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Find out what effect altering the concentration of sucrose solution would have on the occurrence of osmosis in potato chips.

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Introduction

BIOLOGY An Experiment to Investigate Osmosis Aim To find out what effect altering the concentration of sucrose solution would have on the occurrence of osmosis in potato chips. Background Osmosis is the net or overall movement of solvent molecules (often water) from an area of higher concentration to an area of lower concentration through a semi-permeable membrane (often called selectively permeable or partially permeable membrane). Substances often move from an area of higher concentration to an area of lower concentration by diffusion, the result of random particle movement. In osmosis, two solutions are separated by a membrane that will only let the solvent particles pass through. This means that the solvent continues to move freely along a concentration gradient. However, the other substance involved (solute) cannot move freely because the particles are too large and cannot pass through the membrane. This means that although there is random movement of the solvent molecules in both directions across the membrane, there will be a net movement of solvent into the area where it is at the lowest concentration, in other words, into the solution containing the highest levels of solute. Terms related to osmosis are: Turgid and Flaccid. Turgid cells contain lots of water due to the diffusion through the vacuole. The cell becomes a lot firmer or even swells because it has taken in so much water, the cytoplasm and cell membrane push up against the cell wall. ...read more.

Middle

Above is a diagram to show osmosis across a partially permeable membrane: Water molecules are smaller than the sugar molecules, they are able to fit/pass through into the cell. But the movement of the water cells becomes restricted nearer the extreme concentrations due to a rigid cell wall. This is not like a cell membrane as it neither expands nor decreases. The reason they put on weight is that they are filled with extra water and the vacuole is removed in one state. When the cell is expanding from its original shape due to excess water this state is called turgid. When it is decreasing due to water traveling out of the cell, this state is called cremating. Fair test To keep my experiment a fair I must keep a control of all the equipment used and use the same method, making sure that the variable factors I have explained earlier remain at a constant. To ensure that the genetic make up of the potato chip is as similar as possible I will use the same type of potato from the same bag assuming they have similar membranes. So the potato chips have a similar surface area I shall cut them from the same cross section of each potato. I am going to make sure that the volume of the sucrose solution is the same at 25ml. I will change the concentration of this 25ml solution. ...read more.

Conclusion

The potato rod decreased in length because that hypertonic concentration had a lower level of water than the potato cells. Again, osmosis took place and the water molecules diffused from the potato cells into the sucrose solution. I predicted that when the sucrose solution was about 0.45, molar, the potato rod would remain the same length. From my graph I can see that this is true. This occurred at 0.46 moles, this is the concentration of sucrose solution in the vacuoles of the cells before the experiment started. The solutions are isotonic, so osmosis will take place but there will be no net movement of water molecules. Evaluation: I am pleased with the way the experiment went and I am confident about the results produced. However, to make the test more accurate, I could have used a different method of cutting and measuring the potato rods, other than a cork borer and ruler. If I had used a scalpel for example, this would have given me a greater degree of accuracy. I could have also used the intermediate concentrations in my experiment. These are: 0.1, 0.3, 0.5, 0.7, and 0.9. Adding these would have made my test more accurate. I noticed that at the concentrations 0.8 and 1.0 moles, the potato rods began to float. This affected the accuracy of the investigation as the whole rod was not completely submerged. I think that I should have used a utensil to push down the potato rod and hold it down for the duration of the experiment. If I had made these adjustments, I would have produced a more precise measurement. Zeiad Freijeh Biology ...read more.

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