class 11th

Ocean thermal energy

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Solar energy stored in the oceans in the form of heat is called ocean thermal energy (OTE).

  • Sun warms the ocean water at the surface and the wave motion mixes the warmed water to the depth of about 100m. This mixed warm layer is separated from the deep cold water layer and the temperature difference b/w these layers ranges from 10 to 300C.  
  • World’s first OTEC plant with a capacity of 100MW is proposed off the coast of Tamil Nadu.
  • Pressurised ammonia is vaporised in an evaporator. Through which sea water (240c to 300c) flows.
  • Resulted becomes expanded through a turbine to generate electricity with the help of a generator.
  • Cold ocean water (at 40c to 80c) is transported to the surface from depth (from 800m to 1000m) and is used to condense ammonia vapour through a condenser.
  • NH3 condensate & pumped back to the evaporator through a pump.   

Since ammonia circulates in closed loop. This OTEC power plant is called closed cycle OTEC system.

The sun warms the water surface of ocean and wave motion mixes the warmed water downwards to the depth of 100m. This mixed warm layer is separated from the deep cold water layer and the temperature difference b/w these layer ranges from 100C to 300C.

The process of harnessing thermal energy of sea called OTEC.


  • It is pollution free and renewable sources of energy.
  • OTEC system does not have daily or seasonal variations in their output as is the case with other solar energy devices.
  • OTEC is the one of the most clean power production technology.


  • OTEC system requires a lot of capital investment.
  • Due to small temperature difference conversion efficiency is low.

Origin of life on earth

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A British scientist J.B.S. Haldane suggested in 1929 that life must have developed from the simple inorganic molecules which were present on the earth soon after it was formed. He said that the conditions on earth at that time (including frequent – Lightning) could have converted simple inorganic molecules into complex organic molecules which were necessary for life. These complex organic molecules must have joined together to form first primitive living organisms. Haldane also suggested from theoretical consideration that life originated in the sea water.

Homologous Organs Provides Evidence for Evolution

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Those organs which have the same basic structure (or same basic design) but Different functions are called homologous organs. The homologous organs of Different animals provide evidence for evolution.

For example:  the forelimbs of a man, a lizard (reptile), a frog (amphibian), a bird and a bat (mammal) seem to be built from the same basic design of bones but they perform different functions.                                  The forelimbs of a Human (man) are used for grasping, the forelimbs of a lizard are used for running.