1. Modelling Bacterial Growth

2. Thinking Activity
It takes 20 minutes for one E. coli bacterium to divide to make two bacteria.
Assuming there is nothing to limit their growth, how many bacteria would there be after eight hours?
More than 16 million!
Answer – 2^24 = 16,777,216

3. Lesson Objectives
To state the scientific unit for temperature is Kelvin.
To use modelling software to investigate how temperature affects the growth of bacteria.
To suggest reasons why fridge temperature should be set at a maximum of 5°C.

4. Measuring Temperature
Celsius or oC is a unit of temperature. So is Fahrenheit or oF.
But scientists use another based on particle vibrations...
How are particles arranged in solids, liquids and gases?

5. Absolute zero – when particles stop vibrating.....
N.B. This image needs to be re-drawn as just taken from bbc bitesize
That is where the Kelvin scale starts, and it is equivalent to oC

6. Try these examples 40oC 313K 0K -273oC 55K -218oC 0oC 273K 100oC 373K
To convert Celsius to Kelvin add 273
e.g. 36oC is 309K
To convert Kelvin to Celsius subtract 273
e.g. 400K is 127oC
40oC
313K 0K
-273oC
55K
-218oC
0oC
273K
100oC
373K
400K
127oC

7. Go to www. combase. cc and follow the instructions on the lab sheet
Go to and follow the instructions on the lab sheet. You will use the research database to investigate bacteria.

8. Plenary
Using the ‘MicroTrumps’ cards, play using temperature as your category.
Stretch and challenge:
Use the Kelvin scale, converting in your heads from the temperature in °C on the card.
The ‘toughest’ microbe wins i.e. grows at lowest temperature rather than just surviving the highest temperature process or surviving freezing

9. Plenary Why is a fridge set at 5°C?
What be the effect of leaving the fridge door open?
Hint: think about the shelf life and bacterial growth
Note that shelf life is defined as the period which the food meets its quality specifications and remains safe. A safe food is one which spoils before pathogens become an issue