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独中高中生物Chapter 8 transport in plants

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独中高中生物Chapter 8 transport in plants

  1. 1. Chapter 8 Transport in Plants Ong Yee Sing 2017
  2. 2. Learning Objectives: • To comprehend the structures and functions of the conducting tissue (xylem tissue and phloem tissue) in plants. • To comprehend the uptake of water and mineral salt (or inorganic salts). • To understand the mechanism of transport of water from the root to the leaf. • To understand the transport of organic nutrients.
  3. 3. 8.1 Transport system in plants
  4. 4. Vascular bundle维管束 • Higher plants such as angiosperms transport various kinds of nutrients, water and mineral salts (or inorganic salts) through the conducting tissue called the vascular bundle. • The vascular bundle consists of phloem 韧皮部, xylem木质部and surrounding mechanical tissue机械组织. • Xylem is responsible for the transport of water and inorganic salts. • Phloem is responsible for the transport of organic nutrients. • Apart from carrying out the transport of substances, the vascular bundle also offer support to the plant.
  5. 5. 8.1.1 Xylem
  6. 6. Evolution of water-conducting cells
  7. 7. Xylem木质部 • from Greek xulon ‘wood’ + the passive suffix -ēma • Xylem transports water and mineral salts. • Xylem is mainly made up of conductive elements and non-conductive elements. • Conductive elements are also known as trachaery elements, which includes vessel导管 and tracheid假导管. • Non-conductive elements includes xylem parenchyma and xylem fibres. Xylem of a celery petiole叶柄.
  8. 8. The death of tracheary elements
  9. 9. Vessels • A chain of elongated cylindrical cells that die at maturity to form a thin, long and hollow tube . • Perforation plates穿孔板 are formed on the cell calls at the end of the cell to allow bulk flow of water from the roots to the leaves. • Pits壁孔 are formed side of the tube to allow transverse 横向 movement of water. Vessels of a stem of Borya sphaerocephala (Boryaceae).
  10. 10. Lignification of vessels • The cell wall of vessel is thickened and lignified木质化 to prevent walls from collapsing from high water pressure. • There are different type of thickening. • The vessels also provide support for the plant.
  11. 11. Tracheids假导管 • from medieval Latin trachea “rough”. • Both ends of the tracheids are tapering尖细 • The lumen (pl. lumina) of tracheids is smaller. • from Latin “opening” • The transverse end walls间隔墙 between two neighboring tracheids is retained. • The transverse end walls possess pits壁孔so that water can be transported from a tracheid to another tracheid. • Pits also are formed side of the tube to allow transverse movement of water.
  12. 12. Differences of vessels and tracheids Vessels Tracheids Larger lumen Smaller lumen Shorter cell Longer cell End wall perforated End wall closed and tapered Continuous tube No continuous tube
  13. 13. Quiz • Which of the following plant cells transports water and minerals from the roots to the leaves? A) epidermal cell B) parenchymal cell C) sclerenchymal cell D) vessel element E) sieve tube cell
  14. 14. Quiz • Which of the following transports organic nutrients, usually from the leaves to the roots? A) epidermal cell B) parenchymal cell C) sclerenchymal cell D) xylem E) phloem
  15. 15. 8.1.2 Phloem
  16. 16. Phloem韧皮部 • from Greek phloos ‘bark’ + the passive suffix - ēma . • Phloem is responsible for the transport of organic nutrients. • Phloem is chiefly made up of sieve tubes and companion cells. • Phloem may also contain phloem parenchyma and phloem fibres.
  17. 17. Quiz • Which of the following cells will always have at least one companion cell associated with it? A) parenchyma cell B) sclerenchyma cell C) tracheid D) vessel element E) sieve-tube cell
  18. 18. Formation of sieve tube and companion cell
  19. 19. Sieve tube • The sieve tube cells are long tubular in shape (narrow, elongated) without nucleus. • Only cytoplasm is present in these cells. • The sieve plates (end walls) possess numerous sieve pores. • The side of each sieve tube is the companion cell(s) which possess a nucleus and dense cytoplasm. • The companion cells can assist the sieve tubes in the transport of nutrients (ATP, proteins etc.).
