The Effect of Sucrose Concentration on Osmosis.
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The Effect of Sucrose Concentration on Osmosis Aim The aim of this experiment is to find out the effect sucrose concentration has on the mass of a potato cell and the rate of osmosis. We also want to find the concentration of the cell sap in a potato. Introduction If water is withheld from a flowering plant, the flowers wilt. If bacterial cells are placed in concentrated salt water solution, they collapse and die. Human red blood cells placed in fresh water expand and burst. These are examples of the effects of osmosis, the process by which water passes through a cell membrane. Osmosis is a specific form of diffusion that only affects water molecules. It is the movement of water molecules from an area of high concentration, to an area of low concentration through a semi-permeable membrane. An example of osmosis occurs when a sugar solution and water, top, are separated by a semi-permeable membrane. The solution's large sugar molecules cannot pass through the membrane into the water. Small water molecules move through the membrane until equilibrium is established, bottom. Osmosis is possible because of the constant state of motion that exists at the atomic and molecular levels of matter. Specifically, in liquid solutions, molecules of solute (the dissolved substance) and solvent (the substance, usually liquid, in which the solute is dissolved) move about randomly, spreading from regions of high concentration into regions of low concentration. This process is called diffusion. If a cell membrane allowed an equal passage of solute and solvent, diffusion through the membrane would lead to a cell whose internal composition would be identical to its environment. This does not occur because the cell membrane is semi permeable. Water molecules pass through the membrane much more readily than dissolved solid solutes, such as sugar and salt. If the environment is hypotonic (having a lower concentration of solute than the cell)
Volume of sucrose solution used each time The volume must stay the same so one can monitor the mass change accurately. If these variables are not kept the same it would influence our results and make them inaccurate. However, we will also be changing some variables to enable us to obtain the results we need. We will be changing the concentration of sucrose in the sucrose solution, so that we can see how the change in mass varies depending on the concentration of sucrose in the solution. *** Preliminary Investigation Aim To decide three aspects of the experiment: * The most appropriate time to use when measuring change in mass. * What shape of potato works most effectively. * What range of sucrose concentrations to use. First we decided to choose the emersion time: Method 1. Set up apparatus needed in preliminary work. 2. Measure out 25cm³ of pure (distilled) water and pour into a test tube. 3. Measure out 25 cm³ of 80% sucrose solution and pour into a second test tube. 4. Cut out two chunks of potato, measuring them to make sure they are the same mass. 5. At the exact same time, drop a chunk of potato into each test tube and start the timer. 6. At regular intervals (e.g. every 5 minutes) stop the timer, and check the change in mass for both potato chunks. Do this for an hour until you have all your results. 7. Choose the most effective time to use Results Time (mins) 0 5 10 15 20 25 30 Mass change pure water, from starting mass (grams) +0.0 +0.1 +0.1 +0.1 +0.2 +0.2 +0.3 Mass change 80% sucrose, from starting mass (grams) -0.0 -0.0 -0.1 -0.3 -0.3 -0.3 -0.4 The time that showed the largest mass change in both pure water and 80% sucrose was 30 minutes, so we decided to use 30 minutes for our immersion time.
But, in my investigation, there were three tests done, to ensure the accuracy of the mean result, this was a very good aspect of the investigation, and could've only been improved by doing more tests, which would be time wasting. Our immersion time was also sufficient, because we were able to extract the necessary information from it with ease. It ensured that a wide range of results were obtained, and wasn't too long, so the experiment was completed in an reasonable time at ease. During our preliminary investigation, there was a slight problem with the potatoes, they kept sinking to the bottom of the test tube, posing a problem in their retrieval for the measuring of change of mass. This could have been avoided if the potatoes were smaller so they could float in the solution. There are other investigations one could carry out, if the study were to be extended. To find out about osmosis in plant roots and cells, one could do a detailed study over a period of time measuring the change in mass of a plant in earth. To do this one would need to take a cutting from a plant, with the roots and measure its mass at the start. Then one would plant this in a small pot of earth with a certain amount of water poured over it. To prevent evaporation, the plant would have to be covered. A specific environment would need to be maintained in order for the experiment to be successful. The amount of water would need to be decided on and kept the same throughout the experiment. After a fixed period of time, longer than in this investigation, one would take out the plant and measure the change in mass. This would tell one more about osmosis and how it works in plants, including the rate of osmosis in plants. Rabab Salem 10B1 Osmosis Coursework 1
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