growth curves of micro-organisms

Question 1

how is bacteria divided

Answer 1

binary fission

Question 2

what kind of reproduction is binary fission

Answer 2

asexual reproduction

Question 3

explain the lag phase

Answer 3

-after inoculation there is normally a brief period of adaptation by the cells to the new conditions
-bacteria are producing the enzymes necessary to digest nutrients
-the rate of growth begins to increase towards the end of this phase

Question 4

explain the log/exponential phase

Answer 4

-there is a rapid period of growth during this phase due to:
1. bacteria have developed the necessary enzymes and there are plenty of nutrients
2. there are few waste products being produced
3. the rate of cell division is currently at its maximum with the number of bacteria doubling as often as every twenty minutes

Question 5

explain the stationary phase

Answer 5

the rate of growth levels off during this period because:
1. the nutrients are becoming used up
2. the amount of waste produced by the bacteria themselves is increasing
3. the rate at which new cells are produced is equal to the rate at which the other cells are dying

Question 6

explain the death/decline phase

Answer 6

during this phase more bacteria are dying than being produced because:
1. very few nutrients are left
2. many bacteria are poisoned by the waste produced by such large numbers
3. the rate of growth is falling

Question 7

what is the survival phase

Answer 7

when some bacteria form endospores to allow themselves to survive adverse conditions

Question 8

explain the process of endospore formation

Answer 8

1. the bacterial chromosome replicates
2. one of the new strands become enclosed by a tough walled endospore formed inside the parent cell
3. the parent cell then breaks down
   4.endospores can remain dormant for a long period of time
4. when conditions are favourable a new bacterium can be formed again and continue to reproduce

Question 9

what is a bioreactor

Answer 9

a vessel in which biological reactions take place

Question 10

examples of products of bio-processing

Answer 10

yoghurts
cheeses
artificial sweeteners
flavourings
vitamins
alcohol

Question 11

what are the two main methods of food processing

Answer 11

-batch food processing
-continuous flow food processing

Question 12

explain the process of batch food processing

Answer 12

• a fixed amount of sterile nutrient is added to the micro-organisms in the bioreactor
  -the micro-organisms go through the stages of the typical growth curve
  -the reaction may be stopped before the death stage as very little product will be formed
  -at the end of the production the bioreactor is cleared out
  -the product is separated from the rest of the solution and is purified
  -the bioreactor is cleaned and re-sterilized and the process is repeated

Question 13

explain the process of continuous flow food processing

Answer 13

-nutrients are continuously fed into the bioreactor
-at the same time the culture medium is continually withdrawn
-micro-organisms are maintained in the log phase so the process can continue uninterrupted for weeks or even months
-bioreactors factors such as temperature, pH, oxygen etc are monitored in order to maintain growth in the log phase