Louis Pasteur

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  • Louis Pasteur
    • French Scientist : 1822 - 1895
    • Disproved the theory of spontaneous generation
      • The ancient historical opinion was that when wine, juice or milk became contaminatedthe micro-organisms causing the contamin-ation spontan-eously appeared
        • This idea, that microbes, living things or organisms arose spontan-eously from non-living matter was called the spontaneous generation theory
    • Carried out work on fermentation of yeast.
      • He showed that bacteria making wine go sour could be killed in sugar solutions by heating the solutions before yeast was added.
        • It let him to believe that when food went bad it was not caused by bacteria in the food but by bacteria in the air that reached the food.
    • Pasteur's Swan Neck Flask Experiment
      • Pasteur suggested that if the broth was sterilised by boiling before the start of the experiment, killing any microbes present in the broth, then the flasks with the swan necks would remain clear (not become cloudy)
        • showing no change in the broth, because the microbes present in the air would be prevented from entering.
      • Other containers left open to the air (with the necks broken off) would become cloudy as micro-organisms from the air will enter.
      • Pasteur reasoned that if microbes were present in the air then they would remain trapped by the bend in the glass and not enter the container.
      • Pasteur had been working with microbes and thought that they were carried out in the air.
        • He carried out experiments using specifically designed glass containers.
        • These had a bend in a glass tube, called a swan neck.
      • In 1861 Pasteur's research disproved the spontaneous generation theory using his 'swan neck' flask experiment.
        • It was believed that a flask of nutrient both became cloudy because microbes developed in it even if there were no microbes already present.
      • The results were consistent with Pasteur's idea that microbes were present in the air and so the spontaneous generation theory was disproved.
      • Pasteur also suggested that food goes bad due to microbes that are present in the air.
      • Pasteur's work has helped us understand a feature of many well-known diseases in humans - the microbes have to gain entry to the body before they cause harm.
    • METHOD
      • 1. Nutrient broth poured into flasks
        • 2. Neck of flasks heated and made into S shape
          • 3. Broth boiled for a few mites to kill any bacteria present and drive out the air (sterilise bacteria)
            • 4. Broth allowed to cool in one flask
              • 5. Neck of another flask broken off - used as a control
                • Cloudy after a few days as the bacteria entered from air and decayed
                • Another control for this experiment - flask with no swan neck but sealed
              • Bacteria remained clear as the bacteria are trapped in bend or S shape neck
          • Swan nec has an open end to allow oxygen to enter & leave
      • Organisms / micro-organisms / named e.g arise from non-living tissue


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