L3. OSMOSIS

1.Introduction
Osmosis is the spontaneous movement of solvent molecules trough a semipermeable membrane into a region of higher solute concentration (hypertonic), in the direction that tends to equialize the solute concentrations on the two sides.

When a cell is submerged in water, the water molecules pass trough the cell membrane from an area of low solute concentration to a high solute concentration.

PLASMOLYSIS: When the extracellular concentration is hypertonic and the water moves out of the cell so this cell becomes flaccid.

TURGID: When the extracellular concentration is hypotinc so the water moves inside the cell.

2.Objectives
1-Know about the osmosis phenomena.
2-Understand the osmosis in plasmatic membranes.

3. Hyphotesis
The concentration of salt inside the egg is higher that outside so, the egg will absorve the distilled water trough the semipermeable membrane and the egg will become turgid.

4. Materials
-Egg
-Potato
-Salt
-Distilled water
-Acetic acid (or vinegar)
-Spatula
-600 mL Beaker
-3 clock glass
-Pen
-Spoon
-Knife


5. Procedure
The egg experiment will be divided in two diferent days.
1st day:
Before we start the osmosis experiment we must remove the egg's hard outer shell. So we will star by:
1-Taking a 600 mL beaker and putting the egg inside of it.
2- Then we will cover the egg with vinegar and make note of what's happening.
 Once the egg's shell is removed and the egg is rinsed dry and clean, we will measure and weigh the egg. After that we have to record the dimensions of each egg in a table.
3- Now, we will clean the beaker and put the egg inside again.
4- We cover it with distilled water, and take notes of the volume of solution inside the beaker.

2nd day:
5- After we have left for about a day the egg in the distilled water, we remove the egg using a spoon.
6- We mesure again the dimensions and recod its weight.
7-Making note of the solution volume in the beaker we look if there has been any difference.
8-We observe the results and write the conclusions in our lab worksheet.

Potato experiment
1-Lay out three watch glass
2-Slice the potato in three parts lenghtwise. Each slice must be of 1,5 cm thick.
3-Place each slice onto a watch glass and make a hole in the middle of each slice, but it's important that the hole don't cross the slice.
4-In the first slice hole, don't put anything. The second one fill it with salt and the third with water.
5-Left the preparation 30 min and make note of whats happening.

6. Conclusions
The egg has suffered turgidity.
The potato fulled with water has been inflated, so it has suffered turgidity. The salted potato has wrinkled, it has suffered plasmolysis.

7. Questions
Egg esperiment:
1-What is happening when the shells are soaking of acetic acid?
You can see bubbles that are produced from CO2
2-Write the results of the dimensions and weigh of the egg before and after immersing it in distilled water. Write and draw a simple diagram of the water direction.

Potato experiment:
3-Explain the results of this experiment.
The control potato that has nothing inside the holl keeps normal, without change.
The potato with salt inside the hole becamed fulled of water
The potato with destilled water has becomed turgid, because it has absorved the water completely.
4-Why have we left the first slice without any treatment? (salt or distilled water)
To have a control potato to compare with the other ones and see the results.
5-Which are the dependent and independent variables?
Dependent: the turgency and the potato
Independent: The salt and distilled water, because that are the ones that we have to modify.


General questions:

6-How can you explain (through osmosis) the ability of plant roots to draw water from the soil?
Inside the cells of the plants there are salts and when you put the plants inside water, the cells are more concentrated so the water goes to the roots.
7-What will happen if a saltwater fish is placed in a freshwater (low concentration of salts) aquarium? It will die because of the difference of concentrations.
8-Look at the image and explain what is happening to the erythrocytes: