The cellulose fibres shown in Fig. 4.1 are made up of bundles of cellulose microfibrils. Explain how cellulose molecules are organised to form a microfibril.
The width of stomatal openings in A. thaliana is controlled by ion movement. These ions pass through channel proteins in the guard cells’ cell surface membranes. Draw a diagram to show part of a cell surface membrane with a channel protein. Label your diagram.
Explain why channel proteins are necessary for ions to move into and out of cells.
Outward movement of ions from guard cells makes stomata close. One variety of A. thaliana lacks channel proteins for the outward movement of ions in the guard-cell cell surface membranes. Suggest and explain the effect of missing these channel proteins on transpiration.