What happens in cells (and what do cells need)?

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Question 16
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Some students investigate the fermentation of glucose by Lactobacillus bacteria. The bacteria produced enzymes that convert glucose into lactic acid.

The students carried out this method:

  • Pour 30 cm3 of glucose solution into 3 different test tubes.
  • Add 2 cm3 of active bacterial culture to each test tube.
  • Keep each test tube in a water bath at a different temperature: 20∘C20^\circ\text{C}20∘C, 30∘C30^\circ\text{C}30∘C, and 40∘C40^\circ\text{C}40∘C.
  • Measure the pH of the solution at regular intervals over 48 hours.

The table shows their results.

$ \begin{array}{|c|c|c|c|c|c|} \hline \text{Temperature } (^\circ\text{C}) & \text{at the start} & \text{after 12 hours} & \text{after 24 hours} & \text{after 36 hours} & \text{after 48 hours} \\ \hline 20 & 7.0 & 6.8 & 6.6 & 6.3 & 6.0 \\ \hline 30 & 7.0 & 6.6 & 6.2 & 5.7 & 5.2 \\ \hline 40 & 7.0 & 6.4 & 5.8 & 5.1 & 4.4 \\ \hline \end{array} $

a.

Explain why the students measured the pH of the solution.

[2]
b.

Describe how the students should display their results in a graph.

[3]
c.

Explain the effect of increasing the temperature on the rate of lactic acid production in this experiment.

[3]
d.

The students plan a further experiment where they boil the bacterial culture first before adding it to the glucose solution. Predict what effect this would have on the pH of the solution. Explain your answer.

[2]

What happens in cells (and what do cells need)? Questions

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  2. /Biology
  3. /What happens in cells (and what do cells need)?