(a(i))[2]
Cell X and cell Y in Fig. 3.1 are sieve tube elements. Explain why cell X and cell Y look very different in this transverse section.
(a(ii))[4]
Sucrose is made from the glucose synthesised by mesophyll cells in the leaves of C. pepo. Explain how companion cells help transfer sucrose into phloem sieve tubes.
(b(i))[2]
Hydrogen bonding is important in the movement of water in xylem. Explain how hydrogen bonding arises between two water molecules.
(b(ii))[3]
Outline how hydrogen bonding helps water transport in the xylem of a plant stem.
(b(iii))[2]
Hydrogen bonding between water molecules gives water a relatively high latent heat of vaporisation. Suggest why a high latent heat of vaporisation is important to plants.
(iii)[2]
Suggest why a high latent heat of vaporisation is important to plants.