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Investigating osmosis

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Introduction

Investigating osmosis Aim: I am going to investigate the mean water potential of potato cells to the point of equilibrium by putting pieces of potato into different concentrations of sucrose solution and recording the change in mass. Prediction: I predict that potatoes immersed in solutions with a water potential lower than (i.e. more concentrated) that of the potato cells, will decrease I mass after being left for a period of time. The potatoes will decrease in mass as water has moved out of the cells through a partially permeable membrane by osmosis. The potato will become flaccid and is said to be plasmolysed. Potato immersed in solutions with higher water potential than that of the cells (i.e. more dilute) will increase in mass (after being left for a period of time) because water has moved into the cell through a partially permeable membrane by osmosis. The potato will become turgid. There will be a point where there is no change in mass. This is where the water potential is equal on each side of the partially permeable membrane. ...read more.

Middle

If the cell is in a solution more dilute than that of the cell, the water potential is higher outside the cell so water enters by osmosis. The pressure builds up inside the cell and the water bursts and dies. However, plant cells do have a cell wall enabling them to keep their structure so they don't burst or shrivel up. If the water potential is higher inside the plant cell, water moves out by osmosis. This causes the cytoplasm and vacuole to shrink and the cell membrane is pulled away from the cellulose wall. The cell is then said to be plasmolysed. If the water potential is higher outside the cell, water moves in by osmosis. The cytoplasm and vacuole become filled with water and press against the cell wall. However, the cell wall prevents the cell from bursting. The cell is said to be turgid. Like any plant, potato plants make their food by the process of photosynthesis: Chlorophyll Carbon dioxide + Water ( Glucose + Oxygen Sunlight energy The glucose made in photosynthesis is used by the plant in a number of ways e.g., respiration. ...read more.

Conclusion

> Put the 7 solutions into the 7 petri dishes and label each dish with which concentration it is. > Weigh potato strips separately and record each mass. > Put two strips of potato into each petri dish and cover with lids. Make sure to note which potato has which mass. > Leave for one hour. > After one hour, take the potato strips out of the solutions and weigh once again. > Record the new mass and calculate the difference between this and the original mass. In my pilot I ascertained that 40 mls were needed to make up the solution in order to cover the potato strips completely. To do this, as I also discovered, I will need to use petri dishes as they have the right width and depth for the potato strips and solutions to fit into. I also decided that to leave the potato strips in the solutions for 2 hours would give me more accurate results. However, this proved quite difficult with the time given to carry out the experiment. Therefore I decided to leave the potato in the solutions for an hour. This document was downloaded from Coursework.Info - The UK's Coursework Database Click here to visit Coursework.Info/ ...read more.

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