Aim:
I want to investigate different disinfectant concentrations can affect the growth and reproduction of micro-organisms (Bacteria).
Research
Chloroxylenol, also known as para-chloro-meta-xylenol (PCMX), is an antiseptic and disinfectant which is used for skin disinfection and cleaning surgical instruments. (https://en.wikipedia.org/wiki/Chloroxylenol)Hypothesis
I think the more concentrated the Detol is, the more bacteria it would kill.
Variables
Independent Variable:
The variable I will be changing is the disinfectant, I will do this by adding the same amount of disinfectant to different amounts of water
I will use:
- Full strength Dettol.
- The manufacturer's instructions.
- No Dettol just water.
- Diluted Dettol
Dependent Variable
The dependent variable I will be measuring is the size of the clear zone around the Dettol disk. I will measure the diameter of the clear zone using a ruler, which then I can use the formula π x radius^2 to get the area of the clear zone, I can get the radius by halving the diameter of the clear zone.
Other Variables
Other variables that can impact the outcome of the experiments are...
- Growing temperature - we need to grow the bacteria at the same temperature.
- Growing medium - we need to grow the bacteria on the same medium.
- Growing time - we need to grow the bacteria for the same amount of time.
- Size of the disk - we need to make sure that we have the same amount of Dettol.
Reliability
To ensure reliability, I will repeat the experiment three times.
Equipment
- Detol
- Vivid
- Water
- Filter Paper
- Agar Plate
- Sellotape
- Hole Punch
- A solution of bacteria
- Pippete
- Tweezers
- Ruler
Method
- Gather equipment needed
- Punch out 4 disks of filter paper using the hole punch
- Using a pipette, transfer some of the bacterial solution onto the agar plate and then swirl until it covers the surface of the agar plate, then tip out the excess solution from the agar plate.
- Mark the agar plate into quadrants using a vivid.
- Label the quadrants using the vivid making sure you label the bottom so the top can't spin around. Since the bacterial solution won't move on the bottom the label will always remain the same.
- Make the solutions, by mixing 400ml's of water with one cap full of Dettol to make the manufacturers instructions and then by adding another 400ml's of water we created a weaker concentration.
- Place filter paper in each different strength of Dettol, starting with water to the weaker solution then to manufacturers instructions then to the full strength and every time you use different strengths of the Dettol shake/wash the tweezers so you don't get extra solutions onto the bacteria which then could ruin your experiment.
- Label the agar plate with your name so you can identify. Once labelled seal off the agar plate with sellotape.
- Incubate upside down so moister falls to the bottom at 20 degrees for 24 hours.
- Observer the agar plate. Use a ruler to measure the diameter of the clear zone around each disk.
- Repeat experiment
Results
Plate 2
Plate 3
Plate 4
The aim of the investigation was to see how the different concentrations of Dettol would affect the growth of bacteria. My graph shows an increasing trend. This means that as the concentration increased the clear zone increased in diameter, meaning the higher the concentration, the more bacteria it killed.How did we figure out the percentage of the different concentration?
For full strength, we know it is 100% since we didn't add or dilute the concentration.
For water, we know it is 0% since we didn't add any Dettol.
For manufacturers instruction we added 20ml's of Dettol and 400mls of water, we figured out the percentage by using 20/420, the second number is 420 because we added 400ml's to 20ml's (400:20) so it is 20/420 which equals 5.
For the diluted manufacturer's instruction, we added 400ml to the current manufacturer's instruction, meaning there is 800ml's of water to 15ml's of Dettol (800:20) so that means we have 820mls in total liquid, so we do 20/820 to figure out the percentage of concentration which is 2.5%.
Discussion
What happened to the bacteria?
Bacteria is a microscopic single-celled organism that has no nucleus. Bacteria have a cellular structure as seen in the left picture. The outer layer is called a capsule, this protects the bacteria/bacterium. Between the capsule and the cell membrane there is a cell wall, this protects the cell contents and keeps the structure of the cell. After the cell wall there is a cell membrane, this controls what enters and exits the cell. Philis is located around the capsule but comes out from the cell membrane, this allows the bacteria to sense around them and attach themselves to other cells. Flagellum (Tail) allows the bacteria to move around. Inside the bacteria, there is plasmid, ribosomes, cytoplasm and the DNA.
The plasmid is a part of the DNA that has no essential processes, the ribosomes are where the proteins are made, cytoplasm is the jelly fluid in the bacteria that create chemical reactions and the DNA is the genetic information for the bacteria. Bacteria reproduce through a process called "binary fission" this is where the cell replicates the DNA inside and then elongates/grows, then it starts to divide, once they divide it creates 2 daughter cells as seen in the image above. There are two ways of bacteria receiving nutrition, one is diffusion, this is where particles from a high to low concentration, just like a sponge in water. The other way is active transport, this is where the bacteria uses a pump to suck in the nutrients, they only do this when there is not as many nutrients around as seen in the image on the right.
The bacteria killed off by a chemical in the Dettol called chloroxylenol (PCMX C8H9OCl), this
chemical is found in most household cleaning items. This chemical kills the bacteria by destrupting the cell wall and stopping the functions of the enzymes (proteins or chemicals that has a function), which are used for growth, reproductions, since this is what is the basic structure every living things needs, the bacteria will be unable to continue meaning they will be killed off. In my clear zones I noticed some bacteria that weren't killed by the Dettol, this might have been because the active chemical that kills bacteria in Dettol chloroxylenol is very effective against gram positive bacteria and not against gram negative bacteria. Another possible reason for bacteria growing in the clear zone is that some of the bacteria could be resisted towards antiseptics. With this experiment, I now know that I can implement this when I am using Dettol to clean at home. Since I know that I do not require full strength Dettol to kill our everyday household bacteria, instead we can diluted the Dettol by like 400ml's for every 15ml's of Dettol used and still get the same effect as full strength Dettol since only a little bit of Dettol is needed to kill bacteria, but if we use too diluted water there will be barely any of the chemicals that killed the bacteria getting into the bacteria cell. Through a process called diffusion, the chemicals from Dettol would be able to get into the bacteria cell killing the bacteria.
Evaluation
I think this investigation went good. This was successful because we were able to see the clear zones of the bacteria killed. This is reliable because I collected 3 different results and came out with some reliable results. There were a couple anomalies in my data which includes in all the plate for the diluted manufacturers solution there is a 15 mm, 12 mm, and 6 mm, this might be because of us forgetting to clean the tweezers or us mixing around the solutions. For the water solution there shouldn't be a single bacteria killed but there is some, this might be because since there is chlorine in our water system, that might be killed our bacteria. This means that if we want to repeat this experiment we might need to used distilled water (boiled or bottled) and remembering to clean the tweezers. I wasn't able to calculate the areas of the bacteria killed since the bacteria that was growing in the clear zone and that the circles were perfectly rounded.
