Health, Disease and Practical/Experimental Skills
What this domain tests
This domain combines health and disease with practical and experimental skills. It tests pathogens, transmission, immunity, treatment, lifestyle diseases, and your ability to design, carry out and evaluate investigations.
Core rules
- Pathogens include bacteria, viruses, fungi and protozoa. They may spread by air droplets, contaminated water and food, vectors, body fluids and direct contact.
- The body's defences include skin, mucus, cilia, stomach acid, phagocytes and antibodies. Vaccination introduces antigens so the body produces memory cells and antibodies without causing the disease.
- Antibiotics kill bacteria but do not treat viral infections. Overuse and incomplete courses encourage antibiotic resistance.
- In an experiment, the independent variable is changed, the dependent variable is measured, and control variables are kept constant. A control group is not treated with the independent variable and is compared with the experimental group.
- Reliability improves with repeats and calculating a mean; validity depends on controlling variables and measuring what you claim to measure.
- Tables need headings and units; graphs need labelled axes, suitable scales and a line or bars as appropriate.
Worked example
A student tests the effect of pH on amylase. The independent variable is pH; the dependent variable is the time taken for starch to disappear, detected with iodine. Control variables include temperature, amylase concentration, starch concentration and volume. A fair test changes only pH. Repeating each pH and using the mean improves reliability. The conclusion should state the optimum pH, not merely that pH affects the enzyme.
Traps
Do not confuse a control group with a controlled variable. Do not say antibiotics cure viruses. A correlation between two measurements does not prove causation. Avoid claiming a result is proved from one trial; say the evidence supports the conclusion.