certainly occur).
Health risks also;
- need a timescale (e.g. the risk of someone dying in the next month is 100% rather than just stating the risk of someone dying is 100%)
- are often relative- risk is also measured by comparing the likelihood of harm occurring to those exposed to a hazard with those who are not (e.g. smokers are 15 times more likely to develop lung cancer than non-smokers)

Question 31

11.3 What other factors need to be considered to be able to understand risk even if its quantified?

Answer 31

• Impact of the quantity of the variable on the likelihood/ risk of the hazardous event
• Other factors such as, pollution, location/area, gender, lifestyle, etc..
• Whether or not statistical tests have been done e.g. standard deviation
• Are there error bars on the graphs (smaller error bar = more reliable)

Question 32

11.3 Why are statistics misleading sometimes?

Answer 32

Media reports may be misleading because it focuses on a single figure, giving the impression that this figure applies to everyone when often this is far from it.

Question 33

11.3 What are risk factors?

Answer 33

A factor that increases the likelihood of developing a disease

Question 34

11.3 What is cancer? And what is its causes? (include the different types)

Answer 34

Cancer refers to a disease in which some of the body’s cells grow uncontrollably, forming a malignant tumour.
Some causes of cancer are beyond our indivdiual control such as, age and genetic factors. While others are lifestyle factors which are within our powers to change.

Question 35

11.3 What are the risk factors of cancer?

Answer 35

• smoking- smokers and people who passively breathe tobacco smoke also have an increases risk of developing cancer
• obesity- being overweight increases the risk of developing cancer
• diet- there is strong evidence that a low-fat, high-fibre, rich in fruit and vegetables diet, reduces the risk of developing cancer
• physical activity- people who exercise regularly are at a lower risk from some cancers than those who do little to no exercise
• sunlight- the more that someone is exposed to sunlight/ light from sunbeds, the greater the risk of skin cancer

Question 36

11.3 What is coronary heart disease? And what is its causes? (include the different types)

Answer 36

CHD refers to a narrowing or blockage of your coronary arteries caused by plaque build up.

Some causes of CHD are beyond our indivdiual control such as, age and genetic factors. While others are lifestyle factors which are within our powers to change.

Question 37

11.3 What are the risk factors of coronary heart disease?

Answer 37

• Smoking
• High blood pressure- excessive prolonged stress, certain diets and lack of exercise all increase blood pressure
• High blood cholesterol levels- can be kept lower by fewer saturated fatty acids in the diet
• Obesity- A body mass index of over 25 is associated with an increased risk of CHD
• Diet- high concentration of salts increase blood pressure and high levels of saturated fatty acids increase cholesterol levels, increasing the risk of CHD. However, foods like dietary fibres, reduce the risk of CHD by lowering blood cholestrol levels
• Physical activity- aerobic exercise can lower blood pressure and blood cholestrol, as well as helps prevent obesity, reducing the risk of CHD

Question 38

11.3 How do you reduce the risk of cancer and CHD?

Answer 38

• giving up/ not taking up smoking
• avoiding becoming overweight
• reducing salt intake
• reducing intake of cholestrol and saturated fatty acids
• regular aerobic exercise
• keeping alcohol consumption to safe limits
• increasing intake of dietary fibre and antioxidants

Question 39

11.3 Important note

Answer 39

Risk is about probabilities not certainties