OxfordAQA International A Level Biology
OxfordAQA International A Level Biology 3.2.1 The Causes of Disease: Pathogens, Lifestyle and Genes Exam Questions
Free OxfordAQA International A Level Biology revision for 3.2.1 The Causes of Disease: Pathogens, Lifestyle and Genes: what you need to know, common mistakes and exam-style questions with answers. Covers how bacteria and viruses cause disease, routes of entry, and risk factors for heart disease and cancer.
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About OxfordAQA International A Level Biology 3.2.1 The Causes of Disease: Pathogens, Lifestyle and Genes
This topic opens Unit 2 by looking at why people become ill. You need to explain how bacteria and viruses act as pathogens, how they enter the body through the interfaces of the digestive, reproductive and gas-exchange systems, and how they cause disease by damaging host cells or producing toxins. You also need to know the risk factors associated with coronary heart disease and cancer and the lifestyle changes that reduce risk. A key skill is analysing and evaluating data on risk and incidence. It sets up cholera, HIV, immunity, heart disease and cancer later in the unit.
What you need to know
- Pathogens A pathogen is a microorganism that causes disease, such as a bacterium or virus. Pathogens cause disease by damaging host cells or by producing toxins.
- Entry into the body Pathogens enter through interfaces with the environment: the gas-exchange system, the digestive system and the reproductive system. These surfaces are thin, moist and have a large surface area, so they are easier to penetrate.
- Risk factors A risk factor increases the probability of developing a disease. For coronary heart disease these include smoking, high blood pressure, high blood cholesterol and diet; for many cancers they include smoking, diet, alcohol, sunlight exposure and inherited genes.
- Reducing risk Lifestyle changes such as stopping smoking, eating less saturated fat and salt, keeping a healthy body mass and exercising reduce the risk of coronary heart disease and some cancers.
- Correlation and cause A correlation between a factor and a disease does not prove that the factor causes it. Evaluate data by considering sample size, other variables, whether the study was controlled and whether there is a plausible biological mechanism.
Common mistakes in 3.2.1 The Causes of Disease: Pathogens, Lifestyle and Genes
- Saying a correlation proves a risk factor causes disease. A correlation shows an association; a causal link needs further evidence such as a mechanism or a controlled study.
- Describing bacteria and viruses as the same. Viruses are not cells and reproduce only inside host cells; bacteria are prokaryotic cells.
- Saying risk factors cause a disease. They increase the probability of the disease developing.
- Ignoring sample size and control groups when evaluating data. Examiners expect these points in evaluation answers.
Try three 3.2.1 The Causes of Disease: Pathogens, Lifestyle and Genes exam-style questions
1. Suggest why the gas-exchange surface is a common point of entry for pathogens. (2 marks)
Show the mark scheme answer
Thin / short diffusion distance; large surface area; moist; constantly exposed to air containing microorganisms. (Any 2)
2. A study found that people who smoke have a higher rate of lung cancer. Explain why this does not prove smoking causes lung cancer. (2 marks)
Show the mark scheme answer
It shows a correlation only; other factors / variables may be involved, such as diet or occupation.
3. Give two ways in which pathogens cause disease. (2 marks)
Show the mark scheme answer
By damaging host cells / tissues; by producing toxins.
3.2.1 The Causes of Disease: Pathogens, Lifestyle and Genes FAQs
What does OxfordAQA International A Level Biology 3.2.1 The Causes of Disease: Pathogens, Lifestyle and Genes cover?
It covers how bacteria and viruses cause disease, routes of entry, and risk factors for heart disease and cancer.
Which unit is 3.2.1 The Causes of Disease: Pathogens, Lifestyle and Genes examined in?
It is part of Unit 2, Biological systems and disease, which is examined at International AS. The Unit 5 synoptic paper at A2 can also draw on this content.
How do I evaluate risk data in the exam?
State the trend, then comment on correlation versus causation, sample size, whether other factors were controlled and whether the data come from a representative population. Use figures from the data to support each point.
