Question

Learning task 16.1: Cell Growth rates

Bacterial cells reproduce far more rapidly than other microorganisms. This is one of the reasons why diseases develop so fast. Bacteria are able to grow and cause symptoms rapidly and are able to be passed from person to person. See the table on the next slide for growth rates and temperatures of different microorganisms.

PART A

You need to calculate the population for each of the microorganisms, based on their doubling times:

Time (min)	0	30	60	120	200	400	600
# of E.coli	1
# of C. botulinum	1
# of E. gracilis	1
# of S. cerevisiae	1

Sketch the graph of the microorganisms, comparing the number of microorganisms to time.

PART B

All cells also have the optimal temperature that they grow at. At a slightly higher or lower temperature, E. coli grows at a slower rate. Much higher or lower temperatures also causes E. coli to form endospores or else die.

Based on laboratory testing, it was discovered that the Doubling Time for E.coli at 25^oC is 40 min. Also, based on laboratory testing, it was discovered that E.coli die at 45^oC.

Fill in the table with the estimated number of bacteria:

Time (min)	0	30	60	120	200	400	600
# of E.coli at 25 oC	1
# of E.coli at 37 oC	1

Sketch the graph of the microorganisms, comparing the number of microorganisms to time.

Questions:

1. What impact do you think the rate of growth of microorganisms has on the spread of disease?
2. How do you think growing conditions, like temperature, can be used to prevent the spread of disease?
3. What impact would heating or refrigerating food have on bacteria such as E.coli?

Answer 1

Answer-1 The rate of spread of infection increases with the increased rate of growth of microorganisms.

Answer-2 An excess of increase in temperature will produce the unfavorable conditions for the growth of microorganism. This will reduce the spread as less microorganisms will be available for the interview.

Answer-3 The bacteria growth is supported by an optimal temperature range. The temperature below and above the optimal temperature doesn't support the growth of microorganisms so this will prevent the food from getting any infection causing agent.