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Yeast cells can respire aerobically or anaerobically - AQA - A-Level Biology - Question 3 - 2018 - Paper 2
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: - positioned... show full transcript
Worked Solution & Example Answer:Yeast cells can respire aerobically or anaerobically - AQA - A-Level Biology - Question 3 - 2018 - Paper 2
Step 1
03.1 Suggest one reason why it was important that the student left the apparatus for one hour after the yeast culture reached a constant temperature.
Answer
It was important for the student to leave the apparatus for one hour to ensure that the yeast had acclimatized to the constant temperature. This period allows the yeast cells to reach a steady metabolic rate, ensuring that the measurement of respiratory rate reflects optimal conditions.
Step 2
03.2 Explain why it moved to the right.
Answer
The coloured liquid moved to the right due to the production of gases, specifically carbon dioxide, as a result of aerobic respiration in the yeast. This gas production causes an increase in pressure within the closed system, pushing the liquid through the capillary tubing.
Step 3
03.3 Calculate the volume of gas produced in cm³ hour⁻¹. Show your working.
Answer
To calculate the volume of gas produced, we first convert the distance moved by the liquid into volume. The volume of the capillary tubing can be calculated using the formula for the area of a circle:
ext{Area} = rac{ ext{π} imes d^2}{4}
Where . So,
ext{Area} = rac{3.14 imes (0.1)^2}{4} = 0.00785 ext{ cm}^2
The volume is then:
To find the volume per hour:
ext{Volume per hour} = rac{0.011775 ext{ cm}^3}{24 ext{ hours}} imes 60 ext{ minutes} = 0.0296 ext{ cm}^3 ext{ hour}^{-1}
Thus, the volume of gas produced is approximately 0.0296 cm³ hour⁻¹.
Step 4
03.4 Explain why a log scale is used to record the number of cells.
Answer
A log scale is used to record the number of cells because it allows for a more manageable representation of exponential growth. This scale compresses large ranges of data, making it easier to visualize and analyze rapid increases in population size. It also helps to illustrate trends more clearly when dealing with large numbers.
Step 5
03.5 Suggest one reason why many yeast cells die during the death phase.
Answer
Many yeast cells die during the death phase due to the depletion of essential nutrients and the accumulation of toxic byproducts, such as ethanol and carbon dioxide, which can become harmful at high concentrations.
Step 6
03.6 Assuming no yeast cells died, calculate the predicted size of the population after 10 hours. Show your working.
Answer
To find the predicted population after 10 hours, we apply the growth equation:
Where:
- (initial population)
- (growth rate)
- hours
Calculating:
\approx 2000 imes 148.41 \ \approx 296820$$ Thus, the predicted size of the population after 10 hours is approximately 296820 yeast cells.