The document discusses plant transpiration and water transport. It covers: 1. Transpiration occurs through stomata in leaves and is driven by water evaporation and tension forces. 2. Water is transported from the roots to the leaves through xylem vessels. The cohesive properties of water and xylem structure allow transport under tension. 3. Environmental factors like temperature, humidity and light intensity affect transpiration rates, which can be measured using a potometer.

1. 9.1: Transport in the xylem of plants
http://131.229.88.77/microscopy/Portfolios/Arlene/Portf
olio4_files/Portfolio2.html
Orange xylem (magnified 2500x)
Essential Idea: Structure and function are correlated in the xylem of
plants

2. Understandings
Statement Guidance
9.2 U.1 Transpiration is the inevitable consequence of gas
exchange in the leaf
9.2 U.2 Plants transport water from the roots to the leaves to
replace losses from transpiration
9.2 U.3 The cohesive property of water and the structure of
the xylem vessels allow transport under tension
9.2 U.4 The adhesive property of water and evaporation
generate tension forces in leaf cell walls
9.2 U.5 Active uptake of mineral ions in the roots causes
absorption of water by osmosis.

3. Applications and Skills
Statement Guidance
9.1 A.1 Adaptations of plants in deserts and in saline soils for
water conservation.
9.1 A.2 Models of water transport in xylem using simple
apparatus including blotting or filter paper, porous pots
and capillary tubing.
9.1 S.1 Drawing the structure of primary xylem vessels in
sections of stems based on microscope images
9.1 S.2 Measurement of transpiration rates using potometers.
(Practical 7)
9.1 S.3 Design of an experiment to test hypotheses about the
effect of temperature or humidity on transpiration
rates.

4. http://www.greenpeace.org/international/Global/international/photos/forests/2010/7/01amazon-clouds.jpg
9.1 U.1 Transpiration is the inevitable consequence of gas exchange in
the leaf

5. https://lifeofaplant.file
s.wordpress.com/2014
/05/transpiration.gif
9.1 U.1 Transpiration is the inevitable consequence of gas
exchange in the leaf

6. 9.1 U.1 Transpiration is the inevitable consequence of gas
exchange in the leaf
• Transpiration is the process where
plants absorb water through the
roots and then give off water vapor
through pores in their leaves. The
exchange of H2O and CO2 as gases
from the leaves must take place in
order to sustain photosynthesis.
Underside of the leaf contains:
• Stomata – pores
• Guard cells – found in pairs (1 in
either side stoma), control
stoma and can adjust from wide
open to fully closed
*Abscisic acid (hormone) stimulates
the stoma to close, stopping the
release of the two gases.
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Water enters the
leaf as liquid
from the veins
Water leaves the
leaf as gas
through
Stomata

7. 9.1 U.1 Transpiration is the inevitable consequence of gas exchange in
the leaf
• Stomata are pores in the lower epidermis formed by two specialized Guard Cells.
• If the water loss is too severe the stoma will close. This triggers mesophyll cells to
release abscisic acid (hormone). Which stimulates the stoma to close by releasing
water from the Guard Cells.
• Decrease in water loss abscisic acid levels decrease, Guard Cells fill with water and
Stomata pore opens. The gases exchange of CO2, O2 and H2O can continue
http://pixgood.com/stomata-
open-and-close.html
Emptied
Of
water
Full
Of
water

8. Remember the Penny Lab

9. 9.1 U.2 Plants transport water from the roots to the leaves to replace
losses from transpiration
• Water evaporates into the air, leaving
the leaf, pulling as it leaves.
• This pulling action draws new water
vapor into air space in the leaf.
• In turn the water molecules of
the air space draw water molecules
from the end of the xylem tube
(connecting all the way down the
plant roots).
*Water molecules are weakly attracted
to each other by hydrogen bonds
(Cohesion). Therefore this action
extends down the xylem creating a
'suction' effect.

