4. Explain the following cycles in your
own words with suitable diagrams.
a. Carbon cycle.
b. Nitrogen cycle.
c. Oxygen cycle.
Answers
Answer:
Oxygen cycle
Oxygen is an important component of life. We cannot survive without oxygen. It comprises about 21% of atmospheric air. It is also present in dissolved form in water bodies and helps in the survival of aquatic life. In combined form, it is found both in Earth's crust and in the air. In the air, it occurs as carbon dioxide. In the crust, it is present as oxides of most metals and Silicon and also as carbonate, sulphate, nitrate and other minerals.
Oxygen is also a part of several essential bio-molecules such as carbohydrates, proteins, nucleic acids and fats. There are processes that utilize atmospheric oxygen. At the same time, the balance of oxygen in the atmosphere is also maintained.
∙ Oxygen is utilized during respiration, combustion and formation of oxides of nitrogen.
∙ Oxygen is returned to the atmosphere in only one major way, and that is photosynthesis.
Answer
. Carbon cycle:
i. A major part of the carbon dioxide from the atmosphere enters into the living organisms through photosynthesis.
ii. The green plants make the organic compounds (carbohydrates).
iii. These compounds are passed from green plants to the consumers (herbivores and carnivores).
iv. During respiration, plants and animals release carbon in the form of carbon dioxide back to the atmosphere.
v. The dead bodies of plants and animals as well as the body wastes, which are also rich in carbon compounds, are broken down by decomposers such as bacteria and fungi to release carbon dioxide.
vi. Carbon is also recycled during the burning of fossil fuels such as coal, petroleum products.
. Nitrogen cycle:
i. Approximately 78% of air is nitrogen and it is a part of many molecules essential to life like proteins, nucleic acids (DNA and RNA), ATP, and some vitamins.
ii. Neither plants nor animals can use atmospheric nitrogen. Plants or animals use nitrogen when it is fixed by nitrogen-fixing bacteria present in the root nodules of pulses plants.
iii. These organisms convert fixed nitrogen into ammonia. After that other bacteria convert ammonia into nitrate, in a process called nitrification. It is two steps process. In the first step, Nitrosomonas convert ammonia into nitrite. In the second step, Nitrobacter converts nitrite into nitrate. This nitrate is then consumed by plants.
iv. Thus, nitrate is the usable form of nitrogen. Through the process of denitrification by denitrifying bacteria converts nitrates nitrogen gas which is released into the atmosphere. This complete the cycle.
Explanation:
a. The carbon cycle is an important biogeochemical gaseous cycle. Carbon dioxide is present in the atmosphere is abundant.
Plants use the carbon in the process of photosynthesis. In this process, sunlight and carbon dioxide are used to form a carbon compound called glucose, which is used by other living organisms. In this way, atmospheric carbon comes in every organism. To make the balance, it is necessary to recycle back this carbon in the atmosphere. It is done by several processes.
The process of respiration breaks down glucose molecules to liberate carbon dioxide. Carbon dioxide is also liberated in the atmosphere by the process of decomposition of the dead organic matter. Combustion of fuels, industrialization, forest fires, volcanic eruptions, deforestation is also the sources of carbon dioxide. Again the process continues to complete the cycle.
b.
