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Water Potential quiz #3

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  • How does the cohesion-tension theory explain the upward movement of water in plants?
    The cohesion-tension theory states that evaporation (transpiration) from leaves creates negative pressure (tension), which pulls water upward through the xylem. Cohesion between water molecules and adhesion to xylem walls help transmit this tension from leaves to roots, enabling water to move against gravity.
  • Describe the pressure-flow hypothesis for sugar transport in phloem.
    The pressure-flow hypothesis explains that sugars are loaded into the phloem at the source, lowering solute potential and causing water to enter from the xylem, increasing turgor pressure. At the sink, sugars are removed, water exits, and turgor pressure drops. The resulting pressure difference drives bulk flow of phloem sap from source to sink.
  • What two components make up water potential in plants, and how is water potential calculated?
    Water potential is made up of solute potential and pressure potential, and is calculated as the sum of these two (Ψ = Ψs + Ψp).
  • How does water move in relation to water potential within plant tissues?
    Water always moves from areas of higher water potential to areas of lower water potential.
  • What is the role of the Casparian strip in root water uptake?
    The Casparian strip blocks the apoplastic route, forcing water to enter endodermal cells, which allows the plant to control ion flow and solute concentration before water enters the xylem.
  • How do guard cells regulate the opening and closing of stomata?
    Guard cells use proton pumps to move protons out, allowing potassium ions and water to enter, increasing turgor pressure and opening the stomata; to close, potassium and water exit, reducing turgor pressure.
  • What is the main idea of the cohesion-tension theory for water movement in xylem?
    The cohesion-tension theory states that evaporation (transpiration) from leaves creates negative pressure (tension), which pulls water upward through the xylem, aided by cohesion and adhesion.
  • Describe the pressure-flow hypothesis for sugar transport in phloem.
    Sugars are loaded into the phloem at the source, causing water to enter and increase turgor pressure; at the sink, sugars are removed, water exits, and turgor pressure drops, creating a pressure difference that drives bulk flow from source to sink.
  • What is turgor pressure and why is it important for plant cells?
    Turgor pressure is the pressure of the cell contents against the cell wall, keeping non-woody plants upright and preventing wilting.
  • How do aquaporins facilitate water movement in plant cells?
    Aquaporins are membrane channels that increase the efficiency of water movement across cell membranes, allowing rapid osmosis.
  • What happens to most of the water taken up by a plant?
    Most of the water taken up by a plant is lost to the atmosphere through transpiration, which is the evaporation of water from the leaves via the stomata.
  • How does transpiration benefit a plant during the summer?
    Transpiration helps a plant in the summer by cooling the plant through evaporative water loss and by creating negative pressure (tension) that pulls water and dissolved minerals upward from the roots to the leaves, ensuring continued nutrient and water supply.
  • What substances are transported in the xylem of a plant?
    The xylem of a plant transports water, dissolved minerals, nutrients, and some hormones from the roots to the rest of the plant.