Question

(a) Briefly describe the structure of chloroplast in relation its functions.
(b) State the chief functions of chloroplast.

Answer 1

(a) Chloroplasts are greenish plastids which possess photosynthetic pigments, chlorophylls and carotenoids and take part in the synthesis of food. Majority of the chloroplasts of the green plants are found in the mesophyll cells of the leaves. They vary in size, shape and number. Chloroplasts are double-membrane bound organelle having outer and inner membrane. The inner membrane is relatively less permeable to substances than outer membrane and thus, has more proteins including carrier proteins. The space enclosed by the inner membrane of the chloroplast is called stroma. Stroma contains a large number of organised flattened membranous sacs called thylakoids. The thylakoids of different grana are connected by flat membranous tubules called the stroma lamellae. The membrane of the thylakoids enclose a space called a lumen. The stroma of the chloroplast contains enzymes required for the synthesis of carbohydrates and proteins. It also contains small, double-stranded circular DNA molecules and ribosomes.
(b) Following are the chief functions of chloroplast:

• Chloroplasts are the centres of photosynthesis or formation of organic compounds from inorganic raw materials.
• Chloroplasts are able to trap sun energy and change it into chemical energy. The chemical energy is used by all living organisms to perform their life activities.
• Chloroplasts liberate oxygen which is passed into the atmosphere. This keeps the balance of oxygen constant in the atmosphere, as oxygen is being consumed in respiration and combustion.
• Chloroplasts pick up carbon dioxide and use the same in photosynthesis. This keeps the percentage of this gas balanced in the atmosphere as carbon dioxide is being constantly added up to it through combustion and respiration.
• They store starch either temporarily (in higher plants) or permanently (in several algae).