LIFE 103 1st Edition Lecture 14 Outline of Last Lecture II Living Things as Machines III Arabidopsis thaliana IV Production of the Plant Body V Plant Cell Expansion VI Location and Fate VII Homeotic Genes VIII ABC Model of Flower Development IX Special Features of Water X Solute Transport across Cell Membranes Outline of Current Lecture I Solute Transport across Cell Membranes I Active II Passive II Diffusion of water III Plant water facts IV Major pathways of transport V I Apoplastic II Symplastic III Transmembrane Soil to xylem VI Tension cohesion theory Current Lecture Solute Transport across Cell Membranes These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute I II Passive transport diffusive movement of an ion along concentration and charge gradients I Requires no energy input Active transport pumping of an ion against a concentration or charge gradient I Requires energy input ATP II Conducted by transport proteins Active Transport Proteins I II III IV V VI Proton pumps use ATP to pump H out of cell creating a charge and ion gradient a This gradient has potential energy that can be used to move other ions Cation uptake cations move along H charge gradient via cation transport protein Anion co transport H and anion brought into cell together by a transport protein with two active sites Neutral solute co transport H and a neutral solute transported by a protein with two active sites Fig 36 6 Fig 36 7 co transport of an anion with H higher concentration of nitrate in roots compared to outside Diffusion of water osmosis I II III IV Osmosis diffusion of water across a membrane Determined by solute concentrations and pressure I At equal pressures water moves from regions of low solute concentration towards high solute concentrations Water potential sum of the factors that determine the direction of osmosis psi value of pure water 0 Addition of solutes lowers more negative Water moves towards regions of lower water potential Units are megapascals MPa pressure Fig 36 8 Plant water tidbits I II III IV Animal cells would burst at high solute concentrations Plant cell walls allow pressure to build up Turgor pressure pressure of cell contents against the cell wall I Typically 0 5MPa or 2x pressure of car tire II Loss of turgor pressure wilting Aquaporins recently identified membrane proteins that facilitate water transport Major pathways of transport I Apoplast continuous space joining everything outside the plasma membrane I Includes cell wall and dead tracheid and vessel cells II III IV V VI II Apoplastic route transport only via apoplastic spaces Symplast continuous cytosol joined between cells by plasmodesmata objects that join the plasma together I Symplastic route transport across cell wall and membrane once then through symplast the rest of the way Transmembrane route repeated crossing of apoplast cell membrane and symplast Xylem tubes have no cell membrane so water movement through the xylem is an example of apoplastic transport Fig 36 11 In which route do transport proteins have some effect Transmembrane route Soil to xylem transport of water and minerals into roots I II III IV V Water and minerals much reach xylem to be transported to rest of plant Endodermis inner most root cortex cells are a checkpoint Casparian strip waxy barrier between endodermal cell walls stops apoplastic transport to xylem I Requires all ions entering plant to pass through a plasma membrane Symplastic route is unaffected by Casparian strip Fig 36 12 Tension cohesion theory I II III IV V Water loss out of stomata dries the cell wall surface of internal leaf cells Water is attracted by surface tension out of the xylem to re wet these cell walls This re wetting pulls water up xylem because water molecules are strongly cohesive stick together Transpiration water loss from leaves pulls water through xylem at 15 to 45 m hr Fig 36 14