Enzymes: catalysis, specificity and stability | 16-18 years

In this activity, students write an account of how enzymes work using a set of key words. Other students judge the content and quality of the written explanation about enzymes against a given set of criteria for success.

Learning objectives

Students will be able to describe and explain:

• How enzymes catalyse reactions.
• Why enzyme action is specific to particular substrates.
• Why enzymes are affected by heat and pH.

Sequence of activities

Introduction

1. Remind students about the function of the liver (to break down alcohol etc).
2. Place a piece of fresh liver in a boiling tube. Add some 30% hydrogen peroxide solution.
3. Invite students to comment on what they see and draw out the idea of an enzyme catalysed reaction.
4. Share the learning objectives with students and outline how they are to achieve them. Indicate the time limit to complete the task.

Activity: stage 1

Hand out a ’How do enzymes work?’ sheet to each student. Circulate and support with prompts while they:

• Work individually.
• Write a response to the questions, making use of the key words provided.

Activity: stage 2

Ask students to exchange accounts with a partner. Hand out a ‘Success criteria’ sheet to everyone.

Circulate and support with prompts while they:

• Work individually.
• Assess the work of another student using the ‘Success criteria’ sheets.

Activity: stage 3

Organise the students to hand back the written accounts and the ‘Success criteria’ sheets. Allow time for students to:

1. Read through the assessment.
2. Explain and discuss what has been written on the ‘Success criteria’ sheet with their assessor partner.
3. Identify the ideas that they found most difficult or missed out.
4. Add, at the end of the ’Success criteria’ sheet, any changes/additions that would improve the account.

Feedback

1. Take in the written accounts and the ’Success criteria’ sheets.
2. Give further feedback on the individual’s responses.
3. As well as acknowledging achievement, help students to recognise their next steps and how to take them.

Commentary

Although writing the account of enzyme action leads to a summative assessment, in this instance the assessment is carried out by fellow students. Using the same criteria for the subsequent review of their own work enables students to have a sharper picture of their strengths and weaknesses.

Final comments written by the teacher serve to validate the responses and offer support if needed.

Practical notes for the demonstration

Apparatus

• Forceps
• Boiling tube
• Tongs
• Boiling tube rack

Chemicals

• Piece of fresh liver
• 30% hydrogen peroxide in aqueous solution (IRRITANT)

Health, safety and technical notes

• Read our standard health and safety guidance.
• Wear eye protection.