Respiration (Cambridge (CIE) IGCSE Biology)

A student investigated the rate of respiration of yeast at two different temperatures.

Fig. 1

Fig. 2

(i)

Prepare a table and record the student’s results shown in Fig. 2.

[3]

Fig. 3

(ii)

Use the information in step 2 and Fig. 3 to complete Table 1.

Table 1

[1]

(i)

State a conclusion for the results.

[1]

(ii)

Counting the number of gas bubbles produced may not be an accurate method of measurement. 

Explain why and suggest an improvement.

[2]

(iii)

Identify a variable that should have been kept constant during this investigation but was not. Suggest how this variable could have been kept constant. 

[2]

(iv)

Identify the variable that was changed (independent variable) and the variable that was measured (dependent variable) in this investigation. 

[2]

A group of scientists investigated the effect of different concentrations of glucose on the rate of carbon dioxide production in yeast cells. They measured the volume of carbon dioxide produced by the yeast cells in five minutes.

The scientists decided to test their method before beginning the investigation.

They performed three trials using one concentration of glucose.

The results are given in Table 2.

Table 2

(i)

Calculate the average volume of carbon dioxide produced in 5 minutes.

Give your answer in cm³

Calculate the average rate of carbon dioxide production per minute. 

Give your answer in cm³ per minute

[2]

(ii)

The scientists performed the investigation. Their results are shown in Table 3.

Table 3

Plot a graph on the grid, using the data in Table 3, to show the effect of glucose concentration on the rate of carbon dioxide production. Include a line of best fit. 

[4]

(iii)

Describe the effect of glucose concentration on the rate of carbon dioxide production by respiring yeast cells, shown in your graph.

[3]

(iv)

Estimate the concentration of glucose the scientists used to test their method. Use your answer for c)i) and your graph to find this value.

Give your answer using the unit %.  

[1]

(i)

Describe how the student could show that the glucose used in the investigation is a simple (reducing) sugar.

[3]

(ii)

Identify one hazard when testing for simple (reducing) sugars.

Describe one precaution that could be taken to reduce the risk.

[2]

An investigation was conducted to determine the effect of temperature on the rate of respiration in yeast.

The experimental procedure was conducted as follows:

1. A thermostatically controlled water bath was set up at 20°C

2. The investigators added 10 cm³ of a yeast suspension and 20 cm³ of a 10% glucose solution to each of three test-tubes

3. The test-tubes were placed in the water bath and left for 10 minutes

4. After 10 minutes, five drops of methylene blue were added to each test-tube using a dropper pipette and the test-tubes were then shaken for 10 seconds to mix

5. The test-tubes were returned to the water bath

6. A stop watch was started when the drops were added

7. The time taken for the methylene blue to turn colourless in each test tube was recorded

8. Steps 1 to 7 were repeated at temperatures of 30°C, 40°C, 50°C and 60°C

Fig. 1 shows the experimental set up of one test tube.

Fig. 1

The mean time taken for a colour change to occur was calculated at each temperature and this was used to calculate the rate of respiration.

Table 1 shows the results of the investigation.

Table 1

(i)

Calculate the rate of respiration at 60°C.

[1]

(ii)

Identify a potential source of error in step 7 and suggest a possible improvement.

[2]

(i)

State a conclusion for the results.

[2]

(ii)

Identify two variables that should be kept constant and describe how this would be achieved for each.

[4]

(iii)

Using a dropper pipette to add the methylene blue may not be the most accurate method.

Explain why and suggest an improvement.

[2]

(iv)

Identify the dependent variable in this investigation.

[1]

(i)

Use the data in Table 1 to plot a line graph on the grid to show the effect of temperature on the rate of respiration.

[4]

(ii)

Estimate the rate of respiration at 36°C. 

Indicate on your graph to show how the answer was obtained.

[1]

Explain the importance of repeating this experiment at least three times.