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9.1 transport in the xylem of plants

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IB Biology 2015

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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. 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. 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. Click4biology.com Water enters the leaf as liquid from the veins Water leaves the leaf as gas through Stomata
  7. 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. 8. Remember the Penny Lab
  9. 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. 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. 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. Click4biology.com Click4biology.com
  12. 12. 9.1 U.4 The adhesive property of water and evaporation generate tension forces in leaf cell walls
  13. 13. 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
  14. 14. 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
  15. 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. 16. 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
  17. 17. 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
  18. 18. 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
  19. 19. 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
  20. 20. Rolled Leaves / Stomatal Pits / Hairs on epidermis (Grasses)
  21. 21. 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
  22. 22. 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.
  23. 23. 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
  24. 24. 9.1 A.2 Models of water transport in xylem using simple apparatus including blotting or filter paper, porous pots and capillary tubing.
  25. 25. 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
  26. 26. 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
  27. 27. 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.
  28. 28. 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)
  29. 29. 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)
  30. 30. 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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