Biology 2.6

Question 1

What are microorganisms?

Answer 1

• Microorganisms include species from archaea, bacteria and some eukaryotes.
• Microorganisms can be found in a wide range of ecological niches.
• This is due to their adaptability and their ability to utilise a wide range of substrates.

Question 2

What are archaea?

Answer 2

• Archaea have no nucleus or organelles.
• They appear similar to bacteria but have a metabolism closer to a eukaryote.
• Most archaea are extremophiles.

Question 3

Why are microorganisms used?

Answer 3

• They are easily cultivated and have fast growth rates.
• They produce a wide range of products from their metabolic pathways which can be used for human benefit.

Question 4

What are the requirements for growing microorganisms?

Answer 4

• A growth medium
• An energy source (from chemical substrates or light in photosynthetic microbes)
• Complex molecules for biosynthesis (amino acids, vitamins, fatty acids)
• Some microorganisms can make these, others must be provided with them.

Question 5

What is growth media?

Answer 5

• In a lab, microorganisms are grown in a liquid or solid medium to which essential nutrients have been added.
• When culturing microorganisms, their growth media require raw materials for biosynthesis as well as an energy source.

Question 6

What are industrial fermenters?

Answer 6

• Industrial fermenters are controlled automatically by computers.
• Sensors monitor the conditions.
• If any of these vary from the optimum the supply is adjusted.

Question 7

What conditions must be controlled in fermenters?

Answer 7

• Sterility
• Temperature
• Oxygen levels
• pH

Question 8

Why do fermenters have to be sterile?

Answer 8

Sterility reduces competition with desired micro-organisms for nutrients, and reduces the risk of spoilage of the product.

Question 9

What is the doubling rate?

Answer 9

The time taken for a cell to divide in two.

Question 10

What are the phases of growth?

Answer 10

• Lag,
• log (exponential)
• stationary
• death

Question 11

What is the lag phase?

Answer 11

When the microorganisms adjust to the conditions of the culture by inducing enzymes that metabolise the available substrates.

Question 12

What is the log (exponential) phase?

Answer 12

When the population doubles with each round of cell division due to plentiful nutrients.

Question 13

What is the stationary phase?

Answer 13

• Production of new cells is equal to the death rate of old cells.
• The nutrients in the culture media become depleted.
• Secondary metabolism takes place.

Question 14

What is the death phase?

Answer 14

When a lack of substrate and the accumulation of toxic metabolites cause the number of cells dying to be higher than the number being produced.

Question 15

What is secondary metabolism?

Answer 15

• Secondary metabolism results in the production of secondary metabolites (antibiotics).
• These are not used for the growth or production of new cells, but may give the microorganism an ecological advantage.
• Antibiotics, for example, inhibit competing microorganisms.

Question 16

What are viable and total cell counts?

Answer 16

• Viable cell counts involve counting only the living microorganisms.
• Total cell counts involve counting viable and dead cells.
• Only viable cell counts show a death phase where cell numbers are decreasing.