The Effect of Temperature on the Permeability of Beetroot Membrane
The graph shows the colorimeter readings increase as the temperature
increases, they increase by the most at higher temperatures. This is
shown by a smooth curve.
This means that the beetroot samples release more dye at higher
temperatures. This is because higher temperatures cause the membrane
structure to break down.
The membrane structure:
Membranes have two layers of molecules called phospolipids to make up
their structure. Phospholipis consist of a glycerol molecule plus two
molecules of fatty and a phosphate group, this looks like a head with
two legs, their head is attracted to water, this means theyÂ’re
hydrophilic. The rest of the lipid (the fatty acid legs) is
hydrophobic, which means they repel water. In aqueous solutions the
phospolipids automatically arrange themselves into a double layer so
that the hydrophobic legs are packed inside the membrane (away from
the water) and the hydrophilic heads face outwards into the aqueous
solutions. The molecules are represented in the Â‘fluid mosaic modelÂ’
shown below (the red bits are the legs of the phospolipids):
[draw diagram here]
If it was only made from phospolipids the membrane would be a barrier
to water, this is why there are other components scattered throughout
the phosphlipid by-layer.
Glycolipids are lipids which have combined with polysaccharides. These
may be involved with cell recognition but their exact role is not yet
known. They are found in the outer layer of cell membranes.
Glycoprotiens (seen in green on the diagram) are proteins with
polysaccharides attached. They are chains of monosaccharides, which
branch off to form different shapes. The shape depends on what cell
they are attached to, allowing the cell to be recognised correctly.
Intrinsic proteins occur across the whole width if the protein
allowing the intake of substances into the cell. Extrinsic proteins
occur only in the outer or inner phospholipid bi-layer, but not
through both. These proteins are usually receptors.
Intrinsic channel proteins allow water soluble molecules to pass
through it by forming a tiny gap in itself, this is large enough for
Intrinsic carrier proteins carry water-soluble molecules through the
membrane, this method is called Â‘Active TransportÂ’
Extrinsic proteins recognise and bind on specific molecules, eg.
hormones. Membranes can also be embedded in the inner membrane
The reason why the membrane structure breaks down at higher
temperatures is because the proteins are not very stable and break
down with heat, called denaturing. An enzyme denatures because the
heat changes the shape of the active site o the substrate can not fit
into it. Enzymes are always denaturing, but at higher...