Revision notes for AQA GCSE Biology Health issues. Open the guide for explanations and worked examples. Written against the AQA GCSE Biology (8461) specification, so the content matches what's examinable rather than general Biology background.
Health issues
What you'll learn
- What health means in GCSE Biology, and how it is linked to disease.
- The difference between communicable and non-communicable diseases.
- How different types of disease can interact and make health worse.
- How to interpret disease data using tables, bar charts, histograms, scatter diagrams and sampling.
Health means more than “not ill”
In this topic, you need to think of health as a broad idea. Someone may not have an obvious infection, but they could still have poor mental health, poor diet, high stress, or a long-term condition affecting their wellbeing.
Definition
Health
Health is the state of physical and mental well-being.
A disease is a condition that affects the normal functioning of the body or mind. Diseases are major causes of ill health, but they are not the only causes. Diet, stress and life situations can also have a big effect on both physical and mental health.
This concept map shows how health is affected by different causes, and how diseases can interact with each other.
Key Idea
Big picture
Health is not just the absence of disease. It includes both physical and mental well-being, and it can be affected by disease, lifestyle and living conditions.
Factors that can affect health
Some factors directly affect the body. For example, a poor diet may increase the risk of obesity, type 2 diabetes or heart disease. Other factors affect mental health. For example, long-term stress may contribute to anxiety or depression.
A person’s life situation means the circumstances they live in, such as housing, income, access to healthcare, social support and working conditions.
Example
Linking factors to health
A student is asked to explain how stress and diet can affect health.
- Separate the factors: stress is mainly linked to mental well-being, while diet is mainly linked to physical well-being.
- Link each factor to an effect: long-term stress may contribute to mental illness, while a poor diet can increase the risk of non-communicable diseases such as heart disease.
- Show that health is connected: poor physical health can also make mental health worse, so the effects are not always separate.
Communicable and non-communicable disease
Diseases can be grouped into two main types.
Definition
Communicable disease
A communicable disease is a disease that can be spread between organisms. It is usually caused by a pathogen, which is a microorganism that causes disease.
Examples include measles, flu, HIV and malaria.
Definition
Non-communicable disease
A non-communicable disease is a disease that is not passed from one organism to another.
Examples include cancer, coronary heart disease, asthma and type 2 diabetes.
Common Mistake
Assuming all diseases are infectious
Not all diseases are caused by pathogens. Cancer, asthma and heart disease are examples of non-communicable diseases, even though they can still seriously affect health.
How diseases can interact
Different types of disease can affect each other. This is important because real health problems are often connected rather than separate.
Immune system defects and infectious disease
The immune system is the body’s defence system against pathogens. If it is damaged or not working properly, the person is more likely to suffer from infectious diseases.
For example, HIV can damage the immune system, making a person more likely to develop infections that their body would normally fight off.
Viruses and cancer
Some viruses live inside cells. In some cases, they can damage the cell’s genetic material or affect how the cell divides. This can trigger the development of cancer.
For example, some types of HPV are linked with cervical cancer.
Immune reactions and allergies
Sometimes, an immune reaction that originally happens because of a pathogen can later trigger allergies. An allergy is an overreaction of the immune system to a usually harmless substance.
Allergic reactions can include skin rashes and asthma symptoms.
Physical illness and mental illness
Severe or long-term physical illness can affect mental health. For example, chronic pain, reduced independence or long hospital treatment may contribute to depression.
Key Idea
Disease interactions
One health problem can increase the risk of another. In exam answers, try to show the chain of cause and effect rather than just naming the diseases.
Example
Explaining a disease interaction
A person has a disease that damages their immune system. Explain why they may become ill more often.
- Identify the affected body system: the immune system is responsible for defending the body against pathogens.
- Apply the effect of the defect: if the immune system is damaged, the body is less able to destroy pathogens.
- Link this to disease risk: pathogens are more likely to survive and reproduce, so the person is more likely to develop infectious diseases.
Disease data: incidence
Scientists often study disease using data from populations.
Definition
Incidence
Incidence is the number of new cases of a disease in a population during a particular time period.
Incidence is useful because it shows how quickly new cases are appearing. It is often given as “cases per 100 000 people per year” so that different-sized populations can be compared fairly.
A useful formula is:
incidence rate=number of new cases in a time periodpopulation at risk×100 000\text{incidence rate} = \frac{\text{number of new cases in a time period}}{\text{population at risk}} \times 100\,000incidence rate=population at risknumber of new cases in a time period×100000Common Mistake
Incidence vs total cases
Incidence means new cases in a time period. It does not mean the total number of people who already have the disease.
Example
Calculating incidence
A town has 80 new cases of a disease in one year. The population is 40 000. Calculate the incidence per 100 000 people per year.
