September 27, 2010
When a plant is placed in a hypertonic solution, the environment is more concentrated then that of the cell’s internal environment, the cell will lose water, shrinking and becoming flaccid a process called plasmolysis. When a plant is placed in a hypotonic solution, the cell’s internal environment is more concentrated then that of the surrounding solution, water will rush inward and the cell will swell and expand, keeping the cell walls turgid. In plant cells, the cell wall restricts too much expansion, which results in the build up of turgor pressure. When the turgor pressure becomes high enough it will prevent any further movement of water into the cell. This information helps scientists determine the ideal water content the plant will need for maximum growth and productivity.
The goal of the experiment was to determine the osmolarity of plant cells. This was determined by cutting seven tissue samples from a potato, cutting them to equal lengths, and then weighing them. Each sample was then placed in one of the seven known molarities of sucrose solution ranging from 0.0M to 0.6M and incubated for 1.5 hours. The weight after incubation was recorded and then compared to the original data. To determine the osmolarity of the tissue sample, a graph was constructed with the data from the experiment. From the graph, a curve was constructed that could be used to find the point at which weight change in the potato did not occur. Given the information from the graph, the osmolarity of the potato is at 0.2M.
According to the textbook, Principles of Human Physiology, diffusion is the process in which molecules move from a high state of concentration to a state of lower concentration (Germann, Stanfield, 103). Diffusion plays an important roll in the life of a plant cell. Without diffusion a plant cell could not maintain equilibrium between the internal environment of the cell and it’s external environment. The type of diffusion plant cells use to maintain the state of the cell is called osmosis, which is the passage of water from a high concentration of solution through a semi-permeable membrane to a lower concentration of solution. There are three terms used to describe the relative concentrations of solutions separated by the semi-permeable membrane of the plant cell, hypertonic, hypotonic, and isotonic (Kepler, Marvel, 355). For example, if you put a plant in a solution of water, one of three things will happen:
The water surrounding the plant is very dilute and less concentrated then that of the water in the cell itself, so water will diffuse inward, causing swelling and weight gain. This is an example of a hypotonic solution.
The surrounding water has a very high concentration compared to the water in the plant cells so in order to create equilibrium the cell will release water to its environment, resulting in the cell shrinking and losing weight. This is an example of a hypertonic solution.
The surrounding water and the water in the cell have the same concentration so the same amount of water that is flowing in the cell is flowing out of it and an isotonic state is reached and there will be no weight change. This is an example of a isotonic solution.
Osmolarity is important to the survival of plants. When a plant is in an environment that is more concentrated relative to the cell’s internal environment, the cell’s water will diffuse out to achieve equilibrium. The loss of turgor pressure in the plant cells causes the plant to become flaccid and can eventually lead to plasmolysis. When a plant is in an environment that is less concentrated relative to the cell’s internal environment, the cell takes up water by osmosis. The taking up of water causes the cell to swell and become stable. The rigid cell wall restricts bursting resulting in increased turgor pressure. Eventually the Turgor pressure of the cell becomes...
References: Oparka, Karl J. and Wright, Kathryn M. “Influence of cell turgor on sucrose partitioning in potato tuber storage tissues.” Planta (1988): 520-526
Spychalla, James P. and Desborough, Sharon L. “Fatty Acids, Membrane Permeability, and Sugars of Stored Potato Tubers.” Plant Phisiology (1990): 1207-1230
Kepler, Megan V. and Marvel, Stephen C. “A Simple Membrane Osmometer System & Experiments That Quantitively Measure Osmotic Pressure.” The American Biology Teacher (2009): 355-362
Germann, William J. and Stanfeild, Cindy L. Principles of Human Physiology (2009)
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