GRADIENT USING SUCROSE AND DIALYSIS TUBING

Osmosis is diffusion of water across a differentially permeable membrane in

living organisms and is vital to the functioning of living cells. Osmosis can be simulated by using dialysis tubing; each bag represents an individual cell. This experiment was to determine the flow of osmosis in various types of environments: hypertonic, hypotonic, and isotonic. In order to do this, each dialysis bag was filled with 10 ml of 1%, 25%, or 50% sucrose respectively, weighed, and then placed in two beakers of 50% or 1% sucrose concentrations. The movement of water was tracked by weighing the bags 4 times in one hour. It was found that bags with a lower concentration of sucrose than the environment (Bag A) lost weight. Bags with higher concentrations of sucrose (Bags C&D) gained weight. The bag with the same concentration as the beaker (Bag B) also gained weight. Thus, water moved from areas of low sucrose concentration to areas of high sucrose concentration, which supports the hypothesis that osmosis moves from hypotonic solutions to hypertonic solutions.

The cell is the basic unit of life. Without cells, we would no

Bag C was filled with sucrose solution with a concentration of 25% and placed in a beaker of 1% sucrose concentration. Because Bag C's solution was more concentrated than that of the beaker, Bag C was considered hypertonic to its environment. According to the hypothesis, Bag C should have increased in weight. As shown by Figures 1 and 2, that was what happened. The weight of Bag C increased as time passed, which meant that the water in the beaker moved into to the area of higher concentration, the bag.

The dialysis tubing provided a good simulation of osmosis across a plasma membrane, because the dialysis bags possessed pores that were small enough for water but not large enough for larger macromolecules (such as the solute, sucrose) to pass through. Thus, they were a very good example of a differentially permeable membrane.

Bag B did not remain at the same weight, but experienced an increase of .1 g. This is a very small increase, and can be attributed to a number of factors. Perhaps the dialysis bag was not tied tightly enough, and sucrose managed to leak in. Perhaps the bag was not dried thoroughly enough before the second, third, and fourth weighings. Also, osmosis can be affected by diffusion. In a study by Yao and Le Maguer with potato cells in mannitol, the bulk flow transported about 90% of water removed in osmotic dehydration and washed back about 60% of mannitol penetrating by diffusion (1996). Perhaps the unexpected increase is due to diffusion of the solute, sucrose, acting against the osmotic flow of water.

Table 1 shows the total weight of each dialysis bag with respect to time. Weight was measured in grams. Time was measured in minutes. Figure 1 is the corresponding graph to Table 1. Each curve in Figure 1 represents a different bag. Bag A is blue, Bag B is red, Bag C is green, and Bag D is violet.

t exist. To study life, one must first start at the foundation of life: the cell. For a cell to exist there must be something, some sort of structure, which regulates the flow of materials and liquids into and out of the cell. For both prokaryotic, (bacteria,) and eukaryotic, (all other organisms,) cells, that structure is called the plasma membrane. And that regulation is passive transport, which relies heavily on a little thing called osmosis.

The intent of this study was to determine the flow of osmosis across a semi-permeable membrane such as the plasma membrane of cells. It was hypothesized that the dialysis bags with higher (called hypertonic) concentrations of the solute, sucrose, would experience an increase in weight- a condition called lysed, while the bag or bags with the lower (called hypotonic) concentrations of sucrose would experience a decrease in weight- which is known as crenate. Any bags with a solute concentration approximately equal (called isotonic) to the solute concentration of

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Approximate Word count = 1935
Approximate Pages = 8 (250 words per page double spaced)