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Exponential Growth and Death of Bacteria Worksheet

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          Exponential Growth and Death of Bacteria
Introduction
Bacteria divide asexually through a process called binary fission. One bacteria can split into two new identical
copies. Since bacteria are very small and simple cells, they are able to grow and reproduce very quickly under
the right conditions. For this worksheet, we will follow a population of 100 bacteria on a petri dish as they
grow and die.


Lag Phase
During this phase, the bacteria are getting used to their environment. They are adapting, ingesting food, and
growing in size. Most of the individual bacteria are not fully mature and cannot divide yet.

                                Number of Bacterial                     Number of Bacterial
                      Hours                                  Hours
                                      Cells                                   Cells

                  1            100                      6              131

                  2            100                      7              144

                  3            102                      8              159

                  4            106                      9              178

                  5            114                      10             200



   1.   Sketch the basic shape the graph of the lag phase would take. Make sure you label each axis.




   2. If you were looking at a petri dish in lag phase, would you be able to see any bacterial colonies?




Biology Teaching Resources                                      http://www.aurumscience.com                Page 1
Exponential Phase
During this phase, cell doubling occurs. This growth will continue, unrestricted, as long as the bacteria have
sufficient space, water, and food.


                                Number of Bacterial                     Number of Bacterial
                       Hours                                 Hours
                                      Cells                                   Cells

                  11            200                     17

                  12                                    18

                  13                                    19

                  14                                    20

                  15                                    21

                  16                                    22



   3. Sketch the basic shape the graph of the exponential phase would take. Make sure you label each axis.




   4. Would it be realistic to expect this kind of growth to continue endlessly? Explain.




   5. If you were looking at a petri dish during this phase, how would you expect its appearance to change?




                                                                                                           Page 2
Stationary Phase
Eventually, the bacteria begin to experience limits to their growth. They may start to run out of space and
crowd against each other, water and food may start to become depleted, and their waste products, which are
toxic to growth, begin to accumulate.


                                Number of Bacterial                     Number of Bacterial
                       Hours                                 Hours
                                      Cells                                   Cells

                  23            410000                  26              411000

                  24            411000                  27              410500

                  25            411000                  28              410000



   6. Sketch the basic shape the graph of the stationary phase would take. Make sure you label each axis.




   7. If you were looking at a petri dish during this phase, how would you expect its appearance to change?




Death Phase
As the waste products of the bacteria accumulate and the bacteria run out of nutrients, they quickly begin to die.
All of the colonies that were produced during the exponential growth phase die off in huge numbers.

                                Number of Bacterial                     Number of Bacterial
                       Hours                                 Hours
                                      Cells                                   Cells

                  29            410000                  34              200000

                  30            380000                  35              140000

                  31            340000                  36              75000

                  32            300000                  37              30000

                  33            250000                  38              0

                                                                                                           Page 3
Data Analysis
  8.   Make a line graph to show the growth and death of the bacteria in this petri dish. Time should go on the
       x-axis, and population on the y-axis. Label each of the four phases of bacterial growth on this graph.




  9. Explain why it takes so long for the bacteria to start growing. What is happening in the lag phase?



  10. What form of reproduction is occurring in the bacteria during the exponential phase? Why is this so
      much faster than animal and plant reproduction?



  11. What limiting factors eventually restrict the bacterial growth during the stationary phase?



  12. What causes the eventual demise of the bacterial colonies during the death phase?




  13. Describe a real-life example of this kind of bacterial growth outside of a petri dish.


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Description: A worksheet covering the different phases of bacterial growth, including an opportunity to graph sample data from each phase.