Respiration: Question 5
Syllabus 12.1
A student sets up three identical conical flasks, each containing the same volume of glucose solution and the same mass of dried yeast. The student stands one flask in a water bath at 10°C, one at 25°C and one at 40°C. A delivery tube from each flask leads to an inverted measuring cylinder filled with water, so that gas released from each flask collects at the top of its cylinder. After 20 minutes, the student compares the volume of gas collected in each cylinder.
Which row correctly ranks the volumes of gas collected after 20 minutes, from smallest to largest?
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Worked solution
Step 1: Recall the effect of temperature on respiration in yeast
Respiration in yeast, like other reactions controlled by enzymes, speeds up as temperature rises over a normal working range. A faster rate of respiration means glucose is broken down faster, and gas is produced faster, so more gas collects in a given time.
Step 2: Apply this to the three flasks
- At 10°C, respiration proceeds slowly, so only a small volume of gas is produced in 20 minutes.
- At 25°C, respiration proceeds faster than at 10°C, so a larger volume of gas is produced in the same time.
- At 40°C, respiration proceeds faster still, within this range, so the largest volume of gas is produced in 20 minutes.
Step 3: Rule out the other options
- Option B reverses the correct relationship, treating the coldest flask as producing the most gas.
- Option C places the middle temperature as producing the least gas, with no biological basis for this pattern.
- Option D ignores the effect of temperature entirely; using the same mass of yeast and volume of glucose solution controls those variables, but the rate of respiration itself still depends on temperature.
Final answer
The volumes of gas collected, from smallest to largest, are 10°C < 25°C < 40°C, option A.