Transcript Transpirationx

Xylem – brings water from the root to the
leaves of the plants
 Phloem – transports sugar from one part
of the plant to another

Water – taken up by root hairs
 From root hairs – towards the center
 Here it enters the xylem
 Xylem -> root -> stem -> leaf
 Transpiration - water evaporates from
plant cells and diffuses into air via leaf

In a leaf – water evaporates from wet
cell walls
 Air space inside leaf full of water vapor
 High concentration of water vapor inside
leaf than outside
 Water diffuses from inside to outside
through stomata into air
 This is traspiration

Root hairs grow down
 New root hairs grow behind the old ones
Die
 Lasts for less than a day
 Grow between soil particles
 Water enters via osmosis
 Increases surface area to speed up
osmosis

Root hair cross section
How water travels
into the root:
• passes through
the cortex
•No chloroplast in
cortex cells
•Moves towards the
center of the root
•Some goes into
cytoplasm of cells,
through the cells
and into the next
cell till it reaches
the xylem
•Most goes in
between cells or
though cell walls
and never actually
into cells.
Made of long hollow dead cells placed
end to end to form a continuous tube
 Water enters through tiny holes in the
xylem called pits

Water leaves xylem vessels and some
enters the mesophyll cells
 Water evaporates into air space as
water vapor (cuticle prevents too much
water loss)
 Water diffuses out of stomata into air
 Air takes away water vapor

Type of cells
Function
Root Hair cells:
•Found on outside of
plant roots/ above
root tip
• Long/ thin reaching
out into soil
•Help anchor the plant
to the soil
•Absorb water mineral
ions from soil
•Has large surface
area so that lots of
dissolved nutrients can
get inside the cell
quickly
Xylem Cell:
•Empty / dead cell
• Cell wall fill with lignin
– hardens / strong /
waterproof / with
cellulose
• 1 cell = xylem vessel
element – no end walls
• end to end formation
– forming long
continuous tubing
from roots to leaves (1)
transport water /
minerals from root to
parts of plant (2)
structural support to
plant (lignin)
Picture
Place in pathway
How water travels
Root hair
By osmosis water enters root hairs. From here water
passes into the root cortex
Root cortex
Water moves more in between cells than through
cells into the center towards the xylem
xylem
In the xylem, water moves up the xylem due to the
water potential gradient between the water and
air. Water potential in air is less than water potential
in roots and therefore the water moves up the stem
Mesophyll cells
Water moves down the water potential gradient
from the xylem vessel and into the cell walls of the
mesophyll. This reduces the pressure at the top off
the xylem vessel. The difference in pressure causes
water to move up the xylem (root to the top)
Water produces tension / cohesive (water molecules stick to each other)
Properties that allow water to flow upwards.





The cytoplasm of root cells usually have
much higher total solute concentrations
than water in the surrounding soil.
Thus, water diffuses into root cells by
osmosis.
Water must cross the cortex of the root to
enter the xylem.
water moves by capillary action through
cortex cell walls until it reaches the
endodermis.
90 % of water moves through the route this
way.