Unit 2.6 - Environmental Control of Metabolism

• What is a microorganism/microbe?

  A microscopic organism, which may exist in a single-celled form or a colony of cells.
• What are examples of microorganisms?

  Archaea, bacteria, some species of eukaryotes.
• What do microorganisms use for metabolism and to produce a range of products from their metabolic pathways?

  Wide variety of substrates.
• Why are microorganisms used by scientists?

  Their adaptability, ease of cultivation and speed of growth.
• What is cell culture?

  The process by which cells are grown under controlled conditions, generally outside their natural environment in a lab.
• What is growth influenced by?

  Growth mediums and environmental factors.
• What do growth media require?

  Raw materials for biosynthesis, energy source.
• What is a growth medium?

  A solid, semi-solid or liquid designed to support the growth of a population of microorganisms.
• What are cells cultured in?

  Petri disk, flask and fermenter.
• What needs to be controlled during the culturing of cells?

  Sterility, temperature, pH and oxygen levels.
• What is sterility?

  Not containing contaminating microorganisms. Sterile conditions in fermenters reduce competition with desired microorganisms for nutrients and reduce the risk of spoilage.
• Why is it important to control temperature?

  For optimum enzyme activity.
• Why is it important to control oxygen levels?

  Needed for aerobic respiration to generate ATP.
• Why is it important to control pH?

  Needed for optimum enzyme activity
• What are the four phases of growth in microorganisms?

  Lag, log, stationary, death.
• What happens during the Lag phase?

  No increase in cell number. Enzymes are induced to metabolise substrates.
• What happens during the log phase?

  Most rapid growth of microorganisms due to plentiful nutrients
• What happens during the stationary phase?

  Nutrients become depleted so toxic metabolites are produced. Secondary metabolites such as antibiotics are produced. In the wild, secondary metabolites confer an ecological advantage by allowing microorganisms which produce them to out-compete the microorganisms.
• What happens during the death phase?

  Toxic accumulation of metabolites or nutrients in the culture kill microorganisms
• What does total cell count mean?

  Counting total number of cells including viable and dead cells.
• What does viable cell count mean?

  Only counting living cells