What factors affect the growth of organisms?

Nutrients

All microorganisms need food. The food sources can vary, but the organisms primarily extract carbon and nitrogen from substances such as proteins, fats and carbohydrates. Some microorganisms seek out and absorb such particles. Others may perform chemical reactions with surrounding elements such as carbon dioxide to gain what they need, while still others can produce their own simple sugars through photosynthesis similar to plants. Nitrogen, which is used to synthesize proteins, can be taken from the surrounding atmosphere or from other organic matter.

Temperature

In general, the higher the temperature, the more easily microorganisms can grow up to a certain point. Very high and very low temperatures both obstruct the enzyme processes microorganisms depend on to survive, but individual species of microorganisms have grown to prefer different levels of temperature. Scientists usually divide them into three different groups: psychrophiles, mesophiles and thermophiles. Psychrophiles prefer temperatures from 0 to 5 degrees Celsius; mesophiles like it in the middle, 20-45 degrees Celsius; and thermophiles like it hot, thriving in temperatures around or above 55 degrees.

pH Levels

Microorganisms also prefer a certain pH level in the substance or environment in which they grow--that is, they prefer to have particular acidic qualities in their surroundings. Most microorganisms, including most human pathogens, are neutriphils, organisms that prefer a neutral pH level. Some like high pH levels, but most often, if conditions are too acidic, then the organism's enzymes break down.

Moisture

The free flow of water is vital to microorganisms for their cells to exchange materials and for their metabolic processes. All microorganisms require some level of water, but a few can survive in low-moisture conditions by conserving all the water they find and by staying in a moisture-rich environment. As a general rule, though, the more moisture, the more microorganisms there will be found.

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