Change, measure, control, then say how you will use the data.
What the parts mean
Changethe independent variable and its range
Measurethe dependent variable and how you record it
Controlthe factors you keep the same
Usethe repeats, and what you will do with the readings
How to build your answer
1Name what you change and what you measure.
2Say how the other important variables stay the same.
3Include a range, repeats, and how the results will be used.
4Do not write only a list of apparatus.
Biology exemplar
Original question
Devise a procedure to test whether temperature changes the rate of oxygen uptake by germinating seeds. Follow your school’s safety rules. This plan is not permission to run a practical.
Annotated answer
ChangeThe same mass of one seed type at 10, 20, 30 and 40 °C, after time to reach that temperature. MeasureOxygen volume, or fluid movement in a respirometer, for the same stated time. ControlSeed mass, soda lime and the volume of the apparatus stay the same. UseRepeat at each temperature and plot rate against temperature. Do not claim a statistical result unless a test is supplied.
The labels match the frame. Read them in order. This is one accurate route, not the only one.
Exam habit
If nobody could tell what number you would record, the method is not devised yet.
Common pitfall
Writing “use seeds and see what happens”.
Exam-style question
10 marks
Based on a sample question
Mark points shown after marking
A student wants to find out how temperature affects the rate at which the enzyme trypsin breaks down the protein casein in milk. Trypsin makes cloudy milk go clear.
Devise a detailed method for this investigation, including how you would control and monitor important variables. Write your method in the box, then tick the points it covers.
(10)
Write your method first. Then tick each point your method clearly covers.
Total for this question: 10 marks
Answer discussion
The method has to be detailed enough to follow: the factor changed, the measurement, the controls, and the use of the readings. A list of apparatus is not a procedure. Stay with the investigation in the paper.
Where this comes from
Unit 6 sample paper. Question 3 (c) asks you to devise a detailed method, including control and monitoring of important variables. Sample assessment, not a live paper.
