Multiple Choice
Louis Pasteur designed swan-necked flasks to:
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2. Disproving Spontaneous Generation
Pasteur's Experiments on Spontaneous Generation
Problem 8
Textbook Question
Show where airborne microbes ended up in Pasteur’s experiment.
Verified step by step guidance1
Step 1: Understand the setup of Pasteur's experiment, which involved a swan-neck flask containing nutrient broth. The flask was boiled to kill any existing microbes, and the unique shape of the neck prevented airborne microbes from reaching the broth directly.
Step 2: Identify the path of airborne microbes in the environment. These microbes are present in dust and air particles that can enter the open end of the swan-neck flask but get trapped in the bends of the neck due to gravity and condensation.
Step 3: On your drawing, mark the airborne microbes as small dots or particles entering the open end of the swan-neck flask's neck but accumulating and settling in the curved part of the neck, not reaching the broth.
Step 4: Indicate that the nutrient broth inside the flask remains sterile because the microbes cannot bypass the curved neck to contaminate it, demonstrating that microbes come from the environment and not spontaneously from the broth.
Step 5: Optionally, show what happens if the neck is broken or tilted so that the broth contacts the trapped microbes, leading to microbial growth, which supports Pasteur's conclusion about contamination sources.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Pasteur's Swan Neck Flask Experiment
This experiment demonstrated that microorganisms in the air are responsible for contamination. Pasteur used flasks with long, curved necks that allowed air in but trapped airborne microbes in the bends, preventing them from reaching the sterile broth inside.
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Pasteur’s Swan-Neck Experiment
Airborne Microbes and Contamination
Airborne microbes are tiny organisms suspended in the air that can settle on surfaces or liquids, causing contamination. In Pasteur’s experiment, these microbes were trapped in the curved neck of the flask, showing that contamination comes from the environment, not spontaneous generation.
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Sterilization and Microbial Growth
Sterilization is the process of eliminating all living microorganisms from a medium. Pasteur sterilized the broth by boiling it, and because the microbes were trapped in the flask’s neck, no microbial growth occurred in the broth, proving that microbes come from external sources.
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07:36Terminology of Microbial Growth Control
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