Water movement

first step , water into root

Water (and minerals) that pass from the soil into the root cannot be

transported to the rest of the plant until they enter the xylem;

• Minerals move from the soil into the root by active transport;

• Water diffuses from the epidermis through the root to the xylem

down a water potential gradient

What water cross through by symplast and apoplast

Water then moves by osmosis from cell to cell across the cortex via
plasmodesmata. This is the symplast pathway. Water also moves across the root cortex by
way of the cell walls and intercellular spaces. This is called the apoplast pathway

Water moves through the root by two pathways/by the apoplast and

symplast pathways

(The apoplast pathway)/water stops at the endodermis because of

the waterproof Casparian strip, which seals the cell walls;

• Water has to cross the cell membrane by osmosis;

• And enters the cytoplasm of cells (into the symplast pathway);

• This allows the plant to have some control over the uptake of water

into the (xylem of the root);

• Once water passes the Casparian strip (in the endodermis) to xylem

of the root, it will continue to flow into xylem of the stem and then to

the leaves;

transpiration

This (bulk flow) depends on the loss of water/water vapour by

transpiration, through the leaves;

• This causes low pressure/loss of water in the leaves, so water is

continually sucked up the stem to replace the lost water;

• Due to a pressure gradient;

• The column of water in the xylem vessels (from the roots to the

leaves) is therefore under tension/a stretching force;

• Water has a high tensile strength due to the tendency of water

molecules to stick together by hydrogen bonding/cohesion;

• So the water column does not break under the tension force;

• This mechanism of pulling water up a stem is sometimes called the

cohesion–tension mechanism

The pericycle

pumps ions into the xylem, lowering its water potential, so
water enters the xylem by osmosis

mechanism water pulled upward

Water moves up the xylem by cohesion, due to
hydrogen bonding of water molecules, and by adhesion to the lignin walls. The column of
water in the xylem is ‘pulled’ up by transpiration. This is when water vapour evaporates from
the leaf surface, mainly from the stomata. Water diffuses out of the stomata down a water
potential gradient. Water moves into the air spaces of the leaf to replace it, and this ‘pulls’
water from the xylem to the surfaces of the mesophyll cells and the air space