Question

Why is plant food not produced in any other part of the plant except the green ones?

Answer 1

The process of synthesis of organic compounds from inorganic raw materials like carbon dioxide and water, using radiation or light energy is called photosynthesis. In this process, oxygen is evolved where water is used as a hydrogen donor. In the process of photosynthesis, light energy is converted into chemical or bond energy. As the process involves conversion of inorganic carbon to organic state, it is also called carbon assimilation.

Complete answer:
Only plants and some other organisms are capable of synthesizing organic compounds, they are called producers. All other organisms are consumers because they are directly or indirectly dependent upon the producers of the foods.
Plants obtain their food by using two different modes of nutrition; either autotrophs or heterotrophs. Autotrophic plants prepare their own food by the process of photosynthesis. Heterotrophic plants are parasitic, referred to as holo-parasitic plants because they are unable to synthesize organic carbon and draw all of its nutrients from the host plants.
The most important step in the process of photosynthesis is the photoconversion or change of light energy into chemical energy. For this, there are requirements of certain molecules that can entrap photons of different wavelengths. These molecules are none other than chlorophylls.
Chloroplasts are the second largest organ of the plant (nucleus is the largest) which are specialized to perform photosynthesis. They were first observed by N. Grew in 1682 but were studied by Dutrochet, Sachs, Meyer, and Schimper. Plant chloroplasts are disc-shaped, circular, or oval in outline. They have a diameter of 4-10 mm and a thickness of 2-4 mm. Thylakoid membranes of chloroplasts have two types of photosynthetic pigments, chlorophylls and carotenoids.
Chlorophylls are of five types- a, b, c, d and e. Chlorophyll a occurs in all oxygenic photosynthetic organisms so, named as universal photosynthetic pigment. It is involved in photoconversion that’s why it is also called primary photosynthetic pigment. Chlorophyll b occurs in all green plants, green algae, and euglenophyceae. Chlorophyll c occurs in diatoms, dinoflagellates, and diatoms. Chlorophyll d occurs in red algae. Chlorophyll e is present in xanthophyceae.
Chlorophylls are usually green in color. Therefore, foods are prepared only in the green parts of the plant because they contain chlorophyll pigments.

Note:
Carotenoids are yellow and orange colored pigments that are lipid-soluble. These pigments occur in chloroplasts as well as chromoplasts. Carotenoids are accessory photosynthetic pigments, absorbed radiation energy by them is handed over to chlorophylls. Two types of carotenoids are carotene and xanthophylls.