Answer: a. capillary action.
Water is a taken up by the plants from the roots, which needs to be transferred to all the parts of the plants to conduct cellular metabolic processes like photosynthesis and respiration. The properties of water molecules are responsible for conduction of water from the root to the stem and other higher parts. The cohesion is the property of water which water molecules are combined with each other due to sharing of bonds at the atomic level. The adhesion is the property of water which allows water molecules to attach with other substances or substrate. Adhesion will cause the attachment of water molecules to the wall of the vessel (xylem) of the plant. Capillary action occurs when the adhesive force is greater than the cohesive force between water molecules. The supply will be upward and force of gravity will also be applicable on this. Capillary action mimics the transfer of water from a tube or pipe. In this way water is drawn upward from the roots through plant tissues to the leaves by capillary action.
