L3. Osmosis

On Monday 6th of October we started a a new experiment called "Osmosis", the main objectives were to know about the osmosis phenomena and understand the process of osmosis in plasmatic membranes. This experiment was divided in two other experiments (with the potato and with the egg).

MATERIALS:

-Egg
-Potato
-Salt
-Distilled water
-Acetic acid
-Spatula
-250 ml beaker
-3 clock glass
-Pen
-Spoon
-Knife

PROCEDURE

Potato experiment:
1- First we sliced the potato in three parts lengthwise, the slices had to be 1,5 cm thick more or less.
2- Then we took the spoon and made a hole in the center of the potato (the hole didn't cross the slice) and then we put the potato pieces in three clock glasses.
3- In the first slice we didn't put anything, in the second we put salt and lastly we filled the hole of the third potato with distilled water.
4- We left this preparation for the rest of the class to see what happens.

Results, observations and conclusions: Our hypothesis was that in the second case the potato would expel water because the concentration of salt of the potato is lower, and in the third case the potato would absorve the water because the concentration of salt is higher in the cells of the potato (distilled water doesn't have any salts). The first potato was to control and compare the results. We were correct!! At the end of the class we saw that the second slice was full of water and the third one was dry, also the teacher told us that the second potato will become softer, plasmolysed, because it has less water and the third potato will become harder, turgid.
We saw the osmosis phenomena because the water went from a hypotonic environment to a hypertonic through a semipermeable membrane to equalize the solute concentration on the two sides. So the potato absorved or expelled water because of this phenomena.

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Egg experiment:
1- First we put the egg in a 250 ml beaker with acetic acid and left it a couple of days.
2- When the outer shell was disolved and only the membrane was left we weighed the egg.
3- Then we cleaned the beaker and put the egg in distilled water.
4- We waited some more days and then we poured out the distilled water and weighed the egg again.
5- Next we put the egg in water with 3 spoons of salt.
6- After a couple of days we weighed the egg again.

Results, observations and conclusions: We remembered our last experiment to remove the shell ( "CH3 COOH + Ca CO3 --> CO2 + (Ca (CH3COO)2)" ), then our hypothesis was that the egg would do the same thing as the potato, and it's partially true. The membrane under the hard outer shell of the egg is semipermeable and it allows air and moisture to pass through. Because water molecules can move into and out of the egg but larger molecules cannot, the semipermeable egg membrane allows the osmosis. So when the egg was submerged into distilled water, the cells of the egg had a higher concentration of salts so the water went to the hypertonic environment and the egg absorbed this water and became turgid. We can confirm this because we weighed the egg and the weight was bigger: at the beginning the egg's weight was 156,3 grams and after was 178,8 (the egg gained  22,5 grams of water). Then the egg was submerged into water with salt and we thought that the egg would expell the water so it would loose weight but the opposite happened, the egg absorbed even more water!! We weighed it and it's weight was 186,7 grams (it gained 7,9 grams) This happened because we only put 3 spoons of salt in the water, so the concentration of salts inside the egg was still higher than in the water. We should of put more salt if we wanted the egg to plasmolyse. Again, we saw the osmosis phenomena in both cases.

QUESTIONS

Egg experiment:
1- What is happening when the shells are soaking of acetic acid? Bubbles start to appear (CO2) cos the calcium carbonate starts disolving.

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.
Beginning: 156,3 g
After distilled water: 178,8 g
After water with salt: 186,7 g

Potato experiment:
3-Explain the results of this experiment. 
I already did earlier.

4- Why have we left the first slice without any treatment (salt or distilled water) ? Because it was the control one, it didn't change, we use it to compare  the other results.

5- Which are the dependent and independent variables?
Dependent: the turgidity of the potato
Independent: the treatment, salt or distilled water.

General questions:
6- How can you explain (through osmosis) the ability of plant roots to draw water from the soil?
In the cells of the plant there are salts so when you put water, there is more concentration of salt in the plant and the water goes to the roots (from hypotonic to hypertonic).

7- What will happen if a saltwater fish is placeed in a freshwater (low concentration of salts) aquarium?
It will die because the concentration of salt in it's body will be higher so the water from the aquarium would be absorbed by the fish.

8- Look the image you have below and explain what is happening to the erythrocytes in each situation:

In the first case the water is expelled from the cells because the concentration of salt out of the cells is higher than in them so they loose water and they get plasmalysed. In the second case water is absorbed and expelled so it's isotonic the concentration of salts is already equalized. In the third case water is absorbed so the cells become more turgid, the concentration of salts is higher inside the cells.