Transport in Plants - CAIE Biology IGCSE

Xylem and Phloem

• Transport System
  • Xylem and phloem vessels are responsible for transporting nutrients.
  • Xylem transports water and mineral ions from roots to the rest of the plant (transpiration).
  • Phloem transports sucrose and amino acids in translocation.

Xylem

• Adaptations for water transport:
  • Thick walls reinforced with lignin.
  • Hollow and free from cell contents, maximizing transport space.
  • Cells joined end-to-end without cross walls, forming continuous tubes.

Phloem

• Composed of living cells.
• Transports nutrients such as sucrose and amino acids.

Positioning of Xylem and Phloem

• Roots: Xylem is central in an X shape; phloem surrounds it.
• Stem: Xylem is inside; phloem is outside.
• Leaves: Xylem is above phloem.

Water Uptake

• Process:
  • Osmosis through root hair cells to root cortex cells, then into xylem.
  • Water travels up the stem to leaves, used in photosynthesis.
• Experiment: Plant in dyed water; xylem vessels will show dye movement.
• Adaptations of Root Hair Cells:
  • Increased surface area, enhancing osmosis.
  • Thin walls, reducing diffusion distance.
  • Active transport increases ion uptake.

Transpiration

• Definition: Loss of water vapor from leaves via evaporation.
• Process:
  • Evaporation from mesophyll cell surfaces into air spaces.
  • Diffusion out of leaves through stomata.
• Factors Affecting Rate:
  • Temperature: Higher temp increases evaporation.
  • Wind speed: Wind removes water vapor, increasing rate.
  • Humidity: High humidity decreases transpiration rate due to lower concentration gradient.
• Significance:
  • Maintains plant turgidity.
  • Excessive water loss causes wilting.
  • Stomata closure conserves water.

Translocation

• Process in Phloem: Movement of amino acids and sucrose from sources to sinks.
• Sources vs. Sinks:
  • Sources produce nutrients (e.g., leaves synthesizing sucrose).
  • Sinks store or use nutrients (e.g., roots storing sucrose).
• Dual Role of Leaves: Can act as both source and sink throughout plant life.

These notes cover the essential aspects of plant transport systems, focusing on the roles and adaptations of xylem and phloem, and the processes of water uptake, transpiration, and translocation in plants.