CBSE Class 9 Answered

All the components of xylem except xylem parenchyma are dead, hence xylem is a non-living tissue. The main function of xylem is conduction of water. For this the xylem elements need to form a narrow tube like structure, so that water can rise in the tube through capillary action. For this the cellwalls of the tracheid and vessel components need to be lignified and their inner components lost. This will only be possible in case of dead cells. Also transport of water occurs by physical forces and does not require energy.

All components of phloem are living, except phloem fibres. Since the transport of food is done by active transport which needs energy, most of the phloem parts are alive and not dead like xylem.

The cell that becomes the sieve element undergoes a highly regulated partial autolysis, which results in a large, nearly empty cell that is suitable for transporting of a wide range of molecules. However, specific components and organelles are retained that are important for transportation.