Microbial Growth Requirements Quiz

Physical Requirements

• Microbes are classified into three categories based on temperature ranges: psychrophiles (cold-loving), mesophiles (moderate temperature–loving), and thermophiles (heat-loving)
• Most bacteria grow best at a pH value between 6.5 and 7.5
• In a hypertonic solution, most microbes undergo plasmolysis, except for halophiles that can tolerate high salt concentrations

Chemical Requirements

• All organisms require a carbon source, which can be an organic molecule (chemoheterotrophs) or carbon dioxide (autotrophs)
• Nitrogen is essential for protein and nucleic acid synthesis, and can be obtained from protein decomposition

Oxygen Requirements

• Organisms are classified into five categories based on oxygen requirements: obligate aerobes, facultative anaerobes, obligate anaerobes, aerotolerant anaerobes, and microaerophiles

Bacterial Division

• Bacteria normally reproduce through binary fission, where a single cell divides into two identical cells
• Generation time refers to the time required for a cell to divide or a population to double

Phases of Growth

Lag Phase

• During this phase, there is little or no change in the number of cells, but metabolic activity is high

Log Phase

• Bacteria multiply at the fastest rate possible under the provided conditions

Stationary Phase

• There is an equilibrium between cell division and death

Death Phase

• The number of deaths exceeds the number of new cells formed