Plant Physiology

Turgor Pressure

The hydrostatic pressure exerted by the cell’s fluid content against the cell wall

High Turgor Pressure

Well watered

Low turgor pressure

Flaccid state

Surface tension

Energy required to increase the surface area of a gas-liquid interface

Cohesion

Attraction between water molecules

Adhesion

Attraction between water molecules to solid phase

Hypertonic

Plasmolyzed

Isotonic

Incipient plasmolysis

Hypotonic

Turgid state

Osmosis

Net movement of water from high to low water potential across a selectively permeable membrane.

Water potential

Osmotic potential

Water potential in soil

Normal soil: Psi S = 0

Salty soil: Psi S = -0.2

Wet soil: Psi P = 0

Dry soil: Psi P = less

How does water move in soil

Bulk flow

Contributing factor to water potential in dry soil

Negative hydrostatic pressure that lowers soil water potential.

Where water enters root

Apoplast pathway

Does not cross any membranes. Casparian strip filters air bubbles from water.

Symplast pathway

Water travels without crossing plasma membrane. Travels through plasmodesmata.

Transmembrane

Crossing plasma membrane

Air bubble in xylem

Pits block off gas-filled vessels or tracheids with primary cell walls.

Cohesion-tension theory

Xylem tension pulls

Roots push

97% of water plants absorb is lost through stomata.

Casparian Strip

Filters out air bubbles to prevent embolism.