- Substitute the values into the formula:
incidence rate=8040 000×100 000\text{incidence rate} = \frac{80}{40\,000} \times 100\,000incidence rate=4000080×100000 - Calculate the fraction of the population affected:
80÷40 000=0.00280 \div 40\,000 = 0.00280÷40000=0.002 - Scale up to 100 000 people:
0.002×100 000=2000.002 \times 100\,000 = 2000.002×100000=200 - Give the answer with units: the incidence is 200 new cases per 100 000 people per year.
Turning disease data into tables and graphs
Disease data can be shown in different forms. You need to be able to move between numerical and graphical forms, such as from a table to a chart, or from a chart back to values.
A frequency table shows how often something occurs. For example, it might show the number of people with a disease in different age groups.
| Age group / years | Number of new cases |
|---|---|
| 0–9 | 4 |
| 10–19 | 7 |
| 20–29 | 11 |
| 30–39 | 18 |
| 40–49 | 24 |
A bar chart is used for separate categories. A histogram is used for continuous data grouped into intervals, such as age groups. A scatter diagram is used to look for a relationship between two variables.
This diagram compares the main graph types you are likely to use for disease data.
Bar charts
Use a bar chart when the x-axis has separate categories, such as disease type, gender, country or treatment group. The bars should have gaps between them.
Histograms
Use a histogram when the x-axis is continuous data split into groups, such as age ranges. The bars touch because the intervals are continuous.
Tip
Bar chart or histogram?
If the x-axis categories are separate labels, use a bar chart. If the x-axis is a continuous scale split into groups, such as age, use a histogram.
Scatter diagrams and correlation
A scatter diagram shows pairs of data for two variables. A variable is a factor that can change, such as age, number of cigarettes smoked per day, or disease incidence.
Definition
Correlation
A correlation is a relationship between two variables. In a positive correlation, one variable increases as the other increases. In a negative correlation, one variable decreases as the other increases.
Correlation is useful, but it does not automatically prove that one variable causes the other. Other factors may be involved.
Common Mistake
Correlation does not prove causation
If a scatter diagram shows a correlation, you can say the variables are linked. You should not say one definitely causes the other unless there is enough evidence from further investigation.
Example
Choosing and interpreting a graph
A scientist records the average number of cigarettes smoked per day and the incidence of lung cancer in several groups of people.
- Choose the graph type: there are two numerical variables, so a scatter diagram is suitable.
- Look at the pattern: if the points rise from left to right, lung cancer incidence increases as cigarette use increases.
- Name the relationship: this is a positive correlation.
- Avoid overclaiming: the graph supports a link, but by itself it does not prove that smoking is the only cause.
Sampling and epidemiological data
Definition
Epidemiology
Epidemiology is the study of patterns, causes and effects of disease in populations.
Scientists cannot usually study every single person in a population, so they use a sample.
Definition
Sample
A sample is a smaller group selected from a larger population to collect data from.
A good sample should be representative, meaning it reflects the population being studied. If a sample is not representative, the results may be misleading.
For example, if you only survey people who visit a gym, your sample may not represent the whole town’s health because gym users may have different lifestyles from non-gym users.
Principles of good sampling
Good epidemiological sampling usually involves:
- a large enough sample size
- random selection where possible
- including different groups in the population, such as age groups or sexes
- avoiding biased sources of data
- collecting data in the same way for everyone
- considering other variables that might affect the results
A bias is anything that makes data unfairly lean towards one outcome. A confounding variable is another factor that may affect the result and make it harder to identify the real cause.
Example
Improving a disease survey
A researcher wants to find out whether asthma is more common in a town. They only ask 30 students from one school.
- Identify the weakness: the sample is small and only includes students from one school, so it may not represent the whole town.
- Improve the sample size and range: the researcher should include many more people from different ages, schools, workplaces and areas of the town.
- Reduce selection bias: people should be selected randomly or in a planned way so that the researcher does not just choose convenient participants.
- Keep data collection consistent: everyone should answer the same questions or have asthma status recorded using the same method.
Exam technique
In the exam
- Use the exact definitions: health is physical and mental well-being; incidence means new cases in a time period.
- For disease interactions, write a chain: cause → effect on the body → increased risk or symptom.
- Choose graphs by data type: categories need bar charts, continuous groups need histograms, and two variables need scatter diagrams.
- Be cautious with correlations: describe the trend, but do not claim causation unless the evidence supports it.
- For sampling questions, mention representativeness: a larger, random and varied sample gives more reliable population data.
Self review
Check yourself
- What is the difference between a communicable and a non-communicable disease?
- Why can a defect in the immune system increase the risk of infectious disease?
- When would you use a scatter diagram rather than a bar chart?
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