CBSE Class 10 Answered

The tracheids, fibres, and vessels present in the xylem, become lignified during development, losing their living contents. This makes the tissue impermeable (to water) so none is lost as water is transported via the xylem. Water can move rapidly from cell to cell due to the tracheids' bordered pits.

The lignification of vessels can occur as rings and spirals, which allows for a limited amount of stretching which may occur in young structures.

Both tracheids and vessels provide a pathway for the transportation of water, whilst also contributing to support.

Since the xylem and phloem function in the conduction of water, minerals, and nutrients throughout the plant, it is not surprising that their form should be similar to pipes. The individual cells of phloem are connected end-to-end, just as the sections of a pipe might be. 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. Phloem fibres provide mechanical strength to phloem. The sieve plates contain large pores that allowfor passage of materials between sieve elements. 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.