Osmosis
What is osmosis?
Osmosis is the net movement of water molecules from an area of high water concentration (dilute solution) to an area of low water concentration (concentrated solution) through a partially permeable membrane.
Osmosis is the net movement of water molecules from an area of high water concentration (dilute solution) to an area of low water concentration (concentrated solution) through a partially permeable membrane.
When/Why does osmosis occur?
Osmosis happens when the water surrounding a cell is more concentrated than the water inside of the cell’s cytoplasm. In this case the cytoplasm will push against the cell wall due to the numerous water molecules coming into the cell. It can also happen vice versa, when the water inside of the cell is more concentrated than the water surrounding the cell. When this happens the cytoplasm will then push away from the cell wall as it has shrunk due to the water molecules leaving the cell. This happens due to the water molecules moving from an area of high concentration to an area of low concentration.
Osmosis happens when the water surrounding a cell is more concentrated than the water inside of the cell’s cytoplasm. In this case the cytoplasm will push against the cell wall due to the numerous water molecules coming into the cell. It can also happen vice versa, when the water inside of the cell is more concentrated than the water surrounding the cell. When this happens the cytoplasm will then push away from the cell wall as it has shrunk due to the water molecules leaving the cell. This happens due to the water molecules moving from an area of high concentration to an area of low concentration.
Osmosis Lab example:
A clear example to show the way osmosis works would be the ‘Osmosis in Potato cells’ experiment. In this experiment we use 3 pieces of potato, cut into strands which are about the same mass, which will each be placed into different sugar concentration solutions. To find out where osmosis occurred we weighed the mass of each strand of potato before starting the experiment and we would weigh our strands of potatoes after the experiment again to see if there was a difference in mass and therefore if osmosis had occurred. The first piece of potato will be placed in a sugar concentration of 0 molar, the second in a concentration of 0.5 molars and the third in a concentration of 2 molars. The theory to this experiment was that the piece of potato in the 0 molar sugar concentration would be the one where the water molecules will go inside the potato cells and the piece of potato in the 2 molars sugar concentration would be the one where the water molecules would leave the potato cells to go into the solution. We also thought that the piece of potato which would go in the 0.5 molar solution would stay more or less the same because there would be an equilibrium.
A clear example to show the way osmosis works would be the ‘Osmosis in Potato cells’ experiment. In this experiment we use 3 pieces of potato, cut into strands which are about the same mass, which will each be placed into different sugar concentration solutions. To find out where osmosis occurred we weighed the mass of each strand of potato before starting the experiment and we would weigh our strands of potatoes after the experiment again to see if there was a difference in mass and therefore if osmosis had occurred. The first piece of potato will be placed in a sugar concentration of 0 molar, the second in a concentration of 0.5 molars and the third in a concentration of 2 molars. The theory to this experiment was that the piece of potato in the 0 molar sugar concentration would be the one where the water molecules will go inside the potato cells and the piece of potato in the 2 molars sugar concentration would be the one where the water molecules would leave the potato cells to go into the solution. We also thought that the piece of potato which would go in the 0.5 molar solution would stay more or less the same because there would be an equilibrium.
Our
hypothesis was that in pure water, the mass of the potato would increase and
that in high solute concentration, the mass will decrease.
We
started out by taking our three pieces of potato and weighing each one and we
then recorded their mass. After this, we placed each piece of potato into the
three solutions of sugar and left them in the solution for 25 minutes. After
waiting 25 minutes we took the pieces of potato out of the solution and again
weigh each piece of potato again and record their mass.
Our
results were as expected in our theory:
Sugar concentration (molar)
|
Time (minutes)
|
Mass before experiment
(grams)
|
Mass after experiment
(grams)
|
Mass increase and decrease
(grams)
|
0
|
25
|
3.19
|
3.47
|
+ 0.28
|
0.5
|
25
|
3.04
|
2.96
|
- 0.08
|
2
|
25
|
3.05
|
2.62
|
- 0.43
|
We therefore concluded our experiment by saying that when the piece of potato is in a high sugar solution, it will lose some of its mass and when it is in a low sugar concentration, it will gain mass. This increase and decrease of mass is therefore what proves osmosis happening in cells.
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