Plan an investigation that answers the question

Explanation

Start with a testable relationship, such as how pH affects the initial rate of a catalase-catalysed reaction. The independent variable is what you deliberately change. The dependent variable is the response you measure. Make both operational: state the pH values used and how gas volume over time will give a rate.

Identify variables that could also affect the response. For this enzyme investigation, keep temperature, enzyme amount, substrate concentration and total reaction volume consistent. A buffer controls pH, a water bath controls temperature, and fixed measured volumes make the comparisons reproducible. State how, not simply "keep everything constant".

Use a suitable range and intervals, with repeats at each value. A preliminary trial can identify a workable range, a measurable time interval and any practical difficulty. Repeating independent reaction mixtures estimates variation better than repeatedly reading one unchanged measurement. Keep biological replicates distinct from repeated readings of the same specimen.

A control treatment answers a specific alternative explanation. A mixture without active enzyme can reveal gas production unrelated to the intended enzyme reaction. Keep its other relevant conditions comparable. A controlled variable and a control treatment have different roles.

Plan the analysis before collecting data: calculate a rate for each repeat, summarise the repeats, plot rate against pH and evaluate the pattern. This ensures that the measurements can answer the original question.

Assess the actual hazards and exposure routes. For example, splashes of an irritant hydrogen peroxide solution can harm eyes. Using the school-specified dilute concentration and small volumes, wearing suitable eye protection and transferring carefully reduce exposure. Link each precaution to its hazard and follow the school's material-specific risk assessment. Accurate apparatus handling also needs supervised laboratory practice.