Class 9 Science

Biogeochemical Cycles

The movement and transformation of chemical elements and compounds between living beings, atmosphere and earth's crust is called biogeochemical cycle. Various inorganic materials are taken up by living beings for different biological functions. In due course of time, these materials are cycled back to the environment.

Water Cycle

The water cycle is also known as the hydrologic cycle. It involves the continuous movement of water on, above, and below the surface of the earth. Water changes into different states of matter during water cycle.

Water on earth changes into vapor through evaporation. Water vapor goes up into the atmosphere and changes into clouds after condensation. After that precipitation occurs and water falls on earth in the form of rain and snow.

Nitrogen Cycle

The nitrogen cycle is the biogeochemical cycle that describes the transformations of nitrogen and nitrogen-containing compounds in nature.

Nitrogen Fixation

Living beings cannot utilize the gaseous form of nitrogen. Hence, gaseous nitrogen needs to be changed into a form so that plants can take up and utilize nitrogen. The process of converting gaseous nitrogen into a suitable form for green plants is called nitrogen fixation.

Carbon Cycle

The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth.

Photosynthesis is the major process through which carbon dioxide reaches the living world.

Greenhouse Effect

Some gases trap infrared radiation in atmosphere. This results in a general rise of atmospheric temperature. This is called greenhouse effect. Examples of greenhouse gases are; carbon dioxide, methane and water vapor.

Oxygen Cycle

The oxygen cycle is the biogeochemical cycle that describes the movement of oxygen within and between its three main reservoirs: the atmosphere (air), the biosphere (living things), and the lithosphere (earth’s crust). The main driving factor of the oxygen cycle is photosynthesis, which is responsible for the modern Earth's atmosphere and life.

Energy Cycle

All the above mentioned cycle can be grouped or explained as energy cycle on this earth. The sun is the main source of energy for every activity on earth. This energy facilitates the everlasting cycle of all resources in the biosphere. This system ensures that whatever we take from earth and its atmosphere we return it in some way or other.

Ozone Layer

The ozone layer is a layer in earth’s atmosphere which contains relatively high concentrations of ozone. This layer absorbs 93-99% of the sun’s high frequency ultraviolet light, which is potentially damaging to life on earth. Over 91% of the ozone in Earth's atmosphere is present here. It is mainly located in the lower portion of the stratosphere from approximately 10 km to 50 km above Earth's surface, though the thickness varies seasonally and geographically.

Because of heavy use of CFCs (Chlorofuorocarbons) in refrigerators and pressurized cans by human the ozone layer has broken at some places. This has caused an alarming rise in ultraviolet radiation leading to increased cases of skin cancers.


See Answer

1: (a) Water cycle, 2: (b) Lightning, 3: (d) Chickpea, 4: (d) Ammonia, 5: (c) Protein, 6: (a) Oxygen, 7: (c) Photosynthesis, 8: (b) Photosynthesis, 9: (d) Stratosphere, 10: (a) Chlorofluorocarbons