BIOL 1208 Lab Report Cover Sheet I certify that the writing in this assignment is my individual work and is my sole intellectual property. It does not contain the ideas or writing of other individuals/authors. Matthew Landry______________________ _______11/18/11______________ Author Date _____20_____ Lab Section #
The Effect of Sucrose Concentration on the Relative Osmotic Concentration in Potato Tubers Abstract This lab was conducted in order to determine the molarity of sucrose concentration where the mass of potato tuber segments does not change, indicating an isosmotic concentration. By calculating the change of mass of the potato tuber cells prior to incubation against the mass after incubation in the sucrose solution, our goal was to determine what type of osmotic concentration was created as compared to the potato tissues. The results of our lab indicated three different osmotic concentrations. According to our data, the isosmotic concentration, of a potato tuber disk is around 0.175M. At this sucrose concentration the sucrose solution is isotonic relative to the potato tissues. Anything lower than the isosmotic concentration resulted in a hypertonic concentration. Additionally, anything higher than the isosmotic concentration resulted in a hypotonic solution. Introduction The purpose of a biological membrane is to control the internal environment of a cell. A cell can be surrounded by millions of molecules at any given time, and it is up to the membrane to control what enters and what leaves a cell. Water is the single most important molecule in any living system. Due to water’s small size, it passes through biological membranes with ease even though water is a polar molecule. Water molecules are moving across the cell membrane at all times, and the when more water molecules are traveling in one direction than the other an osmotic situation occurs. The significance of this lab is to determine the relative osmotic concentration of disk of potato tubers that are incubated in different sucrose solutions and to determine at which concentration the mass of the tissues does not change. This will allow us to better understand of osmotic responses and water balance in biological systems. Our null hypothesis for the lab was that our treatment
in varying sucrose solutions would have no effect on the potato tuber’s osmotic concentration. Our alternative hypothesis was that our treatment in varying sucrose solutions would have an effect on the potato tuber’s osmotic concentration. Materials and Methods To begin our lab we gathered six potato tuber segments and used a razor blade to cut all of the segments, each approximately 4cm in length. Next, we cut one of the segments into thin disks approximately 2mm in thickness. We placed the other segments in a moist paper towel to prevent them from drying out. We then placed the disks from the first segment into a beaker and washed off any surface starch. We then blotted off the surface water with a dry paper towel. Next, we calculated the mass of an empty weight boat. We then transferred the potato disks into the boat and determined the mass to the nearest 0.1g. We then placed the disks into a beaker with 100mL of deionized water. We then repeated the steps with the remaining five potato segments; however, we placed the disks from the each new segment into different sucrose concentrations, 0.1M, 0.2M, 0.3M, 0.4M, and 0.5M. We then incubated all the disks, in their various concentrations for one hour, swirling the beakers every ten minutes. At then end of the one-‐hour period, we removed the disks from their concentration. Next, we blotted off any surface water with a dry paper towel. We placed the disks into the weight boat and measured the mass on a scale. Finally, we calculated the percent change in mass by diving the change in mass by the initial mass then multiplying by one hundred. Results Based on the data from the six treatments a regression line was formed. The percent change in mass of the potato cells is positive when incubated in concentrations of 0.0, 0.1, and 0.2 M of sucrose. At these three concentrations, a hypertonic environment was observed within the cell. The percent change in mass of the potato cells is negative when incubated in concentrations of 0.3, 0.4, and 0.5M of sucrose. At these three concentrations, a hypotonic environment was observed within the cell. According to the data, a line of best fit crosses the x-‐axis where an isotonic
relative osmotic concentration is achieved. An isotonic solution was achieved when the sucrose solution is around 0.175 M. Based on the results from the experiment, our alternative hypothesis was correct.
The Effect of Sucrose Concentration on the Relative Osmotic Concenctration in Potato Tubers 15.00%
Percent Δ∆ in Mass (g)
10.00% 5.00% 0.00% -5.00%
-10.00% -15.00% -20.00% -25.00% -30.00%
Concentration of Sucrose Solution (M)
Based on the data, the concentration of sucrose at approximately 0.175 M shows no change in the weight of the potato tuber disks indicating an isotonic relationship between the disks and solution. Discussion According to our data, the relative isosmotic concentration of a potato tuber disk is around 0.175M, which is where the sucrose concentration surrounding the cells creates neither a hypotonic or hypertonic environment. If the concentration of sucrose is greater on the outside of the cell, then the net movement of water is out of the potato cells. A hypertonic situation occurs, and the tuber cells experience a loss in mass .In plant cells, the loss of water from a cell causes the cell to shrivel or
undergo plasmolysis. This trend can be viewed when the sucrose concentration was raised over 0.3M. If the concentration of sucrose is greater on the inside of the cell, then the water enters the potato disks. A hypotonic situation occurs outside of the cells, and the tuber cells experience a gain in mass, as the net movement of water is into the cells. In plant cells, this trend is known as turgid pressure. This trend can be viewed when the sucrose concentration is lowered from 0.2M to 0.0M of sucrose. For this experiment the expected isosmotic concentration is 0.3 molar; however, our data does not support this. Some possible sources of error in our experiment include missteps during setup and preparation for the experiment, inaccurately measuring the mass, or other factors.
The Effect of Sucrose Concentration on the Relative Osmotic Concentration in Potato Tubers Matthew Landry LSU Fall 2011 BIOL 1208 - Biology...