Chapter 1 Causes of Disease:
Common Exam Questions and Model Answers
Give two ways pathogens cause disease.
 Bacteria produce toxins
 Viruses damage cells/tissues
Describe how the control group should be treated.


Same as experimental group
Not given thing that is being tested (e.g. if new drug is being tested, experimental group is given
drug, and control group is not, but otherwise they are treated in the same way).
Must be related and specific to the investigation in the question.
Describe why a control group is needed.

To ensure that results are not due to something else (that they are only due to the thing being
tested).
Must be related and specific to the investigation in the question.
Why is the number of incidents given as a percentage or as per x? (see examples below)
Generic answer (2 marks)


Allows comparison
Because of (different start numbers / population sizes etc.)
Does the evidence from the graph prove that X causes Y? (see examples below)
Generic answer (3 marks):



graph shows (positive/negative) correlation
correlation doesn't mean causation
may be due to another factor example given
EXAMPLES: Why is the number of incidents given as a percentage or as per x?
The student calculated the percentage change in mass rather than the change in mass. Explain the
advantage of this.
-allows comparison
-idea that the cylinders have different starting masses
The number of deaths is given per 100 000 people. Explain why.
-allows comparison
-different numbers of people in each country
EXAMPLES: Does the evidence from the graph prove that X causes Y?
Some people have used this graph to conclude that a high percentage of fat in the diet causes breast
cancer. Evaluate this conclusion.
-positive correlation
-but correlation doesn't show causation/some other (named) factor may be involved
-evidence against positive correlation, e.g. different death rates at same % of fat/ same death rates at
different % of fat/ some countries with higher death rates have lower % of fat.

Scientists concluded that substances in the air from vehicle exhausts did not cause the increase in asthma
between 1976 and 1980. Explain why
-correlation does not mean there is a casual relationship
-may be some other factor/named factor may be involved
-associated with vehicles and asthma, causing a rise in both
- asthma continues to rise but exhaust concentration falls

Do the data show that eating omega 3 fatty acids prevents coronary heart disease? explain your answer.
-graph shows negative corrleation
-correlation doesn't mean causation/preventions/ shows lower risk not prevention
-may be due to another factor example given