Evolution of Bacteria Lab Report
Background:
Bacteria are single celled prokaryote microorganisms. Bacteria can be found anywhere
from water, soil, waste, or in animals and plants. Bacteria reproduce through asexual
reproduction and a process called Binary Fission. Binary fission is the process where a cell
divides itself to create two daughter cells. Some diseases caused by bacteria are Tuberculosis and
Bubonic Plague. Antibiotics are substances that kill or stop the growth of bacteria. Antibiotics
kill bacteria by either penetrating the outer cell wall or attacking the inner membrane of the cell.
Bacteria can form a resistance to certain antibiotics when it is exposed to it and so it creates a
gene and multiplies with that resistance gene. All in all, some bacteria’s are helpful to your body
like the Probiotic bacteria which helps your immune system by fighting illnesses and diseases.
Dependent Variable is the experimental variable being measured in a lab. The dependant
variable in my lab is the growth of bacteria from being tested in different concentrations of
alcohol. We will measure each quadrant of our Petri dish to see the growth of bacteria in
millimeters. We will then determine which quadrant of different concentrations of alcohol that
had the least amount of bacteria growing. We will then record and see in millimeters which
concentration of alcohol did the most damage to the bacteria growth.
Independent Variable is the variable that is being tested in a lab or project. The
independent variables in my lab are different concentrations of alcohol (90%, 70%, and 50%). I
had chosen different alcohol concentrations because alcohol usually is used for killing bacteria to
prevent any type of infections. Disinfectants are agents that kill microorganisms that carry
diseases. The disinfectant we had used was Clorox to remove all bacteria from the desks. The
disinfectant affected the bacteria’s growth by all microorganisms being eliminated so it did not
affect the lab and cause a source of error. The temperatures we had used for the bacteria were 37
degrees Celsius in an incubator. Bacteria grow best in a normal environment where it’s not too
warm or moist.
Purpose
To determine the effect that different concentrations of alcohol have on the growth
bacteria.
Hypothesis
If I put a concentration of 90% alcohol in the ecoli; then I think it would stop the growth
of the bacteria than 70% or 50%; because 90% alcohol has a higher concentration of alcohol and
it could surely stop an infection or bacteria.
Materials
Methods

Petri Dish w/ Agar

Filter Paper

Bacteria

90%, 70%, and 50% of alcohol

Forceps

Incubator

Tape

Inoculating Needle
1. Wash hands and disinfect desk
2. Get Petri dish and agar side must face you
3. Draw 4quadrants on the agar side of the dish
4. Label the disk with your name and period
5. Label the quadrants with your IV(Independent Variables)
6. Dip sterile swab in bacteria and rub carefully on the agar disk. Place covers after you
are done.
7. Pick filter papers using forceps, gently dip into each of your IV’s and place correctly
into each quadrant.
8. After placing filter paper into each quadrant, place lid over disk.
9. Tape the sides of your Petri dish
10. Gently place your disk into the incubator at 37 degrees Celsius.
11. Wash your hands after you are done.
Results – Data Table
Measurement: Trial 1
Measurement: Trial 2
Quad. 1: 90% Alcohol
10 millimeters
20 millimeters
Quad. 2: 70% Alcohol
3 millimeters
5 millimeters
Quad. 3: 50% Alcohol
2 millimeters
0 millimeters
Quad. 4: Distilled Water
0 millimeters
0 millimeters
Caption: In the first trial the 90% concentration of alcohol wiped out 10 millimeters while other
concentrations had done only 0-3 millimeters of damage. In the second trial the 90%
concentration of alcohol did 20 millimeters of damage where 70% did 5 millimeters of damage
and 50% & distilled water had done 0 millimeters of damage.
Conclusion
If I put a concentration of 90% alcohol in the ecoli; then I think it would stop the growth
of the bacteria better than 70% and 50% concentration of alcohol; because 90% alcohol has a
higher concentration of alcohol could surely stop an infection or bacteria. The data supports my
hypothesis because in Trial 1 and Trial 2, the concentration of 90% alcohol had prevented the
bacteria from adapting by wiping out 10 millimeters of the quadrant it was located in; however in
the other quadrants there was only about 0-5 millimeters amount of damage to the bacterial
growth. One source of error could have been an uneven spread of bacteria in each quadrant
causing the areas that had less amounts of bacteria die off easily giving the advantage to the 90%
concentration of alcohol to kill off most of the bacteria in both trials. Another source of error
could have been students moving the dishes making the lids open and air or other substances
exposing the bacteria making the data tainted which lead to the bacteria maybe being more
enhanced so the other concentrations of alcohol did less damage than the 90% alcohol
concentration. The experiment could have been changed to be better by the dishes being pre
spread with bacteria so there is an even amount of bacteria spread into each quadrant, and also to
maybe seal the whole dish so nothing gets in or out of the petri dish. A future experimental
question I could ask is “How can bacteria adapt to different concentrations of Hydro Peroxide?”
Connection
Like species in evolution, the ecoli tried to adapt to different substances to live and so
they would not die off. The bacteria adapting to different concentration of alcohol (90%, 70%,
and 50%) is just like the peppered moths adapting to the black trees after the Industrial
Revolution. The solution of 90% alcohol denied the bacterial growth and killed them off because
they did not have the gene to survive in harsh conditions. As a result they were not fit and could
not adapt to their environment unless a random mutation occurs.