To Investigate the Effect of Water and Sugar Solution of different Concentrations of the Mass of Potato Cylinders.
To Investigate the Effect of Water and Sugar Solution of different Concentrations of the Mass of Potato Cylinders.
PLANNING:
Background scientific Information
Potato Plants:
The potato plant produces glucose through photosynthesis and stores it in the potato. The glucose is carried from the leaves where it is produced, down to the potato in the phloem where it is changed into starch to be stored. The Potato is part of the root of the plant and spreads out just below the surface of the soil, as shown in diagram 1
Diagram 1, The potato Plant
Photosynthesis:
Is the process where Carbon dioxide and water combine to produce glucose and oxygen. The glucose that is made is transported to the potato where it is changed into starch to be stored.
Plant Cells:
A typical plant cell:
Diagram 2, Structure of a typical Plant Cell
Cell Membranes:
Plant cell membranes are selectively permeable, allowing only certain sized molecules to pass through it. It contains pores or holes, which are too small to allow some molecules to diffuse in or out of the cell, such as starch. Other molecules diffuse slowly through it because they must hit the membrane at the right angle, like glucose. But water molecules are small enough to diffuse freely in and out of the cell
Osmosis:
Osmosis is the movement of water molecules from an area of high concentration, to an area of low concentration through a partially permeable membrane.
Turgid and flaccid cells:
When the cell has a higher level of concentration of water on the outside of the cell than inside the cell, the water moves in through the partially permeable membrane to even the concentrations in and out of the cell. This makes the cell turgid and full of water. The Vacuole increases in size and the cell membrane presses against the cell wall, making the cell wall stretch. The cell increases in mass and volume and becomes well supported. Diagram 3.
Diagram 3, A Turgid Cell Diagram 4, A Flaccid Cell
If the plant is placed in a solution with a lower concentration of water on the outside of the cell than inside, then water moves out of the cell into the surrounding solution through the partially permeable membrane. This will cause the vacuole to shrink in size and the cell membrane and cytoplasm starts to pull away from the cell wall. This cell is described as flaccid and has less mass and volume than a typical cell. This cell can become turgid again by surrounding it with ...
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Diagram 3, A Turgid Cell Diagram 4, A Flaccid Cell
If the plant is placed in a solution with a lower concentration of water on the outside of the cell than inside, then water moves out of the cell into the surrounding solution through the partially permeable membrane. This will cause the vacuole to shrink in size and the cell membrane and cytoplasm starts to pull away from the cell wall. This cell is described as flaccid and has less mass and volume than a typical cell. This cell can become turgid again by surrounding it with water. Diagram 4.
When the solution inside the cell and outside the cell have the same concentration of water, their mass and volume will cease to change and osmosis will stop.
Relevant past experiments:
. Effects of Osmosis
What happened: - two sets of visking tubing were taken, one filled with water and the other filled with strong sugar solution, each visking tube had both ends tied up. One one with water inside it was placed in a beaker of a strong sugar solution and left and the other was placed in a beaker of water. They were left.
Results: - the tube surrounded by strong sugar solution shrunk in volume. The tube surrounded by water gain in volume.
Conclusion: - the tube that gained in volume had water pass through the tube by osmosis from a high to a low concentration. This meant that the water was entering the tube to equal out the concentration, but no sugar solution left, meaning that the tube would expand
The tube that shrunk in volume had water pass out of the tubing by osmosis from a high to low concentration. This meant that the water was leaving the tube but nothing was entering, meaning the tube would shrink.
Experiment:
Investigating Osmosis in Potato Cylinders
Background: - Potato cylinders contain cells that are surrounded by a fully permeable cell wall and a partially permeable cell membrane. The cells contain sap inside a vacuole, which is a solution of various substances dissolved in water.
Plan: - I will exercise normal laboratory safety procedures as I do this experiment. And cut away and down form myself when using a scalpel. I will prepare the apparatus I will use in this experiment. This will consist of 1 molar sucrose solution, water, 18 potato cylinders, 18 test tubes, test tube rack, measuring cylinder, and scalpel.
