Question 6

Some students design an experiment to investigate the effect of sucrose concentration on the rate of anaerobic respiration in yeast. The apparatus collected carbon dioxide gas over water in a measuring cylinder.

Method:

Use a stock solution of $20%20\%$ sucrose to make dilution series solutions, including $4%4\%$ and $12%12\%$ sucrose.
Set up a conical flask containing a fixed concentration and volume of yeast suspenson and add the sucrose solution.
Record the volume of carbon dioxide gas given off every $s30\text{ s}$ for $min2\text{ min}$ .
Repeat the experiment three times for each concentration.

Some of the results are shown in the tables below:

Table 1: Results for $4%4\%$ sucrose

Time (s)	Trial 1 ( $cm3\text{cm}^3$ )	Trial 2 ( $cm3\text{cm}^3$ )	Trial 3 ( $cm3\text{cm}^3$ )	Mean ( $cm3\text{cm}^3$ )	Standard deviation
30	6	6	7	6.3	0.6
60	11	12	11	11.3	0.6
90	16	17	15	16.0	1.0
120	20	21	19	20.0	1.0

Table 2: Results for $20%20\%$ sucrose

Time (s)	Trial 1 ( $cm3\text{cm}^3$ )	Trial 2 ( $cm3\text{cm}^3$ )	Trial 3 ( $cm3\text{cm}^3$ )	Mean ( $cm3\text{cm}^3$ )	Standard deviation
30	38	35	38	37.0	1.7
60	62	59	62	61.0	[ To be calculated ]
90	74	70	72	72.0	2.0
120	81	75	78	78.0	3.0

(i) State the independent variable in this investigation.

(ii) Describe how a student could produce a $12%12\%$ dilute sucrose solution from the $20%20\%$ stock solution.

(i) Calculate the standard deviation for the $s60\text{ s}$ result at $20%20\%$ sucrose. Use the formula: $\sqrt{\frac{\sum(x - \bar{x})^2}{n - 1}}$ Give your answer to 1 decimal place.

(ii) Calculate the initial rate of reaction over the first $s30\text{ s}$ for the result at $4%4\%$ sucrose. Include the appropriate unit.