Osmosis Essays

Osmosis in Potato Cells Essay

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Osmosis in Potato Cells

I am going to do an experiment to find the concentration of solute in potato cells. In order to find the best way to do this experiment I am going to do a preliminary test first.

For my preliminary test I decided to use potato cylinders 3cm long and I would see if the cylinders increased or decreased in mass. I used salt solution in three different concentrates: 0.0M, 0.5M and 1.0M. I put 20cm3 of each concentrate into 3 different boiling tubes, which were then placed in test tube racks. I then placed a cylinder of potato in each boiling tube and left them for three days. My results were inconclusive because I left them in the solutions for too long so the potato…show more content…

I will then use the same potato to carefully cut 11 3cm long potato cylinders using an apple corer. I will then cut each cylinder into 10 separate small slices using a scalpel and carefully weigh them and take the mass to 2 decimal places. I will then record the masses and place them into the solution, making sure I know which mass went into which solution. I will leave them for 2 days and then weigh them again. I will then repeat the experiment again so I can take an average of my results so they are more accurate. I am doing the test this way because I feel that this is the most accurate way I can perform this experiment realistically in a school lab.

I will make sure it is a fair test by making sure that I put exactly 20cm3 of solution in each boiling tube, and that I mix the concentrates accurately and wash out the measuring cylinders after each measurement, making sure there are no drops of water or salt solution left in the bottom. I must make sure that the potato is healthy before I start using it, and make sure that my cylinders are cut neatly and are measured accurately. I must take care to make sure I do not loose any of the small slices of potato when measure before and after the experiment, I must also take when using the balance to make sure it reads 0.0 before I

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385911 CXA171 Cell Biology and Function Laboratory Report: Osmosis in a model cell. Introduction: There are many factors which influence the rate at which substances may move in or out of a cell. Some substances may not be able to move in or out of a cell at all or may require assistance from facilitating proteins imbedded in the cell membrane, while other substances may move in and out without assistance. This is a due to the selective permeability of the cell membrane, this allows nutrients to enter the cell while keeping unwanted substances. Transport across cellular membranes occurs in two ways known passive or active processes. Diffusion is a passive process that describes the tendency of molecules or ion to move along their concentration gradient from high concentration to low concentration (Marieb & Hoehn 2013). Diffusion may be simple or facilitated, in simple diffusion small molecules are able to pass directly through the cell membrane while larger molecules such as glucose require assistance from proteins or channels to pass through the membrane, this process is facilitated diffusion. Water molecules may also diffuse in and out of a cell, this net movement of water is known as Osmosis. Osmosis occurs due to varying tonicity of the intracellular and extracellular environments. The tonicity of a solution refers to its ability to cause a change in cell shape or tone by promoting osmotic flows of water (Marieb & Hoehn 2013). The tonicity of a solution is determined by comparing the solute concentration of two substances. Substances that have the same solute concentration are isotonic and the net movement of water is equal between the substances. If the compared solution has a higher solute concentration than the reference solution then it is hypertonic, if it has a lower concentration is it hypotonic. If a cell is placed into a hypotonic solution then there is a net movement of water into the cell as a result of high osmotic pressure. Osmotic pressure is the ability of a cell to draw fluid in through the membrane. The higher the osmotic pressure or the osmotic gradient the quicker/greater the net movement of water (College of Veterinary Medicine 2015). The net movement of water occurs until the two solutions become isotonic and the osmotic pressure is equal to the hydrostatic pressure (Abrahams 2007). The hydrostatic pressure is the pressure required to oppose the net movement of water into the cell. The aim of the experiment is to determine how tonicity affects the net movement of water as a result of hydrostatic and osmotic pressure within hypothetical cells. Method: Please refer to page 51 of the CXA171 Cell Biology and Function Semester 1, 2015 Practical &Tutorial Manual (School of Health Sciences 2015). Results: Table 1: Weight change in experimental cells as a result of hydrostatic and osmotic pressure over time. Tube Numbe r Tube/Beaker Contents Distilled Water/Distilled 1 Water 2 15% Sucrose/Distilled Water 3 30% Sucrose/Distilled Water Tube Weight (g) 0 Mins 20 Mins 6.5 7.8 11.1 6.6 8.8 11.3 Total Weight Change (g) 40 Mins 6.4 9.0 12.5 60 Mins 6.5 9.5 13.9 0.0 1.7 2.8 385911 4 Distilled Water/30% Sucrose 9.0 7.1 6.3 5.3 -3.7 16.0 14.0 Change in Weight (g) 12.0 10.0 8.0 Distilled Water/Distilled Water 15% Sucrose/Distilled Water 30% Sucrose/Distilled Water Distilled Water/30% Sucrose 6.0 4.0 2.0 0.0 0 20 40 60 Time (Minutes) Figure 1: Weight change of dialysis tubing recorded at intervals throughout experiment length Significant observations where made throughout the experiment in regards to experimental tubing set ups three (30% sucrose/distilled water) and four (distilled water/sucrose). The dialysis tubing in set up three appeared to swell and increase considerably in tension, as a result the net movement of water into the tubing exceeded the maximum capacity and extended past the tube boundaries, which proved to reduce the accuracy of readings due to water loss out of open tube boundaries. The opposite occurred in set up four with the dialysis tubing becoming flaccid and appearing to decrease drastically in size. Discussion: The dialysis tubing used throughout the experiment acts as a semipermeable membrane which does not permit the movement of sucrose between solutions, therefore the weight changes of the tubes occurs due to the net movement of water as a result of varying tonicity’s of the substances. Bag one is placed in an isotonic solution as both solutions are distilled water. Due to the equal tonicity the overall net movement of water in and out of the bag is equal and results in no net change. This is shown in Table 1 as the initial and final mass recording for tube one are equal. When the solution is isotonic there is no osmotic pressure as the osmotic equilibrium has been reached. In tube two a weight increase of 1.7g was recorded (Table 1), this occurred as the bag was positioned in a hypotonic environment the osmotic pressure created a net pull of water into the cell. This movement also occurred in tube three however as the solute concentration of the solution in beaker three was higher than that of beaker two the osmotic gradient between the two substances was also higher than that of setup two. As the osmotic gradient is higher in beaker three it is expected that there 385911 would be a greater net movement of water molecules in order to attempt to achieve isotonicity and osmotic equilibrium. This is supported by the data as tube three had the highest overall weight gain. Tube four was placed in a hypotonic solution, this created a high hydrostatic pressure and resulted in the net movement of water out of the dialysis tubing. This tube was the only tube to reduce in weight overall (Figure 1) which supports the expected results. The experimental outcome proved to be rather successful with only one error being noted, and occurring in the measurement of setup three. While effectively showing the properties of hydrostatic and osmotic pressure in regards to varying tonicity within the hypothetical cell arrangements. References: Abrahams, P 2007, How the Body Works, Amber Books Ltd, London. Marieb, E Hoehn, K, 2013, Human Anatomy and Physiology, 9th edn, Pearson Education Inc., United States of America. College of Veterinary Medicine 2015, Ohio State University, Ohio, viewed 15 April 2015, < http://www.vet.ohio-state.edu/assets/courses/vm613/part4/part4.html> School of Health Sciences 2015, CXA171 Cell Biology and Function, Practical & Tutorial Manual, University of Tasmania, Launceston.


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