  20. 20. Quiz • Which of the following cells have perforated end walls and cytoplasm, but no nuclei? A) sclerenchyma cell B) tracheid C) vessel element D) sieve-tube cell E) companion cell
  21. 21. Movement of phloem sap • Thin filaments of cytoplasm (plasmodesma strands) pass through the sieve pores, connecting the sieve elements with the companion cells. • The movement of cytoplasm facilitate movement of material between cells. • The sieve tube cells in the roots are connected to those in the stems and these are connected to those in the leaves.
  22. 22. Comparison of sieve tube elements and companion cells
  23. 23. Comparison of xylem and phloem Phloem Xylem Function Transportation of organic substances. • Transportation of water and mineral ions. • Support by lignin Movement Bidirectional Unidirectional Elements Sieve tubes elements, companion cells, phloem parenchyma, phloem fibres. Tracheids, vessel elements, xylem parenchyma, xylem fibres. Nature of tissue Living tissue with little cytoplasm but no nucleus / tonoplast. Dead tissue at maturity so it is hollow with no cell contents.
  24. 24. Conclusion
  25. 25. Quiz • Which of the following comparisons is NOT correct? A) dermal tissue--epidermal cell B) ground tissue--parenchyma and sclerenchyma cells C) vascular tissue--xylem and phloem D) xylem--tracheids and vessel elements E) phloem--guard cells and vessel elements
  26. 26. 8.2 Absorption and transport of water and mineral salts
  27. 27. Cross-section of roots 表皮 皮层 中柱 内皮层 中柱鞘 木髓
  28. 28. Ranunculus Root Cross Section Casparian strip 凯氏带
  29. 29. Absorption of water and mineral salt • The water in the soil enters the root through osmosis • Mineral salts are absorbed by means of facilitated diffusion and active transport.
  30. 30. 8.2.1 Root and water uptake
  31. 31. Root hair根毛 (root hair zone)• The root hair zone is the zone where a root absorbs water most actively. • The root hair does not contain cuticle角质层. • Cuticles are protective, hydrophobic, waxy coverings • Cuticles minimize water loss and reduce pathogen entry • Numerous number to increase the surface area.
  32. 32. Transportation of water and mineral salt Epidermis (root hair cells) Cortex Endodermis Pericycle Xylem Other plant tissue
  33. 33. Quiz • Write your name, class number, class, and date on the top of the paper. • Write the name of the components of the roots with a blue or black pen. • (2 marks) A B D C E F G H
  34. 34. Osmosis of water into the roots • Generally, the concentration of the cell sap of the root hair cell is higher than that of the soil solution. • Water moves from the soil into the root hair cell through osmosis. • The turgor pressure膨胀压 of the root hair cell increases. • When a plant cell is fully turgid, it will produce an opposite pressure, the wall pressure壁压. • When the wall pressure is equal to the osmotic pressure (i.e. the root hair cell and soil solution have the same water concentration), water will stop moving into the root hair cell.
  35. 35. Pressures • Turgor pressure is the pressure exerted by the cytoplasm on the cell wall. It is the turgor pressure in the plant cells which helps the plants to be erect. • Wall pressure is the pressure applied by the cell wall on the contents of the cell. Wall pressure is opposite to the turgor pressure. • Osmotic pressure is the minimum pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane. It is also defined as the measure of the tendency of a solution to take in water by osmosis.
  36. 36. Movement of water in the cells • This results in the concentration of the cell sap of the root hair cell being lower than that of the cortical cell (cell of cortex) next to it. • Water goes down the concentration gradient by osmosis.
  37. 37. Route taken by water to travel into the xylem • The apoplast is the space outside the plasma membrane within which material can diffuse freely. • The symplast of a plant is the inner side of the plasma membrane in which water and low-molecular-weight solutes can freely diffuse. • The plasmodesmata allow the direct flow of small molecules such as sugars, amino acids, and ions between cells. • Transport velocity is higher in apoplast pathway质体外途径 compare to symplast pathway共质体途径. • The apoplast pathway accounts for a higher proportion of water transport in plant tissues than does symplastic transport.
