Request a call back

Join NOW to get access to exclusive study material for best results

CBSE Class 12-science Answered

Briefly describe origin of life
Asked by 280187046155117 | 26 Sep, 2018, 10:16: PM
answered-by-expert Expert Answer
  • It is believed that the Earth has originated about 4,600 million years ago. It is formed by the condensation and cooling from a cloud of gases and dust. At first, the Earth was very hot and had various gases and vapour of several elements.
  • With the passage of time, the Earth gradually cooled down and the gases condensed. Thus, a solid crust of the Earth was formed. There were torrential rains for thousands of years, resulting in the formation of large water bodies like oceans.
  • There were large quantities of hydrogen, nitrogen, water vapour, carbon monoxide, methane and ammonia in the primitive atmosphere.
  • Continuous series of chemical reactions took place among the gases to form amino acids. Hence, life originated.

 Theory of Spontaneous Generation

  • This theory was put forward at the end of the seventeenth century. It stated that life originated repeatedly from non-living materials in a spontaneous manner.

 Theory of Biogenesis

  • This theory stated that life can arise from pre-existing life and not from non-living matter by abiogenesis.
  • Louis Pasteur prepared hay infusion (a culture prepared from water collected from a pond or lake) in a swan-necked flask. The infusion was boiled to kill the microbes present in the infusion and to make it sterile. Pasteur reported that when the swan-neck of the flask was broken and the infusion came in contact with air, microbes appeared. Thus, Pasteur proved that life comes only from pre-existing life.

 Oparin – Haldane Theory

  • Abiogenesis is not possible but could have occurred under the conditions prevailing in the reducing atmosphere of the primitive Earth which were favourable for chemical evolution.
  • High temperature, lightning and intense UV radiation provided the energy required for chemical reactions
  • Living beings arose from simple inorganic and organic compounds by polymerisation.

 Miller–Urey Experiment

  • Stanley Miller and Harold Urey tested the Oparin–Haldane theory in 1953.
  • They made an apparatus to circulate methane, ammonia, water vapour and hydrogen. All these gases were put in a flask fitted with electrodes. In another flask, water was
    boiled continuously.
  • Electrical charges to provide energy similar to lightning were passed for more than a week. 
  • They then collected and analysed the contents of the apparatus. Several amino acids and acids which are found in living organisms were present in the flask.
Answered by Sivanand Patnaik | 27 Sep, 2018, 08:45: AM
CBSE 12-science - Biology
Asked by patra1204swagish | 01 Jun, 2019, 11:29: AM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 12-science - Biology
Asked by 280187046155117 | 26 Sep, 2018, 10:16: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 12-science - Biology
Asked by Topperlearning User | 11 Jun, 2014, 02:07: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 12-science - Biology
Asked by Topperlearning User | 11 Jun, 2014, 02:07: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 12-science - Biology
Asked by Topperlearning User | 11 Jun, 2014, 02:15: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 12-science - Biology
Asked by Topperlearning User | 11 Jun, 2014, 02:07: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 12-science - Biology
Asked by Topperlearning User | 11 Jun, 2014, 02:07: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 12-science - Biology
Asked by Topperlearning User | 11 Jun, 2014, 02:07: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 12-science - Biology
Asked by Topperlearning User | 11 Jun, 2014, 02:07: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 12-science - Biology
Asked by Topperlearning User | 11 Jun, 2014, 02:07: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
Get Latest Study Material for Academic year 24-25 Click here
×