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Osmosis - how does the concentration of water affect the mass of a potato?

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Introduction

Biology Coursework Osmosis- how does the concentration of water affect the mass of a potato? Abubakar Hatimy Aim: - My aim is to find the percentage change of mass when a small piece of potato is placed in to molar sucrose solution Apparatus: o Molar sucrose solution 0.0 - 0.5 o Potato o Cutting board o Knife o Weighing machine o Glass test tube o Glass test tube holder Plan: - My plan is too find the percentage change of mass of a small piece of potato when placed in to molar sucrose solution by using osmosis. Osmosis is explained below Osmosis Osmosis is the passage of water molecules from a region of their high concentration to a region of their low concentration through a partially permeable membrane. It is best regarded as a form of diffusion in which only water molecules move. For example look at Figure 2. The solute molecules are too large to pass through the pores in the membrane, so the movement of water molecules can only achieve equilibrium. Solution A has the higher concentration of water; so there will be a net movement of water from A to B by osmosis. At equilibrium there will be no further net movement of water. The tendency of water molecules to move from one place to another is measured as the water potential, represented by the symbol ?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? ...read more.

Middle

is ?s. for a solution, ? = ?s. Pressure potential, ?p If pressure is applied to pure water or a solution, it water potential increases. This is because the pressure is tending to force the water from one place to another. Such a situation may occur in living cells. For example, when water enters plant cells by osmosis, pressure may build up inside the cell making the cell turgid and increasing the pressure potential. Also, water potential of blood plasma is raised to a positive value by the high blood pressure in the glomerulus of the kidney. Pressure potential is usually positive, but in certain circumstances, as in xylem when water is under tension (negative pressure) it may be negative. Summary Water potential is affected by both solute potential and pressure potential, and the following equation summarises the relation between the two terms. ? = ?s + ?p Water Solute Pressure Potential Potential Potential Solute potential is negative and pressure potential is usually positive. Osmosis and plant cells The partially permeable membranes of importance in the water elations of plant cells are shown in figure 1. The cell wall is usually is freely permeable to substances in solution, so its not important in osmosis. The cell contains a large central vacuole contents, the cell sap, contribute to the solute potential of the cell. ...read more.

Conclusion

Firstly, I could have made the project better by doing more experiments so that the average results would be more accurate. I only did two experiments so the experiment was accurate by it self but the whole project was not a fair experiment. I could have probably done three more experiments to be accurate. Secondly, what I could have also done to make my experiment better is that I could have timed the small pieces of potato so that they were in the solution the same time and the osmosis processing time will be the same and the potatoes would have a fair experiment., I reckon that this was one of the reasons that the experiment was not so accurate. Thirdly, I should have cut the pieces of potato as the same weight for all. This would have made the experiment simpler to understand and this would have become more accurate experiment. The osmosis process would have worked equally because they all had the same mass, therefore the experiment would be more accurate. 1 Technically ? means potential and water should be presented ?w. Since in living systems the solvent we are concerned with is always water, it is simpler to use ? and assume the w. 2 Pressure was formerly measure in atmospheres (atm), but now Pascal is used (Pa). 1 Pa = 1NM-2 (N = Newton) Abubakar Hatimy Biology Coursework-Osmosis. Page 1 ...read more.

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