Properties of water that make it useful for all biological processes on the earth are
(i) Water is the major solvent through which mineral nutrients enter a plant from the soil solution.
(ii) It is an ideal solvent with neutral pH .
(iii) Water is the major constituent of protoplasm. It constitute approximately $90 \%$ of the protoplasm.
(iv) Water act as a medium for translocation of nutritive substances. Mineral nutrients are absorbed by the roots. Carbohydrates that are formed during photosynthesis are transported by water from cell to cell, tissue to tissue and organ to organ.
(v) In plants, water is involved in photosynthesis by incorporating hydrogen atom into carbohydrate and oxygen atoms are further released as $\mathrm{O}_2$.
(vi) Water act as agent for temperature control. The specific heat of water helps plant in aintaining a relative stable internal temperature.
(vii) In some plants water is necessary for pollination. Like in bryophytes and pteridophytes, they essentially require water for the fertilisation process.
Ion channels are 'gated', i.e., they may be open or closed. The $\mathrm{Na}^{+}, \mathrm{K}^{+}$, ATPase create a charge imbalance across the plasma membrane by carrying $3 \mathrm{Na}^{+}$out of the cell for every $2 \mathrm{~K}^{+}$ion carried inside making the inside negative relative to outside.
The membrane is said to be polarised. That is the reason the intracellular levels of $\mathrm{K}^{+}$are higher than extracellular levels in animals cells.
