Science world

Heredity and Evolution (part – 1)

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HEREDITY – Transmission of characters from parents to the offspring i.e. from one generation to next generation.

VARIATION – Differences shown by the individuals of a species, and also by the offspring of the same parents are referred to as variations.

GENETICS – Genetics is the branch of biology in which we study about heredity & variation.

DOMINANT TRAIT – A genetic trait is considered dominant if it is expressed in a person who has only one copy of that gene.

RECESSIVE TRAIT – A genetic trait that is expressed only when two copies of the gene are present.

SOMATIC CELL – All cells forming the body of an organism, except the reproductive cells.

GENE – A segment of DNA that is involved in producing a polypeptide chain and forms the basic unit of heredity.

TRAIT –A trait is a distinct variant of a phenotypic character of an organism that may be inherited or environmentally determined.

HAPLOID CELL – Cell having only one set of chromosomes.

DIPLOID CELL – Cell having two sets of chromosomes, one of paternal origin, the other maternal.

GENETIC DRIFT — It refers to the random change in gene frequencies in a small population, presumably owing to chance rather than natural selection, thereby providing diversity without any adaptations.

INHERETED TRAIT – those traits which are controlled by genetic material of the individual and are obtained from the parents in inheritance.

ACQUIRED TRAIT – those trait which acquired by organism during their life period.

ALLELS – is an alternative form of a gene (one member of a pair) that is located at a specific position on a specific chromosome.

The transmission of characters (or traits) from the parents to their offspring is called heredity.

What is Consumers

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They are heterotrophic organisms which consume the food produced by the producers. They derive their nutrition by feeding on other living organisms. A consumer which derives nutrition by eating plants is called primary consumer or herbivore. The secondary consumer or carnivore is an animal that gets its nutrition by eating the flesh of herbivores or other animals’. The organisms which can feed on both plants and animals is called an omnivore.

Herbivores: these are called primary consumers or first order consumers which obtain their food directly from plants.

  • Terrestrial herbivores- Deer, rabbit, mouse, goat cattle etc
  • Aquatic herbivores- Crustaceans, protozoan.

Carnivores: Carnivores feed upon other animals. They have been classified as

  • Secondary Consumers: They prey upon primary consumers or herbivores.  E.g. frog, birds, fishes, jackal, fox, snakes.
  • Tertiary consumers:  Carnivores e.g. owl, peacock, lion, tiger etc. Carnivores like lion, tiger etc. which cannot be preyed upon further are called top carnivores and their number is generally low compared to the lower biotic levels of an ecosystem.

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.

Are you know the work of Nuclear power plant

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India’s uranium supply comes from jadugada mines of Bihar. Heavy water is prepared in heavy water plant at Nangal, kota, Vadodra and Talchar.  

  • Boron rod called the control rod because they absorbed the excess neutrons and prevents the fission reaction from out of control.
  • Graphite or heavy water is called a moderator. It slows down the speed of neutrons.

Nuclear chain reaction

In this particle that initiate the reaction is also produced during the reaction and it carries the reaction further and further. Such as fission of uranium-235.

This is called uncontrolled nuclear reaction. It is the basis of Atomic Bomb. Energy released in nuclear fusion is more than that released in nuclear fission and it does not pollution problem.

Nuclear energy

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The energy obtained from the nucleus of an atom is called nuclear energy. The source of energy is same in both types of nuclear reaction is same. Certain mass is disappearing in this type of reaction mainly in the form of energy.

The difference in the mass of reactant and product is called mass defect, which appear in the form of nuclear energy according to Einstein by equation: E = mc2 . This equation was derived by Albert Einstein in 1905.

  1. Nuclear fusion

It is the phenomenon of combining of two or more lighter nuclei to form a more stable heavy nucleus with the liberation of vast amounts of energy.

Such nuclear reactions are the source of energy in the sun other than stars. These reactions are called Thermo nuclear reaction.

  • It is used in formation of Hydrogen Bomb. There is extremely high temperature near about 107degree. It is quite more powerful than hydrogen bomb.
  • Two deuterons can join to form triton and a proton with release of 4.03Mev energy. The nuclear reaction is

 2H1 + 2H1                                              3H1 + 1H1 + 4.03Mev

  • Two deuteron can join together to form a helium nucleus and a neutron and it is represented as:

2H1 + 2H1                                               3He2 + 1n0 + 3.27Mev

  • Nuclear fission

The phenomenon of splitting of an unstable nucleus of a heavy atom into two lighter nuclei with the liberation of an enormous amount of energy. This occurs when it bombarded with neutron.

  • This phenomenon was discovered by Otto Hahn and Fritz Strassman in the year 1939.
  • 235U92 + 1n0                                      139Ba56 + 94kr36 + 31n0 + E
  • Energy produced by burning of one kilogram of uranium is equal to the energy produced by burning of 2500 tons of coal.
  • Nuclear power plant in India, Tarapur in Maharashtra, Kalpakkam in Tamil Nadu, etc. Nuclear Bomb or Atomic Bomb based on the phenomenon of nuclear fission.

1Mev = 1.602 × 10-13J

1U = 1.492 × 10-10J


  • It produce large amount of energy from small amount of nuclear fuel.
  • Once the nuclear fuel loaded into the reactor, nuclear power plant can on producing electricity for two to three years.


  • Leakage of nuclear radiation from reactor.
  • Disposal of nuclear wastes.

Natural gas, class 10th

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Natural gas is formed under the earth by decomposition of vegetable matter lying under water. It is an important fossil fuel and is usually found underground near an oil source. It is lighter than air and mixture of methane (95%), ethane propane & butane.

  • It occurs deep under the earth crust just above the petroleum deposit. It is environment friendly fuel. CNG is a good alternative in comparison of petrol and diesel. Largest reservoir for natural gas is Soviet Union.

Use of natural gas

  • It is used as industrial fuel.
  • It is used as fuel in thermal power plants to generate electricity.
  • It has been a source of hydrogen in the manufacture

Pollution caused by the fossils fuel

  • It produces the acidic gases such as sulphur-di-oxide and nitrogen oxide.
  • It produces large amount of carbon-di-oxide which goes into the air.
  • The burning of coal leaves lots of ash.

Non-conventional sources of energy

  1. Wind energy

The energy possessed by wind due to its high speed is called wind energy. Traditional use of wind energy has now been modified by improvement in technology to generate electricity through wind power generator.

USES: It is used to pump water & To generate electricity.

Merits of wind energy

  • Its use does not cause any pollution.
  • It is renewable and sustainable source of energy.