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Osmosis Investigation

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Introduction

SCIENCE COURSEWORK: OSMOSIS Definition of Osmosis: Osmosis is the transfer of water from a high water concentration to a low water concentration through a partially permeable membrane. Aim: The purpose of this experiment is to find out the effect of Osmosis with sucrose solution on a potato, we intend to discover if sucrose concentration is an important variable in the rate of Osmosis Method: We took a potato and cut out 12 pieces of roughly equal size with approximately the same surface area, we used a scalpel to do this. We then blotted the pieces of potato on kitchen roll to remove excess water; after we had done this we weighed each piece using an electronic scales and recorded their masses in the 'mass before' column on our results table. We had 2 pieces of potato each in six different levels of sucrose concentration. Our control was normal distilled water (H2O) with nothing added; we had two test tubes of this and two test tubes of each of the following sucrose concentrations: 0.2 Molers (M), 0.4M, 0.6M, 0.8M, 1.0M. We had to fill the test tubes enough to cover the potato completely but no more. We then placed a piece of potato in each labelled test tube and left them for 24 hours. ...read more.

Middle

We measured along the x axis and discovered the point was at approximately 0.37M. If a solution is on the isotonic point then the solution is known as an isotonic solution to the potato. This means the concentration is exactly the same and there is no net movement of water. This is why the y axis shows the average percentage change to be 0%, because there is no net movement. This means that anything above this concentration of sucrose is a 'hypertonic' solution to the potato, and anything below this sucrose concentration level is a 'hypotonic' solution to the potato. A Hypertonic solution is one where there is less water and more sucrose, this means that water is transferred to the solution from the potato cells by the potato until the two concentrations are the same. This causes the cells to lose water and become flaccid. If the solution outside the potato is hypotonic then there is less sucrose concentration in the solution outside then there is in the potato cells. This causes water to be transferred to the cells of the potato by osmosis to level the two concentrations out. Osmosis is therefore the process of transferring water into and out of the cells until the solution outside is isotonic (the isotonic point is reached, meaning the solutions both inside and outside are equivalent in concentration). ...read more.

Conclusion

We used a scalpel to cut the pieces of potato. I cut them myself which means there is a margin however slight for human error. We could eliminate this possibility by using a cork borer to make each piece of potato the same. They would all have the same weight and surface area, exactly the same. There are some variables that we could change to investigate the conditions that affect osmosis. Our experiment was conducted at room temperature. We could conduct the same experiment at different temperatures to see if the process is affected. Our experiment was left for 24 hours. We could try leaving it for a shorter time to see how long the process takes. We could also try a different volume of liquid or a different plant to investigate different species' rates of osmosis. We could use this experiment to find isotonic points for different cells. An alternative way of looking at osmosis is to peel away the epidermal layer plant such as onion, leek or rhubarb and put them in varying concentrations of sucrose solution. Then examine the samples under a microscope and observe osmosis happening. When the cell loses water the membrane caves in while the cell wall remains rigid. The cell innards shrivel but the wall keeps the shape so the cell appears normal from the outside whereas an animal cell (because they have no cell wall) just shrivels. This is known as plasmolysis. ...read more.

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