Biology [2 Mark Question Answer]

Carbon in the form of carbon dioxide enters living organisms and then goes back to the atmosphere through several pathways forming the true carbon cycle. Thus, it helps in maintaining the balance of nature.

Carbon cycle is a series of chemical reactions in which atmospheric carbon dioxide is used by the organisms and returned to the atmosphere. Photosynthetic plants use carbon as carbon dioxide from the air synthesizing organic compounds. By respiration, burning, decay, etc. the carbon is returned to the atmosphere.

Carbon dioxide is removed from the atmosphere by:
(i) Producers - Producers or green plants use carbon dioxide through photosynthesis. A small amount of carbon dioxide is used by chemosynthetic bacteria also.
(ii) Marine Organisms - Some amount of carbon dioxide is directly fixed by a few marine organisms and sea water absorbs carbon dioxide in the form of dissolved carbon dioxide, carbonic acid, carbonate and bicarbonates.

The amount of carbon dioxide in the atmosphere is increasing due to increased human activities like burning of fossil fuels, deforestation, etc. which cause the rise in global temperatures. This global warming result in melting of polar ice caps, floods in coastal areas, disturbance in hydrogenic cycle etc. Thus "Human activities are harmful to the balance of nature".

Difference between chloroplast and chlorophyll:

Chloroplast	Chlorophyll
(i) It is an organelle of the cell.	(i) It is the green pigment in chloroplast.
(ii) It is living.	(ii) It is non-living.

Light intensity is directly proportional to sunlight. Increase in intensity of light increases the rate of photosynthesis. Photosynthesis is maximum in red light followed by blue light and is least in green light.

During the day transpiration and photosynthesis are interlinked as the stomata opens to facilitate the inward diffusion of carbon dioxide for photosynthesis which also leads to loss of water vapours to the outside during transpiration.

Photosynthesis: It is an anabolic process by which plants manufacture
carbohydrates or food material with the help of water and carbon dioxide in the
presence of sunlight and chlorophyll.
It is an important process as:
a. It produces food directly or indirectly for all living organisms on earth.
b. It maintains balance between oxygen and carbon dioxide in the atmosphere.

Photosynthesis and respiration are opposite to each other in the following ways:

Photosynthesis	Respiration
(i) It is an anabolic process.	(i) It is a catabolic process.
(ii) It results in a gain in dry mass.	(ii) It results in a loss in dry mass.

Hill reaction and NADP reduction in chloroplast.

Hill reaction	NADP reduction
Hill reaction is a light reaction which is completed in three steps in the presence of light .	NADP reduction is a part of Hill reaction in which NADP reduces to form NADPH.