1. Summary

Cycling of chemicals between biological and geological world is called biogeochemical cycle. Four biogeochemical cycles includes water cycle, nitrogen cycle, carbon cycle and oxygen cycle. Water enters the atmosphere as water vapour by evaporation. Water from plants evaporates as vapour into the atmosphere through transpiration. Water vapour in the atmosphere form clouds, called condensation. Clouds break into rain, snow or fog, called precipitation. Photosynthesis with respect to carbon cycle: Plant use sunlight, carbon dioxide in the atmosphere to form carbohydrates. Respiration with respect to carbon cycle: Plants and animals breakdown carbohydrates for energy and release of carbon dioxide. Decomposition with respect to carbon cycle: Bacteria and fungi decay dead plants and animals releasing carbon dioxide. Combustion with respect to carbon cycle: Burning of fossil feuls release carbon dioxide into the atmosphere. Types of nitrogen fixation include both biological nitrogen fixation and physical nitrogen fixation. Bacteria in the soil decompose the organic matter into ammonia , called ammonification. Bacteria in the soil convert ammonia to nitrate, called nitrification. Denitrifying bacteria convert nitrite and nitrate to nitrogen, called denitrification.

Respiration and Combustion with Respect to
 Oxygen Cycle:
Plants and animals use atmospheric oxygen during respiration and oxygen is used for burning of fossil fuels. Temperature inside a glass house is much higher than the surroundings, such enclosures are called greenhouse. Carbon dioxide trap the heat and thereby increase the temperature on earth, called the greenhouse effect. Ozone absorbs harmful ultraviolet radiations from the Sun. ozone layer is depleting due to an increase in chlorofluorocarbons.

The biotic and abiotic components of the biosphere constantly interact through biogeochemical cycles.

Biogeochemical Cycles

During these interactions, there is a transfer of nutrients between living organisms, or bio, and the non-living environment, or geo.

Water evaporates from the water bodies, and returns as rain and snow, which, in turn, flows back into the seas via rivers. This cyclic movement of water from the land to the ocean to the atmosphere and back to the land is called the water cycle.

Water Cycle

Water from plants evaporates as vapour into the atmosphere through the stoma in the leaves and stems.

Evaporates, Stoma

Water is maintained in the biosphere by rainwater flowing back into the water bodies. Some of it penetrates the earth's surface and is logged as groundwater.

Carbon Cycle – Decomposition: Dead plant and animal remains in the soil are converted into coal, petroleum and natural gas, better known as fossil fuels. These fuels are used for cooking, transportation and industrial processes.

Nitrogen makes up 78 per cent of the earth’s atmosphere. Nitrogen is an essential constituent of proteins, nucleic acids like DNA and RNA, vitamins, and chlorophyll.

Nitrogen, 78%, Proteins, Nucleic Acids, DNA, RNA, Vitamins, Chlorophyll

Legumes have nitrogen-fixing bacteria in their root nodules. These bacteria convert atmospheric nitrogen into ammonia, which is utilised readily by plants.

Legumes, Nitrogen-fixing Bacteria, Root Nodules, Atmospheric Nitrogen, Ammonia

Nitrogen-fixing bacteria along with free living bacteria in the soil achieve 90 per cent of nitrogen fixation.

Nitrogen-fixing Bacteria, Free Living Bacteria

When lightning occurs, the high temperature and pressure makes nitrogen and water combine to form nitrates and nitrites. These compounds dissolve in water and are readily used by plants.

Lightning, Nitrites, Nitrates

The sequence in which nitrogen passes from the atmosphere to the soil and organisms, and then is eventually released back into the atmosphere, is called the nitrogen cycle.

Nitrogen Cycle

Oxygen makes up 21 per cent of the air, and is an essential constituent of carbohydrates, proteins, fats and nucleic acids.

Oxygen, 21%, Carbohydrates, Proteins, Fats, Nucleic Acids

Oxygen is found in air, in combined form as carbon dioxide, and in the earth’s crust as carbonates, sulphates and nitrates.

Oxygen, Carbon dioxide, Carbonates, Sulphates, Nitrates

The sequence in which oxygen from the atmosphere is used by organisms and eventually released back into the atmosphere through photosynthesis is called the oxygen cycle.

Oxygen Cycle

The ozone layer prevents harmful radiations from reaching the earth’s surface, where they might damage life forms.

Ozone Layer

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