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 the flask in a water bath so that the yeast culture reached a constant temperature - then left the apparatus for one hour before starting her investigation. **Figure 3** Suggest one reason why it was important that the student left the apparatus for one hour after the yeast culture reached a constant temperature. During her investigation, the coloured liquid moved to the right. Explain why it moved to the right. The student found that the coloured liquid moved 1.5 cm in 24 hours. The diameter of the lumen (hole) of the capillary tubing was 1 mm. Calculate the volume of gas produced in cm³ hour⁻¹. Show your working. **Answer =** ____________ cm³ hour⁻¹ **Figure 4** shows a typical population growth curve for yeast under laboratory conditions. Explain why a log scale is used to record the number of cells. Many yeast cells die during the death phase. Suggest one reason why. The following equation can be used to make predictions of the growth in the population of yeast cells under ideal laboratory conditions. $$X_t = X_0 e^{rt}$$ A population of 2000 yeast cells was left for 10 hours. The value for the growth rate was 0.5. Assuming no yeast cells died, calculate the predicted size of the population after 10 hours. Show your working.

A-Level AQA Biology Populations in Ecosystems: Yeast cells can respire aerobica

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

Suggest one reason why it was important that the student left the apparatus for one hour after the yeast culture reached a constant temperature.

96%

114 rated

Answer

This is crucial to ensure that the yeast culture is fully acclimatized to the constant temperature, which allows for stable and accurate measurement of the respiration rate.

Step 2

Explain why it moved to the right.

99%

104 rated

Answer

The movement of the coloured liquid to the right indicates that carbon dioxide was being produced as a by-product of cellular respiration. As yeast metabolizes the glucose present in the culture, it releases carbon dioxide, which increases the pressure in the apparatus, causing the liquid to move.

Step 3

Calculate the volume of gas produced in cm³ hour⁻¹. Show your working.

96%

101 rated

Answer

To calculate the volume of gas produced, we use the formula for the volume of a cylinder:

$V = ext{Area} imes ext{Length}$

The area of the capillary tubing's cross-section (lumen) is calculated as:

$A = rac{ ext{π} d^2}{4} = rac{3.14 imes (0.1 ext{ cm})^2}{4} = 0.00785 ext{ cm}^2$

Then, since the liquid moved 1.5 cm in 24 hours:

$V = 0.00785 ext{ cm}^2 imes 1.5 ext{ cm} = 0.011775 ext{ cm}^3$

To find the volume produced per hour:

$ext{Volume per hour} = rac{0.011775 ext{ cm}^3}{24 ext{ hours}} imes 60 ext{ minutes} = 0.0294 ext{ cm}^3 ext{ hour}^{-1}$

Step 4

Explain why a log scale is used to record the number of cells.

98%

120 rated

Answer

A log scale is utilized to accommodate the exponential growth patterns observed in population studies. This makes it easier to visualize large ranges of cell numbers and highlight the relative changes in population size over time, particularly during rapid growth phases.

Step 5

Suggest one reason why many yeast cells die during the death phase.

97%

117 rated

Answer

One reason many yeast cells die during the death phase is the depletion of essential nutrients in the medium, which leads to increased competition for limited resources and ultimately results in cell death.

Step 6

Assuming no yeast cells died, calculate the predicted size of the population after 10 hours. Show your working.

97%

121 rated

Answer

Using the equation:

$X_t = X_0 e^{rt}$

where:

$X_0 = 2000$ (initial population)
$r = 0.5$ (growth rate)
$t = 10$ (time in hours)

We calculate:

$X_t = 2000 e^{0.5 imes 10} = 2000 e^{5}$

Substituting $e^{5} ext{ (approximately 148.41)}$ :

$X_t = 2000 imes 148.41 hickapprox 296820$

Thus, the predicted size of the population after 10 hours is approximately 296820 yeast cells.

Yeast cells can respire aerobically or anaerobically - AQA - A-Level Biology - Question 3 - 2018 - Paper 2

Worked Solution & Example Answer:Yeast cells can respire aerobically or anaerobically - AQA - A-Level Biology - Question 3 - 2018 - Paper 2

Suggest one reason why it was important that the student left the apparatus for one hour after the yeast culture reached a constant temperature.

Explain why it moved to the right.

Calculate the volume of gas produced in cm³ hour⁻¹. Show your working.

Explain why a log scale is used to record the number of cells.

Suggest one reason why many yeast cells die during the death phase.

Assuming no yeast cells died, calculate the predicted size of the population after 10 hours. Show your working.

Join the A-Level students using SimpleStudy...

Other A-Level Biology topics to explore