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To investigate the factors that effect osmosis in living tissue.

Extracts from this document...

Introduction

Biology Investigation by Yasir Al-Wakeel Aim: To investigate the factors that effect osmosis in living tissue. Planning: Introduction Essentially, osmosis is the diffusion of water across a selectively permeably membrane. Osmosis is one of the ways by which substances enter and exit cells. Other ways include diffusion, the Donnan effect1, solvent drag, filtration, endocytosis, exocytosis and active transport. All of these methods are necessary to provide cells with the conditions necessary for their survival. Osmosis helps cells absorb the water that they need and also pass it on from one cell to another. Osmosis occurs in the uptake of water in root hair cells, it also occurs in the return of water from tissues to blood capillaries and is constantly occurring during the opening and closing of the stomata in plant leaves. Factors that shall be tested: Bearing in mind that we have limited time and shall be conducting our experiments in a laboratory, measuring certain things may therefore be impractical. We shall therefore limit our investigation to the effect of three things: Cross-sectional area of plant cylinder, concentration of solution and temperature of solution. Variables There are three main types of variable; Independent (input), control and dependent variables. An independent variable, otherwise known as an input variable, is the variable that is to be tested by experiment and therefore deliberately changed. The control variable is the variable that is kept constant in order to test the independent variable fairly. The dependent variable is the one that depends on the control and independent variables. Since the control is to be kept constant, any effect on the control variable will therefore be due to the independent variable. Throughout our investigation the variables and there complexities shall be as follows: The constants or control variables for this experiment are going to be: * The vegetable used-We shall be using the common white potato. Potatoes are produced by plants of the genus Solanum, of the family Solanaceae. The common white potato is classified as Solanum tuberosum. ...read more.

Middle

* The temperature of the solution -room temperature 22oC. * The cross-sectional area of the vegetable. The steps that shall be taken are as follows: Step1: I shall obtain one vegetable, and using a cork borer of radius 1cm, the volume of the cylinder, given that it shall be of length 5cm can thus be worked out using the formula: Volume of Cylinder = ( x r2 x h ( Volume = ( x 12 x 5 =15.7 cm3 I shall cut cylinders (eleven used for the different concentrations and one for the control experiment) from the vegetable, The cork borer is used to ensure that all the pieces are of the same diameter. Step 2: The cylinders shall be aligned against a straight edge where they shall be cut to a length of 5cm. The straight edge is to ensure that the pieces are of exactly the same length. This may be illustrated as follows: The length shall be determined using a ruler. A ruler is accurate to the nearest millimetre and so the accuracy is 5 + 0.001. It is thus very accurate. The percentage error may be worked out using the following equation: Degree of accuracy x 100 Total measurement ( 0.001 x 100 = 0.02% 5 Step3: The cylinders shall be blotted dry using filter paper, before being weighed on a top-pan balance. They shall be blotted dry in order to receive an accurate reading of their weight. As all the cylinders should be of the same length, and as they are from the same vegetable, their densities should also be the same, we shall thus weihg them all and obtain the mean. A top-pan balance is accurate to 0.01 of a gram. Step4: We must then obtain 15ml of distilled water. This shall be done, as in all the experiments by pouring the distilled water from the container into a measuring cylinder as shown below: It is important that we take our reading from the bottom of the liquid meniscus to reduce error. ...read more.

Conclusion

Although our results appear to have shown much of what was predicted to be correct, they do not allow us to generalise regarding what we have found. For example, although we have found that increasing the temperature to 370C increases the rate of osmosis we have only found this to be true regarding a potato, it may not necessarily be true regarding a different plant and so the theories and models that our experiments have illustrated may not necessarily be applicable in all cases. Putting in mind the tentative nature of hypothesis testing, our results thus do not disprove certain statements such as increasing the temperature to 370C increases the rate of osmosis in all plants. In order to obtain a broader insight into osmosis in living things, we must therefore conduct many more experiments on different living things. If the experiment was performed again, various steps may be taken in order to improve the accuracy of our results. If performed again the vegetables should be left for a longer period of time so the changes can be clearer, however not too long so as to allow the cell turgidity to prevent further endo/exosmosis. Also the measurements used were accurate to the nearest millimetre, this is rather large considering the size of the cells that are being worked on. Thus vernier callipers or even a micrometer gauge may be used to obtain more accurate measurements. Also, a repeat experiment may take into account the fact that the change in diameter across the cylinder was not uniform. Other experiments that may be done on osmosis using a 'Visking' or dialysis tube as an artificial partially permeable membrane. The effects of osmosis on cells may also be studied microscopically. A small piece of epidermis from a red area of a rhubarb stalk placed on a cover slip whilst soaked in a 30% solution of sucrose would be ideal for showing the effect of plasmolysis on cells. Further experiments on the role of enzymes in osmosis as well as other experiments concerning different methods of transport such as active-transport may also be conducted. ...read more.

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