Effect of Ethanol on Beetroot Membrane

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Biology Coursework

Hypothesis: To investigate the effect of different concentrations of ethanol on the permeability of beetroot cell membranes.

Prediction: By exposing a membrane to a solvent, ethanol, it will increase its permeability. So the higher the concentration of the solvent, the more permeable the membrane will be. But if the concentration of the ethanol is beyond a certain limit, it may break down the cell membrane to the point where there is in fact no overall effect as the ethanol would disturb the lipids in the membrane.

Therefore, more of the red pigment in the beetroot would leak as the lipids control the substances that enter and leave the cell membrane.

However the ethanol might also impair particular proteins or denature the structure as protein has a tertiary structure. Higher concentrations of ethanol would destroy hydrogen bonds that clasp the protein structure. As the lipids and proteins in the cell membrane would be destroyed, the pigment is able to leak from the cell at a higher rate due to there being no cell membrane holding it in the cell.

Diffusion to the cell membrane

Cells must acquire needed ions and molecules from their surrounded extracellular fluid meaning that they must be transported through the cell membrane. This happens by diffusion, which is movement of substances from a high concentration to a lower one through a partially permeable membrane. As ethanol would also be surrounding the cell in a high concentration, it would also be diffused therefore destroying the permeability of the cell membrane. Diffusion is also used to transport other ions and molecules such as oxygen and carbon dioxide. Water also diffuses through the membrane, which is called osmosis.

Diffusion and Facilitated Diffusion (Passive transport):
Another type of diffusion also happens in the cell, facilitated diffusion. Hydrophilic molecules which are small and polar, like oxygen can pass easily through cell membranes by normal diffusion. However, larger hydrophilic molecules, like glucose, pass across the cell membrane by facilitated diffusion. In facilitated diffusion, the structure of the proteins only allows specific molecules to cross the membrane, which are the hydrophilic pores. Non-polar hydrophobic molecules are disallowed to cross the cell membrane by phospholipids, meaning that they are small enough to cross between the phospholipids layers.

Active transport:
By active transport, ions and molecules are forced by the use of metabolic energy to move against their concentrated gradient

Function and structure of cell membranes:
The cell membrane surrounds all cells to decide what may enter and leave the cell. In the fluid mosaic model, the membrane structure is made up of a double layer of phospholipid molecules, which is called the lipid bilayer, with a hydrophilic head which is on the outside of the membrane and a hydrophobic tail which is on the inside of the membrane. The cell membrane is fluid and this is helped by cholesterol, which destructs the phospholipids by breaking up the Van der Waals forces. The proteins that float in this bilayer are either on the surface or penetrate the lipid layer. Some substances, including water, are transported directly through the lipid layer.


The lipids in the bilayer are soluble to organic solvents with low molecular weight molecules, such as ethanol; therefore to have beetroot in ethanol would affect the lipids in the bilayer by dissolving them. Hence, more pigment would leak into the solution because there would be less structure to the cell membrane to hold in the pigment if the lipids have been damaged or destroyed.

Other Effects Of Ethanol On The Membrane

Not only does ethanol have an effect on the soluble lipids in the cell membrane by dissolving them, it also affects the proteins in the cell membrane by impairing their functions. This happens as ethanol also impairs hydrogen bonding in lipids and peptide...
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