2.6 Environmental Control of Metabolism

Question 1

What types of micro-organisms are there?

Answer 1

Bacteria, Archaea and (some species of) Eukaryotes

Biology BAE

Question 2

What do micro-organisms do?

Answer 2

Use a wide variety of substrates for metabolism and produce a range of products from their metabolic pathways

Question 3

Why are micro-organisms used? Give 3 reasons

Answer 3

1. adaptability
2. ease of cultivation
3. speed of growth

Question 4

When culturing micro-organisms, what does their growth media require?

Answer 4

raw materials for biosynthesis as well as an energy source

Question 5

What do micro-organisms produce?

Answer 5

All the complex molecules required for biosynthesis
E.G amino acids, vitamins and fatty acids

However, other micro-organisms require these to be supplied in the growth media

Question 6

How is an energy source derived in the growth media?

Answer 6

chemical substrates
OR
from light in photosynthetic micro-organisms

Question 7

What culture conditions do micro-organisms require?

Answer 7

Sterility, control of temperature, oxygen levels and pH

Question 8

What do sterile conditions in fermenters help to do?

Answer 8

reduce competition with desired micro-organisms for nutrients and reduce the risk of spoilage of the product

Question 9

Name the phases of growth and changes in culture conditions

Answer 9

Lag, log/exponential, stationary and death

Question 10

Describe the lag phase

Answer 10

where enzymes are induced to metabolise substrates

Question 11

Describe the log/exponential phase

Answer 11

contains the most rapid growth of micro-organisms due to plentiful nutrients

Question 12

Why does the stationary phase occur?

Answer 12

due to the nutrients in the culture media becoming depleted and the production of toxic metabolites.

Question 13

What is also produced during the stationary phase?

Answer 13

Secondary metabolites such as antibiotics. In the wild these metabolites confer an ecological advantage by allowing the micro-organisms which produce them to outcompete other micro-organisms

Question 14

Why does the death phase occur?

Answer 14

due to the toxic accumulation of metabolites
OR
the lack of nutrients in the culture

Question 15

Name 2 differences between viable and total cell counts

Answer 15

1. Viable cell counts involve counting only the living micro-organisms whereas total cell counts involve counting viable and dead cells.
2. Only viable cell counts show a death phase where cell numbers are decreasing

Question 16

How are growth curves of micro-organisms produced (or interpreted)?

Answer 16

By the use of semi-logarithmic scales