Mass transport- plants

• 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