the transpiration stream

what does tension in water do?

pulls the water up

what does cohesion in water mean?

water sticks to water

what does adhesion in water mean?

water sticks to xylem wall

what does root pressure do?

• water is pushed up

what is root pressure due to?

• it is a result of ions being pumped into the xylem, lowering the water potential below that of the neighbouring cell

what is the major force drawing water up the stem?

transpiration

how does cohesion and adhesion help water move up the xylem?

• Cohesion causes water molecules to stick to each other, while adhesion causes water to stick to the xylem walls.

• Together, this allows the whole column of water to move up the xylem without breaking.

Why is lignin important for adhesion in the xylem?

• Lignin is waterproof, which keeps most of the water inside the xylem walls.

• This maintains a continuous layer of water along the walls, which is essential for effective adhesion.

How does the structure of the xylem vessel aid water movement?

Xylem vessels are very narrow, which increases the effectiveness of adhesion and helps maintain an unbroken column of water.

What is capillary action and how does it relate to the xylem?

• Capillary action is the ability of water to rise up a narrow tube against gravity.

• In the xylem, this occurs due to cohesion, adhesion, and the narrow diameter of the vessels.

How does evaporation from the leaves create a pressure gradient?

• As water evaporates from the leaves, the pressure at the top of the xylem is reduced.

• This creates a pressure gradient from the bottom of the xylem to the top

How does water move along this pressure gradient?

• Water moves down the pressure gradient from high hydrostatic pressure at the bottom of the xylem to lower hydrostatic pressure at the top.

What is mass flow and how does it differ from diffusion or osmosis?

• Mass flow is the movement of all molecules in the same direction, driven by a pressure gradient.

• This differs from diffusion and osmosis, which rely on the random movement of molecules.

How does tension help maintain water movement in the xylem?

Because water molecules stick together by cohesion, a continuous stream of water is pulled up the xylem under tension.

Why does the xylem not collapse under this tension?

Lignin strengthens the xylem walls and prevents the vessels from collapsing under the tension created by water being pulled upwards.

What is the transpiration stream?

The transpiration stream is the continuous movement of water up the xylem to replace water lost by evaporation from the leaves.