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IB Biology 9.1 transport in the xylem of plants

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IB Biology 2015 Curriculum

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IB Biology 9.1 transport in the xylem of plants

  1. 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. 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. 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. 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. 5. 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 Click4biology.com
  6. 6. 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. Click4biology.com
  7. 7. 9.1 U.2 Plants transport water from the roots to the leaves to replace losses from transpiration • Water evaporates into the air • The water loss from the leaf draws new water vapor from the spongy mesophyll (symplastic & apoplastic movement) into air space. • In turn the water molecules of the Mesophyll space draw water molecules from the end of the xylem. • Water molecules are weakly attracted to each other by hydrogen bonds (Cohesion). Therefore this action extends down the xylem creating a 'suction' effect.
  8. 8. 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
  9. 9. 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. Click4biology.com Click4biology.com
  10. 10. 9.1 U.4 The adhesive property of water and evaporation generate tension forces in leaf cell walls
  11. 11. 9.1 U.5 Active uptake of mineral ions in the roots causes absorption of water by osmosis. Pathways for water movement: (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. Click4biology.com
  12. 12. 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 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).Click4biology.com
  13. 13. 9.1 U.5 Active uptake of mineral ions in the roots causes absorption of water by osmosis. • Fungus grows on the surface of the roots (sometimes in the cells of the root) to overcome the problem of ions slow movement as they bind to the surface of soil particles. http://www.sanniesshop.com/images/symbiosis-3.jpg http://planthealthproducts.com/wp-content/uploads/2013/04/mycroot.gif
  14. 14. 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
  15. 15. 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.
  16. 16. 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
  17. 17. 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
  18. 18. 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 click4biology
  19. 19. 9.1 A.2 Models of water transport in xylem using simple apparatus including blotting or filter paper, porous pots and capillary tubing.
  20. 20. 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
  21. 21. 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
  22. 22. 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)
  23. 23. 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)
  24. 24. 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.
  25. 25. 9.1 S.3 Design of an experiment to test hypotheses about the effect of temperature or humidity on transpiration rates.

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