(a) DCPIP is an indicator and can be used to determine the rate of respiration of organisms such
as yeast.
(i) State the category of indicators to which DCPIP belongs.
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(ii) Describe the colour change that occurs in DCPIP during experiments to determine the
rate of respiration.
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(b) An investigation was carried out to determine the effect of temperature on the rate of
respiration of yeast.
• A suspension of yeast cells was added to a test‑tube containing glucose solution.
• A further four test‑tubes were set up in the same way.
• One test‑tube was placed in a water‑bath at 10 °C for 5 minutes.
• DCPIP was added to the test‑tube and the time taken for the DCPIP to change colour
was measured.
• The experiment was repeated using the other test‑tubes at 20° C, 30 °C, 40 °C and 50 °C.
The results are shown in Fig. 6.1.