I aim to investigate how different disinfectant concentrations can affect the growth and reproduction of micro-organisms
Hypothesis
I predict that the bacteria with the strongest concentration of dettol will kill the most bacteria as the concentration contains the most chloroxylenol which is the chemical that kills bacteria
Independent Variable
The independent variable I will be changing is the concentration of disinfectant. The concentration will change by diluting the dettol concentration with water. The disinfectant concentration ranges from full strength dettol solution to a no dettol solution.
I will be using the concentrations of:
- Full Strength dettol - 100% dettol, 0% water
- Water - 0% dettol, 100% water
- Manufacturers recommendation - Two capfuls of dettol, 400mL of water
- Diluted - One capful of dettol, 800mL of water
Dependent Variable
The dependent variable in this experiment is the bacteria. I will measure how much bacteria is killed for each section. To do this I will measure the diameter of the killed area. This area will be a clear zone, I will use a ruler and put the results in millimetres.
Other variables that need to be controlled
Environment
Bacteria thrive in warmth so if the environment of each filter paper is different then bacteria growth would be different. Each filter paper will be in the same agar dish and kept in the same area for the entire time the experiment is taking place. I will grow the bacteria in an incubator to ensure the temperature is the same throughout the experiment.
Size Of The Filter Paper
The filter paper for each of the four sections needs to be the same size, if one of the filter papers is larger then it would be able to soak in more dettol. I will hole punch four holes of filter paper as the size of the hole punch does not change.
Amount Of Bacterial Solution In Each Section
If there were to be more bacterial solution in a quadrant compared to another then the dettol would need to fight more bacteria which makes the experiment uneven. To prevent this I will drop the bacterial solution around the agar dish and then swirl it around to ensure the agar is covered, then tip out the excess bacterial solution.
Reliability
I will ensure the results are reliable by recording two other groups data and calculate the average of the results. This ensures that the results are reliable as if a mistake were to be made it would be found out. If I only recorded one result then I wouldn't know if the results were accurate or if something went wrong.
Method
Equipment
- Agar Plate
- Vivid
- Bacterial Solution (peppercorn water)
- Dropper
- Filter Paper
- Hole Punch
- Tweezers
- Disinfectant (dettol)
- Measuring Cylinder
- Spotting Tile
- Sellotape
Instructions
- Gather equipment
- On the jelly side of Agar Plate, using vivid, draw four quadrants and label each (full strength - F.S, water - W, diluted - D and manufacturers recommendation - M.R
- Using a dropper transfer bacterial solution onto the jelly side of the Agar Plate
- Swirl solution around to cover the entire Agar Plate
- Drain excess bacterial solution
- Hole punch four holes of filter paper
- Measure and create all solutions
- Use a dropper to transfer each solution into a different spot on the spotting tile (use a different dropper for each solution)
- Use tweezers to drop a filter paper disc in each tile (clean tweezers before picking up each disc)
- Use tweezers to remove each disc and place into the centre of its quadrant (clean tweezers before picking up each disc.
- Write your name on the side of Agar Plate
- Put the lid on the Agar Plate and sellotape around the outside of the Agar Plate
- Place the Agar Plate in the incubator with the jelly side facing up. This ensures that the condensation that is formed goes onto the jelly side of the Agar Plate, if it was on the other side then the condensation would drip and move things around.
Results
Diameter length of bacteria killed from different trials
Conclusion
In my hypothesis, I predicted that the full strength dettol would kill the most bacteria. From my results
I see that the full strength solution did, in fact, kill the most bacteria, I know this as it had the largest diameter of killed bacteria. The water I conclude that the more dettol in the solution the higher effect of growth and reproduction of microorganisms.
Discussion
Bacteria is a microscopic, single-celled micro-organism that has a cellular structure and consists of water, enzymes, nutrients, wastes and gases. There are different parts that make up a bacterium cell.
Pili transfer genetic material and attach bacteria to each other, pili are located on the outside of the cell
Flagellum are also located on the outside of the cell and is known as the tail, the flagellum moves the cell
and acts as the sensory organelle. The capsule is the outer layer of the bacterium, it protects the bacteria and enhances the ability to cause disease. The cell wall is the second layer and supports and keeps the
structure of the cell. The cell membrane is the third layer, it transports molecules into the cell and controls
what enters the cell. Cytoplasm fills the centre of the cell, cell growth, metabolism and replication occur in
the cytoplasm. The DNA nucleoid is in the centre of the cytoplasm and is the length of the cell, the nucleoid carries the cells genetic code. Ribosomes are located in the cytoplasm, they receive genetic information and decode it to create the proteins they code for. Plasmids are also located
in the cytoplasm, their function is to provide its bacterium with a genetic advantage such as resistance to
Discussion
Bacteria is a microscopic, single-celled micro-organism that has a cellular structure and consists of water, enzymes, nutrients, wastes and gases. There are different parts that make up a bacterium cell.
