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

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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. The cytoplasm of a plant cell and the cell SAP in its vacuole contain salt, sugars and proteins, which effectively reduce the concentration of the free water molecules inside the cell giving a low water potential. The cell wall is freely permeable to water and dissolved substances but it is the cell membrane will acts as the partially permeable membrane. For this experiment the easiest plant cells to use would be that of a potato (chips) and the solution I will use is Sucrose solution.

Variables:

There are many factors that could be varied that would affect the process of osmosis in living plant tissue. It is important that if the factor is not chosen as the variable, it should remain the same throughout the experiment. The factors are shown in the following table:

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The factor that I have chosen to investigate is the affect of the Concentration of the Sucrose solution on osmosis on plant tissue. This factor is important as it determines the water potential of the solution, which is a main factor in osmosis. The concentration of the solution will be my variable.

Preliminary Tests:

Before I could carry out the actual experiment I needed to conduct a series of pre-tests that would help me decide on the conditions for the experiment. Here are some of the points that I had to consider:

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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.