Investigation into the effect of osmosis on potatoes.

Authors Avatar

Investigation into the effect of osmosis on potatoes

Background

        Osmosis is a specialised form of diffusion where water molecules from a higher water concentration (hypotonic) diffuse through a partially permeable membrane to a lower water concentration (hypertonic).  

        When a substance dissolves in water to form a solution that substance attracts water molecules therefore reducing the number of free water molecules in a solution which in effect reduces the concentration.  Free water molecules can travel faster through partially permeable membranes than larger molecules of other substances that have a cloud of water molecules surrounding due to their smaller size

        Therefore when there are two solutions either side of a partially permeable membrane with a hypotonic solution on one side and a hypertonic solution on the other side the greater number of free water molecules in the hypotonic solution will move through the membrane faster than the higher number of large solute molecules with their water molecules surrounding them in the hypertonic solution and as there are less free water molecules in the hypertonic solution which are also moving more slowly, than those in the hypotonic solution due to the increased level of solute molecules, there will be a higher rate of movement of free water molecules from the hypotonic solution to the hypertonic solution and so the water concentration in the hypotonic solution will begin to decrease while the hypertonic solution’s water concentration will increase until there is an equilibrium and the movement from either side to the other side is equal and then the water concentration on either side will not change unless more solute is added to either solution.

        

Osmosis is a very important process in a living organism, where the cell membrane is an organic partially permeable membrane, because of the need for the distribution of water as substances in the cytoplasm of a cell must be kept at a specific concentration for many body processes to take place successfully.

        As well as moving down concentration gradients water in osmosis moves across pressure gradients as well as many other gradients including temperature and entropy gradients and these gradients come under water potential which is the driving force behind osmosis and so it can be described as the ability of water to move.  Water potential is the chemical potential of water and it is a measure of the energy available for movement of water molecules in aqueous solutions.  Water always moves from a solution with a high water potential to a solution with a low water potential.  

        In plant cells when water diffuses into the cell the protoplast expands and pushes against the cell wall until it takes up the maximum space it can without the cell wall moving.  The cell can then be described as turgid and the turgor pressure is the pressure the protoplast exerts on the cell wall when the cell is turgid.  If the opposite happens and water diffuses out of a plant cell the cell becomes plasmolysed and flaccid as the protoplast will shrink and if it continues for long enough the plant will wilt.

Join now!

        

In plant cells water potential has two main components which are solute potential and pressure potential.  

Solute potential is the effect of dissolved substances on the potential energy of a solution and a hypotonic solution has a high solute water potential while a hypertonic solution has a lower water potential.  Solute potential is a always 0 or below with pure water having a solute potential of 0 and a hypertonic solution having a smaller solute potential.  Solute potential is the key factor in water potential because as we know the major factor in osmosis is the movement ...

This is a preview of the whole essay