  38. 38. Unidirectional flow of water in the root • The cells of the endodermis contain casparian strip, a band-like structure formed from the lignification木质化 and suberization栓质化 of the endodermis cell wall. • Lignin is a complex organic polymers that is hydrophobic. • Suberin is a another highly hydrophobic waxy substance • This strip is oily.
  39. 39. • It is able to prevent the backflow of salt solution from the xylem vessel to the cortex. • It blocks the passage of substances through the pits of the cell wall, so the substances have to move into the cells of endodermis. • The movement of the water and water-soluble substances can be controlled by the endodermis cells. Function of the casparian strip
  40. 40. Quiz • Which tissue in the dicot root regulates the entrance of minerals into the vascular cylinder? A) epidermis B) cortex C) endodermis D) root hairs E) pericycle
  41. 41. Quiz • The ring of waxy material that borders the endodermal cells on four sides is known as the ______ . A) plasmodesmata B) Casparian strip C) cotyledon D) pericycle E) vascular cambium
  42. 42. Conclusion • Movement of water in the roots is: Epidermis (root hair cells)  Cortex  Endodermis  Pericycle  Xylem • Osmosis of water in the plant cells is controlled by the osmotic pressure, turgor pressure and wall pressure. • The cell wall of the endodermis cells contain a casparian strip, which is lignified and subrised to prevent the backflow of salt solution from the xylem vessel to the cortex and to block the passage of substances through the pits of the cell wall.
  43. 43. 8.2.2 Absorption of mineral salts by the root
  44. 44. Mineral salts and mineral ions • Generally, mineral elements exist in mineral salts (inorganic salts) found in the soil. • Salt is the product of the reaction between an acid and a base (other than water). • Table salt (NaCl) is the product of a reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH). • An inorganic salt is any salt that doesn't contain carbon.
  45. 45. Absorption of mineral • Plants can only absorb soluble minerals as ions. • They absorb minerals ions from the soil through their root hair cells. • For example, potassium and nitric acid dissolve in water to form K+ and NO3 - , K and N are absorbed by the root in the form of K+ and NO3 - respectively.
  46. 46. Energy in mineral uptake • Absorption of mineral ions required energy. • The concentration of minerals in the soil is very low. • Active transport is required if facilitated diffusion is not able to satisfy the need of the cell.
  47. 47. Selective absorption of mineral ions • The absorption of inorganic salt is relatively independent to water. • Cucumber plant absorbs more water in the dark, but the amount of sodium and bromine absorbed does not change. • The absorption of inorganic salt is selective. • When using ammonium sulfate fertilizer, the plant absorbs more sulphate ion than ammonium ion.
  48. 48. 8.2.3 Mechanism of the ascent of water from the root to the leaf
  49. 49. Mechanisms of ascent of sap in xylem tissue • The ascent of water from the root to the leaf requires the following mechanisms: • Root pressure • Transpiration pull • Adhesive-cohesion forces
  50. 50. Root pressure根压 • Root pressure is the transverse横向 osmotic pressure within the cells of a root system that causes sap to rise through a plant stem to the leaves. • There is a difference in the concentration of the cell sap of the root cells and that of the xylem vessels. • The difference in concentration creates an osmosis gradient. • Water will move down the concentration gradient until equilibrium is reach (then no net movement). • This will produce a pulling force which causes water molecules to move in by endosmosis内渗 (osmosis toward the inside of a cell or vessel), a.k.a the root pressure.
  51. 51. Demonstration of root pressure Demonstration of root pressure. 吐水作用 e.g. lady’s finger (Alchemilla vulgaris)
  52. 52. Strength of root pressure • As for tall trees, root pressure is not strong enough to force water up to this height. • The ascent of water must depend on the transpiration pull, the cohesive forces (cohesion forces) between water molecules and the adhesive forces.
  53. 53. Quiz • Which of the following statements about water movement is FALSE? A. The flow of water depends upon air pressure and humidity. B. Water initially moves into the root hair cells by osmosis because the mineral content of the surrounding environment is higher than that of the cells. C. Water movement from the roots to the leaves is dependent upon both adhesion and cohesion.
