1. Water is an essential and major constituent of protoplasm. In fact bulk of protoplasm is water. All the cell organelles maintain their structure and function in the presence of adequate quantity of water.
2. Distribution of various dissolved substances from one cell to another and from one part to another can take place only in the medium of water.
3. Water is an excellent solvent. It also acts as a reagent in various reactions in plant cells. In photosynthesis and respiration water plays an important role.
4. Breakdown of various chemical compounds takes place only in the medium of water. During germination, complex food substances stored in the seed breakdown into simple constituents. This is possible only when water is present.