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Investigate a factor which can affect the process of osmosis in a living plant tissue

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Introduction

Meetal Odedra 11V Biology coursework Investigate a factor which can affect the process of osmosis in a living plant tissue Planning For this coursework investigation I will be investigating factors that affect the process of osmosis in a living plant cell, but mainly focusing on one factor I have chosen. In order to do so, I have conducted some background research on osmosis to help me understand the investigation in hand. Background Scientific Research (Using D.G. Mackean's GCSE Biology textbook) Osmosis is defined as the movement of water molecules from a high concentration of water (potential) to a lower concentration of water (potential) down a concentration gradient, through a partially permeable membrane. When a substance such as sugar dissolves in water, it reduces the concentration of the water molecules because the sugar molecules attract some of the water molecules and stop them moving freely. Osmosis can be explained with the help of the diagram below: The diagram shows that the sugar molecules on the right have attracted half of the water molecules. There are now more free water molecules on the left than on the right so water molecules will diffuse more rapidly from left to right across the partially permeable membrane, than from right to left. This is because the net movement of the water molecules move from the high concentration of water (left) to the lower concentration of water (right). For this investigation I will be looking at the affects of osmosis on plant tissue. ...read more.

Middle

Pre-Test 2 ~ Whilst conducting this pre-test I found that the beaker allowed the chips to group together which would have affected the accuracy of the results. The size of the chips I found to be too small and difficult to handle. The volume of sucrose was just enough to cover this size chips as the beaker was a larger area. Also the 20cm measuring cylinder was not large enough to measure some amounts accurately. Pre-test 3 ~ I found that this pre- test worked the best for this experiment. The boiling tubes allowed the chips to stay separated and the 30cm of solution covered the chips entirely. I found using the range, increasing the concentration in intervals of 0.25mol, gave me a suitable range of data and by not drying the chips gave more distinct results. The measuring cylinder was large enough to measure all the amounts of solution in the experiment. Although I did find that a longer time span was needed to get better results. Using the information gathered from the pre-tests I decided to use the following apparatus and conditions for the actual experiment: > 15 Boiling Tubes > 15 uniform cut chips ~ to be cut to 30mm > Distilled water ~ for dilutions to be made from > 1 molar sucrose solution ~ for dilutions to be made from > 30cm volume of dilutions > Range of dilutions ~ 0, 0.25, 0.5, 0.75, 1 mols > 30cm measuring cylinder > Electronic balance ~ to 100th of a gram > Knife > Tile > Ruler > Labels ...read more.

Conclusion

From this point of concentration of sucrose I predict the chips will decrease in mass and length. The theory suggests that if the plant cell is surrounded by a solution more concentrated than its content, water will pass out of the vacuole by osmosis. This would mean that the net movement would be the higher concentration of free water molecules in the potato cell vacuole would move out to the low concentration of water molecules in the sucrose solutions. This can be shown in the diagram below: As water molecules move out of the vacuole the potato cells the potato cells lose their turgor pressure and become flaccid. A potato chip with flaccid cells will be limp as the vacuoles of the cells become smaller, therefore the chips would decrease in mass and length. In an extreme case, which may be reached in this experiment, if the plant is placed in a solution with a very low water potential, the vacuole may loose so many water molecules moving to the low potential area that the cytoplasm and vacuole pulls away from the cell wall. The cells are said to be plasmolysed. I predict that the graphs for this experiment should follow a general trend shown below where 0 mol of sucrose concentration will the highest point for largest increasing change in length and mass and 1 mol concentration will be the lowest point for largest decreasing change in mass and length. Turgor pressure Change in Mass or Sucrose Length Concentration Becomes flaccid I carried out the experiment and the results are found on the following pages. ...read more.

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Here's what a teacher thought of this essay

4 star(s)

Despite the omission of results and conclusions from the report, this is a highly competent piece of scientific writing which balances detailed theory about osmosis in plant tissue with a well-designed experiment. It suffered only from minor weaknesses: the reader had to wait until page three before being told what variables were being measured; no mention was made of previous work carried out by other biologists on the same topic. However, overall, this was a well-constructed report and assuming that the conclusion and evaluation were of a similar standard, would gain a high GCSE grade.

Marked by teacher Ross Robertson 10/04/2013

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