Aim:
I want to investigate how the concentration of dettol effects the growth of bacteria.
Hypothesis:
I think that as you increase the concentration of dettol the amount of bacteria will decrease, and so as you decrease the concentration of dettol the more bacteria will grow.
Equipment:
- Spotting Tile
- Agar Plate
- Dettol
- Vivid
- Hole Punch
- Filter Paper
- Q tip
- Yogurt or Pepper Corn Solution
- Cello tape
- Tweezers
- Ethanol
- Bunsen Burner
- Pipette
Method:
- Using the pipette put 10 drops of Dettol in a space of the spotting tile.
- Take 1 drop of the 1st solution and put it in another space in the spotting tile. Add 9 drops of water to that. This will create a solution with the dettol concentration ratio of 1:10.
- Take 1 drop of the 2nd solution and put it in another space in the spotting tile. Add 9 drops of water to that. This will create a solution with the dettol concentration ratio of 1:100.
- Take 1 drop of the 3rd solution and put it in another space in the spotting tile. Add 9 drops of water to that. This will create a solution with the dettol concentration ratio of 1:1000.
- Take your Agar plate and spread either yogurt or the pepper corn solution on it.
- Punch for small circles out of a piece of filter paper.
- Soak the filter paper circles in the 4 solutions.
- Split your agar plate into 4 and label them A, B, C and D.
- Place your soaked filter paper in the corresponding quarter of the agar plate, the first solution will be A, the second B and so fourth.
- Put the lid on the agar plate and seal the sides with cello tape. Write your name on the side.
- Put it upside down in the incubator at 20 degrees.
- Get results from 2 other groups to compare results after leaving it for at least 1 day.
Planning Our Assessment:
Purpose of investigation (this may be an aim, testable question, prediction or hypothesis)
How the concentration of dettol effects the growth of bacteria.
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2. FAIR TEST
Which variable will be changed? (This is the independent variable)
The concentration of dettol will change the variable.
How will the independent variable be changed?
The independent variable will be changed by putting different ratios
of water and dettol on the spotting tile.
Give a suitable range of values for this variable
The first value will be 100%, the second will be 10%, the third will be 1%,
and the last will be 0.1%.
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3. FAIR TEST
Which variable will have to be measured or observed in order to get some data or
information from the investigation? (This is the dependent variable)
The variable that will be measured is the growth of bacteria on the agar plate.
How will the dependent variable be measured or observed?
The dependent variable will be observed by measuring the clear zone.
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Other variables that need to be controlled to make your results more accurate.
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Other variables
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Describe how this variable will be controlled or
kept the same.
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The amount of solution in the agar plate.
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Measure the amount of solution going
into each of the agar plates.
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How much air gets into the agar plates.
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Make sure that the agar plates are
closed as often as possible, so that you
don’t let too much air into the plate.
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The temperature of the agar plates.
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Keep them in the same place.
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How will you ensure that your results are reliable?
By treating all the agar plates the same, and making sure that I do the experiment right.
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Notes from your trials.
Our trial didn’t work, but we know where we went wrong and how to fix it.
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Results (Trial):
| Quarter: | Clear zone (mm) |
| A | 20 |
| B | 15 |
| C | 3 |
| D | 0 |
Our trial experiment didn't work, but I borrowed some results from my classmates. Next time we will use the peppercorn solution instead of yogurt.
Results:
| Quarter: (Ours) | Clear zone (mm) |
| A | 20 |
| B | 7 |
| C | 3 |
| D | 2 |
| Quarter: | Clear zone (mm) |
| A | 6 |
| B | 2 |
| C | 3 |
| D | 1 |
| Quarter: | Clear zone (mm) |
| A | 6 |
| B | 2 |
| C | 3 |
| D | 2 |
The pictures I have taken are both of our agar plate. You can't really see the bacteria, but around the filter paper you can see the clear zone.
Conclusion:
I hypothesized that the more you increase the concentration of dettol, the more bacteria the dettol will kill off, meaning the larger the clear zone. From the graph you can see an increase in the trend, indicating an increase in the concentration of dettol and therefore the clear zone. This shows that my hypothesis was correct, the increase in concentration of dettol relates to an increase in the size of the clear zone.
