Department of Biology
Grand Valley State University
1 Campus Drive
Allendale, MI 49401
The lab for this paper was conducted for the topic of osmosis, the movement of water from high to low concentration. Five artificial cells were created, each being filled with different concentrated solutions of sucrose. These artificial cells were placed in hypertonic, hypotonic, or isotonic solutions for a period of 90 min. Over time, the rate of osmosis was measured by calculating the weight of each artificial cell on given intervals (every 10 minutes). The resulting weights were recorded and the data was graphed. We then could draw conclusions on the lab. Introduction
Diffusion and Osmosis are two concepts that go hand in hand with each other. Diffusion is simply described as the movement of a substance from a region of high concentration to a region of low concentration. In another words, the substance will move down its concentration gradient which is “the region along which the density of a chemical substance increases or decreases” (Campbell Biology pg. 132). If you understand the concept of diffusion then osmosis is a very simple process. It can be defined as the diffusion of water across a permeable membrane. Osmosis can be cellular or artificial, so even though we are creating artificial cells in this lab, it is still considered to be osmosis. During osmosis, a solvent is trying to get through a selectively permeable membrane to make the concentration of that solvent the same on both sides of the membrane. The rate of osmosis depends on the type of environment the cell is in. There are three different environments that a cell can find itself in, a hypertonic environment, a hypotonic environment, or an isotonic environment. The environment a cell is in will determine its tonicity which is “the ability of a surrounding solution to cause a cell to gain or lose weight” (Campbell Biology pg. 133). “In a hypertonic solution, the cell will lose water, shrivel up, and most likely die” (Campbell Biology pg. 133). The reason this happens is because there is a higher concentration of water in the cell then there is in the environment the cell is in. Like I said before, water travels down its concentration gradient from high concentration to low concentration. So the water inside the cell will cross the membrane and enter into the solution outside the cell and it will continue to do this until the concentration inside the cell membrane and outside the cell membrane are equal. The opposite of this would be if the cell was in a solution that is hypotonic to the cell. In a hypotonic solution, “water would enter the cell faster than it leaves and the cell will swell up and lyse (burst)” (Campbell Biology pg. 134). This will also cause the cell to die. Both a hypertonic and hypotonic solution are very harmful to cell and in most cases will cause the death of the cell. A solution that a cell wants to be in is an isotonic solution. If the concentration of water in the cell and in the surrounding environment is equal, there will be no net movement of water across the membrane and therefore the cell will not shrivel up or swell up. ). An experiment has been conducted to find out whether or not osmosis is occurring by using artificial cells made of dialysis tubing. To test this hypothesis the experiment will show the change in weight of each artificial cell across a 90 minute time span. The experiment will also show which type of environment (as previously stated) each cell is placed in and taken out of to be weighed. Materials and Methods
This experiment will look at the effects of various sucrose concentrations on the rate of osmosis in artificial cells made up of dialysis tubing. To begin the experiment one strip of dialysis tubing will be filled with 10mL of tap water, the second will be filed with 10mL of 20% sucrose, the third...