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An Investigation into Osmosis.

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Year 11 Biology Coursework: An Investigation into Osmosis Introduction In this investigation, I am trying to find the answer to these two key questions below: 1 What are the factors that determine whether water moves in or out of the potato? 2 How does the concentration of a solution surrounding a cell affect movement in and out of cell across its semi- permeable membrane? In order to do this I will need to consider what osmosis is and make some experiments to help me investigate and find answers for the key questions. Background Information Osmosis is diffusion of water molecules moving from a particularly permeable membrane from a high concentration to a lower concentration. The water molecules can pass both ways through the membrane in two- way traffic, but there is a steady net flow of water molecules into the lower concentration of water. In figure 1 is a diagram showing how osmosis takes place. Figure 1 - What happens in Osmosis Osmosis is important for living things such as plant and animal cells. For animal cells they can easily burst if they take in too much water by osmosis as they do not have a cell all to contain it. However, for plant cells, osmosis makes them swell up when they are surrounded by weak solution and makes the flaccid cells to become turgid cells, this means that it gives the cells support to open the stomatal porb guard cells and to support the plant tissues. Leaves from plants are supported by the turgar pressure, without this, the plant will wilt and the leaves will droop, and plasmolysis will take place in the plant cells. Another plant cell that osmosis can affect is the root hair cell. The root cells are responsible to absorb minerals such as water from the soil fro growth. The concentration of minerals is higher in the root cell than in the soil, meaning osmosis of diffusion will not take place for the root to absorb the minerals. ...read more.


I will then mix into a test tube, thus keeping the same total volume of 10cm� in the mixture but changing its concentration. I chose to do 6 different concentrations as this will give me a more accurate result to compare with my prediction and the outcome of the investigation. The length of potato will be the same as I am not investigating the different length of potato and its effects on rate of osmosis, but I will need to keep in the same so that only the concentration is affecting the rate of osmosis, I will keep the potato at maximum of 2cm long, and the size of it will always be at whatever potato borer I use, so that only concentration and its effects on rate of osmosis is investigated and that all my tests are fair. In this experiment I will need to leave the potato for approximately 10 minutes so that osmosis can take place for fair amount of time, giving me an accurate and correct result. I will need to keep every reactions occurring in each test tube starting and ending at the same time, so that the rate of osmosis can be accurately recorded and are not anomalous and so that it will be a fair test. To calculate the change in mass, I will measure the mass of potato using an electronic balance before and after the osmosis reaction, the difference between them will help me to determine whether rate of osmosis in the potato with different concentrations, which also shows how much the potato, is saturated or unsaturated. To make the test fair I will try and keep the weight of the potato the same or very similar throughout the experiments, so that all conditions are the same except for concentration, so that I can investigate and analyse its effects on osmosis successfully. Another major issue that I need to take care of its keeping it a fair test by repeating the experiment more than once, ...read more.


should all be negative numbers as mass of potato should have decreased due to the osmosis theory, I found out that in experiment 2, the change in mass was +0.02 when it should have been a minus, there is no wrong calculations done, which means that there has been an error in concentration of the solutions used for 15% solution. In order to improve my overall results and make my results more reliable for my investigation, I will need to do the following: 1 Keep the temperature same throughout the experiment, as temperature increases it can give kinetic energy and cause an increase in rate of osmosis 2 How out the age of potatoes used and use the same potato throughout the experiment- the age of potato can affect the permeability of the membrane, thus affecting the rate of osmosis when water molecules passes through. 3 Do more number of the same experiments, this gives more results chance to ignore anomalous data when drawing a graph. 4 Make sure the volumes of the solution are exact and accurate from the cylinder before pouring it into a mixture; otherwise there may be different concentrations of solutions for a specific concentration, thus giving anomalous data and results. 5 The star and end time for osmosis should be exactly the same as best as possible in all experiments, therefore osmosis does not take place longer than needed 6 Weight the potatoes all together at the same time on individual electronic balance, so that osmosis does not take place to one potato while another potato is being weighed I might also investigate all the factors that will affect the rate of osmosis rather than just the concentration of the solutions, so I am able to contrast this data with other experiments, enabling to link different concepts and results together and give me a clear idea how much does each factor affects rate of osmosis, (i.e. investigating length of potatoes with different concentrations of solutions of at different temperature). ...read more.

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