IB Biology SL C1.2.6 Respiration rate

[Maximum number: 6]

A student carried out an investigation to test cell respiration in yeast (Saccharomyces cerevisiae). Bottles were filled with 5 g of yeast and $80 \mathrm{~cm}^{3}$ of water maintained at $40^{\circ} \mathrm{C}$ . A different mass of sucrose was added to each bottle: 5,15 and 30 g 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 $\mathrm{CO}_{2}$ was calculated. Three trials per treatment were performed.

The diagram shows one trial, and the graph shows the mean of three trials.

Figure for Question IB Biology SL C1.2.6 Variables Affecting Rate Questions question 1 — IB Biology SL

(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 $40^{\circ} \mathrm{C}$ .

[ 1 ]

(d)

Suggest a conclusion of this experiment.

[ 1 ]

a. higher masses of sucrose prevent respiration/fermentation;
b. higher mass (of sucrose), less volume (of $\mathrm{CO}_{2}$ ) produced;
c. negative relationship between sucrose mass and respiration;
OWTTE

(e)

Explain how the method could have been carried out more effectively by the student.

[ 2 ]

Candidate gives modification for 1 mark and 1 mark for reason. The reason must match the modification.
a. include a control of $0 \mathrm{~g} /$ without sucrose;
b. to compare other results;
OR
c. use more masses of sucrose;
d. to get intermediate values;
OR
e. more trials/samples/replicates;
f. to increase reliability / take mean/average / identify outliers/anomalies / enable statistical analysis / example of statistical analysis;
OR
g. use a different method to measure carbon dioxide;
h. to avoid errors in measuring gas volume (with balloons);
g and h. may be with an example such as. collect gas under water using measuring cylinder, use a gas pressure sensor;
syringe. airlock, respirometer or by measuring the pH .

IB Biology SL C1.2.6 Variables Affecting Rate Questions question 1

Question (a)

Question (b)

Question (c)

Question (d)

Question (e)