Transcript absorption of water_final

Entry of
water into
plants
Vascular tissues
Root
Stem
Phloem
Xylem
Xylem and phloem in
‘vascular bundle’ ,
arranged in a ring
around the pith.
Xylem and phloem
alternate with each
other and found at
the centre of a root
Absorption of water by roots
Root hair cell has
Large surface area : volume ratio for efficient absorption
Root hair
Epidermal layer and root hair cell
 Piliferous layer
Water would enter root hair cell by osmosis.
Root hair cell
High
conc.
Lower
of
sugar
water
and
salts
potential
Soil
Dilute
Higher
solution of
water
mineral salt.
potential
Absorption of water by roots
Water would pass from root hair cell to the
inner cell by osmosis
Lower
water
potential
Higher
water
potential
Water would pass from one cell to the next cell in
the cortex until the water enters the xylem tube
Cortex – cells in between epidermis and xylem
http://www.kscience.co.uk/animations/transpiration.swf
Absorption of mineral salts by roots
•Ions enter mainly by active transport
•Energy from cellular respiration
Lower
conc. of
Higher
ions (K, Na)
conc.
of ions
Absorption of mineral salts by
roots
•Ions also by diffusion (not common)
Lower
conc. of
ions
Higher conc.
of mineral
ions
This plant has been
given excessive
potassium fertilizer.
Explain why the
plant will die
although fertilizer is
suppose to support
plant growth.
Recap
• What is the main process by which water
moves from cell to cell and finally into the
xylem vessel called?
Recap !
http://www.kscience.co.uk/animations/anim_1.htm
Recap!
• Mineral salts enter the root hair cell mainly by
______________.
Moving water up the xylem vessels
Moving water up the xylem vessels
• Via 3 processes:
– Root pressure
– Capillary action
– Transpiration pull 
the main process
Process 1:
Root pressure
What will happen to the water
level?
Water
level
Pump
water in
Movement of water from the root hair cells to the
xylem vessels would create an upward force to
push the water up the xylem vessels. This is known
as root pressure.
How is root pressure generated?
1) Ions pumped from cortex
into xylem
Angular in
shape
Cell in
coretx
xylem
2) Water enters by osmosis
Movement of water from the root hair cells to the
xylem vessels would create an upward force to
push the water up the xylem vessels. This is known
as root pressure.
A demonstration to show root pressure
What would
happen to the
water level after
5 hrs?
Glass tubing
Connector
Cut stem with
roots
• A experiment to demonstrate capillary action.
• What did you observe?
Capillary action
• Movement of water up a narrow tube
The narrower
the tube, the
higher level
the water
level
Capillary action
Force of attraction
between water
molecules and
wall of vessel
‘pulls’ water
molecules into a
vessel.
(adhesion force)
Force of attraction
between water
molecules ‘pull’ the
next molecule
along. (cohesion
force)
Drinking ribena
Sucking of water up the
straw
Movement of water up
straw
Transpiration pull
Transpiration of water
from the leaves
Movement of water up a
xylem tube
 Transpiration pull is a suction force caused
by transpiration, that pulls the water up the
xylem tube.
It is the strongest force that moves water up
a xylem tube.
Do not be confuse between…..
• Transpiration
 evaporation of water
• Transpiration pull
 suction force
• Transpiration stream the stream of water up
the xylem vessels
Adhesion and cohesion forces
move the stream of water
molecules up a xylem vessel.
1) Water
continuously moves
out of mesophyll
cells to form a thin
layer of moisture.
2)water evaporates
from the thin film of
moisture and moves
into the intercellular
air spaces as water
vapour.
Moving water up the xylem vessels
• Via 3 processes:
– Root pressure
– Capillary action
– Transpiration pull  the main process the causes
water to move up a xylem tube.
Transpiration
What is transpiration?
– The evaporation loss
of water vapour
through the stomata
of the leaves is known
as transpiration.
How is the
suction force
being created at
the leaves by
transpiration?
Transpiration
occurs here
Water evaporates
from the thin film
of moisture to give
water vapour.
Lower conc. of
water vapour
Water vapour would move down the
concentration gradient into the atmosphere.
Water moves out of
mesophyll cells to
replace the thin film of
moisture surrounding
the mesophyll cell.
Mesophyll
cell A
Transpiration
set up an
suction force
to pull water
up the xylem
tube
True or false
• When transpiration stops for a long time,
photosynthesis ceases.
• The sun provides energy for water to moves
through the xylem.
Think about it!
• Usually, only 99% of the water absorbed is lost
through transpiration.
• Where is the remaining 1% of water?
Importance of transpiration
• To pull water and mineral salts from roots to
leaves.
• Evaporation of water cools the leaves.
• Water used for photosynthesis; to keep cell
frim and turgid.
Factors affecting the rate of
transpiration
•
•
•
•
Humidity
Wind or air movement
Temperature
Light
Humidity
• What is humidity?
- >Refers to the amount of water vapour that
the air can hold.
Higher conc. of water
vapour
(100% saturated)
Lower conc. of
water vapour
The drier the air, the steeper the concentration
gradient, the faster the rate of transpiration.
Wilting
Rate of transpiration >
rate of absorption of
water
What happens to the
leaves when they
wilt?
How does wilting
benefit the plant?