Transport in Plants - CIE Biology IGCSE

Plant Transport Systems

• Plants have a transport system composed of:
  • Xylem: Transports water from roots to stem and leaves via transpiration.
    • Made up of hollowed-out dead cells forming tubes.
  • Phloem: Transports sugars and nutrients through translocation.
    • Made of living cells.

Water Uptake

• Root Hair Cells:

  • Absorb water via osmosis.
  • Water moves from root hair cells to root cortex cells before entering xylem.
  • Adaptations:
    • Large surface area for efficient water uptake.
    • Thin walls for shorter diffusion distance.

• Water Movement:

  • Drawn up the stem to leaves.
  • Diffuses into mesophyll cells for metabolic reactions like photosynthesis.

Transpiration

• Definition: Loss of water vapour from mesophyll due to evaporation exiting via stomata.
• Functions:
  • Maintains plant structure by keeping cells turgid.
  • Excessive water loss leads to wilting as turgor pressure decreases.
• Stomata: Close to prevent water vapour loss.
• Transpiration Pull:
  • Water molecules are cohesive, aiding their upward movement.
  • As water evaporates, more is drawn up from roots.
• Factors Affecting Transpiration Rate:
  • Temperature: Higher temperatures increase evaporation and diffusion, increasing transpiration.
  • Humidity: High humidity lowers the transpiration rate due to a lower concentration gradient.

Translocation

• Occurs in phloem vessels.
• Transports amino acids and sucrose from sources to sinks.
  • Sources: Sites of production (e.g., leaves).
  • Sinks: Sites of storage or usage (e.g., roots).
• Process:
  • Sucrose and amino acids produced in leaves.
  • Transported to roots for storage or used where needed for growth and respiration.
• Note: Some plant parts can function as both source and sink depending on the plant's life stage.