Origin of Life – Biochemical Theory (Modern Theory) – Biology Class 11

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Origin of LifeReference Notes | Zoology
Origin of Life – Biochemical Theory (Modern Theory)
For: Science Class 11 (Biology)

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.

Origin of earth:
About 4600 million years ago, the earth originated. The earth was a molten fireball having temperature of about 4000 to 8000 ºC. The earth began to cool down and the volume decreased. During the process, the heavier elements settled towards the centre forming the crust of the earth and the lighter elements remained on the outer surface-forming atmosphere. In the atmosphere, there were free atoms like C, H, O, N etc. The free atoms combined forming molecules like O2, N2, and H2.

O+O……..O2 /N+N…….. N2 /H+H……… H2

Origin of Inorganic Molecules:Origin of Life - Biochemical Theory (Modern Theory) Pic 1
Then these molecules started to combine to form inorganic molecules.
H2+O2…………  H2O      |  H2+N2…………  NH3
C+O2………….. CO/CO2  | C+H2………….. CH4

Origin of Simple Organic Molecules:
The inorganic molecules combined to form simple organic molecules.
H2O + CH4…………….   Sugar/Fatty Acid/Glycerol
H2O+NH3+CH4……….    Amino Acid/Nitrogen Base

Origin of Complex Organic Molecules
The organic molecules again combined together to form complex molecules

Sugar + Sugar…………………………………       Starch/Glycogen/Cellulose etc.
Fatty acid + Glycerol…………………………       Fats
Amino Acid +Amino Acid……………………     Protein
Nitrogen Base + Sugar + Phosphoric Acid…… Nucleotides’
Nucleotide + Nucleotide ………………………   Nucleic Acid (DNA/RNA)

On further cooling water vapor condensed into rain and thunderstorm occurred. UV rays and electric discharge enhanced these reactions. The nucleic acid combined with protein and nucleoprotein particle formed. It was self-replicating particle and was first living particle ‘the virus’.

Origin of Primitive Cell:
The complex organic molecules aggregated together forming colloidal mass called coacervate. The nucleic acid controlled the activities of coacervate and the fats formed a layer around it. This structure is called Eobiont. It was first cell like structure. The eobiont absorbed food materials from the surrounding. It was heterotroph, prokaryotic cell, and present day bacteria.

Origin of Heterotrophs and Autotrophs:
Later on, some of the eobiont became able to make food by using chemical energy. So they became chemoautotroph.
CO2+H2S……………….. C6H12O6 + H2O + S

Some other eobionts developed chlorophyll molecules, which trapped solar energy to manufacture food from CO2 and H2O. They became photoautotroph.
CO2+H2S……………….. C6H12O6 + H2O + O2

In this way, photosynthetic organisms were originated on the earth. On other hand the heterotrophs modified and different types of animals evolved. They started to consume autotrophs and used O2 to break down food material to release energy.

Miller and Urey’s Experiment:
To prove Oparin and Haldance biochemical theory of origin of life Miller and Urey in 1952 conducted an experiment. They designed an apparatus containing glass tube, flask, and gas chamber. They kept NH3, CH4, H2, CO in gas chamber and water is boiled in the flask to produce water vapor. The energy was supplied by heating and by electric sparks.

The condenser was used to cool reaction. They run the experiment for a week. Finally, they analyzed the products formed within the tube. They found different organic compounds like fatty acid, amino acid, sugar, glycerol etc in the tube. Then they proved Oparin and Haldance’s theory of origin of life through a series of chemical reaction among the inorganic gases under the influence of temperature, electric discharges, and cooling.

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