factors affecting the growth of bacteria Flashcards
List the five factors that affect the growth of bacteria
temperature, oxygen concentration, pH, external solute concentration, pressure
What are limiting factors?
Factors that slow down a process when in short supply are called limiting factors
At what temperature do bacteria grow best? What is an exception to this?
20 to 30 degrees C but some bacteria can tolerate much higher temperatures without their enzymes being denatured
How do low temperatures affect the rate of bacteria growth?
They slow down the rate of bacterial growth
What do aerobic bacteria require?
They require oxygen for respiration
What do anaerobic bacteria require?
They do not require oxygen to respire
Are most bacteria aerobic or anaerobic?
aerobic
What does a low concentration of oxygen cause?
It often slows down bacterial growth, especially in liquids.
Give an example of aerobic bacteria
streptococcus bacteria that cause sore throat are aerobic bacteria
Give an example of anaerobic bacteria
clostridium (causes tetanus or botulism)
What can facultative anaerobes do?
They can respire with or without oxygen
Give an example of facultative anaerobes and where can they be found?
Escherichia coli are found in the intestines
What can obligate anaerobes do?
They can only respire in the absence of oxygen
Give an example of obligate anaerobes and what it causes and where it can be found
Clostridium tetani causes tetanus (or lockjaw) by infecting deep cuts, where there is a poor oxygen supply.
What are bacterial enzymes designed to do?
They are designed to work at specific pH values.
What happens when bacterial enzymes when they are placed in an unsuitable pH?
They become denatured
What do most bacteria grow at?
at or near neutral pH (i.e. pH 7)
What can some bacteria tolerate?
They can tolerate very low (acidic) or very high (alkaline) pH values.
Why is the growth of bacteria affected by the external solute concentration?
This is because bacteria gain or lose water by osmosis
What happens when the external solution has a higher solute concentration than the bacterial cytoplasm?
Water will move out of the bacteria and this dehydrates the bacteria and stops their enzymes from working.
This is the principle behind the methods of food preservation such as salting or sugaring.
What happens when the external solution has a lower solute concentration than the bacterial cytoplasm?
Water will enter the bacteria.
The cell walls of bacteria can normally prevent bacterial cells from bursting in these circumstances.
What type of concentrated solutions do most bacteria live in
Most bacteria live in less concentrated solutions.
What is the growth of most bacteria inhibited by?
inhibited by high pressures.
Why are most bacteria inhibited by high pressures?
This is because the bacterial walls are not strong enough to withstand the high pressure.
