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A study of Osmosis in plant cells

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Introduction

A study of Osmosis in plant cells Introduction In my following investigation, I will be studying osmosis. Osmosis is the process whereby water molecules pass across a semi permeable membrane from a less concentrated solution in to a higher concentrated solution. Because the holes in the membrane are very small, only small molecules can pass through them. For example, water is a small molecule, and sucrose is a big molecule, only the water can pass through the semi permeable membrane. When the two solutions either side of the membrane are of equal concentrations, the water does not stop moving through the membrane, there is just a net movement from each side. If you have two solutions of different concentrations, the solution with the higher concentration is said to be hypertonic and the solution with the lower concentration is said to be hypotonic. When the concentrations of the two solutions are the same, it is said to be isotonic. The exact concentration of the solutions when they are isotonic is known as the isosmotic point. If a semi-permeable membrane separates a hypotonic solution and a hypertonic solution, the water molecules will pass from the hypotonic to the hypertonic solution by the process of osmosis, turning it into an isotonic solution. Hypertonic Solution Hypotonic Solution Isotonic Solution I will be conducting an experiment, to test how Osmosis works, on plant tissue. Planning I will be investigating how the length of plant tissue will change when I put it in different concentrations of a solution. ...read more.

Middle

I conducted a preliminary experiment, to investigate what concentrations to use. I decided that I would base many of my concentrations around the isosmotic point. The isosmotic point is when the concentrations of both solution and the chip are the same or Isotonic; this means the chip will neither grow nor shrink. The isosmotic point was 0.3 molar; the concentrations I decided to use are below. My concentrations table Results Table Concentration Initial Length Final Length Change in Length Average Change Average %change (Molar) mm mm mm mm (%) 50 46.0 -4.0 1 50 45.5 -4.5 -4.5 -9.0 50 45.0 -5.0 50 45.5 -4.5 0.8 50 46.5 -3.5 -3.7 -7.3 50 47.0 -3.0 50 48.5 -1.5 0.6 50 48.0 -2.0 -2.3 -4.7 50 46.5 -3.5 50 48.5 -1.5 0.5 50 46.0 -4.0 -2.2 -4.3 50 49.0 -1.0 50 48.0 -2.0 0.4 50 51.0 1.0 -0.8 -1.7 50 48.5 -1.5 50 49.0 -1.0 0.3 50 50.5 0.5 0.2 0.3 50 51.0 1.0 50 51.5 1.5 0.2 50 51.0 1.0 0.8 1.7 50 52.0 0.0 50 52.0 2.0 0 50 53.0 3.0 1.8 3.7 50 50.5 0.5 These results were collected at 24�C. Analysis By examining the graph I can conclude that my quantitative predictions were correct, when the concentration of the sugar solution was more than 0.27 molar (the isosmotic point), the chip shrunk and became flaccid. This process is called plasmolosys. This was because the chip had a lower concentration of sugar than in the solution, so by the process of osmosis the water moved from the chip into the sugar solution. ...read more.

Conclusion

I would use a burette instead of a measuring cylinder. This would make my measurements of the sugar solution and water much more accurate. 2) I would conduct the experiment with a narrower range of concentrations. The burette would enable me to do this easily. 3) I would get all my chips from the same potato. 4) I would take the mass the chips using a balance, instead of measuring the length. This method would be quicker, much easier and more accurate. Extension To extend the previous enquiry, I would repeat the experiment with different types of plant cells, probably an apple or a carrot. I might also repeat using a different part of the potato plant, the stem for instance. It would also be interesting to put a potato in different concentrations of a salt solution. It would be good to repeat the experiment using plants that live underwater, for example seaweed and pondweed, and seeing how they react when placed in both salt water and fresh water. It would be interesting to conduct this experiment with an animal cell, for instance a strip of chicken. As animal cells do not have cell walls, they do not become turgid in the same way that a plant cell does. It would be interesting to observe what would happen to an animal cell in a hypotonic solution. I expect it might explode without a cell wall. In a hypertonic solution it would shrink. I have seen a slug dehydrate and turn to mush when covered in salt. I now think that this is due to osmosis. ...read more.

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