Question 1

What is the difference between accuracy and precision in biology experiments?

Accepted Answer

Accuracy refers to how close a measurement is to the true value, while precision refers to how consistent repeated measurements are. For example, if you measure the same mass three times and get 10.1 g, 10.2 g, and 10.1 g, your results are precise but may not be accurate if the balance is not calibrated. To improve accuracy, calibrate equipment and use appropriate techniques; to improve precision, take multiple repeats and control variables tightly.

Question 2

How do I write a good hypothesis for an OCR A-Level Biology experiment?

Accepted Answer

A good hypothesis is a clear, testable statement predicting the relationship between the independent and dependent variables. It should be written as an 'if... then...' statement. For example: 'If the concentration of sucrose solution is increased, then the mass change of potato chips will increase due to osmosis.' Include a brief biological explanation. Avoid vague terms like 'affect' – be specific about the direction of change.

Question 3

What should I include in a risk assessment for a biology practical?

Accepted Answer

A risk assessment should identify hazards (e.g., chemicals, sharp objects, microorganisms), evaluate the risk (likelihood and severity), and describe control measures to reduce risk. For example: 'Hazard: 1 mol dm⁻³ hydrochloric acid is corrosive. Risk: Skin burns. Control: Wear gloves and goggles, use a fume hood if needed, and wash spills immediately.' Also include emergency procedures (e.g., tell teacher, use eyewash).

Question 4

How do I choose the range and interval for my independent variable?

Accepted Answer

The range should be wide enough to show a clear trend or effect, but not so wide that results become unsafe or impractical. For example, if testing enzyme activity at different pHs, use a range from pH 2 to pH 10. The interval should be regular (e.g., every 1 pH unit) and provide enough data points to plot a meaningful graph. Typically, 5-7 intervals are sufficient. Consider pilot studies to refine your range.

Question 5

What is a control experiment and why is it important?

Accepted Answer

A control experiment is a treatment where the independent variable is absent or set to a baseline level. It allows you to compare results and confirm that any effect is due to the independent variable, not other factors. For example, in an osmosis experiment, a control could be a potato chip in distilled water (0 mol dm⁻³ sucrose). Without a control, you cannot be sure that changes are caused by the variable you are testing.

Question 6

How many repeats should I do in a biology experiment?

Accepted Answer

Typically, you should repeat each condition at least three times to ensure reliability. More repeats (e.g., 5-10) can improve precision and allow you to calculate a mean and standard deviation. However, consider practical constraints like time and resources. In OCR exams, you may be asked to justify the number of repeats – mention that repeats help identify anomalous results and increase confidence in the data.

Planning

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How to Revise Planning — OCR A-Level Biology

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Common Mistakes in Planning

Key Marking Points