Osmosis and its Effects on Plant & Animal Cells

 Transport (Osmosis) Lab Report 

Osmosis and its Effects on Plant & Animal Cells

 

Osmosis is the net movement of water across the semi-permeable cell membrane (Libretexts & Malik, 2023). In Osmosis, water will move from a less concentrated solution to an area of highly concentrated solution (Libretexts & Malik, 2023). This movement of water makes the solution with higher solute particle concentration hypertonic, and the opposite is hypotonic, which has lower solute particle concentration (Libretexts & Malik, 2023). Animal cells survive well in an isotonic solution with the same solute concentration (Libretexts & Malik, 2023). When an animal cell is in a hypertonic solution, a process known as plasmolysis happens, thus making the cell shrink and die eventually. In the hypotonic solutions, cytolysis will occur, in which the animal cell will become engorged and eventually burst (Lopez, 2023). Temperature, pressure, and concentration gradient are the three main factors affecting the rate of osmosis (Binod G C, 2023). An experiment was conducted in the lab, and the results are discussed in this report on cell membranes using potato sticks and NaCl solution.  The experiment will help see how osmosis affects the cells and further test how concentration affects the rate of osmosis, and the results are discussed in this report. The hypothesis was that higher salt concentrations would result in more osmosis, and the prediction was that the highest concentration of salt (3M) would result in the greatest change in the potato length.

The experimental methods for testing the effect of concentration in osmosis included making solutions of different salt concentrations, such as 0M, 1M, 2M, and 3M. A potato was cut into four wedges of 5 cm length to be placed in each solution of different concentrations. Those wedges were then completely submerged into each solution and left for approximately an hour for osmosis. Once the time had elapsed, the wedges were measured and observed for other physiological changes.

The results of the experiment are as shown below:   

Salt Solution - Concentration	Mean Percent Change in Length
0M	3.11111
1M	-4.44444
2M	-5.11111
3M	-6.00000

The experiment data on the concentration will affect osmosis. If there were higher solute concentrations, there would be a greater osmosis. This is the hypothesis.  The prediction showed that the potato length change would be the greatest in the 3M solution when osmosis happens. The above-stated prediction and hypothesis were formed because, during the osmosis process, water will move towards the solute, thus decreasing Potato length due to the cells' shrinking. The rate of osmosis is directly proportional to the concentration; as one increases, the other increases.  

0M solution has zero salt in the solution, as it is a 0M (M-Molarity) salt solution. This means it is water-based with no significant salt concentration. The mean percent change in potato length for the 0M solution was 3.1111. There was not expected to be any discernable change in potato length, but we noticed a change when the potato wedge was submerged in 0M solution. There should not be a change because the solution has zero salt concentration. This solution is a control group that differentiates from the experimental group. Still, a change was observed due to potential human error in cutting and measuring the potato wedges.  

The 1M solution was made using 58.44g of salt and 1L (1000 mL) of water. (Yu & Wellesley.edu, 2004). The mean length percent change in the potato wedge for the 1M solution was -4.44444. A change in length was observed as expected, due to the presence of salt in the solution. Based on the data, osmosis has occurred, and the wedge has shrunk due to being submerged for over an hour in the hypertonic 1M solution.

The 2M solution was made using 116.88g and 1L(1000mL) of water (Alvanipour, 2016). The mean length percent change in potatoes for the 2M solution was -5.11111. It was predicted that a greater change in the length would be observed for the 2M solution, and the salt concentration was higher than 1M. Based on the data, as expected, and due to the increased amount of salt in the solution, osmosis occurred at a greater rate, and the wedge shrunk further due to being submerged for over an hour in the hypertonic 2M solution.

The 3M solution was made using 175.32g and 1L (1000mL) of water (Whole, 2023). The mean length percent change in potatoes for the 3M solution was -6.00000. The greatest change in the length was expected for the 3M solution, and the salt concentration was higher than 2M. As expected, and based on the data, and due to the increased amount of salt in the solution, osmosis occurred at the greatest rate, and the wedge shrunk further due to being submerged for over an hour in this hypertonic 3M solution.

