If apple slices are dropped on the floor for no time (control) 5, 10, 15, and 30 seconds then the apple slice dropped on the floor for 30 seconds will have the most colony’s of bacteria because the bacteria will have more time to spread and grow on the apple slice.

Agar is a substance that can be super helpful. First of all, agar is a jelly or gelatin-like substance. It is made out of red algae from a species called gelidium. Agar supports the growth of bacteria by helping it speed up its growth and making it more visible on a petri dish. Agar has the ability to not break down too quickly, that's what helps bacteria grow. Another reason is because it does not dry out too fast which is good for bacteria growth because bacteria needs a moist environment. Agar is named after jelly in the language malay.

Bacteria is a cool organism that can be helpful and not helpful. Bacteria is a single cell living organism. Bacteria can be found everywhere. They are even be in the human body and help people with digestion. There are millions, maybe billions of different types of bacteria. One of them is bacilli rod shaped bacteria that can be found in soil and sometimes water. There are two types of bacteria good and bad. An example of a bad bacteria is like spirochetes, it can grow on an animal like a tick and cause lyme disease. An example of a good bacteria is bifidobacterium. It helps people digest fiber and also helps produce vitamins. There are hundreds of types bacteria that scientists haven't discovered yet.

Bacteria can spread in different ways depending on the material. Different types of food like dry or moist food can change the way the bacteria grows. Apple slices have a bigger chance of having more bacteria because bacteria needs a moist environment. If you have something like a muffin then it will have less bacteria because it is dry and makes it hard for bacteria to grow. Now different types of flooring can also change the way bacteria grows. If something spilled on wood flooring and it is not washed and it stays at room temperature for 12 hours that would be the one of only time that bacteria would grow in wood. Then if there was tile flooring there would be more bacteria because it has the energy and moisture for the bacteria to grow. There are some cool ways we can prevent bacterial growth. One way is to put silver. It works because it disrupts the bacteria’s metabolism and stops it from getting the energy the bacteria needs to grow. Bacteria needs many different conditions to grow and spread.

An incubator is a very useful tool. It can be used to help grow the bacteria. It does this by tricking the bacteria it is in its natural habitat. Another thing is that incubators can change temperature.  They can also keep a consistent temperature by lowering and raising the temperature. Incubators originate in ancient Egypt and China. They were used to help hatch eggs. Incubators have been used for centuries for different reasons. Fungi can grow in petri dishes. The fungi that can be seen growing on petri dishes will typically look like black tiny dots. In some cases it can look like it’s vining out on the agar. This happens because the agar provides a healthy living environment from not just bacteria but also fungi. Fungi can also grow because of the food or substance that was swabbed. If something was swabbed like an apple slice the juices could have got on the petri dish causing the fungi to grow.

Manipulated variable is time the apple slice is on the floor. Responding variable is how many colony’s of bacteria grow in ten days. Controlled variable is: Time on floor Heat of incubator Time in incubator Size of apple amount of agar

1. Put on sterile gloves
2. Wash petri dish in soapy water (If they are not sterile)
3. Put a boiling pot of water on the stove
4. Now dunk each petri dish and measuring spoons  into the water 5 seconds
5. Then lay out paper towel on a sterilized surface place each dish upside down so the water can drip out
6. With the bigger measuring bowls and the big bowl put them in the microwave for 2-4 minutes
7. In the big bowl put 1 tablespoon and ¾ teaspoons of powder agar
8. Then 1 cup and 4 tablespoon and 1 ½ teaspoons the liquid should be around 303 milliliters
9. Mix solution until the the agar has dissolved
10. Put the mixture into a pressure cooker for 15 minutes
11. Now pour 3 millimeters into the petri dish
12. Make the solution even in the petri dish
13. Let solution cool
14. You can put the petri dish in the refrigerator or a cold place
15. Tape off spot on the floor
16. Tape it into 12 sections
17. Now cut apples with an apple cutter to ensure equal sizing
18. Drop the first apple on the taped off section 1, leave on floor for 5 seconds
19. Then swab the apple and do a couple strokes with it in the agar petri dish repeat this step with no time 0 seconds, 10, 15, 30 seconds in a different sections do this with an apple that did not touch the floor
20. Repeat this step for two more trials
21. Now put the petri dish in the incubator upside down
22. Put the incubator at 25-27 degrees celsius
23. Leave the petri dishes in the incubator for 5-10 days observer the growth of the bacteria
24. Take photos

In all of the trials one thing that stayed the same was the colour of bacteria, the colour of the bacteria was a faint yellow or a light yellow. In a few trials the colour of the bacteria was black which could have not been bacteria and may have been mold. One of the trials had a bacteria that was black and looked like it was vineing out of the agar.  The one with the most colonies was 30 seconds (trial 3) and 15 and an area where it had a whole bunch of little black bacteria measuring too 5 cm, making it not countable but measurable. The one with the least amount of bacteria is 0 seconds (trial 3), which only had 3 colonies Something that I noticed in 0 seconds trial 2 was the bacteria was growing in lines or ovals rather than the spots or circles like the rest. The petri dish for five seconds (trial 2) had a couple of lines where there were a lot of bacteria spores. It made it visible to see where the q tip was swabbed on the agar. It was surprising that the lines on agar didn't come until day 9. All the trials for 10 seconds stayed pretty consistent. One thing I noticed from trial 1 was that the bacteria was super spread out on the agar and most of the bacteria was on the edges of the agar. For 15 seconds (Trial 1) there was a bacteria where it looked like a big black bacteria and when you zoomed in it looked like it was vining out. On the 30 seconds (trial 3) there was an area where it had a whole lot of little specs of black bacteria and measured to 5 cm across it had the most bacteria out of them all.

