Table 3.1 gives some characteristics of two cell types in plant tissue that are adapted for efficient assimilate transport. Numerous plasmodesmata join type A cells to type B cells. Identify cell type A and explain why the plasmodesmata are important.
The polysaccharide callose occurs in the cell walls of cells near plasmodesmata. Fig. 3.1 is a simplified diagram of the structure of callose. Not all hydrogen atoms are shown. Complete Table 3.2 to compare the structure of a callose molecule with a cellulose molecule.
Hydrogen bonding is important for the movement of water through xylem vessels in a plant. Describe the roles of hydrogen bonding in the movement of water through xylem vessels.
Water that has moved through xylem vessels reaches the leaves. The leaf cools as a result of water evaporation during transpiration. Water has a high latent heat of vaporisation because water molecules form hydrogen bonds. With reference to hydrogen bonding, suggest why cooling of the leaf occurs as a result of evaporation of water during transpiration.