Use scientific knowledge and practical skills to determine the effect of a range of salt solutions (0.2, 0.4, 0.6, 0.8 and 1.0M plus distilled water) on living cells (potato).

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Gcse biology osmosis

Aims of the investigation: to use scientific knowledge and practical skills to determine the effect of a range of salt solutions (0.2, 0.4, 0.6, 0.8 and 1.0M plus distilled water) on living cells (potato).

What factors might affect it? Length - of membrane, Temperature - of water, Concentration - of solution

The factor I will change will be. The Independent variable (things you change), the thing that I will be changing in this investigation into the factors affecting osmosis, is the concentrations of the solution that helps me to investigate osmosis with potato tissues. The different sugar concentrations will be changed to see the result of the potatoes when placed in sugar solutions placed in different molarities (strengths).

Planning

My aim for this experiment is to see the results of potato tissue's mass difference, when placed in different concentrations of sugar solutions.

Variables involved:

For this experiment I would expect to have 3 different variables, Independent, Dependent, and fixed variables, which all helps me to plan and explain the experiment thoroughly.

The Independent variable (things you change), the thing that I will be changing in this investigation into the factors affecting osmosis, is the concentrations of the solution that helps me to investigate osmosis with potato tissues. The different sugar concentrations will be changed to see the result of the potatoes when placed in sugar solutions placed in different molarities (strengths).

Dependent Variable (things that you measure) the things that I'll be measuring in this experiment on osmosis is the mass change and length change of the potatoes placed in different molarities of sugar solutions. I will record the masses in grams by using a balance and the length changes by using a ruler.

Fixed Variables (Things that you keep the same) the things that I have chosen to keep the same in each individual experiment to keep it a fair test is to keep the same sizes of each potato tissue the same by using the same cork borer and same ruler. I will be keeping the same amount of solution placed in the test tubes for each different experiment, which I will measure using a measuring cylinder. I will also be keeping the same potato through out the whole experiment to as using a different one might give me anomalous results as some might have more water in it then others.

Hypothesis:

Osmosis is the passage of water molecules from a weaker solution into a stronger solution, through a partially permeable membrane. In this case, the tiny holes in the membrane of the potatoes will allow the water molecules to pass through in and out of the solution and the potato, depending on the concentration gradient of the two substances. So in this case, when the water concentration is lower in the tissue, the water will go inside the tissue of the potato, and the potato will gain mass. If there is very little different in the two water concentrations, there shouldn't be such a big change in mass. Also if there is a higher concentration of water in the potato, then the water will go out of the potato and into the liquid solution, as osmosis is the movement of water molecules from a region of high concentration to a region of low concentration, through a partially permeable membrane.

The potato, cut up into pieces, will need some sort of element to survive, and in this experiment, it would be light and water. With both of these sources, the potato will keep on working until it dies of either lack of water or too much water, or will stop, as both sides would become equal, making no more reactions. When the concentration gradient is lower in the potato, the water will transfer from the solution into the potato.

In the distilled water, I believe that the water is more concentrated in the potato, and therefore the water should transfer from the water to the potato, making the potato bigger in size, and heavier in weight. The potato tissues, being surrounded by a weak solution, will be most likely to swell up and become turgid, taking in all the water it can possibly take in.

With the potato in 0.2 molar solutions of sucrose, I don't think there will be much change in the weight of the potato. This is because there isn't much difference between the two substances. I believe that the weight and the size of the potato won't be altered much.

The 0.4 molar solutions of sucrose, similar to the 0.2 molar solution of sucrose, compared to the potato, both substances have very close concentration gradients. And that is why I am predicting that the weight of the potato in this experiment should be decreased by only a fraction.

The 0.6 molar solution of sucrose, I think, should make a big difference now, noting that it should be a large difference between the two concentration gradients. And therefore the weight should decrease, at least noticeable for us to notice.

The difference between the water concentration in the potato and the 0.8 molar solution of sucrose is big, and the water in the potato should be transferred from the potato, through the permeable membrane, to the solution surrounding the potato. As a result, I am sure that the weight of the potato will increase largely. This is because the potato tissues are surrounded by a stronger solution and it will probably become smaller, and shrink. But because of such high molars of sucrose, the water can diffuse all the way, throughout the two substances, equalling the concentration gradient of the two substances.

My theory in this experiment is that, due to the difference in the water concentrations of the two substances, I believe that the weight of the potato will start decreasing when it is tested on 0.2 molar solutions of sucrose and greater.

Scientific explanation of what would happen:

Osmosis is defined as the movement of water molecules from an area of high water concentration to an area of low water concentration, across a semi-permeable membrane.

In a high concentration of water the amount of solute (e.g. sugar) is low. This could be called a weak or dilute solution.

In a low concentration of water the amount of solute (e.g. sugar) is high. This could be called a strong or concentrated solution.

When two such solutions are divided by a semi-permeable membrane the water will move from the area of high concentration to the area of low concentration, until both sides are equal (have reached equilibrium).

This can be seen in living cells. The cell membrane in cells is semi-permeable and the vacuole contains a sugar/salt solution. So when a cell is placed in distilled water (high water concentration) water will move across the semi-permeable membrane into the cell (lower water concentration) by osmosis, making the cell swell. This cell is now referred to as turgid. If done with potato cells the cells would increase in length volume and mass because of the extra water.

If these potato cells were placed in a solution with a low water concentration, then the opposite would happen. Water would move out of the cell into the solution. In extreme cases the cell membrane breaks away from the cell wall and the cell is referred to as plasmolysed. The potato cells will have decreased in length, volume and mass.

The greater the concentration of water in the external solution the greater the amount of water that enters the cell by osmosis. The smaller the concentration of water in the external solution the greater the amount of water that leaves the cell.

However, there will be a point where the concentrations of water inside and outside the potato cells are equal (isotonic). At this point there will be no change in the length, volume and mass of the potato, as the net movement of water will be zero, no osmosis has occurred.

Using this information a graph and prediction can be made, which can be seen below:

At point A the graph suggests that no osmosis has occurred, suggesting that the concentration of water inside the cell is equal to the solution outside.

At point B (high water concentration), there is no indication that the cell is increasing further in size. This is because the cell is fully turgid and no more water can enter.

At point C (low water concentrations), there is no indication that the cell is decreasing further in size. This is because the cell is fully plasmolysed and no more water can leave the cell.

Osmosis is the net movement of water molecules from a region of their higher concentration through a partially permeable membrane. This movement usually takes place through a membrane which is permeable to water but not to solutes.

In my investigation I am going to be investigate the factors affecting the rate of Osmosis. Some factors affecting this are:

Length - of membrane

Temperature - of water

Concentration - of solution

The factor I am going to investigate is the length.

Prediction
Osmosis is defined as ¡§the movement of water molecules across a partially permeable membrane from a region of high water concentration to a region of low water concentration¡¨.

In a high concentration of water the amount of solute (e.g. sugar) is low. This could be called a weak or dilute solution. In a low concentration of water the amount of solute (e.g. sucrose) is high. This could be called a strong or concentrated solution. When two such solutions are divided by a semi-permeable membrane the water will move from the area of high concentration to the area of low concentration, until both sides are equal (have reached equilibrium).

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Knowing that osmosis will occur across a semi-permeable membrane whenever there is a difference between the water concentrations on the two sides of the membrane, and knowing that when this happens to cells they will either become turgid if water flows into them, or plasmolysed if water flows out of them, and thus change their volume, we want to test the hypothesis that:
If the concentration of a solution into which a cylinder of potato is placed is greater than a certain level the cylinder will contract, and if the concentration is less than that level it will expand. This can ...

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