  54. 54. Transpirational pull蒸散牵引力 • The evaporation of water from leaves result in a suction force, which pulls water up the xylem vessels, called the transpirational pull. • Transpiration steam蒸散水柱, i.e. uninterrupted stream of water and solutes which is taken up by the roots and transported via the xylem to the leaves where it evaporates into the air. • Transpiration pull is not affected by the height of the trees. Evaporation of water Water ↓ = Concentration of cell sap ↑ Draw water from cells deeper inside the leaf by osmosis Water removed from veins (xylem vessels)
  55. 55. Transpirational pull
  56. 56. Adhesive-cohesion forces • A combination of two forces: • Adhesive force • Cohesion force • These forces originate principally because of coulomb (electric charge) forces. When two molecules are at an intermediate distance, their potential energy is at a minimum, requiring the expenditure of work to either approximate or separate them, whether they be of the same or different material.
  57. 57. Cohesion of water • from Latin cohaerere, from co- ‘together’ + haerere ‘to stick.’ • Cohesion is the mutual attraction between like molecules that causes them to stick together. • This allow the transpiration stream remains as a continuous stream. Dew drops on a the stalk of a water horsetail (Equisetum fluviatile) formed by cohesion.
  58. 58. Adhesion of water • from Latin verb adhaerere: ad- ‘to’ + haerere ‘to stick.’ • Adhesion is the mutual attraction between unlike molecules that causes them to cling to one another. • The adhesion of water molecules to other molecules allow them to cling at a higher level around the edges of the surface. Getty Image: Dorling Kindersle
  59. 59. Capillary action • Capillary action is the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity. • If the diameter of the tube is sufficiently small, then the combination of surface tension (which is caused by cohesion within the liquid) and adhesive forces between the liquid and container wall act to propel the liquid. • As the diameter of the lumen of the xylem vessel is small, capillary action is produced.
  60. 60. Water climbs higher in tube with smaller diameter
  61. 61. Quiz • Which of the following capillary tubes has the largest diameter? A. A B. B C. C When a glass capillary is placed in liquid water, water rises up into the capillary. The smaller the diameter of the capillary, the higher the water rises. The height of the water does not depend on the angle at which the capillary is tilted. A B C
  62. 62. Conclusion • The ascent of water is propelled by the following forces: • Root pressure = the transverse osmotic pressure within the cells of a root system that causes sap to rise through a plant stem to the leaves. • The transpirational pull = resulted suction force created by the evaporation of water from leaves, which pulls water up the xylem vessels. • The capillary action which is a result of the adhesive-cohesion forces. • Cohesionis = the mutual attraction between like molecules that causes them to stick together. • Adhesion = the mutual attraction between unlike molecules that causes them to cling to one another.
  63. 63. 8.3 Transport of organic nutrients
  64. 64. Functional of phloem • Phloem transports organic substances produced during photosynthesis from the leaves to other parts of the body. • Phloem also transport • Some mineral salts • Amino acids • Vitamins • Plant hormones
  65. 65. Transportation of photosynthetic products • Photosynthesis produces PGAL as a product. • PGAL is transported to other regions of the plant body by the phloem. • In most plants, these organic products have to be converted into soluble sucrose before they can be transported. • Sucrose = glucose + fructose + water
  66. 66. Why sucrose? • Soluble in water • Disaccharides are soluble in water, hence can be transported with the phloem. • Increase energy storage • Sucrose is a more efficient energy storage compound compare to glucose and fructose. • Starch will be even more efficient but starch is insoluble in water. • Removing unwanted intermediate reactions • Glucose is highly reactive. • Sucrose is a non-reducing sugar, hence it is less reactive.
  67. 67. Bidirectional translocation of sucrose • In phloem tissue the transport of organic nutrients is bidirectional. • Some are transported upwards • to the buds, young leaves, flowers • to provide energy for carry out cellular respiration and growth • Some are transported downward • to the storage organ such as roots and stems • to be converted into starches, lipids and fats, proteins etc. to be stored.
