Exercise 17 Starch as Indirect Evidence of Photosynthesis

Exercise 17Starch as Indirect Evidence of Photosynthesis1A PH Group 3PROCEDUREObtain two variegated leaves of Coleus (mayana): a light leaf from light-exposed plant and dark leaf from another plant exposed to darkness for 3-4 days. To identify the two, cut off the petiole for the dark leaf.

Sketch the variegation pattern of the leaves in column A of question sheet. Then, place both in boiling water for three minutes.

Get the leaves and spread them in a Petri dish containing a small amount of water. Sketch any change in the variegation pattern in column B.

AB4Transfer both leaves in boiling 95% alcohol for five minutes.

Spread in the Petri dish with water, and sketch any change in column C.

6Add four drops of iodine solution to the plate, agitate gently, and observe the color reaction. Sketch in column D.

ABRESULTS

Dark brownDark brownDISCUSSION Anthocyanins are vacuolar pigments soluble in water. They may appear red, blue, or violet. The violet area of the mayana leaf mixed with the water resulting to no change in color of the water.

After placing the two leaves into the beaker of boiling alcohol, the color of the alcohol changed because it extracted the green pigment. Chlorophyll is a green pigment found in the chloroplast of plants and soluble in alcohol. Iodine solution is used as color indicator to determine the presence of starch. If the color of the leaf turns to blue-back, starch is present. The places where green changed to blue-black indicate that starch was present where the chlorophyll was.

Normally, the light leaf will turn to blue/black since it stored starch, whereas, the dark leaf will not change in color. Starch is a carbohydrate consisting of large number of glucose units. Since the dark leaf was not able to undergo photosynthesis (because of the absence of light), it did not produce glucose.