Investigating Osmosis

Investigating Osmosis

Introduction

Definitions - Osmosis is the movement of water molecules from where

they are at a high concentration to where they are at a lower

concentration through a selectively permeable membrane. A selectively

permeable membrane is one which allows only molecules of a certain

size through.

[IMAGE]

This very basic diagram shows osmosis occurring between sugar

solutions and water in visking tubing and beakers. The bag expands

because the water moves from the beaker where it is at a higher

concentration through into the tubing where it is at a lower

concentration.

Example of osmosis - Osmosis is the way in which plants absorb water

(and get their minerals).The cell walls in the root hairs are

semi-permeable. In the soil, the water is fairly pure and has no

dissolved sugar in it so there are lots of water molecules and no big

sugar molecules blocking their way. Many water molecules hit the cell

walls and pass through to the inside. Inside the cell there is more

dissolved sugar, so not many water molecules hit the cell wall from

the inside. As a result, more water molecules go in than come out.

Overall, the effect is that water molecules pass from the area of low

sugar concentration (the soil) into the area of high sugar

concentration (the cell) and any minerals dissolved in the water get

carried into the cell as well.

[IMAGE]Osmosis in red blood cells- red blood cells have no rigid cell

wall, therefore they cannot become turgid and if they are put into a

very dilute water solution they will fill up with water and eventually

burst. . In concentrated solutions, water is sucked out of the cell by

osmosis and the cell shrinks. Both could be fatal if allowed to carry

on in the body. This does not happen though because the blood water

levels are kept constant by the process of homeostasis. The kidneys

are the main regulator of the amount of water in the blood as well as