Osmosis

Osmosis

Introduction - Osmosis is a form of passive transport, and a

specialised form of diffusion. It is the movement of water from a

dilute solution to a more concentrated one, through a semipermeable

membrane. Hence it is where water moves from a high to a low

concentration. I will design an experiment to test this process on a

typical example of osmosis' effect on plant cells, taking as the

sample, potato. It is through osmosis and the fluctuating levels of

water in the cell that the concentrations of minerals in the plant are

regulated.

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Expt. 1 Last year, I conducted two experiments in which dialysis

tubing was used to simulate the semipermeable membrane. In the first

experiment a knot was tied in one end of a length of soaked dialysis

tubing and a pipette was used to half fill it with a strong glucose

solution. The air bubbles were expelled and a knot was tied in the

other end. At this point the tubing was flaccid (limp). When it was

then placed in a test-tube full of distilled water, it became turgid

(firm). [See diag.1]

Expt. 2 In the second experiment red-dyed sugar solution was placed in

a bell-shaped piece of apparatus, with a capillary tube off it and a

cellulose film over the bottom [See diag.2]. This was then placed in a

beaker full of distilled water and left for half an hour, by which

time the level of water in the beaker had gone down, and red dye had

moved up the capillary tube. The water in the beaker had not turned

red. The experiment was then repeated with a stronger solution. The

volume of water in the beaker decreased further; t...

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...raphy -

1.

http://biog-101-104.bio.cornell.edu/BioG101_104/tutorials/osmosis.html

This is a tutorial, so that I had to go through the "test" typing in

answers to their questions. Each time they would correct or confirm my

answers. It is here that I learnt some of the terminology I have used,

and here that I learnt the units of Ψs and Ψw.

2. http://www.howstuffworks.com/question29.htmand

http://www.purchon.com/biology/osmosis.htm#defexpl both gave simple

explanations of osmosis.

3. http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm In

many ways the best site, this explained clearly, but also used

terminology such as "hypotonic and isotonic".

4. My Exercise book and Maclean's GCSE Biology book - I gained

information about Expts. 1 and 2 from early class work and textbook

material.