Hint: The colour in the beetroot is due to the presence of a water-soluble red pigment known as betacyanin. The pigment is located in the cell vacuole not in the chloroplast. The betacyanin pigment only loses its colour when in hot water due to denaturation of plasma membrane whereas in cold water the plasma membrane remains intact, so no colour is released.
Complete answer:
> Option A:
The cell wall disintegrates in boiling water and hence no plasmolysis occurs. Hence, the pieces of beetroot do not lose colour in hot or cold water. The cell wall has no effect on it. So, it is incorrect.
> Option B:
Hot water can enter the cells readily cannot be the right choice as it depends on the disintegration and permeability of the cell membrane, not on the mobility of cells.
> Option C:
The plasma membrane disintegrates in boiling water and becomes permeable due to the presence of fluid in the cell vacuole. And on boiling it disrupts the plasma membrane so that the water-soluble pigments are released into the medium and beets lose their colour.
> Option D:
The pigment is not soluble in cold water. Yes, it is true but first the hot temperature helps in leaking of plasma membrane and release of pigment. So, it is incorrect.
Hence, the correct answer is option (C).
Note: The disintegration of plasma membrane leads to leaking of colour. Because the pigment present in the vacuole is covered by a membrane single layer called tonoplast gets destroyed due to non-functioning of membrane proteins and their structure gets desiccated too.
