AS & A Level Biology - 9700 Paper 5 2013 Winter Zone 1

A student used the respirometer shown in Fig. 1.1 to compare the rate of respiration in:

• germinating seeds
• insect larvae
• single celled green algae living in water.

After putting the germinating seeds into the air-filled container and attaching the graduated tube, the respirometer was lowered into a water bath. The seeds respired using oxygen and water moved into the graduated tube. The procedure was repeated for the other two organisms.

(a) (i) Suggest a hypothesis about the respiration of the different organisms that the student could test using this apparatus.
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(ii) Identify the independent and dependent variables in this investigation.
independent variable .....................................................................................................................
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dependent variable .......................................................................................................................
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(iii) Describe a method, using the respirometer in Fig. 1.1, that the student could use to compare the rates of respiration of germinating seeds, insect larvae and a single celled green algae living in water.
Your method should be detailed enough for another person to use.
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(b) The student calculated the rate of respiration as oxygen used per unit mass of the organisms.
Explain how this rate of respiration was calculated.
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(c) The student determined the respiratory quotient (RQ) for each of the organisms. To do this the student needed to measure the rate of carbon dioxide production.
Outline how the student should use the respirometer to find the rate of carbon dioxide production.
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(d) Table 1.1 shows the student’s results.
[Table_1]
(i) Complete Table 1.1 by writing in the RQ values for the insect larvae and the single celled green algae.[1]

(ii) With reference to the RQ values in Table 1.1, what conclusions can be drawn about the type of substrate respired by each of the organisms tested?
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Table 2.1 shows the results of the investigation.

[Table_1]

(a) State the evidence in Table 2.1 that supports hypothesis B.

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(b) (i) State what the standard deviations (s) in Table 2.1 show about the reliability of the estimate of the mean of the measurements of auxin concentration.

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(ii) Suggest one way in which the reliability of the results could be improved.

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(c) Using the information in Fig. 2.1 and Table 2.1 sketch a diagram to show how the shoot would grow after treatment.
Use the space next to Fig. 2.3 for your diagram. [2]

(d) The movement of auxin through the plant was measured using radioactive auxin.

Fig. 2.4 shows the main steps in the procedure.


Two sets of 20 samples of plant tissue were treated as shown in Fig. 2.4. Both sets were kept in air, one set in the light, the other set in complete darkness.
A $t$-test was used to find out if the difference in the rate of movement in light and the rate of movement in complete darkness was significant.

(i) Suggest a null hypothesis for this statistical test.
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(ii) Calculate the number of degrees of freedom that should be used for the $t$-test in this investigation.
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