To make this test as fair as possible I will cut each potato cylinder down to 40mm using a scalpel. This will also remove the skin, which needs to be discarded in this experiment because we are only looking at the inner potato cells. When using the scalpel I will cut away and down from myself as to reduce the risk of cutting myself. I will also use exactly the same volume of liquid in each test tube. This will be 5 cm^3. I chose this amount of solution so that it covers the cylinder completely and uses as little as possible as not to waste it. I will also put every cylinder in its solution for 7 minuets 30 seconds to increase the fairness of this test. I decided on this time because it should be enough to have a noticeable change in the mass of the cylinders I will dry the cylinder before I weigh them, before and after the experiment to make sure no excess water is still on them.
I will make 6 observations of the potato cylinder in different concentration solutions. These concentrations are equally spread out between pure 1 molar solution and no water, and no 1 molar solution and pure water. This should give me spaced out results and so I can learn more about the osmosis in plant cells. I will do 3 tests in each of these solutions to give me an average and accurate reading for each solution. For the first solution
I will use pure molar solution (5cm of molar), pure concentration of molar
One will be 4cm^3 of molar and 1 cm^3 of water, 0.8 molar, 0.2 water concentration
Another will be 3cm^3 of molar and 2cm^3 of water, 0.6 molar, 0.4 water concentration
The next will be 2cm^3 of molar and 2 cm^3 of water, 0.4 molar, 0.6 water concentration
Then 1cm^3 of molar and 4cm^3 of water, , 0.2 molar, 0.8 water concentration
Then pure water.(5cm^3 of water) , Pure concentration water.
I have chosen these readings because they give an even distribution of concentrations and should give me interesting results. So all together I will get 18 readings and then I will get 6 average results for the 6 solutions.
Before each test I will dry and then weigh the potato cylinder and note its mass. I will then place it in the solution for 7.5 minuets and then take it out, dry it and then weigh it. The weights will be measured in grams and the liquids in cm^3.
Hypothesis: - I predict that as the concentration of sugar solution increases, the cells will become lighter, smaller and more flaccid. The heaviest and largest percentage gain in mass will be the potato cylinder surrounded by pure water, and the lightest and smallest gain in mass will be the potato cylinder surrounded by one hundred percent sugar solution.
I predict these results because osmosis states that water will move through a partially permeable membrane to equal the concentration inside and outside the cell. This means that is there is a lot of water outside the cell, it will move into the cell, and therefore become heavier and larger. The same principle applies if there is a low concentration of water outside the cell except the water will move out of the cell to equalise the concentration.
Aim: - To investigate the effect of water and sugar solution on potato cylinders.
Risk Assessment: - Exercise caution when using a scalpel to trim the potato cylinders.
Use general laboratory practise including wearing and apron and goggles.
Apparatus:-
* 18 potato cylinders measuring 40mm long with no potato skin on it.
* 45cm^3 of molar solution
* 45cm^3 of water.
* Scalpel
* 18 test tubes
* test tube rack
* scales
* stop watch
* measuring cylinder.
Diagram: - The apparatus will be set up as shown below.
Method:
Six potato cylinders were taken measuring 10mm in diameter from a potato. All of the cylinders were cut down to 40mm in length by cutting down and away to avoid injury by using a scalpel, so each cylinder was the same length. Each of these cylinders was dried and then weighed. These weighed cylinders were allocated a concentration of the solutions. This is so the mass before and after the experiment can be compared. These masses were recording in grams to two decimal places as 'Mass before experiment' in the result's table.
Six test tubes were then taken and filled with 5cm different concentrations of 1 molar solution and water. These concentrations were as follows:
. 1, 1 molar solution, and 0, water concentration
2. 0.8, 1 molar solution, and 0.2, water concentration
3. 0.6, 1 molar solution, and 0.4, water concentration
4. 0.4, 1 molar solution, and 0.6, water concentration
5. 0.2, 1 molar solution, and 0.8, water concentration
6. 0, 1 molar solution, and 1, water concentration
then the allocated cylinders were placed in their allocated concentration and left for 7.5 minuets.
They were then taken out and dried. The dried cylinders were weighed in grams and to two decimal places, these were recorded as 'mass after experiment' in the result's table.
This exact same experiment was repeated two more times as to gain a reasonable average.
