Final answer:
The coloured liquid moved to the left in the respirometry experiment because the woodlouse performed aerobic respiration, consuming oxygen and producing carbon dioxide, which decreased the gas volume and caused the movement of liquid.
Step-by-step explanation:
The drop of coloured liquid in the student's apparatus moved to the left because of aerobic respiration occurring within the woodlouse.
During this process, the woodlouse consumes oxygen (O₂) and produces carbon dioxide (CO₂). When oxygen is consumed, there is a decrease in the gas volume inside the closed system.
This reduction in gas volume caused the liquid to move towards the side with lower pressure, hence to the left.
As the woodlouse respirates aerobically, the consumption of oxygen is larger than the volume of carbon dioxide produced due to the binding of oxygen into carbon compounds.
To accurately measure the rate of aerobic respiration, one would need to add a substance like sodium hydroxide (NaOH) or potassium hydroxide (KOH) to the setup to absorb the CO₂, ensuring that only the changes in oxygen levels affect the movement of the colored liquid.