Investigate immobilised enzymes in alginate
Compare an enzyme trapped in alginate with the same enzyme free in solution, then evaluate practical advantages.
AS Level · Cambridge International Biology 9700, 2028–2030. These lessons teach enzyme concepts and experimental reasoning. Written practice is self-checked; it does not demonstrate supervised practical competence or replace teacher-reviewed assessment.
Before you begin
- Recognise that proteins have specific three-dimensional shapes and that reaction rates can be compared using controlled measurements.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What does immobilised enzyme mean in an alginate-bead investigation?
What you will learn
- Outline a fair comparison of immobilised and free enzyme activity
- State practical advantages of using immobilised enzymes
Immobilise enzyme in alginate beads
Mix enzyme solution with sodium alginate and add drops to a suitable calcium salt solution to form beads in which enzyme is immobilised. Follow local laboratory instructions for chemicals and disposal; the practical must be supervised.
Compare with the same enzyme free in solution. Use equal enzyme amounts where feasible, equal substrate concentration and volume, and the same temperature, pH and reaction time. Keep bead size and number consistent and mix both systems comparably.
Compare activity and weigh advantages
Measure product formation or substrate disappearance over a defined time using the same assay. Immobilisation can alter the observed rate because substrate must diffuse into a bead and product must diffuse out; do not assume bead and free-enzyme rates will be identical.
Immobilised enzymes can be separated from the product and reused, and can help prevent enzyme contamination of the product. Reuse may reduce costs in a process. These are advantages to evaluate against diffusion limitations, bead handling and possible activity changes.
Pause and explain
Which is an advantage of using an immobilised enzyme?
Worked example
A student compares free amylase with alginate-immobilised amylase but uses different pH values. Identify the problem and propose a fair comparison.
Show the worked solution
- pH is a confounding variable because it affects activity.
- Use equal conditions and enzyme amounts in both systems.
Answer The pH difference confounds the comparison because pH can alter amylase activity. Use the same pH, temperature, substrate concentration and reaction time, and compare equivalent enzyme amounts using the same progress measurement.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Outline how to compare immobilised amylase with free amylase.
Give me a hint
Use the same enzyme, substrate and assay conditions.
Compare my reasoning
- Prepare alginate beads containing enzyme and a free-enzyme comparison.
- Use equal amounts where feasible and control pH, temperature, substrate, volume and time.
Prepare enzyme immobilised in alginate beads and a free-enzyme solution. Compare them with the same substrate concentration and volume, pH, temperature and reaction time, using equivalent enzyme amounts where feasible and the same assay to measure progress.
Look for these in your work
- Both enzyme forms compared
- Key conditions controlled
A process uses immobilised enzyme so that it can be recovered after product formation. State two advantages and one possible limitation.
Give me a hint
Think about reuse, product separation and diffusion.
Compare my reasoning
- The enzyme can be separated from product and reused.
- Substrate or product diffusion through beads may limit rate.
The immobilised enzyme can be separated from the product and reused, which may reduce enzyme contamination and process costs. A limitation is that substrate must diffuse into the beads and product out, potentially reducing the observed rate.
Look for these in your work
- Two related advantages stated
- Diffusion limitation acknowledged
Alginate beads are twice as large in one trial as another. Explain why this could affect the comparison.
Give me a hint
Consider diffusion distance and keep bead geometry consistent.
Compare my reasoning
- Larger beads can increase diffusion distance.
- Substrate access and product movement may change.
Larger beads can increase the diffusion distance for substrate entering and product leaving the immobilised-enzyme matrix. Keep bead size and number consistent, or measure them and include the difference when interpreting results.
Look for these in your work
- Diffusion link explained
- Fair comparison improvement stated
Common mistakes
- Assuming immobilisation always increases reaction rate
- Ignoring substrate and product diffusion through alginate
- Listing reuse without explaining how the enzyme is separated from product
What can you explain now?
What does immobilised enzyme mean in an alginate-bead investigation?
Compare with the explanation
Enzyme is trapped or held within the alginate beads
The enzyme is retained in a support matrix.
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Make it stick
How would you compare immobilised and free enzyme fairly, and what are an advantage and a possible limitation of immobilisation?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.