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Understanding Plant Transport Systems

May 20, 2025

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.