Plants have specialised cells for the efficient transport of assimilates. (a) Table 3.1 shows some of the features of two different types of cell found in plant tissue, which are adapted for the efficient transport of assimilates. Table 3.1 feature of cell cell type A cell type B cytoplasm ✓ ✓ nucleus ✗ ✓ mitochondria few many cellulose in the cell wall ✓ ✓ ribosomes ✗ ✓ Key ✓ present ✗ absent

1. (a)Many plasmodesmata connect type A cells with type B cells. Identify cell type A and explain why the plasmodesmata are important. cell type A explanation[3]
2. (b)The polysaccharide callose is found in the cell walls of cells close to plasmodesmata. Fig. 3.1 is a simplified diagram showing the structure of callose. Not all hydrogen atoms are shown. [Fig. 3.1] Complete Table 3.2 to compare the structure of a callose molecule with a cellulose molecule. Table 3.2 feature of polysaccharide callose molecule cellulose molecule monosaccharide used to synthesise the polysaccharide ẞ-glucose bond connecting the monomers 1,4 glycosidic bond shape of molecule helix orientation of monosaccharides in the molecule alternate glucose molecules are rotated by 180°[4]
3. (c)Hydrogen bonding is important for movement of water through xylem vessels in a plant. Describe the roles of hydrogen bonding in the movement of water through xylem vessels.[3]
4. (d)Water that has travelled through xylem vessels reaches the leaves. Cooling of the leaf occurs as a result of the evaporation of water 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.[2]

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