Structure of a Cell Membrane:
Cell membranes are composed of phospholipid bilayer which are made up of two layers of phospholipids. In a phospholipid there is a phosphate head that is polar meaning that one end is slightly positive and the other slightly negative, this allows other polar molecules, e.g. water, to be attracted to it, giving it hydrophilic properties. There is also a tail which is non-polar so does not attract polar molecules but instead repels them. The phospholipid bilayer gives the membrane selectively permeable membranes and allows the fatty acid tails to avoid contact with the water.
With in the cell membrane there is also proteins, cholesterol, glycoproteins and glycolipids, some of which are able to move within the membrane due to its fluid and flexible structure. These properties also allow the cell for cell movement and growth.
Beetroot cells contain a purple pigment known as anthocyanin which is contained in the cell’s vacuole, surrounded by a membrane known as a tonoplast. The anthocyanin is water soluble and not lipid soluble and so remains inside the membrane when the cells are healthy. For the anthocyanin to escape and spill out into the surroundings, the tonoplast and cell surface membrane must be damaged. It will diffuse into the surroundings down the concentration as the solution will be hypotonic and so it will move from the area or high concentration- the beetroot cells, to the area of low concentration- the solution it is in. The intensity of the colour is proportional to the amount of cellular damage, so the stronger the colour is, the higher the amount of damage done to the cells will be.
Effect of temperature on the Cell Membrane:
The perfect temperature for a cell to function at is at 37?, the natural temperature of a healthy human body as it allows the membrane to have the right fluidity and permeability and is the optimum temperature for the proteins to function.
As temperature increases, energy is transferred to the phospholipid molecules in the form of kinetic energy which causes them to move and vibrate faster and more frequently. The increase in movement causes disruption to the cell membrane as well as the tonoplast and causes temporary gaps to be created, which allows molecules that were originally unable to move through the membrane to pass through. The increase in energy also causes the proteins to gain more energy and vibrate more which can lead to them coming apart or being misshapen which leads to further holes in the membrane and further increasing the permeability. If the temperature increases too high than the proteins will be denatured and will no longer be able to carry out their function.
If the temperature decreases, it will have the opposite effect and the phospholipids will become more rigid and therefore will decrease the overall fluidity and permeability of the membrane. If the temperature becomes too low, the liquid in the cell may turn into crystals that will expand and pierce the cell membrane.
Effect of Alcohol on the Cell Membrane: