Yeast cells can respire aerobically or anaerobically - AQA - A-Level Biology - Question 3 - 2018 - Paper 1
Question 3
Yeast cells can respire aerobically or anaerobically. A student used the apparatus shown in Figure 3 to measure the rate of respiration in yeast.
She:
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Worked Solution & Example Answer:Yeast cells can respire aerobically or anaerobically - AQA - A-Level Biology - Question 3 - 2018 - Paper 1
Step 1
Suggest one reason why it was important that the student left the apparatus for one hour after the yeast culture reached a constant temperature.
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Answer
This is important to ensure that the rate of respiration is stabilized, allowing for accurate measurement of gas production.
Step 2
During her investigation, the coloured liquid moved to the right. Explain why it moved to the right.
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Answer
The coloured liquid moved to the right because the yeast cells consumed oxygen for respiration, creating a partial vacuum in the flask. This causes a reduction in pressure, resulting in the liquid being drawn into the capillary.
Step 3
Calculate the volume of gas produced in cm³ hour⁻¹. Show your working.
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Answer
The volume of gas produced can be calculated as follows:
First, convert the diameter of the capillary tubing from mm to cm: 1 mm = 0.1 cm.
Calculate the radius, r = diameter/2 = 0.1 cm / 2 = 0.05 cm.
Using the formula for volume:
V=extπr2extl
where l is the length of the gas produced in cm, which is 1.5 cm in 24 hours.
Apply the values:
V=3.14×(0.05)2×1.5=3.14×0.0025×1.5=0.011775extcm3
To find the volume produced per hour, divide by 24:
rac{0.011775}{24} ext{cm}^3 ext{hour}^{-1} ext{ = 0.00049 cm}^3 ext{hour}^{-1}
Hence, the volume gas produced is approximately 0.00049 cm³ hour⁻¹.
Step 4
Explain why a log scale is used to record the number of cells.
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Answer
A log scale is used because the number of cells can vary widely; it allows for easier visualization and comparison of data over several orders of magnitude.
Step 5
Suggest one reason why many yeast cells die during the death phase.
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One reason could be the depletion of nutrients or accumulation of toxic metabolic by-products, leading to unfavorable conditions for survival.
