Question

The source of atmospheric oxygen is
(A) Nitrogen cycle
(B) Green Plants
(C) Water
(D) Carbon Cycle

Answer 1

Hint: The atmospheric oxygen found in the troposphere. It is the most important need of living organisms especially for humans. The oxygen in the earth is maintained by oxygen cycle.

Complete answer: The oxygen cycle is the biogeochemical transition of oxygen between various oxidation states, oxides, and molecules in redox reaction.
The steps of oxygen cycle involve photosynthesis, that is the phenomenon carries out by the plants in day time to prepare their food and produces carbon-dioxide from air and water, the next step is respiration, the oxygen produce during photosynthesis is used by humans, animals and other aerobic organism through breathing and releases carbon dioxide which is then used again by the plants through photosynthesis to produce oxygen. Therefore, we can say that photosynthesis is the source of oxygen which is formed by green plants and blue green algae.

Now lets us find the solution from the given options:
1. Nitrogen cycle produces atmospheric nitrogen. The source of nitrogen cycle is urban waste, geological source, atmospheric precipitation, etc. the nitrogen cycle helps to maintain the fertility of the soil by converting it into ammonia.
2. Next, green plants are the source of oxygen. As green plants undergo photosynthesis for the preparation of their food, we know that photosynthesis is the main source to form atmospheric nitrogen.
3. Water is maintained through the water cycle. In this process the water gets evaporated from the water bodies and transpiration takes place through plants and then it undergoes precipitation and falls as rain.
4. Carbon cycle produces carbon through dead and decomposed organic matter and through burning fuel.

Hence, the correct option is (B). Green Plants.

Note: Other than green plants there is bacteria named cyanobacteria or blue green algae also involved in maintaining the oxygen cycle in the sphere. They are photosynthetic bacteria and they also use water, sunlight, and carbon-dioxide to form oxygen same as plants.