How will exposure of E. coli to different kinds of light affect its growth? Hypothesis: Under the exposure of no light, E. coli will thrive and grow at maximum speed

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Abdel Rahman Negm

I.B. Biology H1

Research Project #1

Escherichia Coli and Light

November 5, 2004

Abstract:

        There are thousands of kinds of bacteria in the world, each one with its own special unique characteristics.  In this experiment, one will work to discover certain aspects of the bacteria known as Escherichia Coli (E. coli). E. coli is not necessarily deadly bacteria, but it can cause bloody diarrhoea and maybe even kidney failure.  This awful kind of bacteria can be transmitted to humans through uncooked meat or drinking raw milk or contaminated water. One will use different combinations of E. coli (growing on agar) and light to explore and understand what kind of habitat is more suitable for it and which habitat E. coli favors for growth.  Through this experiment, one will learn and understand more about this harmful kind of bacteria and learn about the conditions (of light) that it favors the most.

Problem:  How will exposure of E. coli to different kinds of light affect its growth?

Hypothesis: Under the exposure of no light, E. coli will thrive and grow at maximum speed.

        It’s very well known that most bacteria does thrive and flourish in dark, moist conditions (such as one’s arm pit; after a long, sweaty jog outside in the heat, one’s body will most probably give off a bad smell known as body odor and this is because of the bacteria living in the dark, and now wet, conditions of the arm pit- the bacteria grows faster and gives off that odor.)  And so, it’s these facts that I based my hypothesis on.

Variables: In this experiment, as any others, there are several variables- dependent and independent variables - in this experiment that can be listed

        Independent- Blood agar, Light

        Dependent- E. coli, space available for growth of bacteria

Blood agar is independent because one manipulates that agar and changes it by infecting it with the bacteria.  Light is also independent for one changes and manipulates that as well; for some Petri dishes with the bacteria colonies growing, one exposes them to light while for other Petri dishes, one prevents light from reaching them completely (except when data is being collected).  Light is also one of the variables that has to be controlled as for some Petri dishes, light has to be kept constant at all times and for others, there can be no light exposure and it has to be kept like this at all times so the data can be accurate and so the goal and objectives of this experiment can be accomplished.  E. coli on the other hand is dependent for it depends on the agar and the light we put on it (if any) and so one doesn’t manipulate this but it does change accordingly to the different independent variables and to what one did.  The space available for the growth of the bacteria is another dependent variable, and it depends on the speed of the growth of the bacteria, for as the number of bacteria colonies increase, the less space there is left for the bacteria to grow.

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Materials:

  1. Blood agar
  2. Petri dishes
  3. Inricular loops
  4. Non-heat lamp
  5. E. coli
  6. 4 Petri dishes
  7. Matches
  8. Masking tape
  9. Ruler
  10. Marker
  11. 250ml Beaker
  12. Water
  13. Hot plate
  14. Goggles, apron and gloves (safety equipment)

Methods for controlling controlled variables:

        The one and only controlled variable is the amount of light that has to remain constant at all times and to achieve this consistency, one has to make sure of 2 factors at all times and this will ensure proper control of these controlled variables:

  1. Petri dishes supposed to be exposed to light and the Petri dishes ...

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