Published on January 1, 2008
Chapter 36: Chapter 36 Transportation Transportation: Transportation This occurs on three levels. A. The uptake and loss of water and solutes from cell B. Transport of water and substances from cell to cell. C. Long distance transport with sap in xylem and phloem along the whole plant. Transportation: Transportation A. Transport systems at the cellular level: A. Transport systems at the cellular level Passive transport Use of embedded proteins in the cell membrane. Transport proteins are selective to which substances they will accept. Active transport molecules move against a concentration gradient. Cells spend ATP Ex. Proton pump: Ex. Proton pump Use ATP to pump H+ across a membrane. Higher concentration of H+ on the outside producing a membrane potential. Used to pull other ions through EX. K+ EX. NO3- enters against the electrochemical gradient by contransport (intake of H+). Cellular Transportation: Cellular Transportation Water Potential and Osmosis ().: Water Potential and Osmosis (). Give us and idea of which way water will flow Water will always move across a membrane from high to low. EX. Pure water is zero ( = 0) Addition of solutes lowers the . Negative pressure is called tension will move water across the membrane. Called bulk flow. Water Potential: Water Potential Role of the Tonoplast: Role of the Tonoplast Tonoplast is the membrane surrounding the large central vacuole found in plant cells. Helps regulate solutes between the vacuole and the cytosol by proton pumps. Short-Distance (Lateral) transport at the level of Tissues and Organs.: Short-Distance (Lateral) transport at the level of Tissues and Organs. Occurs along the radial axis. Occurs across the plasma membranes and cell walls. Two types of route. Symplast route: passes through the plasmodesmata (pores) between cells. Apoplast route: passes through the spaces between cell walls. Or by both routes. Long-Distance Transportation at the Whole-Plant Level.: Long-Distance Transportation at the Whole-Plant Level. Bulk flow moves water and solutes through xylem vessels and sieve tubes. Transpiration reduces pressure in the leaf xylem; creates a tension pulling sap from the roots. Hydrostatic pressure develops at one end of the sieve tubes in the phloem; forcing sap to the other end of the tube. A. The absorption of water and minerals by roots.: A. The absorption of water and minerals by roots. What happens: Enter the root through the epidermis, cross the cortex, pass into the stele, and flow upward in xylem Most absorption occurs near root tips where the epidermis is permeable to water. Root hairs help Lateral transport helps in this process. Slide15: Need extra help of absorption through active transport of minerals by carrier proteins. Water and minerals cross the root cortex in two ways: symplasts or apoplasts. Only symplasts are able to direct water and solutes to the vascular tissue. Apoplasts are blocked by a membrane. B. Ascent of xylem sap: B. Ascent of xylem sap (Water and how it gets into the entire plant) Transpiration: is the evaporation of water from the aerial parts of a plant. A. Pushing xylem Sap: Root Pressure: A. Pushing xylem Sap: Root Pressure When transpiration is low in plants ions pumped into the xylem decrease the stele's water potential and cause water flow into the stele. This increases pressure which forces fluid up the xylem. (root Pressure). Causes guttation ( water droplets at leaf margins) Not able to keep up with transpiration. Guttation: Guttation B. Pulling Xylem Sap: The Transpiration-Cohesion-Adhesion Mechanism.: B. Pulling Xylem Sap: The Transpiration-Cohesion-Adhesion Mechanism. Two forces at work that are produced by the polarity of water. Force 1. Adhesive force of water to the wall of the Xylem helps produce a meniscus. Force 2. Cohesive force of water with itself will lift the water dependent on the size of the tube. With the pull from transpiration water will be drawn up through the xylem. IV The Control of Transpiration:: IV The Control of Transpiration: A. Photosynthesis-Transpiration Compromise. Large surface area of the leaf's airspaces are needed for CO2 intake for photosynthesis by increases the amount of Transpiration. Stomata are found on the bottom of the leaves. Waxy cuticle Benefits of Transpiration: Benefits of Transpiration Assists in mineral transfer form roots to shoots. Evaporation also helps in cooling. B. How Stomata Open and Close: B. How Stomata Open and Close When turgid guard cells are open. When flaccid guard cells are closed. K+ is taken into the Tonoplast and water potential decreases taking water in opening the guard cells. K+ is released increasing the water potential making the cell flaccid and closing the guard cell. Guard cells:: Guard cells: Open at night and close in the day due to circadian rhythms. Increased transpiration will close the cells. V. Transport in Phloem : V. Transport in Phloem Translocation: the transport of the products of photosynthesis by phloem to the rest of the plant. Sieve-tube members are the specialized cells. Sap caries sucrose, minerals, amino acids and hormones. A. Source-To-Sink Transport.: A. Source-To-Sink Transport. Source= organ where sugar is produced by photosynthesis or by the breakdown of starch Ex. Leaves. Sink= Organs that consumes or stores sugar ( growing parts of plants, fruits) Ex. Tuber. B. Pressure Flow (Bulk Flow) of Phloem Sap: B. Pressure Flow (Bulk Flow) of Phloem Sap Phloem loading causes high solute concentration Water is absorbed and pushes the solute from the source to the sink area. The sink end pressure is release and water is recycled. The End!!!!: The End!!!!