Osmosis in potato cells.

Osmosis in Potato Cells

Scientific Theory

Osmosis is similar to diffusion, but a little different. It is the movement of water molecules across a partially permeable membrane, from a region of high water concentration to a region of low water concentration, (along a concentration gradient).

A partially permeable membrane, is a membrane with tiny holes, however these holes are so tiny that only water molecules can pass through and no other substance, for example glucose.

When a substance, for instance sugar, dissolves in water it attracts the water molecules and stops them from moving freely, this actually reduces the concentration of water.

In the diagram above, there are more free water molecules on the right of the membrane than on the left. Therefore water will diffuse more rapidly from right to left across the membrane, rather than left to right. The sugar molecules can diffuse from left to right across the membrane, but because they are big molecules they will diffuse more slowly than water. The effect of this is to gradually dilute the sugar solution.

Osmosis also takes place in plant cells, when the cell is in a less concentrated solution. When the cell can take no more water we say it is fully turgid and supports the plant.

Osmosis also takes place in animal cells, these do not have cell walls, and therefore they take up too much water and as a result burst open.

Visking tubing is a partially permeable membrane, which is used in kidney dialysis machines show the effects of osmosis.

Prediction

I think that potato cells in water will swell and as a result grow bigger, in the same form as a plant cell swells up when it is surrounded by a weak solution. The water will diffuse into the potato cells and therefore making the potato heavier.

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Osmosis also takes place in animal cells, these do not have cell walls, and therefore they take up too much water and as a result burst open.

Visking tubing is a partially permeable membrane, which is used in kidney dialysis machines show the effects of osmosis.

Prediction

The potato tubes placed in a glucose solution would lose its mass and shrink. This is because when a substance such as sugar is dissolved in water, the sugar molecules attract some of the water molecules and restrict them from moving freely. This reduces the concentration of water molecules and therefore it would weigh less and shrink in size.

Fair Test

To make the test as fair as possible I will make sure that the amount of water the potatoes are immersed in water is the same, and that all the potato cells are immersed for the same amount of time.

Safety

To wear a laboratory coat is not quite necessary, as no chemicals are needed, however it is better to wear one.

As some chemicals react with water, no chemicals should be close by. Gloves should be worn too. The knife should be handled with great care.

Apparatus

2 Potatoes
Water
Knife
Board
Weighing scale
Ruler
Glucose
Measuring cylinder
Test tubes

Diagram

Method

Place a large potato on a board
Cut the potato as thin chips
Measure and weigh the potatoes
Prepare a number of potatoes in this way
Prepare two test tubes, A and B

Fill test tube A with water, and test tube B with a twenty- percent sugar solution. Water of 20 ml

Leave the solutions for three hours
After three hours, measure and weigh the potatoes from each test tube A and B. Note the differences.

Results

Below are the results for the potato tubes immersed in pure water.

Average increase in length = (6+10+14+11+8)/5 = 9.8%

Average increase in mass = (14+13+18+17+13)/5 = 15%

Below are the results for the potato tubes immersed in a twenty- percent sugar solution.

Average decrease in length = (-11-13-10-7-10)/5 = 10%

Average decrease in mass = (-43-42-30-38-38)/5 = 38%

Conclusion

I found that the potato tubes immersed in pure water swelled and grew bigger, they still remained hard. They increased in length by approximately ten percent, and in mass by fifteen percent.

The potato tubes immersed in the twenty percent glucose solution decreased in size and in mass. They turned soggy. I noticed that once the potato tubes were immersed in the solution they began to float in twenty minutes.

The experiment went exactly according to my prediction, except that I never thought the potato tubes in water would become stiff and those in the glucose solution would become soft.

This experiment proves that the potato immersed in water allows water to diffuse in and this is why the length and mass increases. The potato tubes immersed in the glucose solution shows that partially permeable membrane doesn’t allow the glucose particles in and therefore shrinks in size and loses its mass.

The experiment proved to me that osmosis does take place in potato cells and there is movement of water molecules from a dilute solution to a more concentrated solution through a partially permeable membrane that allows the passage of water molecules but not solute molecules.

Evaluation

Though my experiment proves that osmosis took place, I feel my experiment was not as fair as possible. This is because the potato tubes were not immersed in their respected tubes at the same time. This may effect the amount of osmosis taking place. Also all the potato tubes were not of the same length and mass, if I had taken care of this my results would be more accurate.

I also feel that potatoes from different countries may also affect the rate of osmosis, as the rate of osmosis would be according to their climate and maybe the type of soil too.

I could also try an experiment with Visking tubing and compare the results to this too.

However as I cannot see the membrane of the potato I will not be able to compare properly.

Also some of the tubes not increasing a lot may be because in the water solution some tubes may have had more water than the rest. And in the glucose solution less decrease may be because there was less glucose and more water in that solution than the rest.

I can improve the experiment by using more potato cells to get stronger correlation on the graph.

However, though my experiment was not too reliable because of the method used, my experiment strongly proves that osmosis occurred and so my experiment must have a considerable amount of reliability. My results also are sufficient for me to conclude that osmosis does take place in potato cells.