Biogeochemical Cycles Description:

Biogeochemical cycles are cycles which combine both biotic and abiotic components of our planet through the aid of various cycles namely – water cycle, nitrogen cycle, carbon cycle and oxygen cycle. Since these cycles are inter-dependent, instability of these cycles tend to damage the life on our planet earth.


Biogeochemical Cycles

Water Cycle:

The water that falls on land in the form of rain, snow or hailstones, flows back into seas and other water bodies. The water is then evaporated from these water bodies, resulting in the formation of water vapor and clouds. This completes the whole water cycle.


Water is also used up by living organisms – plants and animals for transpiration and respiration process respectively. Some of the water fallen on land seeps into ground and is used up by roots of plants to conduct water through stem, while some water is evaporated by the sun’s heat.

Nitrogen Cycle:

Our air is composed of 79% nitrogen, but it cannot be used directly by the plants. But there are some micro-organisms which have the ability to fix the nitrogen from the atmosphere into the soil. Thus, they are called as biological nitrogen fixers. Once the microbes fix the nitrogen as nitrogenous compounds like nitrates and nitrites, these compounds are used up by the plants during the process of food preparation and storage (nitrification).

The animals obtain nitrogen directly or indirectly from the plants. After a certain period of time, the death of plants and animals result in decomposition of dead and decaying matter by specialized micro-organisms that release ammonia and other nitrogen compounds in to the air and soil (de-nitrification). This completes the nitrogen cycle.


Carbon Cycle:

Carbon is found in the form of diamonds and graphite in the crust of earth and in the form of carbohydrates, nucleic acids and fats in all living creatures. Carbohydrates and fats are energy-rich food and their basic component is carbon, hydrogen and oxygen. Carbon is also found in exoskeleton and endoskeleton in the form of carbonate salts. The percentage of carbon dioxide present in the atmosphere is very small about 0.03%.

The carbon dioxide in the air is taken up by plants during photosynthesis process. The carbon dioxide along with water forms simple and complex carbohydrates. The carbohydrates are prepared by plants and stored in various parts of the plant. All animals depend on plants for food source directly or indirectly. The animals release the carbon in the form of carbon dioxide during respiration and decomposition. Other than this, carbon compounds from plants and animals are also used to prepare fossil fuels like coal, limestone and petroleum and carbonate shells.

Figure 3 Carbon cycle


The Greenhouse Effect:

A greenhouse is a place where plants are grown in a house that is completely surrounded with glass. Greenhouses are seen in countries with extremely colder climate during the winter season. In a greenhouse, the glass traps the sun’s heat, thus resulting in increasing the temperature of the greenhouse compared to its surroundings.

Thus, these keeps the plants warm and ensures the growth and development of plants during winter season. A drawback of greenhouses is that some gases cannot prevent the heat escape from the planet earth. Hence these gases remain in the atmosphere, resulting in increasing the temperature of the atmosphere. This phenomenon is known as global warming.