The student uses glucose as the respiratory substrate. The student wants to prepare a $0.02{mol\; dm}^{-3}$ glucose solution for each yeast culture.

The student uses the following method to prepare each $0.02{mol\; dm}^{-3}$ glucose solution:

• Perform two sequential dilutions from a $2.0{mol\; dm}^{-3}$ glucose stock solution.
• For each dilution, use a measuring cylinder to measure the volume of distilled water and a plastic transfer pipette to transfer the glucose solutions.

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

Complete the sentences below to outline a robust experimental procedure:

• To avoid contamination by unwanted microbes, the yeast should be added to glucose solutions made with sterile or ............................... water.
• To maintain anaerobic conditions throughout the experiment, the respiration vessel must be completely ............................... .
• After repeating the measurement with 15 populations of each strain, the student calculates the mean rate of respiration and the ............................... for each strain to determine the precision and spread of the data.