Which scientist conducted experiments using swan-necked flasks to disprove spontaneous generation?

• A. Louis Pasteur
• B. Edward Jenner
• C. Carolus Linnaeus
• D. Robert Koch

Answer: (A)

The main concept is biogenesis—the idea that life arises from existing life, not from inanimate matter. Louis Pasteur demonstrated this with his swan-neck flask experiments. He boiled nutrient broth to sterilize it, then allowed air to enter the flask through a long, curved neck that trapped dust and microbes. Because the bend kept potential contaminants out while still letting air in, the broth stayed sterile and clear for a long time. This showed that microbes did not spontaneously appear; they came from existing organisms in the environment. When the neck was bent or the flask broke, dust and microbes could reach the broth and growth occurred, confirming that contamination came from outside, not from the broth itself. Jenner, Linnaeus, and Koch contributed in different ways to microbiology and medicine, but they did not perform this swan-necked flask demonstration.