Louis Pasteur by careful experimentation demonstrated that/the

Options

A. Phenomenon of chemical evolution
B. There is pontaneous generation of life
C. Life comes from pre-existing life only
D. Abiogenic origin of life

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about Louis Pasteur's contributions to the understanding of the origin of life, specifically through his experiments.

2. **Identifying Key Concepts**:
- **Spontaneous Generation**: This is the idea that life can arise from non-living matter.
- **Abiogenesis**: Similar to spontaneous generation, it refers to the origin of life from non-living matter.
- **Biogenesis**: This is the principle that life arises from pre-existing life.

3. **Pasteur's Experiment**:
- Louis Pasteur conducted experiments in the 1860s that demonstrated that microorganisms do not spontaneously generate from non-living matter.
- He used a swan-neck flask in his experiments. The flask was filled with nutrient broth and heated to kill any existing microorganisms. The design of the flask allowed air to enter but prevented dust and microbes from contaminating the broth.

4. **Results of the Experiment**:
- The broth in the swan-neck flask remained free of microbial growth as long as the neck was intact, indicating that life (microorganisms) did not arise from the broth itself but from external sources (dust and microbes in the air).
- When the neck was broken, the broth became contaminated, supporting the idea that life arises from pre-existing life.

5. **Conclusion**:
- Pasteur's work disproved the theory of spontaneous generation and abiogenesis, establishing that all life comes from existing life (biogenesis).
- Therefore, the correct answer to the question is that Louis Pasteur demonstrated that life arises from pre-existing life.

**Final Answer**: Louis Pasteur demonstrated that life arises from pre-existing life, disproving the theories of spontaneous generation and abiogenesis.

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