10. 9.1 U.3 The cohesive property of water and the structure of the
xylem vessels allow transport under tension
Xylem Structure
•Structural adaptations which provides
support for the plant.
•Transpiration pull utilizing capillary action,
this is the primary mechanism of water
movement in plants. The intermolecular
attraction of water allows water flow upwards
(against the force of gravity) through the
xylem of plants.
Thickening of the
cellulose cell wall
and lignin rings

11. 9.1 U.3 The cohesive property of water and the structure of
the xylem vessels allow transport under tension
• In the diagram to the above
left the xylem shows a
cylinder of cellulose cell
wall. The xylem also rings of
lignin providing additional
strength
• The photograph to the left
show the thickening of the
cellulose walls of the xylem.
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13. 9.1 U.4 The adhesive property of water and evaporation generate
tension forces in leaf cell walls

14. 9.1 U.5 Active uptake of mineral ions in the roots causes absorption of
water by osmosis.
Loading water into the xylem:
Concentration of mineral
ions in the root 100 times
greater than water in soil.
ATP is used to pump ions
into the root hairs
•Diffusion of Ions Water
flows by osmosis from an area of
high concentration to an are of
low concentration. As minerals
are actively loaded into the
roots. A change in the
concentration of water in the
roots is created . Water diffuses
into the plant
Root
Hair
Clay Soil

15. 9.1 U.5 Active uptake of mineral ions in the roots causes absorption of
water by osmosis.
• Plant have a mutualistic
relationship with fungus.
There gains are a higher
absorptive capacity for water
and mineral nutrients due to
the funguses large surface.
http://www.sanniesshop.com/images/symbiosis-3.jpg
http://planthealthproducts.com/wp-content/uploads/2013/04/mycroot.gif

16. 9.1 A.1 Adaptations of plants in deserts and in saline soils for
water conservation.
• Plants adapted to reduce water
loss in dry environments.
Examples of such water stress
habitats include:
• Desert (high temp, low
precipitation)
• High Altitude & High
Latitude (low
precipitation
• Tundra where water is
locked up as snow or ice.
• Areas with sandy soil
which causes water to
rapidly drain.
• Shorelines that contain
areas of high salt levels

17. Plants adapted to dry
Environments are called
Xerophytes. Xerophytes are
adaptations to reduce water loss
or indeed to conserve water.
They
occupy habitats in which there is
some kind of water stress.
Adaptations include:
1. Life Cycle Adaptations
2. Physical Adaptations
3. Metabolic Adaptations
9.1 A.1 Adaptations of plants in deserts and in saline soils for
water conservation.
Example: Waxy Leaves:
The leaves of these plant have waxy
cuticle on both the upper and
lower epidermis

18. 1. Life Cycle Adaptations
I. Perennial plants bloom in the wet season
II. Seeds have the ability to stay dormant for many years
until conditions are ideal for growth

19. 9.1 A.1 Adaptations of plants in deserts and in saline soils for water
conservation.
Firs and Pines:
•Confers have their
distribution extended beyond
the northern forests. Plants in
effect experience water
availability more typical of
desert environments.
•Needles as leaves to reduce
surface area.
•Thick waxy cuticle
•Sunken stomata to limit
exposer.
•No lower epidermis.
http://fc08.deviantart.net/fs71/i/2014/127/1/c/pine_needles_by_neelfyn-d7hj7z4.jpg

20. 2. Physical Adaptations
I. Waxy Leaves: •The leaves of this plant
have waxy cuticle on both the upper
and lower epidermis
II. Rolled leaves The leaf rolls up, with the
stomata enclosed space not exposed to
the wind.
III. Hairs on the inner surface also allow
water vapor to be retained which
reduces water loss through the pores.
IV. Spikes Leaves reduced to spikes to
reduce water loss
V. Deep roots to reach water

21. Rolled Leaves / Stomatal Pits / Hairs on
epidermis (Grasses)

22. 9.1 A.1 Adaptations of plants in deserts and in saline soils for water
conservation.
Succulent
•The leaves have been
reduced to needles to
reduce transpiration.
•The stem is fleshy in
which the water is
stored.
•The stem becomes the
main photosynthetic
tissue.
http://upload.wikimedia.org/wikipedia/commons/c/c9/Echinocactus_grusonii_kew.jpg

23. 3. Metabolic Adaptations
CAM: reduces water loss by opening pores at night but closing them
during the day.
At night CO2 is combined with (C3) to form Malic Acid (C4). This stores
the CO2 until required for photosynthesis during the day.
During the day the pore are closed and the Malic Acid degenerates to
PEP (C3) and CO2. The CO2 is then used in photosynthesis.

