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 ExpansionVI. 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 MembranesI. Active II. Passive II. Diffusion of water III. Plant water factsIV. Major pathways of transport I. ApoplasticII. SymplasticIII. Transmembrane V. Soil to xylem VI. Tension-cohesion theory Current LectureSolute 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. Passive transport: diffusive movement of an ion along concentration and charge gradients I. Requires no energy inputII. Active transport: pumping of an ion against a concentration or charge gradientI. Requires energy input (ATP)II. Conducted by transport proteins Active Transport ProteinsI. 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 II. Cation (+) uptake: cations move along H+ charge gradient via cation transport protein III. Anion co-transport: H+ and anion brought into cell together by a transport protein with two active sites IV. Neutral solute co-transport: H+ and a neutral solute transported by a protein with two active sites V. Fig. 36.6 VI. Fig. 36.7 (co-transport of an anion with H+)  higher concentration of nitrate in roots compared to outside Diffusion of water: osmosis I. Osmosis: diffusion of water across a membrane. Determined by solute concentrations and pressureI. At equal pressures, water moves from regions of low solute concentration towards high solute concentrations II. Water potential: sum of the factors that determine the direction of osmosis III. Ψ: “psi” value of pure water = 0. Addition of solutes lowers Ψ (more negative). Water moves towards regions of lower water potential. Units are megapascals (MPa, pressure).IV. Fig. 36.8 Plant water tidbitsI. Animal cells would burst at high solute concentrations II. Plant cell walls allow pressure to build up III. Turgor pressure: pressure of cell contents against the cell wall I. Typically, 0.5MPa, or 2x pressure of car tireII. Loss of turgor pressure = “wilting” IV. Aquaporins: recently identified membrane proteins that facilitate water transport Major pathways of transport I. Apoplast: continuous space joining everything outside the plasma membraneI. Includes cell wall and dead tracheid and vessel cellsII. Apoplastic route: transport only via apoplastic spaces II. 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 III. Transmembrane route: repeated crossing of apoplast, cell membrane and symplast IV. Xylem tubes have no cell membrane, so water movement through the xylem is an example of apoplastic transport V. Fig. 36.11 VI. In which route do transport proteins have some effect: Transmembrane route Soil to xylem: transport of water and minerals into roots I. Water and minerals much reach xylem to be transported to rest of plantII. Endodermis (inner-most root cortex cells) are a “checkpoint” III. Casparian strip: waxy barrier between endodermal cell walls stops apoplastic transport to xylemI. Requires all ions entering plant to pass through a plasma membrane IV. Symplastic route is unaffected by Casparian strip V. Fig. 36.12 Tension-cohesion theory I. Water loss out of stomata dries the cell wall surface of internal leaf cells II. Water is attracted (by “surface tension”) out of the xylem to re-wet these cell walls III. This re-wetting pulls water up xylem, because water molecules are strongly cohesive (stick together)IV. Transpiration: water loss from leaves, pulls water through xylem at 15 to 45 m/hr! V. Fig.