Question 1

How do I calculate the rate of reaction from a graph?

Accepted Answer

To calculate the rate of reaction, draw a tangent to the curve at a specific time point (usually the start for initial rate). The gradient of the tangent (change in y divided by change in x) gives the rate. For example, if the tangent shows a change in product concentration of 0.4 mol dm⁻³ over 20 seconds, the rate is 0.02 mol dm⁻³ s⁻¹. Ensure you include units and use a large triangle for accuracy.

Question 2

What's the difference between a control and a standard?

Accepted Answer

A control is a sample that is treated identically to the experimental group except for the variable being tested. For example, in an enzyme experiment, a control might have boiled enzyme (denatured) to show no reaction. A standard is a known concentration used to create a calibration curve, like using glucose solutions of known concentration to determine an unknown concentration via colorimetry. Controls validate the experiment; standards allow quantification.

Question 3

How do I choose the right statistical test for my data?

Accepted Answer

First, determine if your data is categorical (e.g., colour) or continuous (e.g., height). For comparing two sets of continuous data (e.g., growth in light vs. dark), use a Student's t-test if data is normally distributed. For categorical data (e.g., observed vs. expected ratios in genetics), use a chi-squared test. For correlation between two continuous variables (e.g., temperature and enzyme activity), use Spearman's rank. Always check assumptions: t-test requires equal variances (use F-test) and normality (use Shapiro-Wilk).

Question 4

Why do I need to repeat my experiment multiple times?

Accepted Answer

Repeating experiments (at least three times) allows you to calculate a mean and measure variation (e.g., standard deviation). This reduces the impact of random errors (like slight timing differences) and increases reliability. If results are consistent across repeats, you can be more confident in your conclusions. In exams, you'll be expected to explain that repeats improve precision and allow identification of anomalous results.

Question 5

How do I write a risk assessment for a biology practical?

Accepted Answer

A risk assessment should identify hazards (e.g., corrosive acid, sharp scalpel), evaluate the risk (e.g., low, medium, high), and state control measures (e.g., wear gloves, use a cutting mat). For example: 'Hazard: 1M hydrochloric acid. Risk: Skin burns (medium). Control: Wear goggles and gloves; use a pipette filler; wash spills immediately.' Also include emergency procedures (e.g., inform teacher, use eyewash). In exams, you may be asked to suggest safety precautions for a given procedure.

Question 6

What is the practical endorsement and how do I pass it?

Accepted Answer

The practical endorsement is a separate pass/fail assessment (not graded A*-E) that demonstrates your competence in 12 core practicals. You must complete all practicals, keep a lab book with detailed records (aim, method, results, conclusion, evaluation), and show proficiency in key skills like using a microscope, measuring accurately, and following procedures safely. Your teacher will assess you against five criteria: following procedures, applying investigative approaches, safely using equipment, making and recording observations, and researching and referencing. To pass, attend all practicals, ask questions, and write up your work promptly.

Practical skills

Topic Overview

Key Concepts

What You Need to Demonstrate

Marking Points

Examiner Tips

Common Mistakes

Frequently Asked Questions

Before You Start

Likely Command Words

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How to Revise Practical skills — OCR A-Level Biology

Examiner Tips for Practical skills

Common Mistakes in Practical skills

Key Marking Points