Experiment to prove that sunlight is essential for photosynthesis
(i) A potted plant is taken and kept in dark for about 36 hours to destarch the leaves. Some portion of the leaf is covered with black strips on both the surfaces
(ii) The plant is then placed in sunlight for 6 hours.
(iii)The leaf is plucked, strips are removed and leaf is tested for starch by boiling it in water and alcohol for decolourizing it. The decolourized leaf is treated with iodine.
(iv) The part which was covered by black strips became yellow while the exposed part becames blue.
This shows that only lighted part synthesised food (starch). Hence we can conclude that light is necessary for photosynthesis.


 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.

(i) Nitrogen.
(ii) Nitrogen is obtained by plants to take up it in the form of inorganic nitrates or nitrites. It may be taken up by plants as organic compounds which have been prepared by bacteria from atmosphere.

The three modes of heterotrophic nutrition are:

(i) To break down of the food material outside the body and then absorb it. For example, bread moulds, yeasts and mushroom.
(ii) To take in whole material and break it down inside the body. For example, animals eating grass, fruits, insects, fish etc.
(iii) Parasitic nutrition - To derive nutrition from other plants or animals without killing them. For example, custuta (amar-bel), orchids, leeches, tape-worms etc.