📊 Bar charts
Use a bar chart when the data is in separate categories, such as types of disease. The bars have gaps between them. To go back to numbers, read the height of each bar.
Animal Tissues, Organs and Systems » Health and Disease
What you'll learn this session
Study time: 30 minutes
AQA spec: 4.2.2.5
- What health means and how disease, diet, stress and life situations affect it
- How different types of disease interact
- How to turn disease data into tables, bar charts, histograms and scatter diagrams
- Why sampling matters when scientists collect data about disease
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Unlock This CourseWhat is health?
Many people think health just means "not being ill". In biology it means more than that. Health is the state of physical and mental well-being. A healthy person has a body that works properly and a mind that is coping well.
Ill health can have many causes. Diseases are major causes of ill health, and they come in two types.
Key terms:
- Health: the state of physical and mental well-being.
- Communicable disease: a disease that can be passed from one person to another, or from an animal to a person. It is also called an infectious disease.
- Non-communicable disease: a disease that cannot be passed from one person to another.
Disease is not the only factor
Diseases are not the only things that affect how healthy you are. Other factors can have a profound effect on both physical and mental health.
🍎 Diet
The body needs the right nutrients to work. A poor diet can harm physical health, and it can also affect how people feel.
⚡ Stress
Long periods of stress can damage mental health and can have effects on the body too.
🏠 Life situations
Where and how a person lives, such as their home, money worries or relationships, can help or harm their health.
The details of which lifestyle choices are linked to which diseases are covered in Lifestyle and Non-Communicable Diseases. Here the key point is that health depends on many things working together.
How different diseases interact
Diseases do not always act alone. One type of disease can make another more likely. You need to know four examples.
- Immune system defects: if the immune system does not work properly, a person is more likely to suffer from infectious diseases.
- Viruses and cancer: viruses living in cells can be the trigger for cancers.
- Infection and allergies: immune reactions that were first caused by a pathogen can trigger allergies, such as skin rashes and asthma.
- Physical ill health and mental health: severe physical ill health can lead to depression and other mental illness.
Common mistakes
1. Thinking health only means "not having a disease". It includes mental well-being too.
2. Saying that all diseases can be caught from other people. Non-communicable diseases cannot.
3. Saying that a virus always causes cancer. The spec says viruses living in cells can be the trigger.
Disease data: tables and charts
Scientists collect data on how many people have a disease, which is called the incidence of the disease. You need to be able to turn this data between numbers and graphs.
Frequency tables. A frequency table shows how many times each value or group occurs. Imagine a clinic records the ages of 40 patients:
| Age (years) | Frequency |
|---|---|
| 0 to 19 | 4 |
| 20 to 39 | 10 |
| 40 to 59 | 16 |
| 60 to 79 | 10 |
The frequencies add up to 40. The percentage aged 40 to 59 is 16 ÷ 40 × 100 = 40%.
📈 Histograms
Use a histogram when the data is continuous, such as age. The bars touch, because one group runs straight into the next. The table above can be drawn as a histogram with four touching bars.
Worked example
A bar chart of cases of a disease in four towns has bars of height 12, 18, 6 and 24. To translate it into numbers, write a table: Town A 12, Town B 18, Town C 6, Town D 24. The total is 12 + 18 + 6 + 24 = 60 cases. Town D has 24 ÷ 60 × 100 = 40% of the cases.
Scatter diagrams and correlation
A scatter diagram plots one variable against another, with one point for each pair of values. It is used to look for a correlation, which is a link between two variables.
- Positive correlation: as one variable increases, the other increases. The points slope upwards.
- Negative correlation: as one variable increases, the other decreases. The points slope downwards.
- No correlation: the points show no pattern.
Draw a line of best fit through the points to see the pattern clearly. A correlation shows that two variables are linked. It does not on its own prove that one causes the other.
Sampling
It is rarely possible to test every person in a population. Instead, scientists collect data from a sample, which is a smaller group chosen to represent the whole population. This applies to all scientific data, including epidemiological data, which is data about how often a disease occurs in groups of people.
A good sample follows these principles:
- Large enough: a bigger sample gives results that are more reliable, because a few unusual people matter less.
- Representative: it should include a mix of people, such as different ages, to match the population being studied.
- Random: choosing people by chance avoids bias, so that the results are not skewed by the choices of the person collecting the data.
Worked example
A scientist wants to know how common asthma is in a town. Asking only 10 people at a sports club would be a poor sample: it is too small, and sporty people are not representative of everyone. Asking 1000 people chosen at random from the town gives a better sample.
Exam-style question
(a) Give the meaning of the word "health". [1 mark]
(b) Explain how a defect in the immune system can lead to ill health. [2 marks]
(c) A scientist collects data from a sample of people to study a disease. Give two ways to make the sample suitable. [2 marks]
Model answer
(a) The state of physical and mental well-being (1).
(b) The person is more likely to suffer from infectious diseases (1); so they are more likely to become ill (1).
(c) Any two from: the sample should be large enough (1); it should be representative of the population (1); people should be chosen at random (1).
Exam tip
For "health", always mention both physical and mental well-being. Writing only "not being ill" does not earn the mark.