The isotonic point is where the line on the graph crosses zero, which indicates zero net movement of water. The point can be calculated using a linear equation's y = mx+b slope-intercept form. The isotonic point for the data from the experiment is the x value of 0.389. To calculate the isotonic point, substitute the y value with 0, then subtract the b or slope intercept value from itself and the zero so the equation is –b=mx. The value is then plugged in the slope value for m and the intercept value for –b. The equation would be –1.0889 = -2.8x. Then, divide the slope from the intercept in the equation to get the x value of 0.389.

Osmosis affects plant and animal cells differently (Libretexts & Bergtrom, 2022). The rate of osmosis always depends on the concentration of solute. Animal cells function optimally in isotonic environments. When placed in hypertonic solutions, animal cells undergo plasmolysis, shrivel, and eventually die due to the absence of a cell wall (Libretexts, 2021a). While animal cells fill up with too much water and burst in a hypotonic solution, plants thrive instead due to osmotic pressure, helping them build up turgor pressure against themselves because of their thick cell walls, thus preventing excess water from entering the cells (Biology Dictionary, 2020). Though they appear to have gone through cytolysis, plant cells will not die but can return to normal quickly. Thus, animal cells are optimal in isotonic environments, and plant cells do best in hypotonic environments (Libretexts, 2021b).

Weaknesses in the experimental process could be human errors in measuring the potato wedges accurately and recording the data precisely. Problems may have occurred due to the preparation of the concentrated solutions as per the measurements defined, such as not taking the accurate amount of salt and water that was needed and or rushing the experiment by not giving enough time for osmosis to happen properly, which could have a direct impact on the outcome and results of the experiment.

 

References 

Alvanipour, S. (2016, October 5). Molarity. ChemistryBytes.com. Retrieved September 26, 2023, from https://chemistrybytes.com/welcome/concepts/solutions/molarity/

Binod G C, B. G. (2023). Osmosis and diffusion: differences and factors affecting them. The Science Notes. https://thesciencenotes.com/osmosis-and-diffusion-differences-and-factors-that-affect-them/

Biology Dictionary. (2020). Osmosis. Biology Dictionary. https://biologydictionary.net/osmosis/

Libretexts. (2021a). 2.1: Osmosis. Biology LibreTexts. https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Introductory_Biology_(CK-12)/02%3A_Cell_Biology/2.01%3A_Osmosis#:~:text=In%20a%20hypertonic%20solution%2C%20a,This%20is%20demonstrated%20inFigure%20below

Libretexts. (2021b). 2.1: Osmosis. Biology LibreTexts. https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Introductory_Biology_(CK-12)/02%3A_Cell_Biology/2.01%3A_Osmosis#:~:text=In%20a%20hypertonic%20solution%2C%20a,This%20is%20demonstrated%20inFigure%20below

Libretexts, & Bergtrom, G. (2022). 17.3: Osmosis. Biology LibreTexts. https://bio.libretexts.org/Under_Construction/Cell_and_Molecular_Biology_(Bergtrom)/17%3A_Membrane_Function/17.03%3A_Osmosis

Libretexts, & Malik, M. A. (2023). 5.5: Osmosis. Chemistry LibreTexts. https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Introduction_to_General_Chemistry_(Malik)/05%3A_Solutions/5.05%3A_Osmosis

Lopez, M. J. (2023, March 13). Physiology, osmosis. StatPearls - NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK557609/

Whole, D. (2023, March 6). How many grams of NaCl are required to make 250 mL of 3m solution? The Donut Whole. https://www.thedonutwhole.com/how-many-grams-of-nacl-are-required-to-make-250-ml-of-3m-solution/

Yu, C. & Wellesley.edu. (2004, July 1). Molar Solutions. Retrieved September 26, 2023, from http://academics.wellesley.edu/Biology/Concepts/Html/molarsolutions.html