In trees, death of protoplasts is essential for vital function such as

Water transport is a physical process and not a physiological process. It does not require living cells and protoplasm. The driving force is the transpiration pull generated by loss of water through leaves. This is the reason why xylem tracheids and vessels are dead on maturity. Food transport is a physiological process and requires living cells similarly stomatal movement also is a physiological process and requires living cells.