Question

Cut pieces of beetroot, do not leave colour in cold water but do so in hot water. Explain.

Answer 1

Plasma membrane:

The plasma membrane is a bilayer lipid layer containing peripheral and integral proteins. The fluidity of the lipid layer and the presence of carrier proteins make the plasma membrane selectively permeable



Effect of temperature on semipermeability:

The permeability of the membrane depends upon temperature. As temperature increases the lipids liquify and the proteins become denatured allowing substances from inside of the cell to leak out.

Betanin:

The pigment (betanin) present in beetroots is actually present in the vacuole of the cells. The vacuole is covered by a semipermeable membrane called tonoplast.

In hot water:

In hot water, because of the increasing temperature, the tonoplast and the plasma membrane get disrupted and the red betanin is released. The high temperature also aids in diffusion resulting in further release of the pigment into water. This does not happen in cold water as the membrane is still intact.