Essay: No evidence to support correlation between temperature and rate of osmosis

Abstract
Temperature could significantly affect many biological processes. The purpose of this experiment was to determine if temperature also had an effect on the rate of osmosis, one of the many biological processes that are crucial to living organisms. Dialysis bags containing premade starch solution were placed into beakers of water that were each at different temperatures. These bags were weighed, and the change in mass between each time interval helped determine the rate of osmosis. The results of the experiment did not support hypothesis. Change in mass for the bags at each temperature was similar and had no significant difference. There was no major evidence to support the correlation between temperature and rate of osmosis.
Introduction
Diffusion is a significant biological process for living organisms. It allows important molecules, necessary for cellular process, to pass the through cell membrane (Beals, Gross, & Harrell, 1999). Osmosis is a form of this diffusion process. Osmosis is defined as the movement of water molecules from low solute concentration to high solute concentration (Gutzler and Brewer, 2018). These processes are affected by many factors like pressure, temperature, membrane thickness, and surface area (“RATE OF DIFFUSION,” n.d.).
It is important to know the reason why these factors affect diffusion and osmosis. For example, temperature and pressure affect these processes because they affect the kinetic energy of the molecules (“RATE OF DIFFUSION,” n.d.). Also, it is important to know which molecules are able to pass through in diffusion. Through normal diffusion, only small molecules are able to pass through the membrane by passive transport, a transport that does not require energy (Gutzler and Brewer, 2018). This leads to the questions that this experiment will answer: will temperature have an effect on the rate of osmosis of a starch solution, and will starch be able to diffuse through a cellular membrane?
Higher kinetic energy increases the rate of diffusion (“RATE OF DIFFUSION,” n.d.). The hypothesis is that if temperature has an effect on the rate of osmosis, then there will be a greater rate of osmosis when the surrounding temperature is higher. This hypothesis is tested in the following ways. Clamped dialysis tubing will represent the cellular membrane. Starch will represent the solute inside the dialysis tubing. Water in the beakers will have different temperatures (cold, room temperature, and warm) to represent water on the other side of the membrane, and the tubing will be placed in those beakers. The masses of the dialysis bags are measured to determine the rate of osmosis because if osmosis occurs, the masses of the bags will become greater than their initial masses. The negative control experiment is the beaker at room temperature because room temperature represents no occurrence of temperature change.
Methods
Preparation of Beakers
Beakers of different temperatures were prepared. About 400 mL of water were added to each beaker. One beaker, representing warm temperature, was heated on the hot plate to 40°C. The beaker representing cold temperature was placed into an ice bath until the temperature lowered to 10°C. The beaker representing room temperature was set aside in an environment at 20°C.
Preparation of Dialysis Bag
To prepare the dialysis bags, 3 mL of pre-made starch solution were transferred into each bag, and the open ends of the bags were sealed with clamps. The starch-containing dialysis bags were weighed for initial mass, and each bag was placed into each beaker with different temperatures.
Observing Osmosis
Osmosis was observed for a total of 45 minutes. At every fifteen-minute intervals, the bags were taken out of the beaker, slightly dried with a towel, and weighed. Using transfer pipets, one mL of water from each beaker was transferred to test tubes where iodine test was performed. The bags were placed back into the beakers for another fifteen minutes. This process was repeated until the 45-minute period had passed.
Results
The mass increased for all temperatures at the 15-minute interval, indicating that osmosis did occur, and the weight of the dialysis bag at cold temperature increased the most (Table 1). At the 30-minute interval, the weight of dialysis bag at cold temperature decreased, while the masses of the bags at both room temperature and warm temperature slightly increased. At the last time interval, the mass of the dialysis bags slightly decreased for all temperatures (Table 1).
Iodine tests were performed on the beaker water outside the dialysis bags at each time interval to determine if diffusion of starch would occur. The negative results indicated that no starch was present in the beaker water at all temperatures and time intervals (Table 2).
Table 1. Weight of Dialysis Bags at Each Time Interval During Osmosis.
Weight of Dialysis Bags (in g)
Cold Temperature Room Temperature Warm Temperature
0 minutes
(beginning) 17.4 g 17.7 g 17.5 g
15 minutes
19.6 g 18.7 g 18.6 g
30 minutes
18.9 g 19.0 g 18.9 g
45 minutes (end) 18.8 g 18.5 g 18.5 g
The weight of each dialysis bag was recorded every fifteen minutes for a total of 45 minutes. The changes in weight between each interval was used to determine the rate of osmosis.
Table 2. Results of Iodine Test.
Indicator Test Result (+ or -)
Cold Temperature Room Temperature Warm Temperature
0 minutes — — —
15 minutes — — —
30 minutes — — —
45 minutes — — —
Iodine test was performed to determine if starch diffused out of the dialysis bag. A “+” indicated presence of starch outside the dialysis bag, and a “—” indicated that no starch was present.
Discussion
The hypothesis was that if temperature had an effect on the rate of osmosis, then there would be a greater rate of osmosis when the surrounding temperature is higher. However, no significant correlation existed between temperature and the rate of osmosis. There were no major differences in the rate of osmosis, if any, between the different temperatures, so the hypothesis was not supported. Overall, the observed results were different than the expected result of faster osmosis rate at high temperatures. Lastly, the negative iodine test results showed that starch did not diffuse out of the dialysis bag at all temperatures and time intervals.
However, there were some possible errors. First, the drastic mass change in the cold-water dialysis bag during the first 15-minute interval was likely human error caused by incomplete drying of the bag. The excess water still attached to the bag caused the mass to increase. Also, the starch solution was pre-made. There was a chance that the concentration of starch in each dialysis bag were distributed unevenly because starch is a large and nonpolar molecule (Gutzler & Brewer, 2018), so it cannot dissolve in water. The dialysis bag at room temperature might have had a higher starch concentration than the bag at room temperature. The higher concentration of starch at room temperature might have caused a faster rate of osmosis than warm temperature.
To further this research, the experiment should be repeated once for more accurate results. The concentration of starch in each bag should be carefully calculated to make sure that each bag contains the same amount of starch. Instead of starch, the hypothesis can also be tested using other macromolecules like fats that are also too large to diffuse through membrane (Gutzler & Brewer, 2018). It is also possible to test osmosis and diffusion simultaneously if sugar is used. A sugar molecule is small enough to diffuse through the dialysis tubing (Gutzler & Brewer, 2018). If there were no limitations, other methods of measuring osmosis could be utilized for more accuracy. A positive control experiment could also be useful in furthering this research.
Literature Cited
Beals M., Gross L., & Harrell S. (1999). DIFFUSION THROUGH A CELL MEMBRANE. Retrieved from http://www.tiem.utk.edu/~gross/bioed/webmodules/diffusion.htm
Gutzler SJ, & Brewer MW. (2018). Principles of Biology: BIOL 2107/2108 Laboratory Manual (4th ed.). Plymouth, MI: Macmillan Learning Curriculum Solutions.
RATE OF DIFFUSION ACROSS THE MEMBRANE. (n.d.). Retrieved from https://www.pathwayz.org/Tree/Plain/RATE+OF+DIFFUSION+ACROSS+THE+MEMBRANE
2019-2-11-1549927770