  68. 68. Transportation in phloem requires energy • There are more sucrose in the sieve cells compare to the companion cells and other plant tissues. • ATP is required to pump sucrose into the phloem against concentration gradient. • Companion cells provide the ATP. • Sieve cells lost most its organelles, includes nucleus and mitochondria.
  69. 69. Experiment to test for movement of organic nutrient • It is difficult to obtain uncontaminated samples of phloem sap. • In many plant species, phloem-specific protein (P-protein) provides an almost instantaneous seal. • Some experiment can be carried out: • Tracer experiment • Alphids’ stylet test
  70. 70. Tracer experiment • Radioactive carbon isotope 14C is used to produce 14CO2. • The 14C is incorporated into organic compounds during photosynthesis. • Autoradiography can shows the movement of these organic compound in the phloem. • Experiment also can be carried out by direct injection of 14C-sucrose into the leaves. • When the ring of phloem is removed, the 14C-sucrose only travelled in one direction.Autoradiogram visualizing carbon transport to sink tissues. Picture (A) and autoradiogram (B) of a Col-0 plant labelled with 14CO2. Leaf 8 was labelled for 5 min followed by a chase period of 1 h. The leaves are numbered as described in Figure 2. Plant material was exposed to the film for 13 days.
  71. 71. The sap can be collected and analysed. 口器 Scale bars: top = 1 mm, bottom = 1.5 mm
  72. 72. 8.4 Transpiration
  73. 73. Transpiration 蒸散作用 • Transpiration is the process of water movement through a plant and its evaporation from aerial parts of the plant body, such as leaves, stems and flowers. • In transpiration, water is lost as vapour. • Only a small portion (1 – 5%) of water absorbed by terrestrial plants is used for metabolism. • Water is transpired out to the atmosphere mostly through the stomata on the surface of the laves, i.e. stomatal transpiration气孔 蒸散. • A small amount of water can be transpired through the cuticle layer of epidermis (epidermal/cuticular transpiration) and lenticels (lenticular transpiration) .
  74. 74. Function of transpiration • Lower plant body temperature. • Evaporation cooling • Help in the absorption and transport of water and mineral salts. • Create negative pressure • Remove excessive water
  75. 75. Quiz • Which one of the following is not a function of transpiration? A. It is responsible for keeping the plant cool. B. It causes minerals to travel up through the plant. C. It is responsible for water travelling from the roots to the leaves. D. It gives leaves their green colour.
  76. 76. 8.4.1 Process of transpiration
  77. 77. Pathway of transpiration soil root hair xylem mesophyll cell surface of mesophyll cell air chamber stomata atmosphere
  78. 78. Wet walls • Water fills the whole vacuole and enters the cell wall through osmosis. • Water coats the walls of mesophyll cells as a film. • Humidity in the air chamber is saturation. • Water evaporates. • Water diffuse out the leaves as the relative humidity in the atmosphere is lower than that of the sub-stomata chamber.
  79. 79. Quiz • Water vapour evaporates from cells in the leaves of plants and exits the leaves by way of tiny pores in their leaves. What is this process called? A. Excretion B. Transpiration C. Respiration D. Mutation
  80. 80. Quiz • The diagram shows an experiment whose purpose is: A. to show that water enters a plant through its roots. B. to show that a plant makes its own food through photosynthesis. C. to show that water evaporates from a leaf by transpiration. D. to show the path of water through a plant.
  81. 81. 8.4.2 Factors affecting transpiration
  82. 82. Factors • Light intensity光强度 • Temperature温度 • Humidity湿度 • Wind speed风速
  83. 83. Light • In bright light transpiration increases. • The stomata open to allow more carbon dioxide into the leaf for photosynthesis.
  84. 84. Temperature • Transpiration is faster in higher temperatures. • Evaporation and diffusion are faster at higher temperatures.
  85. 85. Humidity • Transpiration is slower in humid conditions. • Diffusion of water vapour out of the leaf slows down if the leaf is already surrounded by moist air
  86. 86. Wind • Transpiration is faster in windy conditions. • When there is very little wind, this means that the layer of water vapour directly surrounding the leaves is not being swept away. • When there is more wind, water vapour is removed quickly by air movement. • This speeds up the diffusion of water vapour out of the leaf.
