Origin of Life: Panspermia vs Spontaneous Generation — NEET Biology
📚 Practice ConceptDid life come from outerspace? Some scientists believe that it came from outside. Early Greek thinkers thought units of life called spores were transferred to different planets including earth. 'Panspermia' is still a favourite idea for some astronomers. For a long time it was also believed that life came out of decaying and rotting matter like straw, mud, etc. This was the theory of spontaneous generation. Louis Pasteur by careful experimentation demonstrated that life comes only from pre-existing life. He showed that in pre-sterilised flasks, life did not come from killed yeast while in another flask open to air, new living organisms arose from 'killed yeast'. Spontaneous generation theory was dismissed once and for all. However, this did not answer how the first life form came on earth.
Which of the following statements regarding the theory of spontaneous generation and its refutation are NOT correct? S1. The theory of spontaneous generation proposed that life arose spontaneously from non-living, decaying, and rotting matter. S2. Louis Pasteur's experiments definitively demonstrated that life could only arise from pre-existing life. S3. Pasteur's setup involved pre-sterilised flasks where life did not appear, even when exposed to 'killed yeast' and open to air. S4. The dismissal of spontaneous generation paved the way for the acceptance of chemical evolution as the origin of the first life form. S5. While Pasteur disproved spontaneous generation for complex organisms, he supported the idea for microbial life forms.
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Correct answer: C — S3 and S5
The core concept for this question is the theory of spontaneous generation and its experimental disproval by Louis Pasteur. S1: The NCERT states, 'For a long time it was also believed that life came out of decaying and rotting matter like straw, mud, etc. This was the theory of spontaneous generation.' This statement is correct. S2: The NCERT mentions, 'Louis Pasteur by careful experimentation demonstrated that life comes only from pre-existing life.' This statement is correct. S3: Pasteur 'showed that in pre-sterilised flasks, life did not come from killed yeast while in another flask open to air, new living organisms arose from ‘killed yeast’.' The statement incorrectly claims life did not appear 'even when exposed to killed yeast and open to air'. In fact, life *did* appear in the flask open to air. This statement is NOT correct. S4: The text states, 'Spontaneous generation theory was dismissed once and for all. However, this did not answer how the first life form came on earth. Oparin of Russia and Haldane of England proposed that the first form of life could have come from pre-existing non-living organic molecules... and that formation of life was preceded by chemical evolution.' This indicates that the dismissal of spontaneous generation led to the exploration of chemical evolution. This statement is correct. S5: Pasteur's experiments were general and demonstrated that 'life comes only from pre-existing life', applying to microbial forms as well. His experiments were crucial for disproving spontaneous generation for *all* observed life forms, including microorganisms. Therefore, supporting it for microbial life forms is incorrect. This statement is NOT correct. Thus, statements S3 and S5 are NOT correct, making option B the correct answer. This question assesses the understanding of the historical theory of spontaneous generation, the experimental design and conclusions of Louis Pasteur, and the impact of his work on theories of life's origin.
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