Pili transfer genetic material and attach bacteria to each other, pili are located on the outside of the cell
Flagellum are also located on the outside of the cell and is known as the tail, the flagellum moves the cell
and acts as the sensory organelle. The capsule is the outer layer of the bacterium, it protects the bacteria and enhances the ability to cause disease. The cell wall is the second layer and supports and keeps the
structure of the cell. The cell membrane is the third layer, it transports molecules into the cell and controls
what enters the cell. Cytoplasm fills the centre of the cell, cell growth, metabolism and replication occur in
the cytoplasm. The DNA nucleoid is in the centre of the cytoplasm and is the length of the cell, the nucleoid carries the cells genetic code. Ribosomes are located in the cytoplasm, they receive genetic information and decode it to create the proteins they code for. Plasmids are also located
in the cytoplasm, their function is to provide its bacterium with a genetic advantage such as resistance to
an antibiotic.
 |
| http://www.scienceprofonline.com/cell-biology/bacterial-glycocalyx-capsule-slime-layer.html |
Bacteria reproduce by the asexual process of binary fission. During binary fission, a single cell parent replicates its DNA and makes to create a replicate of its cells. The double cell elongates (grows) and divide. The cells fully divide and separate from each other, now there are two cells that are reproducing.
This process continues creating more and more bacteria each time. Bacteria need to grow to reproduce, for
bacteria to grow they consume food. The bacteria secrete enzymes onto their food and absorb their food by two processes, direct transport and diffusion. Bacteria use the process of diffusion when there is a high concentration of nutrients surrounding
them, the nutrients diffuse from a high concentration, outside the bacteria, into a low concentration, in the bacteria. Bacteria
use direct transport when there is a low amount of nutrients surrounding the cell, the walls of the
bacteria act as a vacuum and suck in the surrounding nutrients.
 |
| https://byjus.com/biology/binary-fission/ |
Dettol is a disinfectant that humans use to fight back against unwanted bacteria. We use dettol in everyday life to cleanse items. We use it to kill bacteria on items such as bench tops or door knobs and use it to clean wounds to prevent infection from bacteria carrying disease.
The active ingredient responsible for the bacterial kill is chloroxylenol. Chloroxylenol is an atom of chlorine. This chemical breaks down the cell walls of a bacterium, which allows dettol to filter into the cell through the membrane which allows all the things that kill it into the cell, the cell wall is also responsible for the structure of the cell, when the structure is damaged it can prevent survival. Once inside the cell, it attacks the enzymes this means the bacterium can not secrete enzymes onto their food, therefore no consumption is made and the cell does not grow which stops reproduction
In the experiment we can see that the dettol kills the bacteria by stopping enzyme function and structure, preventing growth and reproduction. This is because the dettol from the disc diffuses into the bacteria in the bacterial solution. From the results, I can see that at home in my everyday life I can use two different amounts of disinfectants. For the best result, I think full strength dettol should be used, we can see that on average full strength kills the most bacteria by 11.80mm.
Evaluation
I can say that the results from my experiments were reliable. I repeated the trial as well as another contender in my results. I also got the results from five different Agar Plate trials and calculated the average. This gave me a number of results and finding the average allowed me to find the most common results, going on one result would have been unreliable as something could have gone wrong.
There were two abnormalities. Crystals result from her second trial with her water quadrant showed a ring with a 19mm diameter, this result should have been 0mm as there was no dettol in the solution. I'm guessing she did something wrong, maybe some dettol from another quadrant dripped onto the disc whilst placing them in. The other abnormality was from my second trial with the manufacturer's quadrant, this result showed a ring with a diameter of 1mm, the other trials had a ring with a diameter around the 10mm mark. I am not too sure why this didn't kill as much bacteria as the others.
Something that I should have done during the trial was clean all of my instruments. Even though I used different droppers and tweezers I did not sterilise them first. As the instruments are available to the entire school it is not certain they were cleaned properly before putting away. I should have dipped things in alcohol then burnt it on the bunsen burner to kill any previous chemicals. This could have affected my results. Another thing that might have altered the experiment results is that there is chloride in Christchurch water, so the water used in the experiment is chlorinated. As chloroxylenol is an ion of chlorine that means there was extra chlorine in the water. If I was to do this experiment again I would sterilise my instruments and use filtered water so there is no extra chlorine. I would of like to calculate the area instead of the diameter but the circles were not perfectly round, some were large on one side and some others had clear zones in a line on one side of the quadrant.
