Photosynthesis

Osmosis investigation

Aim: To investigate how sugar concentration affects the mass or size of a potato and find out the sugar solution.

Introduction: Osmosis is the movement of water molecules across a partially permeable membrane form a region of high water concentration to a region of low water concentration until the concentration on both sides is equal. This means that osmosis is like diffusion involving water molecules. Osmosis occurs across a partially permeable membrane, with holes only small enough for water molecules to pass through and not larger ones like glucose. An example of a partially permeable membrane is visking tubing. Osmosis happens so that the concentration outside the membrane is equal to the concentration inside the membrane. This means that there will be a steady net flow into the stronger solution, (of glucose) causing this region to fill with water and dilute it. This is how the concentration is balanced. Higher water concentration means a more dilute solution; because water makes up a high proportion of the molecules present, conversely lower water concentration means a more concentrated solution.

Osmosis is important for organisms because this is how water is transported into and out of cells. The osmosis that takes place in plant cells when surrounded by a weak solution makes the cells swell up and become turgid. This is useful for the plant as it gives support for opening stomata guard cell. Leaves are entirely supported by the turgor pressure that is created when a plant is well watered and all the contents of the cells start to push against the cell wall and thereby giving support to the plant tissue. This is important as it makes green parts of the plant "stand up" into the sunlight.

In the diagram below the water has passed into the cell, into the strong solution by osmosis. In the other cell water has passed out of the cell into the strong solution by osmosis.

Prediction: I predict that the higher the concentration of the sugar solution the lower the final weight of the potato chips. I have predicted this because water will pass out of the potato chip into the sugar solution. This happens because the sugar solution has a lower water concentration than the potato chips therefore the chips will lose water to make the water concentration even either side of the membrane. Therefore a sugar concentration of 0.5 will give the largest decrease in mass, compared to weaker sugar solutions. This is because the concentration gradient is greater meaning more water will have to pass out of the potatoes for equalization compared to weaker sugar solutions. I can also predict that the weakest sugar solutions will give the least decrease in potato mass, this is because there is a smaller concentration gradient therefore less water will have to leave the potatoes to equalise the two regions. the and the distilled water will give the largest increase in mass. In distilled water I think that the potato chips will swell because water enters their cells by osmosis. My reasons for this can be seen in osmosis when water diffuses into the cell from a weaker solution (high water concentration) into the stronger solution (low water concentration). This means that because the potato chips are full of starch they will absorb water when put into the distilled water, as this is the weaker solution with a high concentration. Taking this into account I predict that the graph will look similar to the one below.

I can predict that in weak sugar solution that like 0.1M there will also be an increase in the mass of the potato chips. This is because the potato chips contain starch and is a stronger than the weak sugar solution. This means that the sucrose has the lower concentration and will increase the potatoes mass by osmosis.

Preliminary work:

Aim: To find out which root vegetable contains the most sugar (starch).

Equipment: Root vegetables (swede, turnip, potato, parsnip) cut into slices/cubes, 8 Beakers, distilled water, 0.4M sugar solution, balance, paper towels.

Diagram:

Distilled water 0.4M sugar solution

Method:

1. Collect apparatus.

2. Weigh 3 cubes of turnip (to go into distilled water) and record into results table.

3. Weigh another 3 cubes of turnip (to go into sugar solution) and record in results table.

4. Repeat steps 2 and 3 for the other 3 root vegetables.

5. Place 3 cubes of each vegetable into separate beakers of 0.4M of distilled water.

6. Place the other 3 cubes of each vegetable onto separate beakers of 0.4M of sugar solution.

7. Leave the cubes in the beakers for 30 minutes.

8. After 30 minutes remove the cubes. Wipe of / blot any excess liquid with the paper towels.

9. Reweigh each cube and record the new masses into the table.

10. Calculate the total change in mass. Then calculate the percentage change in mass using the following:

% change in mass = final mass -initial mass/initial mass x100%

The preliminary work is similar to the potato chip experiment; this means I will be following the same procedure and using most of the same equipment. This is why the preliminary work helps me to plan for the actual experiment.

Results table:

Potato chips cont.

Equipment: 6 beakers, distilled water, sugar solution (0.1M, 0.2M, 0.3M, 0.4M, 0.5M), potato cubes, balance, paper towels.

Safety: No