Chapter 36

Water to land required: Acquiring sunlight/CO 2 from above Water/minerals from below Further complicated by transport of materials Resources necessary for photosynthesis needed in leaves Come from roots Products for growth needed in the roots Produced in the leaves Even more complicated by competition Taller plants had advantages, but also issues

Stems serve two functions Support Transport Leaf arrangement/size varies considerable Phyllotaxy Leaf Area Indexb Ratio of upper leaf surface area to the surface of the land the plant grows on Leaf orientation also affects light capture Horizontal Vertical

Plants need to obtain minerals from soil Root branching maximizes obtaini8ng these nutrients Also provides anchor Roots have developed mutualistic relationships with fungi Mycorrhiza

Two compartments for material movement Apoplast Symplast Also can travel via the transmembrane route Cell to cell

Selective permeability responsible for movement of solutes H + ion responsible basic transport Also works as a cotransporter Can absorb neutral solutes – sucrose Also nitrate in the root hairs

Water moves via osmosis How do you predict the movement of water? Water Potential Water moves from areas of higher water potential to areas of lesser potential Includes the effects of solutes As water moves it can do work Thus the potential energy of water

Abbreviated by psi (ψ) Measured in megapascals (Mpa) or bars Pure water in open container at sea level, room temperature - O MPa Ψ = Ψ S + Ψ P Ψ S = solute potential Water following through osmosis Ψ S = -iCRT Ψ P = osmotic pressure potential Physical squeeze of a cell

Determining water movement If a cell is flaccid and placed in a high solute solution plasmolysis occurs The cell membrane due to a lack of pressure will pull away from the cell wall

Diffusion is too slow for long distance transport Long distance involves bulk flow Movement of a liquid in response to a pressure gradient Independent of solute concentrations Occurs in the vessel elements, tracheids, and sieve tube elements

Absorption of water/minerals begins in roots These substances pass straight to the cortex Encounter the Casparian strip at the vascular cylinder Once in the vascular cylinder xylem sap is transported by bulk flow

Root pressure push is minor Major force is the pull from transpiration Involves cohesion and tension (Cohesion- Tension hypothesis) Water is attracted to itself (cohesion) and the walls of the xylem (adhesion) Again, based on water potential

Stomata control the rate of water loss through transpiration Stomata made up of guard cells – control opening and closing When water present, guard cells become turgid – open

Sieve tube elements move sugars from source to sink by translocation Source- any site for sugar production Sink – any site for sugar usage