24. 9.1 A.1 Adaptations of plants in deserts and in saline soils for
water conservation
• Species of grass occupying sand
dunes habitat.
• Thick waxy upper epidermis
extends
• Leaf rolls up placing, containing
hairs. The stomata in an enclosed
space not exposed to the wind.
• The groove formed by the rolled
leaf also acts as a channel for rain
water to drain directly to the
specific root of the grass stem.
http://upload.wikimedia.org/wikipedia/commons/a/a2/
AmericanMarramGrassKohlerAndraeStateParkLake
Michigan.jpg
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25. 9.1 A.2 Models of water transport in xylem using simple apparatus
including blotting or filter paper, porous pots and capillary tubing.

26. 9.1 S.1 Drawing the structure of primary xylem vessels in sections of
stems based on microscope images
https://pw-biology-2012.wikispaces.com/file/view/Xylem.png/354386126/800x479/Xylem.png
https://classconnection.s3.amazonaws.com/263/flashcards/1226263/jpg/6959590336_b28341ed7a_z1354494841351.jpg

27. Transpiration
•Transpiration is the loss of water from
a plant by evaporation
•Water can only evaporate from the
plant if the water potential is lower in
the air surrounding the plant
•Most transpiration occurs via the
leaves
•Most of this transpiration is via the
stomata.
9.1 S.2 Measurement of transpiration rates using potometers. (Practical 7)
In the plant: factors affecting the rate of
transpiration
1.Leaf surface area
2.Thickness of epidermis and cuticle
3.Stomatal frequency
4.Stomatal size
5.Stomatal position

28. 6 Environmental Factors Affecting Transpiration6 Environmental Factors Affecting Transpiration
1. Relative humidity:- air inside leaf is saturated
(RH=100%). The lower the relative humidity
outside the leaf the faster the rate of
transpiration as the Ψ gradient is steeper
2. Air Movement:- increase air movement
increases the rate of transpiration as it moves
the saturated air from around the leaf so the Ψ
gradient is steeper.
3. Temperature:- increase in temperature
increases the rate of transpiration as higher
temperature
• Provides the latent heat of vaporisation
• Increases the kinetic energy so faster
diffusion
• Warms the air so lowers the Ψ of the air, so
Ψ gradient is steeper
9.1 S.2 Measurement of transpiration rates using potometers. (Practical 7)
4. Atmospheric pressure:- decrease in atmospheric
pressure increases the rate of transpiration.
5. Water supply:- transpiration rate is lower if there
is little water available as transpiration
depends on the mesophyll cell walls being wet
(dry cell walls have a lower Ψ). When cells
are flaccid the stomata close.
6. Light intensity :- greater light intensity increases
the rate of transpiration because it causes the
stomata to open, so increasing evaporation
through the stomata.

29. A SimpleA Simple
PotometerPotometer
1’’’’’’’’2’’’’’’’’3’’’’’’’’4’’’’’’’’5’’’’’’’’6’’’’’’’’7’’’’’’’’8’’’’’’’’9’’’’’’’’10’’’’’’’’11’’’’’’’’12’’’’’’’’13’’’’
Air tight seals
Plastic tubing
Graduated scale
Capillary tube
Leafy shoot cut
under water
Water evaporatesWater evaporates
from the plantfrom the plant
Movement of meniscus is
measured over time
9.1 S.2 Measurement of transpiration rates using potometers. (Practical 7)

30. 1’’’’’’’’2’’’’’’’’3’’’’’’’’4’’’’’’’’5’’’’’’’’6’’’’’’’’7’’’’’’’’8’’’’’’’’9’’’’’’’’10’’’’’’’’11’’’’’’’’12’’’’’’’’13’’’’
The rate of water loss from
the shoot can be measured
under different
environmental conditions
volume of water taken upvolume of water taken up
in given timein given time
Limitations
•measures water uptake
•cutting plant shoot may damage plant
•plant has no roots so no resistance to water being pulled up
Water is pulled upWater is pulled up
through the plantthrough the plant
9.1 S.2 Measurement of transpiration rates using potometers. (Practical 7)

31. 9.1 S.3 Design of an experiment to test hypotheses about the effect of
temperature or humidity on transpiration rates.