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Transpiration, stomata and environmental effects

Organisation • Plant tissues, organs and systems

Key concepts

What you'll likely be quizzed about

  • Transpiration refers to the loss of water vapour from the aerial parts of plants, primarily the leaves.
  • This process begins with the evaporation of water from internal leaf surfaces, followed by the diffusion of water vapour through stomata into the surrounding air.
  • As water evaporates from the spongy mesophyll, a concentration gradient forms, causing water to diffuse out of the leaf.
  • This loss creates a tension in the xylem vessels, which is sustained by the cohesive forces between water molecules.
  • Enhanced evaporation increases the tension within xylem, promoting greater water absorption from root hair cells through osmosis.
  • Xylem vessels, characterized as hollow tubes, facilitate a continuous upward flow of water; however, factors such as soil water availability and xylem cell issues can limit this movement.

Flashcards

Test your knowledge with interactive flashcards

Why do stomata open during the day?

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Stomata open during the day to allow CO2 entry for photosynthesis, which also increases water loss through transpiration.

Key notes

Important points to keep in mind

Transpiration combines evaporation and diffusion; the transpiration stream is dependent on cohesion and tension.

Translocation occurs in phloem through pressure-flow; phloem cells remain living throughout the process.

Guard cells regulate stomatal opening and closing through turgor changes driven by solute movement.

Increased temperature heightens evaporation, increasing transpiration until stomata close or soil water limits flow.

High humidity diminishes vapour gradients and lowers transpiration; low humidity enhances transpiration.

Air movement disrupts the humid boundary layer, promoting increased transpiration.

Light intensity influences stomatal opening for CO2 uptake, elevating transpiration during the day.

Soil water availability and xylem integrity are critical in determining maximum transpiration rates.

Leaf adaptations, such as a waxy cuticle and strategic stomatal placement, help minimize water loss.

Record environmental factors like temperature, humidity, wind, and light when measuring transpiration.

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