Page 99 - Photosynthesis: The Green Miracle

Guard
cell
Stoma
Perspiration Xylem
Air outside the
leaf (lowest wa-
ter potential)
Xylem (woody tissue) plant’s most important supports.
Xylem
(woody tissue)
Root hair
Water
Soil outside the
root (highest water
potential)
The tubes known as
phloem carry food-
stuffs to the leaves and
water containing sugar
from them. The picture
(right) shows the de-
tails of this transporta-
tion process.
Xylem tubes provide some of a
This woody tissue’s hard structure
keeps the plant upright and also
transports water and minerals from
the soil.
Active
Phloem
Source: leaf transportation Xylem
cells
Soluble food molecules
(substances) are trans-
ported in an active
manner from the
source to the phloems.
This reduces the water
potential there and
causes water to enter
the phloem from the
woody tissue.
The rising hydrostatic
pressure causes the
sap to be transported
in the phloem.
Food molecules are
transported to the root
cells. This reduces the
water potential there
and causes the water
to flow passively in the
woody tissue.