7. Transport in plants

7.1 Structure of transport tissues

Learning outcomes: 

1. draw plan diagrams of transverse sections of stems, roots and leaves of herbaceous dicotyledonous plants from microscope slides and photomicrographs 

2. describe the distribution of xylem and phloem in transverse sections of stems, roots and leaves of herbaceous dicotyledonous plants 

3. draw and label xylem vessel elements, phloem sieve tube elements and companion cells from microscope slides, photomicrographs and electron micrographs 

4. relate the structure of xylem vessel elements, phloem sieve tube elements and companion cells to their functions 

7.2 Transport mechanisms 

Learning outcomes: 

1. state that some mineral ions and organic compounds can be transported within plants dissolved in water 

2. describe the transport of water from the soil to the xylem through the: 

• apoplast pathway, including reference to lignin and cellulose 

• symplast pathway, including reference to the endodermis, Casparian strip and suberin 

3. explain that transpiration involves the evaporation of water from the internal surfaces of leaves followed by diffusion of water vapour to the atmosphere 

4. explain how hydrogen bonding of water molecules is involved with movement of water in the xylem by cohesion-tension in transpiration pull and by adhesion to cellulose in cell walls 

5. make annotated drawings of transverse sections of leaves from xerophytic plants to explain how they are adapted to reduce water loss by transpiration 

6. state that assimilates dissolved in water, such as sucrose and amino acids, move from sources to sinks in phloem sieve tubes 

7. explain how companion cells transfer assimilates to phloem sieve tubes, with reference to proton pumps and cotransporter proteins 

8. explain mass flow in phloem sieve tubes down a hydrostatic pressure gradient from source to sink