Importance of Water and Its Properties-Cohesion and Adhesion PT2

Cohesion and adhesion draw water up the xylem

Water conduction through vessels and tracheid of the xylem

What separates and what does it cause?

Xylem and Phloem separate and this causes massive radioactivity

Cohesion-tension theory

The cohesion and adhesion of water in the vessel element helps water move up the vessel without breaking under tension.

• happens when water molecules are attracted to each other.

• Water molecules move up the xylem (1 direction).

Cohesion-tension theory
Adhesion

Occurs when water molecules are attracted to the walls of the vessel element.

-Vessel element has thick walls with lignin

-Water has polarity

What affects bulk flow?

The diameter of the tube affects bulk flow.

-Flow increases with the radius of the tube

-Wider conduits are more conductive

• Difference in pressure between tubes will depend on viscosity and length of tube.
  
  

The diameter of the tube affects bulk flow.

As the vessel radius decreases, the cross-sectional area needed for the flow…

As the vessel radius decreases, the cross-sectional area needed for the flow increases.

Cavitation

Rupture of the water column

→ Air bubbles (air) can break the continuity of water in the xylem.

Embolism

Filling of vessels/tracheids with air or water vapor.

→ in larger trees, embolisms can plug xylem vessels, making them non-functional

→ An embolism of a vessel element consisting of water vapor that blocked the movement of water

water is able to detour via the bordered pit-pairs between adjacent vessels

Softwood bordered pit

Found along the tracheid, allow for efficient flow of water between the cells.

Bordered pit-airs in conifer tracheid IN GYMNOSPERMS

The impermeable thickening, or torus (green), in the center of the membrane block one of the apertures.

The permeable part of the membrane surrounding the torus, the margo (dashed), is flexible.

Torus and Margo

Margo

permeable (the threat)

Torus

impermeable (the ball)

Angiosperm vessel elements

• Wide and joined into one long continuous tube

• good flow

Angiosperm vessel elements
good or poor safety?

Poor safety because they don’t have a border pit and if one vessel gets embolism a lot of water movement is affected.

Gymnosperms -tracheids

-poor flow

-good safety (border pit)

Angiosperms - vessels

-good flow

-poor safety (no border pit)

-efficiency