1. 9.1: Transport in the xylem of plants
Orange xylem (magnified 2500x)
Essential Idea: Structure and function are correlated in the xylem of plants

2. 9.1 U.1 Transpiration is the inevitable consequence of gas exchange in the leaf

3. David attenborough on xylem

4. Liverworts – exception of stomata
9.1 U.1 Transpiration is the inevitable consequence of gas exchange in the leaf
Exchange of these H2O and CO2 gases must take place in order to sustain photosynthesis
Stomata – pores
Transpiration – loss of water vapor from the leaves and stems of plants
Guard cells – found in pairs (1 in either side stoma), control stoma and can adjust from wide open to fully closed
Liverworts – exception of stomata
Liverworts = NO stomata
Have air chambers
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5. 9.1 U.1 Transpiration is the inevitable consequence of gas exchange in the leaf
Stomata ( singular Stoma ) are pores in the lower epidermis formed by two specialized Guard Cells.
The epidermis and its waxy cuticle is impermeable to carbon dioxide and water.
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.
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6. Do Stomatal peel

7. Water evaporates into the air though stomata
9.1 U.2 Plants transport water from the roots to the leaves to replace losses from transpiration
Water evaporates into the air though stomata
The water lost is replace by water from the xylem
Water is forced up the xylem by transpiration pull (due to cohesive and adhesive properties of water
REMEMBER - Water molecules are weakly attracted
to each other by hydrogen bonds
(Cohesion). Therefore this action
extends down the xylem creating a
'suction' effect.
Water moves from the soil into the roots by osmosis

8. Pathways for water movement:
9.1 U.5 Active uptake of mineral ions in the roots causes absorption of water by osmosis.
Pathways for water movement:
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(a) Water enters epidermal cell cytoplasm by osmosis. The solute concentration is lower than that of soil water due to the active transport of minerals from the soil water to the cytoplasm.
Symplastic Pathway (b) to (c): water moves along a solute concentration gradient. There are small cytoplasmic connections between plant cells called plasmodesmata. In effect making one large continuous cytoplasm.
Apoplastic Pathway (d) to (e):water moves by capillarity through the cellulose cell walls. Hydrogen bonding maintains a cohesion between water molecules which also adhere to the cellulose fibers.

9. Loading water into the xylem:
9.1 U.5 Active uptake of mineral ions in the roots causes absorption of water by osmosis.
Concentration of mineral ions in the root 100 times greater than water soil
Active transport, protein pumps
Minerals are actively loaded into the xylem in the roots which in turn causes water to enter the xylem vessel.
Chloride for example is actively pumped creating a water potential gradient that moving water passively into the xylem.
Pressure within the xylem increases forcing water upward (Root Pressure).
Loading water into the xylem:
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10. 9.1 U.5 Active uptake of mineral ions in the roots causes absorption of water by osmosis.
Fungus grows on the surface of many roots (sometimes even in the cells of the root) Fungi help increase the absorption of minerals by the roots by both increasing surface area and increasing concentration of minerals near root.

12. Thickening of the cellulose cell wall and lignin rings
9.1 U.3 The cohesive property of water and the structure of the xylem vessels allow transport under tension
Plants are however more
'architectural' in their
Structure with adaptations
which provide support for a
static structure, much in the
same way as seen in
buildings.
Thickening of the cellulose cell wall and lignin rings

13. 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 with annular lignification in rings.
The photograph to the left show the thickening of the cellulose walls of the xylem.
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14. 9.1 U.4 The adhesive property of water and evaporation generate tension forces in leaf cell walls

15. 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

16. 9.1 A.1 Adaptations of plants in deserts and in saline soils for water conservation.
Waxy Leaves:
The leaves of these plant have waxy cuticle on both the upper and lower epidermis
•The waxy repels water loss through the upper and lower epidermal cells. If an epidermal cell has no cuticle water will rapidly be lost as the cellulose cell wall is not a barrier to water loss.

17. Needles as leaves to reduce surface area. Thick waxy cuticle
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.

18. The leaves have been reduced to needles to reduce transpiration.
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.

19. 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.
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20. http://prezi. com/f25nx9tnjkpe/
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21. 9.1 S.1 Drawing the structure of primary xylem vessels in sections of stems based on microscope images

22. 9.1 A.2 Models of water transport in xylem using simple apparatus including blotting or filter paper, porous pots and capillary tubing.

23. 9.1 A.2 Models of water transport in xylem using simple apparatus including blotting or filter paper, porous pots and capillary tubing.

24. Transpiration is the loss of water from a plant by evaporation
9.1 S.2 Measurement of transpiration rates using potometers. (Practical 7)
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.
In the plant: factors affecting the rate of transpiration
Leaf surface area
Thickness of epidermis and cuticle
Stomatal frequency
Stomatal size
Stomatal position

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

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

27. 6 Environmental Factors Affecting Transpiration
9.1 S.2 Measurement of transpiration rates using potometers. (Practical 7)
6 Environmental Factors Affecting Transpiration
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  gradient is steeper
Air Movement:- increase air movement increases the rate of transpiration as it moves the saturated air from around the leaf so the  gradient is steeper.
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  of the air, so  gradient is steeper
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 ). 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.

28. 9.1 S.3 Design of an experiment to test hypotheses about the effect of temperature or humidity on transpiration rates.