The data shows that an apple slice that is on the floor for 30 seconds averages out to have the most colony's (spores) of bacteria. Trial 1 (30 seconds) had an end amount of 41 spores, trial 2 had 27 and trial 3 had an amount of 15 but had an area where there were tiny specs of black bacteria that measured to be 5 cm. That compared to 10 seconds is a lot less with trial 1 having 15 and trial 2 having 16 and finally trial 3 ending with 5  comparing that to an average of 30 colony’s with the thirty second trials. The petri dish with the least amount of colony’s was the control (no time on the floor) (trial 3) with 3 colony’s and the two other trials with 9 colonies. The most surprising was 5 seconds trial 2, which had 56 bacteria. This bacteria was where the swab was stroked and looked like they were growing in dotted lines which made it have lots of bacteria. Then the two others trial 1 had 4 colony’s and trial 3 had 9 colony’s. Something else that was noticed was the petri dishes with less bacteria dried out faster. That helps prove the background research that bacteria needs a moist environment to grow. Something that could have impacted this experiment would be not keeping a consistent amount of cleanliness on the floor surface.

The experiment showed the apple slice on the floor for 30 seconds will have the most colonies (spores) of bacteria. This makes the hypothesis proven because the hypothesis stated that 30 seconds would have the most colonies of bacteria because it would give the bacteria more time to spread and grow on the apple slice. The background research supports the data collected. One thing that was disproven was the 5 second rule, the apple slices that were dropped on the floor for five (trial 2) 56 collines but the other trials had around 10 collines, this goes to show it really does matter where the apple slices are dropped. This is something that is hard to control because bacteria can move and spread on surfaces. One next step to improve this experiment would be testing more times like 20 or 25 seconds, or even a longer amount of time like 1 minute. Something that could be changed to help this experiment be more accurate would be trying to keep a consistency of the floor cleanliness to get more accurate results. 

This experiment connects to the real world because it tested the five second rule which is a commonly used phrase people use when they drop food on the floor. In this experiment the 5 second rule was disproven. This shows that when you drop a piece of food on the floor it will get some bacteria on it. Which is not a bad thing because it can be good for the human body. It also showed that the spot on the floor impacts the amount of bacteria.

Something that could have impacted this experiment was not keeping a constant amount of bacteria on the floor where the apple slices were dropped. Another thing that could change the results of the experiment there was a mistake making the agar the first time so it had to be remade and  the petri dishes had to be resterilized. When the petri dishes were getting sterilized some of them got dented or warped in the sink. Something else that could have changed the results was not picking the apple slice up at exactly the right. This could have given the bacteria a couple more milliseconds. The cleaner also said it only removes 99.9% of the bacteria which could have left some bacteria on the work space.

Agar, Britannica (December 16 2025)https://www.britannica.com/topic/agar-seaweed-product

What is agar and why is it used in microbiology, Gino biotech (October 23 2024)https://ginobiotech.com/what-is-agar-and-why-is-it-used-in-microbiology/

Bacteria growth plate, Michigan Science Center https://www.mi-sci.org/wp-content/uploads/2020/07/Bacteria-Growth-Plates.pdf

Bacteria, Cleveland clinic (December 2 2022)https://my.clevelandclinic.org/health/articles/24494-bacteria

Incubating and viewing plates, Royal society of biology (October 2011)         https://practicalbiology.org/standard-techniques/incubating-and-viewing-plates

Is the five second rule a urban legend, Daisy Coyle (June 26 2023)     https://www.healthline.com/health/5-second-rule

Fact or fiction?: The five-seconds rule for dropped food, Larry Greenemeier (March 25 2014)           https://www.scientificamerican.com/article/fact-or-fiction-the-5-second-rule-for-dropped-food/

Exploring Germs and Bacteria at Home (DIY Agar Petri Dishes) Experiment, Renee Lacona  https://www.astrazeneca.com/content/dam/az/media-centre-docs/article_files/articles-2020/11229%20-%20AZ-USASEF-Agar-Experiment-v7-STEM-Day-Version-GY-FH.pdf

How to use agar and petri dishes, Home science tools resources center https://learn                    Don’t let microbes walk all over your floor, Microban   https://www.microban.com/blog/dont-let-microbeShe'ss-walk-all-over-your-floors

Cutting boards of plastic and wood contaminated experimentally with bacteria  https://pubmed.ncbi.nlm.nih.gov/31113021/

Thank you to: - My Mom and dad for gathering my materials and helping design my incubator - My teacher Miss.Kelly for reviewing my work and giving me helpful advice - Mr.Bykovshikh for helping me with getting on the CYSF cite and helping answer my questions