Transport in plants
Transport in plants — Cambridge International AS & A Level Biology (9700, AS Level, Topic 7).
Structure of plant transport tissues (xylem, phloem and companion cells)Sign up
understand the structure and function of starch and cellulose, including the role of hydrogen bonds between β-glucose molecules in cellulose microfibrils · understand how the arrangement of cellulose microfibrils and secondary thickening in plant cell walls contributes to the physical properties of xylem vessels and sclerenchyma fibres · know the similarities and differences between sclerenchyma fibres (support), xylem vessels (support and water/mineral transport) and phloem (translocation of organic solutes), and their positions in the stem · CORE PRACTICAL 7: use a light microscope to make labelled plan diagrams of transverse sections of roots, stems and leaves; identify sclerenchyma fibres, phloem, sieve tubes and xylem vessels
Water uptake, transport and transpiration in plantsSign up
state that some mineral ions and organic compounds can be transported within plants dissolved in water (7.2.1) · describe the transport of water from soil to xylem through the apoplast pathway, including the role of lignin and cellulose in cell walls (7.2.2) · describe the transport of water from soil to xylem through the symplast pathway, including the role of the endodermis, the Casparian strip and suberin in directing water into the symplast (7.2.2) · explain that transpiration involves evaporation of water from the internal (mesophyll) surfaces of leaves followed by diffusion of water vapour through stomata to the atmosphere (7.2.3) · explain how hydrogen bonding of water molecules gives cohesion (transpiration pull / cohesion-tension theory) and adhesion to cellulose in xylem cell walls, moving water up the xylem (7.2.4) · make annotated drawings of transverse sections of xerophytic leaves to explain how adaptations (e.g. sunken stomata, rolled leaves, thick waxy cuticle, hairs/trichomes, reduced leaf area) reduce water loss by transpiration (7.2.5)
Translocation: phloem transport from source to sink by mass flowSign up
state that assimilates dissolved in water, such as sucrose and amino acids, move from sources to sinks in phloem sieve tubes (7.2.6) · explain how companion cells actively load assimilates into phloem sieve tubes, with reference to proton (H+) pumps establishing a hydrogen-ion gradient and sucrose-H+ cotransporter proteins (7.2.7) · explain mass flow in phloem sieve tubes down a hydrostatic (turgor) pressure gradient from source to sink, including water entering the sieve tube by osmosis at the source (lowering water potential) and leaving at the sink (7.2.8)