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"Osmosis" - The Potato Experiment.

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Introduction

GCSE Biology Coursework "Osmosis": - The Potato Experiment Background Information Osmosis can be defined as the movement of water across a semi-permeable membrane from a region of high water concentration to a region of low water concentration. The semi-permeable membrane allows small particles through it but does not allow large particles such as sodium chloride. Osmosis will continue until a state of equilibrium is reached i.e. there is no area with a higher or lower concentration than another area. To land plants, water and osmosis are vital as they play leading roles in the structural support of a plant. Lack of water will lead to a plant wilting (becoming flaccid) and possibly dieing. Osmotic pressure. If a plant was placed in a waterlogged area, where the external solute to the cell (being less concentrated (or hypertonic) to the cell vacuole contents) the cell will not continue to take in water via osmosis for ever. The cell wall made of cellulose acts as a firm barrier to any more expansion. Once the cell is full of water, it is said to be turgid. This means that the inward force is equal to that of the outward force. The inward pressure is called turgor pressure and the outward force is called osmotic pressure. ...read more.

Middle

Salt Solution For the solution. Distilled Water To be mixed with NaCl to make the correct molarity solutions. Test Tube Rack To Keep the test tubes in. Beakers For measuring the solutions. Plan 1. Bore 12 tubes of potato out of the same potato(being careful not to cross them) 2. Cut the ends of the pieces (as there is an impermeable skin layer, which if not removed could prevent osmosis and therefore make the experiment and unfair test) and cut them to the correct length. 3. Weigh each and record the weight in a results table. 4. using some sort of marking system mark one pair of each of the potato sticks as there will be two per test tube. 5. Mark each of the test tubes so you know which test tube holds what concentration of solution. 6. Make the sodium chloride solutions by adding varying amounts of sodium chloride to varying amounts of distilled water. The mounts are shown in the table below. Moles Distilled water /ml Sodium Chloride (NaCl) solution /ml 0 25 0 0.2 20 5 0.4 15 10 0.6 10 15 0.8 5 20 1.0 0 25 7. Place 2 pieces of potato in each test tube. ...read more.

Conclusion

This means that the potato. This means that the potato was turgid after the experiment. o Point B is the point of equilibrium meaning that there is no net movement in or out of the cell. This also means that the concentration of salt inside is equal to the concentration outside of the potato cells. o Between points B and C, there is net movement of water out of the potato as it has decreased in mass. Between the C and D and it is an almost horizontal line. This means that this is the point where all the water in the cells of the potato have moved out of the cell and there is no solute left to leave. The actual graph show the percentage gain and loss in mass plotted against the molar concentration of sodium chloride (NaCl). I have drawn a line of best fit onto the graph. The line is a negatively slopping curve. It doesn't pass through the origin, which means that the percentage gain and loss in mass and the concentration are not directly proportional to each other. However, there is a pattern on the graph. It shows the percentage gain and loss in mass is inversely proportional to the concentration i.e. as the concentration increases the percentage gain and loss in mass decreases. ...read more.

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Here's what a teacher thought of this essay

4 star(s)

****
A sound investigation which could be improved with some simple scientific experimental procedure alterations.
1. Be clear of the aim of the investigation. It is clear that water will move in and out of the potato cell by osmosis, the aim of the experiment was to determine the solute concentration of the potato cell, which
was achieved. The conclusion should have focussed on this.
2. Try to avoid talking in first person throughout the paper instead of saying "I did this, then I did this..." write in third person i.e "Firstly the potato cylinders were added to the sodium chloride solution, they were then left for 24 hours..."
3. Be consistent with terminology. If you refer to the potato cylinders as cylinders at the start of the paper call it this throughout the paper.

Marked by teacher Jon Borrell 08/01/2013

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