A potted plant was kept in the dark for 48 hours. Two leaves X and Y were treated as shown in the diagram below.

The experimental set-up was kept in sun light for six
hours after which a starch test was carried out on the two leaves.
(a) What were the results of the starch test on leaves X and Y?
(b) Give reasons for your answers in (a) above.

Answer:

a)X-iodine solution turned blue black hence presence of starch.
Y-iodine solution retains its yellow brown colour hence absence of starch.

b)
X-Acts as a control, where all requirements are present.
Y-Carbon (IV) oxide (#CO_2#) is absent. It is absorbed by potassium
hydroxide pellets, hence the rate of photosynthesis could not take place.

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