Flatworm Lab

Flatworm Lab: Platyhelminthes

Experimental Design: Planaria are free-swimming mostly freshwater flatworms. Flatworms are very unique creatures because they regenerate lost parts. My groups experiment was, The Effect of Darker Regions on Planaria Movement. The purpose of this experiment was to see whether or not the planaria preferred the white region or the dark region. My hypothesis was, If the Planaria are placed on the white side then they will move to the dark side because the planaria have a strong negative geo-tropism and would move away from white side and go to the dark side. The independent variable was the two sides of the petri dish, which had one white region and one dark region. The dependent variable consisted of how many
planaria moved to the dark side. First thing my group did was assemble two petri dishes into one by taping them together and having a hole in between the two petri dishes, so then the planaria can move from one side to another freely.
The petri dishes when combined formed a make-shift reservoir for the planaria. We then filled both petri dishes with 25 ml of water and covered the outsides of each petri dish with a white paper and a black paper. We then placed the planaria on the white side and waited 5 minutes. When the 5 minutes were up we counted how many planaria were on the white side and the dark side, then we put the data found in a table. We then repeated this process two more times to get more accurate readings. Our constants in this experiment were, 5 minutes per trial, planaria were placed in the middle of the white section, petri dishes, colored paper, elevation of petri dishes, room temperature, and same type and amount of water. To see if our hypothesis was valid
more than 50% of the planaria had to move to the dark side.
Horizontal view of the hole in the petri dish where the two petri dishes are combined
Overhead View of petri dish

Data Collection:

Number of Planaria in Dark Side | Trail 1 | Trial 2 | Trial 3 | 4 | 3 | 4 |

When we were conducting our trials we observed many things that the planaria did. I observed that when a planaria was placed on the white side it curled up into a ball then uncurled and went to the brown side. I believe they did this because many platyhelminthes have a taxis reaction to light since, it exhibits an innate behavior where the movement into a ball is a automatic reaction. When we poured the 25 ml of water into the petri dish, it filled just enough of the petri dish so then the planaria can move around more freely and live. When water leaked from the petri dish, some of the planarians followed it because planarians are very hydrophilic. Also I observed that when the planarians were surrounded by little amounts of water they would become very small. The planarians were also very flexible, because as I observed them crossing petri dishes they were able to bend there small bodies to get across the small hole.

Data Analysis:

From our data we are able to say that the planaria like darker regions than lighter regions. For trial one we had four planarians go to the dark side and one remain in the white side after the five minutes were up. For our second trial three planarians moved to the dark side and two remained in the white side. For our last trial four planarians moved to the dark side while one remained in the white side. From our data we can see that there was always at least one that stayed in the white, and at least three were in the brown side. I believe the results came this way due to natural selection. When you find platyhelminthes in nature they are usually camouflaged in the dirt and ion dark regions to hide from predators. So by this, the planarians moved to the brown side since it was a lot darker than the white side. With the data my group and I found, I have concluded that my hypotheses was supported since more than 50% of the worms were on the dark side on each of the three trials. During our experiment we were faced with several data manipulations. These manipulations were caused by many random occurrences. One possible way our data got manipulated was from when the planaria escaped the petri dish to follow the water that has leaked. This played a crucial role in trial #2 because one of the planarians escaped right as he was crossing petri dishes to got the brown side. Also the timing, of each trial was very hard to get precise since each trial was probably off by a few seconds since we didn’t have a stopwatch. We used the analog clock in the classroom to time our trials. This effecte4d our trial because it gave different amount amounts of time for each trial, so one trial would be 4 minutes and 30 seconds and another one would be 5 minutes. the extra time would have proved very crucial in trial 2, since that was when the planaria had to be placed back middle. The third error we had that disrupted our scores was the placing of the worms. We would try our best to place the worms in the middle for each trial but we would be off by a centimeter or so each time. This influenced the experiment because it altered the lengths in which the planarians had to move to go to the dark side. If my group and I did another experiment on the same topic I would like to test the Effect of Light on Planarian Movement. This experiment would test how a planarian would move when faced with different radiations of light. Evaluation: The purpose of this experiment was to find The Effect of Darker Regions on Planaria Movement.
We created a small reservoir for this experiment to take place using petri dishes. We used brown paper as a dark side of a petri dish and a whit sheet for the light side. We placed the planarians in the middle of the white petri dish for our trials. in the end of the experiment we found out that more planarians went to the dark side instead of remaining in the white side. From the research I have done on platyhelminthes I concluded that the results came to be by natural selection, and how organisms camouflage themselves to hide from predators by blending in with there surroundings. This idea is supported in the observations I made because since the planarians were darkly colored they moved to a spot with more dark colors instead of being in a place with no color(the white side) and being very visible. My hypothesis, If the Planaria are placed on the white side then they will move to the dark side, was supported in this experiment. it was supported because the majority of planaria moved to the dark side instead of staying in the white side. Even though we made few errors in our project, our results should not be changed so much. If I could have changed the experiment in one way, I would have chosen to use a stopwatch instead of a analog clock to keep the time. I believe my partners in the grouped participated in the experiment equally. I also believe that each person did the same
amount of work as the others.