February 27, 2024
By Harper Gillespie & Kayleigh Cottrell
In the past few weeks, we have had exciting opportunities to expand our knowledge of osmosis, plasmolysis, and learn coding using R. These labs have been a lot of fun and helped us improve existing skills while gaining new ones. The goal of our osmosis demonstration using potatoes was to replicate hypertonic and hypotonic cells. Hypertonic cells occur when the substance outside of the cell has a higher concentration than inside the cell. As a result, water will move out of the cell to balance out the concentration. Hypotonic cells occur when the substance inside the cell has a higher concentration than outside. Consequently, water will move into the cell to balance it out. However, isotonic cells occur when the concentration outside and inside of the cell remains the same.
The osmosis demonstration experiment began by mixing solutions of various salt concentrations (1%, 3%, and 5%) with distilled water. Distilled water and the salt solutions were added to four tubes. Twelve potato cylinders were cut and three of them were then added to each test tube within their correct solutions. The beginning mass of the potatoes in distilled water, 1% salt, and 5% salt was 3.9g and the beginning mass of the potato 3% salt was 4.0g. The potato cores were then left within their given solutions for 96 hours, after which their color, flexibility, texture, and strength were analyzed. The potatoes varied in their flexibility and consistency. The mass changed in distilled water by –1.8g and +0.2g for the 1% salt solution. The mass of the 3% salt solution and the 5% salt solution changed by –0.8g. The data showed that distilled water caused the cores to lose the most weight due to hypotonicity; however, since the 96 hours exceeded the given time, the water built up within the potatoes and caused them to burst. The potatoes in the 5% salt solution should have lost the most weight due to the hypertonicity of their environment.
Figure 1. Harper observing the Elodea leaf cells in freshwater.
For the plasmolysis lab, we prepared a microscope slide using one Elodea leaf. Plasmolysis is when a plant cell loses water, and it causes the plasma membranes of the cells to shrink. To do this, we observed the leaf before, with regular pond water on it. The cells were not shrinking because they were at an equal concentration (isotonic). To create plasmolysis, we placed a paper towel at one end of the slide to draw out the freshwater and dropped salt water at the other end of the slide. The paper towel drew out the freshwater causing the salt water to move into the leaf. Then, on the monitor, we could observe that the plasma membranes in the cells were shrinking. This process would be considered hypertonic because the water was moving out of the cells to try to balance the saltwater outside. We repeated the process with a paper towel on the leaf slide to draw out the salt water and add fresh water again. We then were able to watch the plasma membranes expand as they took in water.
Figure 2. Kayleigh observing the Elodea leaf cells after salt water was added, noticing a lot of shrinkage.
Also, we had the opportunity to learn about biogeography using R, a programming language that helps us interpret and organize data. Each of us acquired our data on different species (Kayleigh- Syringa reticulata, Harper- Parthenocissus quinquefolia) and obtained geographical data for the species, finding their native occurrences. We then applied R to extract and analyze the data, correlating the coordinates of the species occurrences with climate data. The climate data we used included annual mean temperature, annual precipitation, and more. We analyzed these data points to determine whether our species was well-suited to its native range or if there was any unique or out-of-place data.
So far, our experiments have been successful. Understanding hypertonic, hypotonic, and isotonic using potatoes was interesting and beneficial. Additionally, the Elodea plant was particularly fascinating to observe, as we could physically witness the cells shrinking and moving due to the salt water. It was successful in displaying plasmolysis. Lastly, the use of R was initially confusing to us, but we hope to improve our skills in working with it.
