Beetroot cells contain a red pigment called betalain. The molecules of this pigment
are too large to pass through intact cell membranes. If the membranes are damaged,
the pigment will leak out of the cells.
An investigation was carried out into the effect of the concentration of two types of
alcohol on the permeability of beetroot cell membranes.
Cylinders were cut from beetroot tissue. These cylinders were rinsed in distilled
water. The cylinders were placed in test tubes containing different concentrations of
two different alcohols: methanol or ethanol.
After five minutes, each cylinder of beetroot tissue was removed. The degree of
redness of the solution in each test tube was then measured using a colorimeter.
A colorimeter is an instrument that measures the amount of light absorbed or
transmitted by a coloured solution. As the intensity of the colour increases, the
absorbance of light by the solution increases and the transmission of light through
the solution decreases.
Explain why the pieces of beetroot tissue were rinsed in distilled water after
being cut.