A1.1.3 - Cohesion of water molecules due to hydrogen bonding and consequences for

Cohesion

• Attraction between ‌water molecules due to hydrogen bonding

• Each water molecule can form hydrogen bonds ‍with neighbouring water molecules

How Cohesion Enables Xylem Transport

• Water evaporates from leaves through stomata (transpiration)

• This ‌creates tension (negative pressure) that pulls water ‍up through the xylem

• Hydrogen bonds between water ‌molecules allow them to be pulled as a ‍continuous column from roots to leaves

• Matters because hydrogen ‌bonds hold water molecules together, preventing the ‌column from snapping and allows water to move up against gravity

Surface Tension

• Water molecules at the surface are ‍pulled inward by hydrogen bonds with molecules below and ‍beside them

• This creates a "skin" ‌or elastic-like layer at the water's surface

• ‍Small organisms can walk on water due to surface ‍tension

Transpiration

• Movement of water from roots to leaves via xylem

Transpiration Steam

• As water leaves the leaf, it is ‍replaced by water drawn up from the roots through the xylem.

• This ‍continuous flow from roots to leaves is the transpiration stream.

• So ‍a cost of gas exchange also delivers water and dissolved minerals to ‌the whole plant.