  87. 87. Conclusion
  88. 88. Quiz • What happens to the transpiration rate as light intensity increases? A. It increases B. It stays the same C. It decreases
  89. 89. 8.5 The mechanism of opening and closing of stomata on the leaf surface
  90. 90. Quiz • The primary function of stomata is to A. minimize water loss B. facilitate gas exchange for photosynthesis C. signal guard cells to open or close D. convert sunlight into usable energy
  91. 91. Stoma • Singular stoma, plural stomata • from Greek στόμα, "mouth“ • Stoma is a pore, found in the epidermis of leaves, stems, and other organs, that allow exchange of air in the plant. • Air enters the plant through these openings by gaseous diffusion. • Stoma = a paired guard cells + the pore (stomatal aperture). • The guard cells control the opening of stoma.
  92. 92. Guard cells • A pair of kidney-shaped cells with a gap between them. • Guard cells contain chloroplast. (Epidermis cell do not contain chloroplast) • The thickness of their cell wall is unevenly. • The inner wall near the side of stoma is thicker than the outer wall. Transmission electron micrographs of paradermal sections through guard cells of a pea (Pisum sativum).
  93. 93. Opening and closing of stomata Stoma open Stoma closed Guard cells absorb water Guard cells lose water Guard cells are turgid Guard cells are flaccid The thin outer walls stretch The thin walls is straighten The cell curves outwards The cell is straighten
  94. 94. Quiz • Stomata close when the guard cells: A) lose water. B) photosynthesis begins and the internal CO2 concentration decreases. C) become turgid. D) gain potassium ions.
  95. 95. Opening of stoma • In the presence of light, the chloroplast of the guard cell carries out photosynthesis. • The concentration of carbon dioxide in the cell decreases during the carbon fixation process of the dark reaction. • The reduction of carbon dioxide cause the pH value of the cell to increase. • The glucose produced from photosynthesis promotes the synthesis of organic acids and accumulation of potassium ions within the guard cells by active transport. • The osmotic pressure of the guard cells rises. • Water from the surrounding epidermal cells enters the guard cell though osmosis, causing it to expand, and therefore the stoma is opened.
  96. 96. Closing of stoma • In the absent of light, the guard cell do not undergo photosynthesis. • The concentration of carbon dioxide in the cell increases during respiration. • The reduction of carbon dioxide cause the pH value of the cell to decrease. • The organic acids are consumed and the potassium ions exits the guard cells by facilitated diffusion. • The osmotic pressure of the guard cells decreases. • Water exits the guard cell though osmosis, causing it to deflat, and therefore the stoma is closed.
  97. 97. Mechanism of stomata movement Light Dark Concentration of CO2 decreases due to photosynthesis ↓ pH increases ↓ K+ moves into the guard cells by active transport + Synthesis of organic acids ↓ Osmotic pressure increases ↓ Water moves into the guard cells through osmosis ↓ Guard cells become turgid ↓ Stomata open Concentration of CO2 increases due to respiration ↓ pH decreases ↓ K+ moves out of the guard cells by diffusion + Consumption of organic acids ↓ Osmotic pressure decreases ↓ Water moves out of the guard cells through osmosis ↓ Guard cells become flaccid ↓ Stomata close
  98. 98. Quiz • The macronutrient, _______________ , is important to the operation of stomata. A) magnesium B) manganese C) sulfur D) potassium E) iron
  99. 99. Quiz • The opening of the stomata is effected by all of the following except A) oxygen concentration B) temperature C) light D) carbon dioxide concentration

Hinweis der Redaktion

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  • https://s3-us-west-2.amazonaws.com/courses-images/wp-content/uploads/sites/1842/2017/05/26232256/figure-30-05-04.png
  • The osmotic gradient is the difference in concentration between two solutions on either side of a semipermeable membrane.
