Experiment to prove that sunlight is essential for photosynthesis
(i) Take a potted plant and keep it in dark for about 36 hours to destarch the leaves. Cover some portion of a leaf with black strips on both the surfaces
(ii) Now place the plant in sunlight for 6 hours.
(iii) Pluck the leaf, remove the strips and test the leaf for starch by boiling it in water and alcohol for decolourizing it. Treat the decolourized leaf with iodine.
(iv) The part which was covered by black strips will become yellow while the exposed part becomes blue.
This shows that only lighted part synthesised food (starch). Hence we can conclude that light is necessary for photosynthesis.
Fig. 6.6. To show that light is necessary for photosynthesis. (A) destarched leaf covered with light screen. (B) covered portion does not turn blue black while tested with iodine.
