The leaves of many plants have stomata that show a regular daily rhythm of opening and closing
over a period of 24 hours.
(a) Explain why it is important for plants to open and close their stomata in a daily rhythm.
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(b) Fig. 2.1 shows the results of an experiment to monitor this rhythm over three days and nights
for the plant Arabidopsis thaliana. The percentage of open stomata is shown. Each day
consisted of 14 hours of light (white bar) and each night consisted of 10 hours of darkness
(black bar).
100
Key
day
open night
stomata 50
/ %