3.4 Movement Of Water And Solutes Through Plant

Question 1

Movement of water through stem.
Transpirational pull
(Cohesion -adhesion-tension theory)

Answer 1

Water moves freely through the xylem vessels and tracheids by MASS FLOW.
They are aided by pits and perforations in these elements.
There is no cytoplasm present to slow down.
Evaporation of water from leaves sets up a LARGE NEGATIVE PRESSURE.
Negative hydrostatic pressure draws through the plant.
Water can reach great heights due to adhesion to xylem walls and cohesion between water molecules and tensile strength.

Question 2

Water movement through the stem.

Root pressure.

Answer 2

Only forces water for a short distance.
When the root of a plant continues to take up water by osmosis, a positive hydrostatic pressure forces water through the xylem, this is called root pressure.
Probably pricing mechanism in spring to form columns of water needed for transpiration.
Root cells increase salute concentration therefore speeding up osmosis.

Question 3

Water - cohesive and adhesive.

Answer 3

Water is cohesive and adhesive.
Hydrogen bonding means water molecules stick to each other this is COHESION.
Water molecules also stick to other,slightly charged, molecules around them. This is ADHESION
The enables them to form columns of water.

Question 4

Movement of water through root: -

The Symplast pathway.

Answer 4

Water passes across the root cortex by passing into and out of cells across their cell membranes by osmosis and through adjacent cells via plasmodesmata.

Question 5

Movement of water through root.

The apoplast pathway

Answer 5

Water passes across the root cortex through the intercellular spaces and cell wall, that is, outside the cells by MASS FLOW.

Most water crosses the cortex of the root by the apoplastic pathway as it offers least resistance to water flow.