Environmental factors such as temperature, availability of
oxygen, water and nutrients and the presence or absence of various chemicals
affect the rate of growth and reproduction of micro-organisms.
Temperature
Different micro-organisms have different optimum (best)
temperatures at which they grow and reproduce most quickly. Eg parasites of
human grow best at 37 degrees as that matched the human body temperature.
Saprotrophs grow best in temperatures around 30 degress but
can grow between 5 and 45 degreess. This is an advantage as they grow on
material that is always changing temperature ( eg night and day). Growth and
reproduction are slower in temperatures above or below the optimum because of
the effect of temperature on processes such as enzyme activity and diffusion.
Oxygen availability
Aerobic micro-organisms require oxygen in their environment.
Some require lots of oxygen, others very little. Eg helicobacter and
campylobacter require very little oxygen so they can survive in the human gut.
Aerobic respiration uses glucose and oxygen. Carbon dioxide water and a lot of
energy is released. Increasing the amount of oxygen increases growth rate of
the bacteria up to a certain point when another factor becomes limiting.
Anaerobic micro-organisms do not require oxygen. Lactic acid
bacteria (used to make yoghurt) are anaerobic. They produce usable energy by
the process of fermentation( a type of anaerobic respiration).
Yeast can respire both aerobically and anaerobically.
Aerobic respiration produces more energy but if the oxygen is used up, yeast
can produce energy anaerobically by fermentation. During fermentation, ethanol
(alcohol) is produced but if fermentation s carried out too long the high
amount of ethanol kills the yeast.
