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Influence of environmental factors on microorganisms

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There are several factors that influence the growth of microorganisms: nutrition, oxygen, pH, temperature, and moisture. Lack of food retards bacterial growth, and growth is favored by a sufficient quantity of the proper kind of food. Moisture is required to carry foods in solution into the cell, to carry wastes in solution away from the cell, and to maintain the moisture content of the cytoplasm. Temperature has a profound influence on the growth rate of microorganisms.

Microorganisms subjected to adverse temperatures are either destroyed or are not able to multiply. The optimum temperature of a microorganism is the temperature that provides for the most rapid growth of that microorganism. The pH of the medium in which microorganisms grow exerts a considerable influence on their rate of growth. All microorganisms have an optimum pH at which they grow best. Most species of bacteria have an optimum pH between 6.0 and 8.5. Molds will grow in a pH range between 2.0 to 8.5. Yeasts have an optimum pH range from 5.5 to 6.5.

Nutrients or foods are substances which are outside the cell and which, upon entering a cell after passing across the cell membrane, can be used by the cell for building material or for obtaining energy. Food requirements of bacteria show great variations from species to species. Some organisms can obtain all their food requirements from inorganic matter while others need many complex organic compounds. Although any one species may be able to use only a small number of materials as sources of food, bacteria as a group are able to utilize all the naturally occurring organic compounds as well as many inorganic substances.

a. Requirements. Bacteria require foods for the same purposes, as do other forms of life, namely, as sources of material for cellular synthesis and for energy in order to perform these synthetic processes. Requirements include carbohydrates (sugar, starches, and celluloses), a source of nitrogen, vitamins, water, and a source of energy.

b. Sources. The majority of bacteria species use naturally occurring organic materials such as carbohydrates, proteins, fats, and so forth, not only as sources of carbon, hydrogen, oxygen, and nitrogen but also for the energy needed to synthesize these materials into protoplasm.


III. Answer the questions:

1. What factors influence the growth of microorganisms?

2. What factor retards bacterial growth of food?

3. What is the function of moisture in microorganisms?

4. What is the influence of temperature on microorganisms?

5. What temperature provides the most rapid growth of microorganism?

6. What are nutrients?

7. From what can some organisms obtain all food requirements?

8. Which requirements are needed?

9. What kinds of sources are needed?

10. Explain the term “inorganic substance”.


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