Question

Why does the grass look green, papaya yellow and edible watermelon red?

Answer 1

Hint: Plastid is semi-autonomous organelles which store and synthesise various types of the organic compound, it develops from colourless proplastids. Plastids are both colourful and colourless depending on the absence or presence of pigments.

Complete answer:
The grass looks green due to the presence of chloroplast, which is green chlorophyll-containing plastids. It helps in the synthesis of organic food from inorganic raw material. The yellow colour of papaya is due to xanthophyll pigment which is present in coloured plastids chromoplast, it consists of fat-soluble carotenoids pigment which is responsible for the yellow, orange or red colour in fruits. The red colour of watermelon is also due to the red pigment lycopene of chromoplast, which changes the colour of fruit during ripening. This change takes place due to the transformation of chloroplast or leucoplast into the chloroplast.

Additional Information: The chloroplast is the main form of plastids which varies in number and size from species to species. It occurs in all photosynthetic plants and algae. The chloroplast is the double membrane-bound with the presence of DNA. The ground substance of chloroplast consists of a matrix which is a semifluid colourless colloidal complex. It consists of flat sac-like thylakoid arranged one over another in the form of grana. Stroma lamellae form a link between different grana. Thylakoid consists of photosynthetic pigments like chlorophyll a, chlorophyll b, carotenoids and xanthophylls. These pigments are involved in photosynthesis by the synthesis of ATP.
Leucoplasts are colourless or white moulded plastids which are oval, spherical and cylindrical. They lack photosynthetic pigment and store food in form of carbohydrate, lipids and proteins in cells of fruits, seeds, tubers and rhizomes. Leucoplast is of three types amyloplast which store starch, elaioplast which store fat and aleuroplast which contain protein in amorphous and crystalline form.

Note: Chlorophyll a is the universal photosynthetic pigment which is also known as primary photosynthetic pigment. Chlorophyll b, chlorophyll c, carotenoids, xanthophylls, phycoerythrin, phycocyanin and allophycocyanin are accessory pigments which transfer light energy to chlorophyll a.