Mass transport- plants

Cards (45)

  • What do xylem vessels transport in plants?
    Water and mineral ions
  • What are xylem vessels made up of?
    Dead, hollow cells with no end walls
  • How do xylem cells form a continuous tube?
    They are stacked on top of each other
  • Why do xylem cells have no organelles or cytoplasm?
    To create more space for transporting water
  • What substance strengthens the xylem vessel?
    Lignin
  • What forces allow water to move upwards in the xylem?
    Tension and cohesion
  • What creates tension in the xylem?
    Water evaporation from leaves (transpiration)
  • How does cohesion affect water movement in the xylem?
    Water molecules stick together, forming a column
  • What is adhesion in the context of xylem function?
    Attraction of water to non-water molecules
  • What is transpiration?
    Loss of water vapor through evaporation
  • Where does transpiration mainly occur in plants?
    Through gaps in the leaf called stomata
  • Why do plants close their stomata at night?
    To minimize transpiration when not photosynthesizing
  • How does light intensity affect transpiration rate?
    Increased light intensity raises transpiration rate
  • How does temperature influence transpiration?
    Higher temperature increases transpiration rate
  • What effect does wind have on transpiration?
    Wind increases the rate of transpiration
  • How does humidity affect transpiration rate?
    Higher humidity decreases the rate of transpiration
  • What does a potometer measure?
    The amount of water uptake by a plant
  • Why is the assumption made that water uptake equals transpiration?
    Because some water is used for turgidity
  • What is the first step in using a potometer?
    Cut a shoot underwater to prevent air entry
  • Why should the shoot be cut at a slant?
    To increase the surface area for water uptake
  • What should be done after inserting the shoot into the potometer?
    Dry the leaves and leave for 30 minutes
  • What is the purpose of shutting the tap on the potometer?
    To create a closed capillary tube system
  • How is the speed of the air bubble calculated?
    By measuring distance moved per unit time
  • What do phloem vessels transport?
    Dissolved substances like sucrose and amino acids
  • What are the two types of cells in phloem vessels?
    Sieve tube elements and companion cells
  • What is the function of sieve tube elements?
    To transport solutes through the phloem
  • How do companion cells support sieve tube elements?
    By providing energy for active loading of sucrose
  • What is translocation in plants?
    Movement of dissolved substances from sources to sinks
  • What happens to sucrose when it reaches a sink?
    It is converted into starch for storage
  • What is the mass flow hypothesis?
    A theory explaining solute transport in phloem
  • What occurs during the first stage of the mass flow hypothesis?
    Sucrose moves from companion cells into sieve tubes
  • How does water enter the phloem according to the mass flow hypothesis?
    By osmosis, increasing hydrostatic pressure
  • What maintains the hydrostatic pressure gradient in phloem?
    Pressure difference between source and sink cells
  • What happens to water at the sink end of the phloem?
    Water moves out by osmosis, increasing water potential
  • How is sucrose actively loaded into sieve tube elements?
    Through co-transport with hydrogen ions
  • What evidence supports the mass flow hypothesis?
    Radioactive tracers track sucrose movement
  • What evidence challenges the mass flow hypothesis?
    Sieve plates may impede mass flow
  • How can translocation be investigated using radioactive tracers?
    By exposing leaves to carbon-14 gas
  • What is autoradiography used for in plant studies?
    To track radioactive sugars in plants
  • What are the factors affecting the rate of transpiration?
    • Light intensity: More light increases transpiration
    • Temperature: Higher temperature increases transpiration
    • Wind: Windier conditions increase transpiration
    • Humidity: More humidity decreases transpiration