Interpreting and evaluating experimental results with graphing

Yeast and different sugars

Units 1 and 3
9 points
About 25 minutes

You can use a calculator on this question, just like on exam day.

A long question with an experiment and a data table that you turn into a graph. On this site you describe the graph you'd draw (type, axes, units, scale, points and error bars), then analyze the data and make and justify a prediction. On the exam: Question 2 of 6 in Section II (90 minutes, 50% of the exam score); about 25 minutes suggested.

The question and its sources

Baker's yeast is a single-celled fungus that can break down sugars by fermentation when O₂ is not available. In yeast, fermentation releases CO₂ gas. Students investigated how well yeast can use different carbohydrates as a source of energy.

Experiment

The students mixed the same amount of yeast with 20 mL of one of five solutions: water with no sugar, or water containing glucose, sucrose, lactose or starch at the same concentration (10 g per liter). Glucose is a monosaccharide. Sucrose (glucose + fructose) and lactose (glucose + galactose) are disaccharides. Starch is a polymer of glucose.

Each mixture was sealed in a tube with no air space, so no O₂ was available, and held at 30°C. The students measured the volume of CO₂ gas released in 30 minutes. There were five tubes for each solution.

Source: Hypothetical study

Table 1. Volume of CO₂ released in 30 minutes

Solution	Mean volume of CO₂ (mL)	±2SE (mL)
No sugar	0.4	0.3
Glucose	9.8	0.8
Sucrose	9.1	0.9
Lactose	0.5	0.3
Starch	0.9	0.4

Source: Hypothetical data

Suggested time: 25 minutes

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Part (a)

1 point

Describe how a disaccharide such as sucrose is broken down into monosaccharides.

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Part (b)

4 points

(i) Describe the graph you would construct to represent the data in Table 1. In your description, name the type of graph, give the label and units for each axis, describe the scale for the y-axis, list the values you would plot, and describe the error bars. (ii) Based on the data, determine whether the yeast given lactose released significantly more CO₂ than the yeast given no sugar.

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Part (c)

2 points

(i) Calculate the mean rate of CO₂ release by the yeast given glucose. Include units. (ii) The yeast produced almost no CO₂ from lactose, even though lactose contains glucose. Explain why.

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Part (d)

2 points

The students set up a new lactose tube and also add lactase, an enzyme that hydrolyzes lactose into glucose and galactose. (i) Predict the volume of CO₂ released in this tube in 30 minutes compared with the lactose tube without lactase. (ii) Justify your prediction.

Your answer to part (d)

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