Lecture Notes: Transpiration in Plants
Introduction to Transpiration
- Transpiration: Water loss through stomata in plants.
- Important for understanding plant tissues.
- Stomata: Small openings on the underside of leaves, sometimes on stems.
Understanding Transpiration
- Water moves from roots to stem, through leaves, and out via stomata.
- Essential knowledge of water movement in plants and related structures.
Structure of Stomata
- Stomata consist of guard cells (jelly bean-shaped cells).
- Guard cells can open (stoma) or close.
- Chloroplasts in guard cells provide energy.
- Surrounded by epidermal cells (no chloroplasts).
Pathway of Water in Transpiration
- Cross-section of a leaf with key structures:
- Cuticle: Waxy layer preventing water loss.
- Epidermis: Protective outer layer.
- Palisade Mesophyll: Site of photosynthesis.
- Vein: Contains xylem and phloem.
- Spongy Mesophyll: Important for transpiration.
- Stomata: Gateway for water and gases.
- Water's route:
- Moves from xylem to spongy mesophyll.
- Evaporates into intercellular air spaces.
- Exits through stomata to atmosphere.
Mechanism of Water Movement
- Driven by concentration gradients.
- Diffusion: Movement from high to low concentration.
- Osmosis: Specific to water movement.
- Water vapor accumulates in air spaces, creating pressure.
Measuring Transpiration
- Potometer: Device to measure transpiration.
- Setup requires:
- Fresh twig, cut under water to avoid air entry.
- Cut stem at an angle for better surface area.
- Use vaseline for airtight setup.
- Potometer function:
- Measures water movement by observing air bubble displacement.
Factors Affecting Transpiration Rate
- Wind:
- Increases transpiration by removing water vapor externally.
- Humidity:
- Reduces transpiration; high external water vapor reduces gradient.
- Temperature:
- Higher temperatures increase transpiration via evaporation.
- Light Intensity:
- Increases transpiration due to higher temperatures and photosynthesis demand.
Recap of Key Terminology
- Xylem: Transports water.
- Diffusion: Movement from high to low concentration.
- Osmosis: Movement of water through membranes.
- Spongy Mesophyll: Site for transpiration.
- Stomata: Leaf openings for transpiration.
- Potometer: Device to measure transpiration.
Ensure you understand the concepts thoroughly, and use flashcards or mind maps to reinforce your learning.