Osmosis is the diffusion of water through a partially permeable membrane.

BIOLOGY COURSEWORK

PREDICTION AND PLANNING

Osmosis is the diffusion of water through a partially permeable membrane. It is the movement of water from a dilute solution to a concentrated solution through a partially permeable membrane. If a dilute solution such as water is separated from a concentrated solution such as sugar solution, by a partially permeable membrane, water diffuses across the membrane from the dilute to the concentrated solution.

Diagram of Osmosis

I am planning to do the investigation on the amount of sugar in the water and see how it will affect the rates of osmosis and the change in mass inside the potato tissues. I think the mass of the potatoes will decrease when the concentration of sugar is higher because when the concentration of sugar in the sugar solution is high; there will be less free water molecules in the solution and comparing to the potato, there are more free water molecules in the potato. So according to what I have said, osmosis will occur and the free water molecules will diffuse through the semi-permeable membrane into the concentrated sugar solution.

Apparatus

Knife
5 beakers
Electronic balance
Measuring cylinder
Tiles
Stop watch

I am going to an experiment to find out whether my prediction is correct. I am going to do my experiment by cutting out tubes of potato using the cork borer. Then I will place all of them in water for 2 days to let water diffuses into the potatoes, this can make the potatoes have a higher concentration of free water molecules, after that I have to measure the weight of it, I will then place 3 tubes of potatoes in each solutions to get a more accurate result: 25% sugar solution, 50% sugar solution, 75% sugar solution and 100% sugar solution. Then I will leave the potatoes in the solution for 10 minutes because it will give the potatoes enough time to carry out osmosis. After that I will take them out of the solution and dry the potatoes, and measure the mass again and check whether the mass will change. After I have got the data, I am going to plot a graph and draw a best-fit line I will make the test fair by measuring the proportions of sugar solution and water correctly because this can affect the experiment results. Then I have to time how long the potatoes are going to stay in the solution correctly and take out all the potatoes immediately after 10 minutes because if the potatoes stay in the solution longer or shorter, it will affect the mass of it. I have to make sure all the potatoes tubes in the experiment come from the same potatoes because different potatoes contain different percentage of sugar.

Safety control

I have to wear goggles, prevent any accidents that can damage my eyes
I have to make sure all the school bags are under the table, in case it trips me over
I have to make sure I handle all the glass wear carefully
I have to make sure I handle the knife and the cock borer very carefully because they can cause serious injuries to people or me

In living cells, the cell membrane is partially permeable and the cytoplasm and vacuole (in plant cells) contain dissolved ...

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Safety control

I have to wear goggles, prevent any accidents that can damage my eyes
I have to make sure all the school bags are under the table, in case it trips me over
I have to make sure I handle all the glass wear carefully
I have to make sure I handle the knife and the cock borer very carefully because they can cause serious injuries to people or me

In living cells, the cell membrane is partially permeable and the cytoplasm and vacuole (in plant cells) contain dissolved substances. So water tends to diffuse into cells by osmosis if they are surrounded by a weak solution, e.g. distilled water. If the cells are surrounded by a stronger solution, e.g. sugar solution; the cells may lose water by osmosis.

ANALYSIS

The results of the experiment are:

After I have got the data, I am going to plot a graph and draw a best-fit line but before that I am going to find the mean of the changed percentage of the mass to make the graph more accurate.

After I have plotted the graph and drawn the best-fit line, I found that the best-fit line is a curve line. When the concentration of sugar is increased in the solution, the mass of the potato is decreased quicker. When the 25% of the solution is sugar solution, the potatoes’ mass decreased a lot slower than the potatoes in 100% sugar solution.

When there are 2 solutions and a partially permeable membrane between them, the side with more free water molecules (high concentration of free water molecules) will get pass the semi-permeable membrane quicker than the side with less free water molecules (low concentration of free molecules). This is because free water molecules are smaller and so they can get pass the semi-permeable membrane more quickly than other molecules, such as sugar molecules because they are a lot bigger than water molecules and they have to get through the semi-permeable membrane that has small pores. So when the concentration of free water molecules is high, the free water molecules will get pass the semi-permeable membrane and goes into the side with low concentration of free water molecules. If the concentration of free water molecules gets higher, the free water molecules will get pass the semi-permeable membrane quicker.

So, in my experiment, osmosis takes place between the potatoes and the solutions. Inside the potatoes, there are sugar and water; in the water, there are sugar and water too. But because I have put the potatoes in water for 2 days, so the water diffuses into the potatoes by osmosis that makes the potatoes full of free water molecules (high concentration of free water molecules) and when I put the potatoes into the solutions, the potatoes have higher concentration of free water molecules than all the solutions.

When the potatoes are being put in the solution with 25% of sugar, the potatoes’ mass decreased slowly. When I put the potatoes in the solution with 50% of sugar, the potatoes’ mass decreased a bit faster than when they are in the solution with 25% sugar. When I put the potatoes in the solution with 75% of sugar, the potatoes’ mass decreased even faster. Finally, when I put them into the solution with 100% of sugar, the potatoes’ mass decreased more quickly than the potatoes in the solution with 75% of sugar. This is because when the concentration of sugar in the solution is higher which means it has a low concentration of free water molecules, but the potatoes have a higher concentration of free water molecules, so when osmosis occurs, the free water molecules in the potatoes diffuse into the concentrated sugar solution that makes the potatoes’ mass decreases.

EVALUATION

I think the experiment is quite successful apart from the easily squash potatoes which I have to throw them into the bin. I have got the results I need. Then, I drew the graph by the mean of the data I got which makes them more accurate and reliable; this gives me a very good graph.

To make the experiment more accurate and reliable, I can put the potatoes in the solutions for a longer period of time because this can let osmosis occurs a longer period of time which let more free water molecules pass into the solutions and the mass of the potatoes will have a more dramatic change. After I take the potatoes out of the solutions, I have to make sure I dry them very thoroughly, or else it will increase the mass of the potatoes when I weigh them. Next time when I have to do experiments with potatoes again, I have to hold them more carefully, or else they will get squash again.