The respiration required practical GCSE commonly appears in AQA, Edexcel and OCR Biology through questions on respirometers, control variables and evaluation. Many students understand that respiration releases energy, but lose marks when explaining how oxygen uptake is measured or how to structure a 6-mark practical answer. This guide focuses on what examiners actually credit.

Respirometer Setup: What You Must Describe

In this required practical, students measure the rate of respiration in organisms such as woodlice or germinating seeds.

A clear method should include:

• Place the organism in a sealed respirometer chamber.

• Add soda lime (or potassium hydroxide) to absorb carbon dioxide.

• Connect to a capillary tube containing a coloured liquid.

• Place the apparatus in a water bath to maintain constant temperature.

• Measure the distance moved by the liquid over a fixed time.

The key scientific explanation: as oxygen is used in respiration, carbon dioxide is absorbed by soda lime, reducing gas volume and causing the liquid to move.

Examiners expect you to link movement of liquid to oxygen uptake. Without this explanation, answers are incomplete.

For structured practical revision, visit GCSE Biology Revision Hub.

Control Variables (Where Marks Are Often Missed)

Across AQA, Edexcel and OCR mark schemes, control variables are essential.

You should state and explain:

• Temperature (kept constant using a water bath)

• Mass or number of organisms

• Volume of air in apparatus

• Time measured

Simply listing variables is not enough. You must explain why they are controlled. For example, temperature affects enzyme activity and therefore respiration rate.

GCSE-Style 6 Mark Question

Question (6 marks)
Describe how a student could investigate the rate of respiration using a respirometer and explain how they would ensure valid results.

How to Structure a 6-Mark Practical Answer

High-level answers usually follow this structure:

1. Clear description of setup

2. Identification of variables

3. Explanation of gas absorption by soda lime

4. Method of measuring oxygen uptake

5. Control of temperature

6. Evaluation (repeat trials, calculate a mean)

Students often forget evaluation. Mentioning repeat measurements and calculating a mean strengthens reliability.

Practise similar extended-response questions at GCSE Science Exam Questions.

Common Examiner Feedback

Frequent mistakes include:

• Saying “carbon dioxide decreases” without explaining absorption

• Forgetting to mention a water bath

• Not stating that liquid movement indicates oxygen consumption

• Missing evaluation entirely

Precise scientific vocabulary is rewarded.

Exam Technique Tip

When answering the respiration required practical GCSE question, always include one sentence explaining why soda lime is used. That single explanation often separates middle-band from top-band responses.

For guided support with practical 6-mark questions, explore GCSE Science Tuition.