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Investigating the effect of Osmosis on potatoes

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Introduction

Double science - investigating the effect of Osmosis on potatoes Hypothesis/Introduction If a plant is deprived of water, it wilts. If bacteria are placed in a high concentrated solution of salt water, they "collapse" and die. Human red blood cells, if placed in distilled water, expand and burst. These are all examples of osmosis and its effects. The aim is to see the change in mass, length, and density of 21/2 cm potatoes in solutions of 1%, 10% and saturated (approximately 85-90% salt). Osmosis is the movement of water molecules from a high-solution of water molecules to a low-solution of water molecules via a semi-permeable membrane. (Fig 1) Water Salt-solution KEY TO DIAGRAM Water molecule Salt molecule Net movement of water molecules The diagram above shows how the process of osmosis occurs. The water molecules move through the semi-permeable until it is equalled. However, the sugar molecules cannot move through the semi-permeable membrane, as they are too big to. This can explain why proteins, fats and carbohydrates are broken down into smaller soluble molecules to pass through the villi. ...read more.

Middle

1%, 10%, saturated), also it would be better to take the mass first as you have to calculate the density. Record your weight of each potato in a table. (See results section) 4. Calculate the density. After the preliminary experiment, I found that it would be easier to fill a measuring cylinder at 20ml, place the potato in the cylinder and calculate the rise of the water and calculate the density using the formula: Density = Mass/Volume. 5. Pour three beakers each with 1%, 10% and saturated solutions respectively. Each beaker must measure 50ml. 6. Place the potatoes in each beaker and start the stop-clock. Wait for 20 minutes. When the 20 minutes has concluded, dry each of them thoroughly and record their weight, density and length. In the preliminary experiment, 10 minutes brought inconclusive results. 7. Repeat this a minimum of three times for an average. Apparatus The following apparatus will be needed for this experiment: Calculator (for density and average calculations) Knife (to cut the potatoes to 21/2 cm) Ruler (to measure the potato to 21/2 cm) ...read more.

Conclusion

4.1g E1. 1.175g/cm E2. 1.170g/cm E3. 1.168g/cm E1. 1.075g/cm E2. 1.073g/cm E3. 1.071g/cm Average 2.1cm 4.7g 4.2g 1.171g/cm 1.073g/cm Results Key: Ex (Experiment x) Exprmnt. (Experiment) Conclusion In conclusion, the hypothesis, which I believed to be true, was correct. Looking at the results table, I can see there is a definite correlation between the amount of salt in the solution and it's decrease in mass. To add to this, length has the same correlation. We can explain this using the Kinetic theory. Molecules of water and salt are continually moving and "bombarding" the semi-permeable membrane. Occasionally, a water molecule will pass through. In pure water, of course, equal numbers of water molecules will pass through via the semi-permeable membrane without any overall change. However, in all three of the solutions, the large salt molecules impede the water coming out of the potato and block the passage through the holes and colliding with the water molecules (this will happen more frequently as the temperature gets higher). Hence, more water molecules flow from the pure water to the salt-solution than the other way. The overall effect is that water flows through the semi-permeable membrane and into the solution. The diagram below can show this: Salt molecules colliding with water molecules move in water molecules ...read more.

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