3.3 Plant transport

• Why do plants need a transport system?

  To ensure reliable supply of nutrients
• What is the role of xylem in plants?

  Xylem transports water and mineral ions
• What does lignin do for xylem vessels?

  Lignin strengthens xylem and prevents collapse
• What type of cells form a continuous column in xylem?

  Dead cells
• What are the main components of a plant root?

  • Xylem
  • Phloem
  • Cambium
  • Cortex
• What do bordered pits in xylem allow?

  They allow water to move sideways
• What does phloem transport in plants?

  Assimilates around the plant
• What are sieve tube elements responsible for?

  Transporting liquids around the plant
• What do sieve plates allow in phloem?

  Movement of sap between elements
• What is the function of companion cells?

  Provide energy for active processes
• What do plasmodesmata allow in plants?

  Flow of substances between cells
• What is the structure of vascular bundles in roots?

  • Xylem in an X shape for stability
  • Surrounded by endodermis
• What is the structure of vascular bundles in stems?

  • Xylem on the inside for support
  • Phloem on the outside
  • Layer of cambium cells
• What is the structure of vascular bundles in leaves?

  • Xylem and phloem form main veins
  • Involved in transport and support
• What is transpiration in plants?

  Evaporation of water from leaves
• What factors increase transpiration?

  Light, temperature, and air movement
• How does humidity affect transpiration?

  Increased humidity decreases transpiration
• What role does the waxy cuticle play in transpiration?

  It prevents excessive transpiration
• What is a potometer used for?

  Measuring rate of transpiration
• What is the apoplastic pathway?

  Water moves through intercellular spaces
• What is the symplastic pathway?

  Water moves through cytoplasm via plasmodesmata
• What is the cohesion-tension theory?

  • Water molecules form hydrogen bonds (cohesion)
  • Water adheres to xylem walls (adhesion)
  • Creates tension that draws water up
• When does highest transpiration occur?

  When stomata are open
• What are the components involved in source loading in phloem?

  1. Sieve plate
  2. Sieve tube element
  3. Companion cell
  4. Xylem
• What are the steps of unloading in phloem?

  1. H+ ions pumped out of companion cells
  2. H+ ions diffuse back with sucrose
  3. Sucrose diffuses into sieve tube elements
  4. Water moves in via osmosis
  5. Water moves towards sink end
  6. Sucrose diffuses into companion cell
  7. Sucrose converted to glucose or starch
  8. Water moves out of phloem via osmosis