Scientific Processes and Skills
Scientific Processes and Skills is the 'doing science' domain. The exam tests whether you can plan a fair investigation, measure and record accurately, present results in tables and graphs, and draw a conclusion that matches the evidence. Questions usually give a short experiment or a results table and ask you to identify variables, spot the error or interpret the trend; school-based practical work is assessed on the same abilities.
Planning a fair test
A hypothesis is a testable prediction that evidence can show to be right or wrong. The independent variable is what the investigator deliberately changes; the dependent variable is what is measured; controlled variables are kept the same so that any change in the result can be credited to the independent variable.
Measuring and recording
Use SI units: length in metres, mass in kilograms, time in seconds, temperature in degrees Celsius, volume in cubic centimetres. Read scales at eye level. Tables carry the quantity and unit in the column heading (time / s), not beside every number. Repeat readings and average them to reduce random error.
Graphs and conclusions
Use a line graph for continuous data and a bar chart for categories. Label both axes with quantity and unit, choose an even scale, plot points and draw a line of best fit rather than joining dot to dot. A conclusion must quote figures from the data and state whether the hypothesis is supported; an evaluation should name a specific source of error and a specific improvement.
Worked example
Hypothesis: as a lamp is moved further from pondweed, the rate of photosynthesis falls. A student counts oxygen bubbles per minute at 10, 20, 30 and 40 cm. Independent variable: distance of the lamp (cm). Dependent variable: bubbles per minute. Controlled variables: same pondweed, same sodium hydrogencarbonate concentration, same temperature, same counting time. Reasoning: the hypothesis predicts a direction of change and can be tested, whereas 'pondweed needs light' cannot be tested as written. Bubbles per minute is a proxy measurement for oxygen released, so it is valid only if plant, solution and timing stay unchanged. Repeat each distance three times and average.
Traps that cost marks
Reversing independent and dependent variables; omitting units; ignoring an anomalous point without comment; joining dots instead of drawing a line of best fit; writing 'it went up' with no figures; naming a controlled variable without saying what it controls.