L1. Osmosis

Introduction:

Osmosis is the spontaneous movement of solvent molecules throught a semipermeable membrane into a region of higher solute concentration that tends to equalize the solute concentrations on the two sides. Is a vital process in biological systems, as biological membranes are semipermeable. Water molecules travel through the plasma membrane in order to equilibrate the intra and extra cellular concentrations.

When a cell is submerged in water, the water molecules pass through the cell membrane from an area of low solute concentration to high solute concentration. When extracellular concentration is hypertonic, water moves out of the cell and the cell becomes flaccid: plasmolysis. When the extracellular concentration is hypertonic, water moves inside the cell and it becomes turgid.

Materials:
- egg
- potato
- salt
- distilled water
- acetic acid
- vinegar
- spatula
- 250 mL beaker
- 3 clock glass
- spoon
- knife

Procedure

Potato

1. Lay out three watch glass
2. Slice the potato in three parts lengthwise.
3. Place each slice onto a watch glass and make a hole in the middle of each slice. (the hole doesn't have to cross the slice)
4. In the first slice hole don't put anything, in the second you have to put salt and the third distilled water.
5. Left this preparation 30 minutes and make note what is happening.

Egg:

Before the egg osmosis experiment could begin the egg's hard outer shell must be removed. Let's start with this:

1. Take a 250 mL beaker and put the egg.
2.  cover the with vinegar (acetic acid) and make note of what's happening.

Once the egg's shell is removed and the egg is rinsed dry and clean, measure and weigh the egg.

3. Clean the beaker and put the egg inside again.
4. Cover with distilled water.

5. Left the egg one day in distilled wáter, after about a day, carefully remove the egg using a spoon. 

Questions

Egg experiment:

1. What is happening when the shells are soaking of acetic acid?

Bubbles

2. Write the results of the dimensions and weigh of the egg before and after immersing it in distilled wate. Write and draw a simple diagram of the water direction.

Potato experiment:

1. Explain the results of this experiments. 

Control: Doesn't change

Potato with salt: there are a lot of water

Potato with water: the water dissaper

2. Why have we left the first slice without any treatment?

To compare all the results

3. Which are the dependent and the independent variables?

dependent: the form of the cells

independent: tractment

General questions

1. How can you explain the ability of plant roots to draw water from the soild?

Perquè les cel·lules de la planta tenen sals i al possar aigua, l'aigua es dirigeix on hi ha més concentració.

2. What will it happen if a saltwater fish is placed in a freshwater aquarium?

It will die

3. Look the image you have below and explain what is happening to the erythrocytes in each situation. 

picture 1: plasmolisi

picture 2: isotónica

picture 3: turgencia

Egg with distilled water

Egg with disitilled water

weight egg

Egg without semipermable membrane