Overview
This lecture explains how plants transport water and minerals through specialized organs (roots, stems, leaves), describes the process of transpiration, and examines environmental factors affecting water movement in plants.
Plant Organs and Their Transport Functions
- Roots absorb water and minerals from the soil via root hairs, anchor the plant, and store carbohydrates.
- Stems contain vascular bundles (xylem and phloem) for transporting water, minerals, and nutrients; they support and store food or water.
- Leaves are the main site of photosynthesis and transpiration, with structures like cuticle (prevents water loss), veins (contain xylem/phloem), and stomata (gas exchange).
The Pathway of Water and Transpiration
- Water enters the roots, moves through the stem via xylem, and exits through stomata in the leaves by transpiration.
- Capillary action (cohesion and adhesion) and root pressure help water move upward against gravity.
- Guard cells regulate the opening/closing of stomata, controlling water loss and gas exchange.
- Transpiration helps cool the plant, maintain nutrient uptake, and regulate water movement.
Importance of Transport Systems in Plants
- Efficient transport is crucial for distributing water, nutrients, and the products of photosynthesis to all plant parts.
- Without these transport systems, plant growth, photosynthesis, and survival would be impaired.
Environmental Factors Affecting Transpiration
- Higher temperature increases transpiration by raising evaporation rates.
- Low humidity increases transpiration; high humidity reduces it.
- Wind increases transpiration by removing humid air near the leaf surface.
- Plants adapt with features like thicker cuticles or fewer leaves to limit water loss.
Key Terms & Definitions
- Transpiration — loss of water vapor from plant leaves through stomata.
- Xylem — vascular tissue transporting water and minerals upward from roots.
- Phloem — vascular tissue distributing sugars from leaves to other plant parts.
- Stomata — small leaf openings for gas exchange and water loss.
- Guard Cells — cells that open and close the stomata.
- Capillary Action — movement of water through small tubes due to adhesion and cohesion.
- Cohesion-Tension Theory — explains upward movement of water via cohesive water molecules and tension from transpiration.
Action Items / Next Steps
- Complete self-assessment and reflection on understanding plant transport.
- Review the process of transpiration and the roles of plant organs.
- Prepare for exercises on environmental effects on plant water movement.