Overview
This lecture covers how water, minerals, and food are transported in plants, focusing on the roles of xylem and phloem tissues.
Water and Mineral Absorption
- Plant roots absorb water and minerals from the soil, mainly through root hairs.
- Root hairs are narrow extensions that increase the surface area for absorption.
- Water and minerals enter roots via two pathways: apoplastic (through cell wall spaces) and symplastic (through cytoplasm).
Xylem and Water Transport
- Xylem vessels are long, narrow, hollow tubes lacking living material.
- Xylem transports water and dissolved minerals from roots to all parts of the plant.
- About 95% of absorbed water is lost by transpiration through stomata in leaves.
Transpiration and Stomata
- Transpiration is the process of water loss through stomata.
- More stomata are present on the lower leaf surface.
- Stomata open during the day when water and potassium ions enter guard cells, making them turgid.
- At night, potassium ions and water leave guard cells, stomata close as turgidity decreases.
- Stomata also facilitate gas exchange for the plant.
Phloem and Food Transport
- Photosynthesis produces glucose in leaves using water and carbon dioxide.
- Glucose is transported to different parts of the plant by phloem tissue.
- Phloem consists of parenchyma cells, sieve tube cells, and companion cells.
- Food transport in phloem can be upward or downward depending on plant needs.
Key Terms & Definitions
- Xylem — plant tissue that transports water and minerals from roots to shoots.
- Phloem — plant tissue responsible for transporting food (glucose) throughout the plant.
- Transpiration — the loss of water vapor through stomata in leaves.
- Stomata — small openings on leaf surfaces for gas exchange and water loss.
- Root hairs — thin extensions of root cells that increase absorption area.
- Apoplastic pathway — movement of water and minerals through cell wall spaces.
- Symplastic pathway — movement of water and minerals through the cytoplasm of cells.
Action Items / Next Steps
- Review the structure and roles of xylem and phloem.
- Understand the mechanisms of water, mineral, and food transport in plants.