Unit 2 Key area 6

Question 1

State the three branches of life?

Answer 1

• bacteria
• Archaea
• Eukaryotes

Question 2

State three reasons why microorganisms are used when researching metabolism.

Answer 2

Microorganisms are used because of their
- adaptability
- ease of cultivation
- speed of growth

Question 3

What is used as an energy source for microorganisms?

Answer 3

Energy sources are derived from chemical substrates or light if the microorganisms are photosynthetic

Question 4

State three conditions that must be controlled when culturing microorganisms?

Answer 4

• Sterility
• Temperature
• pH

Question 5

Explain why culture conditions must be kept sterile?

Answer 5

To reduce competition for nutrients with the desired microorganism. Reducing the risk of spoiling the product.

Question 6

Write notes on the phases of growth and changes in culture conditions?

Answer 6

• The lag phase is where enzymes are “induced” to “metabolise substrates”
• The log phase contains the most rapid growth of the microorganism as at this point there are plentiful nutrients.
• The stationary phase then occurs as the nutrients begin to become depleted the numbers of microorganisms here remains roughly the same.
• Secondary metabolites are produced here such as antibiotics which in the wild would reduce competition for nutrients this would confer an “ecological advantage” as it would allow the microorganisms to “outcompete” others.
• The death phase sees a rapid decline in the number of microorganisms as a result of the toxic accumulation of metabolites and the lack of nutrients.

Question 7

What is meant by a “viable cell count”?

Answer 7

viable cell counts involve counting only living organisms

whereas normal cell counts involve counting both viable and dead cells, only a viable cell count will show a death phase where numbers of cells are decreasing.