Microorganisms and their environment
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Microorganisms and Their Environment October 11, 2004 What are Microorganisms? A microorganism is any living thing of microscopic size or smaller. Bacteria Yeasts Protists 40,000x Mag. 10,000x Mag. 200x Mag. Also Viruses, some Algae, and some Animals

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What are microorganisms l.jpg
What are Microorganisms?

  • A microorganism is any living thing of microscopic size or smaller.

    Bacteria Yeasts Protists

40,000x Mag. 10,000x Mag. 200x Mag.

Also Viruses, some Algae, and some Animals

The importance of microorganisms l.jpg
The Importanceof Microorganisms

  • Microorganisms have positive and negative effects on humanity.

    • Many foods, beverages, and medicines are made with the help of bacteria and yeast.

    • The spoilage of food and many diseases are caused by microorganisms.

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The Benefits of Microorganisms

Beer made with yeast.

Bread made with yeast.

Champagne made with yeast.

Cheese made with bacteria.

Pickles made with bacteria.

Sauerkraut made with bacteria.

Soy Sauce made with bacteria.

Yogurt made with bacteria.

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The Drawbacksof Microorganisms

  • Some bacteria cause infections and diseases like tuberculosis and bubonic plague.

  • Some protists cause diseases like malaria and sleeping sickness.

  • Some viruses cause diseases like the flu, measles, chicken pox, polio, and HIV.

  • Some yeasts also cause infections.

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An Experimental Question

  • What conditions are suitable for growing microorganisms for our benefit?


  • What conditions are necessary to prevent the growth of microorganisms?

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Our Experimental Organism

  • Baker’s Yeast (S. cerevisiae) is found naturally growing on grapes and other fruits.

  • It has been used for thousands of years for baking and brewing.

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Characteristics of Baker’s Yeast

  • Readily available in the grocery store.

  • Can grow in temperatures ranging from 8 to 40 degrees C. (46 to 104 degrees F.)

  • Can survive pH levels between 2.4 and 7.4

  • Reproduces quickly, optimally doubling every hour.

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Metabolism of Baker’s Yeast

  • In the absence of oxygen, yeast will undergo anaerobic respiration.

    C6H12O6 2 C2H6O + 2 CO2

    Glucose Ethanol Carbon


  • Yeast can also use sucrose (cane sugar) and fructose (fruit sugar) as a sugar source.

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pH (Acidity)

Main Sugar


per 10 ml





Grape Juice



1.667 g

Lipton Tea



0.875 g



Fructose / Sucrose

1.125 g



Fructose / Sucrose

0.583 g

Characteristics of Various “Liquids”

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Independent (Input) Variables

  • What conditions should we test in our experiment?

  • We will grow our yeast in liquid to easily deliver the sugar source.

  • But what liquids should we pick?

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Dependent (Output) Variables

  • Remember that we want to determine what conditions are most suited to growing yeast cells.

  • How can we use the reactants and / or the products of yeast metabolism to answer our experimental question?

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Yeast Incubation Tube

Grape Juice Time = 0 hours

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Sealed YeastIncubation Tube

Apple Juice Time = 24 hours

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A Pair of Sealed YeastIncubation Tubes

Apple Juice Milk Time = 24 hours

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The CompleteExperimental Set-Up

CO2 Collection Tubes Incubation Tubes

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CO2 Collection Tubes

Time = 0 hours 0 ml CO2 Collected

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CO2 Collection Tubes

Time = 24 hours 1 ml CO2 Collected

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CO2 Collection Tubes

Time = 48 hours 5 ml CO2 Collected