  • https://www.youtube.com/watch?v=3pKbaF_HwBE
  • http://www.bbc.co.uk/education/guides/zps82hv/revision/3
  • https://image.slidesharecdn.com/33mechanismsinwatertransportwilting-101019024404-phpapp01/95/chapter-9-transport-in-plants-lesson-3-the-3-mechanisms-in-water-transportadvantages-and-disadvantages-ofwilting-13-728.jpg?cb=1287524409
  • http://plantphys.info/plant_physiology/transpire.shtml
  • http://ib.bioninja.com.au/_Media/water-cohesion-and-adhesion_med.jpeg
  • https://www.khanacademy.org/science/biology/water-acids-and-bases/cohesion-and-adhesion/a/cohesion-and-adhesion-in-water
  • http://www.gettyimages.com/detail/illustration/water-molecules-being-lifted-by-adhesive-royalty-free-illustration/98193042
  • https://i.pinimg.com/736x/5d/05/97/5d0597075dbeb28f5899d460432cb6d3--to-the-wall-the-edge.jpg
  • http://web.mit.edu/nnf/education/wettability/gravity.html
  • The stretching of the air-liquid meniscus matches the pressure exerted by the liquid, not the massof liquid in the tube.

  • http://2.bp.blogspot.com/-dypbhiq4sds/VF-A-XDVktI/AAAAAAAAVV0/VxlYOXdOdr0/s1600/transport%2Bin%2Bphloem.png
  • Some plants e.g. coleus, squash and melon also transport raffinose (a trisaccharide composed of galactose, glucose, and fructose) and stachyose (one sucrose molecule + two galactosemaolecules)
  • Arnold,W.N. The selection of sucrose as a translocate of higher plants. J Theor Biol 21:13-20 (1968)
  • http://slideplayer.com/slide/4508057/15/images/13/Translocation+is+Bidirectional+XYLEM+PHLOEM.jpg
  • http://images.slideplayer.com/25/7971456/slides/slide_21.jpg
  • https://ibstudybuddy.files.wordpress.com/2016/04/screen-shot-2016-04-21-at-12-53-38-pm.png?w=1040
  • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4177546/figure/F5/
  • https://ibstudybuddy.files.wordpress.com/2016/04/screen-shot-2016-04-21-at-12-53-38-pm.png?w=1040
  • http://biology4isc.weebly.com/uploads/9/0/8/0/9080078/7396568_orig.jpg
  • https://i.ytimg.com/vi/T3WZ-FAbIAU/maxresdefault.jpg
  • https://i.pinimg.com/736x/f3/ea/40/f3ea409b4aa227400004fcd8dacb2558--biology-jokes-biology-lessons.jpg
  • http://plantphys.info/plant_physiology/transpire.shtml
  • http://images.slideplayer.com/16/5092175/slides/slide_13.jpg
  • https://sites.google.com/a/canacad.ac.jp/dpbio-davef/10-botany/9-1-transport-in-the-xylem-of-plants
  • http://wizznotes.com/biology/transport-in-plants/factors-affecting-transpiration
  • More info here http://www.biologydiscussion.com/respiration/aerobic-respiration/factors-affecting-aerobic-respiration-8-factors-plants/15206
  • http://wizznotes.com/biology/transport-in-plants/factors-affecting-transpiration
  • http://biology-igcse.weebly.com/uploads/1/5/0/7/15070316/3917293_orig.png
  • https://image.spreadshirtmedia.com/image-server/v1/mp/compositions/P1016732969MPC1026549960/views/1,width=300,height=300,appearanceId=2,backgroundColor=E8E8E8,version=1490045615/stomata-men-s-t-shirt.jpg
  • http://www.greenroofs.com/archives/images/content-energy_stomata_evapo.gif
  • https://lima.osu.edu/assets/lima/uploads/Departments/Biology/unsorted/stoma.jpg
  • http://plantsinaction.science.uq.edu.au/edition1/?q=content/15-2-1-stomatal-structure-and-function
  • http://images.tutorvista.com/content/plant-water-relations/stomatal-movement--dicot-plants.jpeg
  • https://studyforce.com/gallery/33_25_07_11_12_56_44.jpeg
  • https://studyforce.com/gallery/33_25_07_11_12_56_44.jpeg
  • http://passel.unl.edu/Image/siteImages/K+_opne&closed-LG.gif