Describe The Different Stages Of Bacterial Growth

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Module 03 Homework Assignment

Use the information presented in this module along with additional outside research to answer the questions:

1 Describe the different stages of bacterial growth.

Bacteria has four different phases. The first stage is lag phase. In this phase bacteria must adapt to the medium before division starts. In this phase the cells are active and producing molecules necessary for cell division. The next phase is logarithmic phase. In this phase growth increases. Each cell in this phase divides by binary fission into two cells. Each cell continues to go through binary fission as long as conditions are favorable. The cell doubles as time goes on. The next phase is called stationary phase. This phase occurs when essential nutrients are depleted or by-products of metabolism. A depletion of nutrients causes cells to decrease in size. This take the ability to grow away. During this phase number of viable cells remain constant. This stage can last a few hours to several days. The last phase is called death phase. This begins when the growth stops and the number of dead cells is larger than the number of viable cells.

VanMeter, K., & VanMeter, W. (2010). Microbiological Laboratory Techniques. In Microbiology for the healthcare professional (p. 120-121). Maryland Heights, Mo.: Mosby/Elsevier

2 Discuss four methods of measuring bacterial growth.
One way to find the measurement of bacteria is dry weight. This allows a more accurate estimation of cell mass, but more time consuming and only useful when dealing with massive populations of cells. The cells need to be washed and then dried before weighing. A second way to measure growth is in liquid media. Liquid media causes turbidity and can be measured with spectrophotometer. It is measured by optical density. The greater the cell mass the less light will pass through the spectrophotometer. To measure large populations will require dilution. A third way to measure bacteria is by microscopically. You count chambers known as Petroff-Hauser chambers. The chambers consists of a grid of 25 small squares etched with one mm^2 under coverslip. The fourth method is viable counts. You only count viable calls in a culture. This is done by pour plating, spread plating, and most probable number method.

VanMeter, K., & VanMeter, W. (2010). Microbiological Laboratory Techniques. In Microbiology for the healthcare professional (p.121). Maryland Heights, Mo.: Mosby/Elsevier

3 Describe the nutritional requirements for bacterial growth.

Every microbe needs different nutritional requirements. There is phototrophs which require energy from light. Chemotrophs require chemical compounds for energy. Microorganisms called autotrophs can obtain carbon from atmospheric carbon. Heterotrophs are organisms that use carbon from organic compounds. Photoautotrophs use sunlight and atmospheric carbon dioxide as their carbon source. Chemoautotrophs use inorganic chemical compounds as the source of energy and carbon dioxide as the carbon source. Photoheterotrophs use sunlight for energy but cannot convert carbon dioxide into energy; they use organic compounds as the source of carbon. Chemoheterotrophs use organic compounds for both the source