- A student carried out an investigation to test cell respiration in yeast (Saccharomyces cerevisiae). Bottles were filled with 5g of yeast and 80 cm³ of water maintained at 40°C. A different mass of sucrose was added to each bottle: 5, 15 and 30g respectively.
Bottles were left for 15 minutes before attaching a standard balloon to the opening of each bottle. After 45 minutes, the circumference of each balloon was measured using a string. The volume of CO₂ was calculated. Three trials per treatment were performed.
The diagram shows one trial, and the graph shows the mean of three trials.
(a) State the independent variable. [1]
(b) Suggest a reason for waiting 15 minutes before attaching the balloons. [1]
(c) Outline a reason for keeping the temperature at 40°C. [1]
(d) Suggest a conclusion of this experiment. [1]
(e) Explain how the method could have been carried out more effectively by the student. [2]