Origin And Evolution of Life – Download Notes of Biology Class 11

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Evolution of manZoology | Biology
Origin And Evolution of Life
For: Science Class 11

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There are different theories about the origin of life on the earth.
Theory of special creation : According to this theory, the life was created by super natural power of the god. This theory is based on religious faith. According to Hindu Mythology, the god of creation is Brahma. He created universe and human beings. According to Christian thought the god created universe, earth, plants, animals, and man within seven days.

Theory of spontaneous generation
According to this theory, the life originates spontaneously from the non-living things. For example the frog, toad, snake originated from mud. The insects and flies originated from the fruit juices and the microorganisms originated from air and water.

Theory of Biogenesis
According to this theory, the life originated from preexisting life but not spontaneously. Francis Redi and Louis Pasteur prove this

Reddi’s Experiment (1688 AD)
He was an Italian biologist. He kept dead fish, snake, and meat in wide mouthed flasks and left them opened. He again placed same things in other flasks and sealed the mouth. He observed little white worms and larvae in opened flasks but absent in sealed flasks. He concluded that the life can arise from pre-existing life only, means some preexisting life went in open-mouthed flasks then worms and larvae were developed in open mouthed flask.

Louis Pasteur’s Experiment (1862 AD)

  • He was French microbiologist. He conducted an experiment to prove theory of biogenesis.
  • He poured nutrient solution into the flask.
  • He bent the neck of the flask in the shape of S using heat.
  • The liquid was boiled for several minutes so that the bacteria were either killed or driven out of flask.
  • The solution was then cooled. The dust particles remained trapped at the bend of the tube. The solution remained sterile for months.
  • When the neck was broken and flask was tilted, liquid came in contact with dust or microorganisms. Bacterial colonies or moulds appeared in the flask within a few days.

Biochemical Theory (Modern Theory)
The scientific theory proposed by A.I. Oparin in 1923 and J.B.S. Hal Dane in 1928 is called biochemical theory or modern theory or Oparine and Haldane’s Theory. According to this theory, the life originated through a series of bio chemical reactions.

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One Comment

  1. Ichhya
    Posted May 23, 2016 at 9:12 pm

    Thank you so much it was really helpful. Tomorrow’s my exam and It just really helped. I didn’t have this unit’s note. Thanks once a again

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