Long Distance Transport of Water (Root Pressure and Transpiration Pull)
Discusses the mechanisms driving water movement over long distances in plants, including positive root pressure and the cohesive-adhesive transpiration pull.
What is Long Distance Transport of Water (Root Pressure and Transpiration Pull)?
A positive hydrostatic pressure that develops in the xylem of plant roots due to the active absorption of mineral ions from the soil, which draws water into the xylem.
Key points
- Explain the pathways of water movement into and through the root.
- Differentiate between apoplast and symplast pathways.
- Describe the mechanism of root pressure and its limitations.
- Explain the process of transpiration and how it creates a pull.
Common exam trap
Confusing root pressure as the primary mechanism for water transport in all plants.
Definitions
- Term
Root Pressure
- Meaning
A positive hydrostatic pressure that develops in the xylem of plant roots due to the active absorption of mineral ions from the soil, which draws water into the xylem.
- Term
Transpiration Pull
- Meaning
A negative pressure (tension) created in the xylem of plants due to the evaporation of water from the leaf surface (transpiration), which pulls water up from the roots.
- Term
Cohesion
- Meaning
The attraction between molecules of the same substance; in water, it refers to the hydrogen bonds between water molecules.
- Term
Adhesion
- Meaning
The attraction between molecules of different substances; in water transport, it refers to the attraction between water molecules and the walls of the xylem vessels.
- Term
Apoplast Pathway
- Meaning
The pathway of water movement through the non-living parts of the plant, such as cell walls and intercellular spaces.
- Term
Symplast Pathway
- Meaning
The pathway of water movement through the living parts of the plant, involving movement from cell to cell via the cytoplasm and plasmodesmata.
- Term
Casparian Strip
- Meaning
A band of suberin in the radial and transverse walls of endodermal cells that prevents apoplastic movement of water and solutes into the stele.
- Term
Guttation
- Meaning
The process of losing water in the form of droplets from the edges or tips of leaves, typically occurring at night or in high humidity due to root pressure.
Learning objectives
Explain the pathways of water movement into and through the root.
Differentiate between apoplast and symplast pathways.
Describe the mechanism of root pressure and its limitations.
Explain the process of transpiration and how it creates a pull.
Understand the role of cohesion and adhesion in water transport.
Compare and contrast root pressure and transpiration pull.
Prerequisites
Cell structure and function (cell wall, cell membrane, cytoplasm, plasmodesmata)
Osmosis and diffusion
Active and passive transport
Plant anatomy (root, stem, leaf structure, xylem tissue)
Common mistakes
Confusing root pressure as the primary mechanism for water transport in all plants.
Underestimating the role of cohesion and adhesion in maintaining the water column.
Not understanding the difference between apoplast and symplast pathways.
Attributing guttation to transpiration instead of root pressure.
Keywords
Xylem
Water Transport
Root Pressure
Transpiration Pull
Cohesion
Adhesion
Apoplast
Symplast
Casparian Strip
Guttation
Plant Physiology
Practice preview
Which of the following is the primary driving force for the upward movement of water in tall trees during the day?…
easy
Root pressure is a positive hydrostatic pressure that develops in the xylem of roots. What is its main contribution to water transport?…
easy
The cohesion-tension theory explains the ascent of sap. Which of the following properties of water is crucial for maintaining the continuous column of water in the xylem under tension?…
medium