The student wants to prepare a $0.05{mmol\; dm}^{-3}$ copper sulfate inhibitor solution for each assay.

The student uses the following method to prepare each $0.05{mmol\; dm}^{-3}$ solution:

• Perform two sequential dilutions from a $5.0{mmol\; dm}^{-3}$ copper sulfate stock solution.
• For each dilution, use a measuring cylinder to measure the volume of distilled water and a plastic transfer pipette to transfer the copper sulfate solutions.

Suggest two ways in which the student can reduce the percentage error in their measurements when preparing these copper sulfate solutions.

Complete the sentences below to outline a robust experimental procedure:

• To ensure that enzyme activity is only affected by the added inhibitor and not by heavy metals or other contaminants, the solutions must be prepared using deionised or ............................... water.
• To prevent fluctuations in pH from affecting the tertiary structure of the amylase, the reaction mixture must be maintained using a suitable ............................... solution.
• After replicating the assay 12 times for each fungal strain, the student calculates the mean rate of reaction and the ............................... for each strain to analyse the spread of the data.