Discussion:
Dettol is a brand of detergent used for cleaning dishes and other household items. The product is used to get rid of bacteria from such household items. The active ingredient in dettol, that kills the bacteria, is chloroxylenol. This chemical is a antiseptic and disinfectant, and is often used in hospitals for cleaning surgical equipment and for disinfecting skin. The bacteria is basically starved to death by the chloroxylenol. The chloroxylenol blocks the bacteria's ability to produce ATP. ATP stands for Adenosine Triphosphate, and it is the primary energy transporter in all living microorganisms. ATP is constantly produced and then broken down and is essential to the health and growth of all bacteria organisms. So if the bacteria can no longer produce ATP then it will not be able to grow or reproduce. This is how the bacteria are killed.
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From top to bottom: Pili - Capsule -
Cell Wall - Cell Membrane - Cytoplasm -
DNA - Ribosomes - Plasmid - Flagellum |
The structure of bacteria is made up of four layers. The outermost layer is called the capsule, this protects the bacteria. When dettol is used against the bacteria, the chloroxylenol breaks down this layer so that it can attack the bacteria. The second layer is called the cell wall. This wall keeps the structure of the bacteria in tact and is also broken down by chloroxylenol so it can kill the bacteria. The third layer is called the cell membrane, this controls what enters the cell, when chloroxylenol is used this layer is also attacked so that the chemical can get into the inner-workings of the cell. The final layer is the cytoplasm, this is where the functions of the cell are carried out, when chloroxylenol gets into this layer, this is where it is able
to stop the cell from producing ATP, which consequently starves the bacteria cell. Inside the cytoplasm there is DNA, ribosomes and a plasmid. The DNA carries the genetic code, and the plasmid is DNA that codes for non-essential processes of DNA, these can be things like fertility and resistance. The ribosomes are where proteins are made, these proteins work with the ATP to help the bacteria move and grow. The bottom of the cell has a flagellum, which is a tail on the bacteria that is used for moving. Finally, all the way outside the bacteria is the pili, these transfer the genetic information.
Bacteria reproduces and grows using a process called binary fission. This process starts with a parent cell. The DNA of the cell is replicated and the cell grows. The cell begins to divide into two cells, each one containing a copy of the DNA. The cell divides so that it is two separate cells, then it completely separates. That is how a cell divides.
As I stated in my conclusion the trend in the graph indicates that as you increase the concentration of dettol more bacteria gets killed off. This shows that dettol is very effective at getting rid of bacteria, and the 100% dettol is significantly more effective then 0.1% dettol. But if we're thinking about real life implications, generally when you use dettol, or any dish washing product, you mix it with water. This means that when your washing your dishes you're not even using 100% dettol because it gets diluted by the water. Also when you're using dettol you are generally spreading the product around every inch trying to get the object clean, as opposed to our stationary pieces of filter paper. So while this experiment was helpful to see how effective dettol is at getting rid of bacteria, it is not incredibly accurate when it comes to real life implications.
Evaluation:
This experiment was fairly reliable, as most of the class had very similar results, although it seems that the trial run worked a lot better than the actual assessment. In the trial run, although ours didn't work, many other of my class members were successful and had very visible bacteria growing on their agar plates. But in the second run I found that the bacteria was significantly less visible, and in fact was almost non-visible. This was most likely because for some reason the agar plates were more dried up, and in some cases the agar was peeling off. The only thing that went wrong was when we were making up the agar plate I forgot to label the top of the plate, and our method of taping the container closed involved rotating the plate, which mean't we had no idea which quarter was which. We fixed this by just re-doing our experiment, luckily it was pretty quick and easy to do, and we hadn't thrown out our solutions yet. We also weren't the only people who did this. The only anomaly I noticed was that the clear zone for our A quarter was 20mm whereas most other peoples I saw were around 3-6mm. I'm not sure why this happened, or whether I just didn't measure my clear zone properly, but this was very confusing once I got other peoples results. One problem that I mentioned earlier is that the agar plates dried out, this was likely due to the fact that they were in the incubator too long, or it was too hot. We could prevent this next time by either adding more moisture to the agar plates, or not leaving them in the incubator as long. This experiment has personally raised the question of how many bacteria were approximately on the agar plate.
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