{"id":231,"date":"2024-03-23T08:36:37","date_gmt":"2024-03-23T08:36:37","guid":{"rendered":"https:\/\/pressbooks.justwrite.in\/interactive-biology-secondary\/?post_type=chapter&#038;p=231"},"modified":"2024-11-30T10:38:11","modified_gmt":"2024-11-30T10:38:11","slug":"2-3-transport-of-water-minerals-and-assimilates","status":"publish","type":"chapter","link":"https:\/\/pressbooks.justwrite.in\/interactive-biology-secondary\/chapter\/2-3-transport-of-water-minerals-and-assimilates\/","title":{"raw":"2.4 Transport of water, minerals and assimilates","rendered":"2.4 Transport of water, minerals and assimilates"},"content":{"raw":"Transport of <span>nutrients, gasses, water, and waste is essential for all living organisms . This is made possible through the process of diffusion in some small plants and animals while carried out by organized\u00a0 transport systems in larger plants and animals.<\/span>\r\n\r\n<span>The structure of plant roots, stems, and leaves facilitates the transport of water, nutrients, and products of photosynthesis throughout the plant.<\/span>\r\n<div class=\"textbox shaded\"><a href=\"https:\/\/ncstate.pressbooks.pub\/introbio181\/chapter\/plant-transport\/\" title=\"Plant transport\">Click on the link to the Chapter on Plant transport from the\u00a0 pressbook on Introductory Biology : Ecology, Evolution and Biodiversity\u00a0 to understand about plant tissues<\/a><\/div>\r\n&nbsp;\r\n\r\nThe\u00a0\u00a0<span> xylem is the tissue primarily responsible for movement of water and the phloem for the transport of\u00a0 nutrients and photosynthetic products. <\/span>\r\n\r\n<span>Plants are able to transport water from their roots up to the tips of their tallest shoot through<\/span>\r\n<ul>\r\n \t<li><span>\u00a0water potential, <\/span><\/li>\r\n \t<li><span>evapotranspiration, and <\/span><\/li>\r\n \t<li><span>stomatal regulation\u00a0<\/span><\/li>\r\n<\/ul>\r\nAs we had discussed about\u00a0 transpiration and stomatal regulation in previous chapters we will focus on water potential.\r\n<h2 class=\"wp-block-heading\">Water Transport from Roots to Shoots<\/h2>\r\n<p id=\"fs-idm67889584\"><strong>Water potential<\/strong><span>\u00a0<\/span>is a measure of the<span>\u00a0<\/span><em>potential energy<\/em><span>\u00a0<\/span>in water.\u00a0It is based on potential water<span>\u00a0<\/span><em>movement<span>\u00a0<\/span><\/em>between two systems. It is\u00a0the difference in potential energy\u00a0 at atmospheric pressure and ambient temperature\u00a0 between any given water sample and pure water .<\/p>\r\n\u00a0Water potential is denoted by the Greek letter \u03a8 (<em data-effect=\"italics\">psi<\/em>)\r\n\r\nand is unit od water potential is <span data-type=\"term\">megapascals<\/span><span>\u00a0<\/span>(MPa).\r\n\r\nThe potential of pure water (\u03a8<sup>pure H2O<\/sup>) is ignored and considered\u00a0 as zero .\r\n\r\nWater potential is calculated using the equation\r\n\r\n\u03a8 system= \u03a8 total= \u03a8s + \u03a8p +\u03a8g +\u03a8m\r\n<p id=\"fs-idm67889584\">Water potential can be positive or negative,<\/p>\r\n\u03a8 system<span style=\"font-size: 1em;text-align: initial\">= \u03a8s + \u03a8p, where <\/span>\r\n\r\n<span style=\"font-size: 1em;text-align: initial\">\u03a8s = solute potential, and \u03a8p = pressure potential.<\/span>\r\n\r\nAddition of solutes decreases the water potential and vice- versa.\r\n\r\nWhile addition of pressure increases the water potential and vice-versa.\r\n\r\nWater always moves from a region of high to low water potential until equilibrium is reached.\r\n\r\nThe water potential at a plant\u2019s roots is predicted to be\u00a0 higher than the water potential in each leaf and the water potential of the lef is predicted to be higher than the water potential in the atmosphere.\r\n\r\nThis fact enables water to continuously move through the plant from the soil to the air without equilibrating\r\n\r\nMathematically: \u03a8<sup>soil<\/sup>\u00a0must be &gt; \u03a8<sup>root<\/sup>\u00a0&gt; \u03a8<sup>stem<\/sup>\u00a0&gt; \u03a8<sup>leaf<\/sup>\u00a0&gt; \u03a8<sup>atmosphere<\/sup>.\r\n\r\n&nbsp;\r\n<h1>The<span>\u00a0<\/span><strong>solute potential (\u03a8<\/strong><sub><strong>s<\/strong><\/sub><strong>)<\/strong><\/h1>\r\nThis is also called osmotic potential,\r\n\r\nThe solute potential of pure water is 0.\r\n\r\nFurther it is to be recollected that as solute concentration increases the water potential decreases.\r\n\r\nThe high concentration of solutes in the cytoplasm of the plant cell makes the solute potential of the plant cell to be negative.\r\n\r\nWater will move from the soil into a plant\u2019s root cells via osmosis until the water potential in the plant root cells is lower than the water potential of the water in the soil.\r\n\r\nFurther plants can metabolically change their solute potential by adding or removing \u00a0solute molecules to increase water uptake from the soil during drought conditions.\r\n<h1><strong>Pressure potential<\/strong><span>\u00a0<\/span>(\u03a8<sub>p<\/sub>)<\/h1>\r\nThis is also called turgor potential,\r\n\r\nIt may be positive or negative.\r\n\r\nPositive pressure or compression increases \u03a8<sub>p<\/sub>, while\u00a0 negative pressure or vacuum decreases \u03a8<sub>p<\/sub>.\r\n\r\nThe turgor pressure produced because of the rigid cell wall creates positive pressure inside cells and can be as high as\u00a0\u00a01.5 MPa in a well-watered plant.\r\n\r\nPlant cells can modify pressure potential by the process of osmosis and by changing the\u00a0 \u03a8<sub>s<\/sub><span>\u00a0<\/span>\r\n\r\nIf cytoplasmic solute concentration is increased\u00a0\u00a0 then \u03a8<sub>s<\/sub><span>\u00a0<\/span>will decline and water will move into the cell by osmosis.\r\n\r\nThis causes \u03a8<sub>p<\/sub><span>\u00a0<\/span>to increase.\r\n\r\nThe opening and closing of stomata also regulates\u00a0\u03a8<sub>p<\/sub><span>\u00a0<\/span>\r\n\r\nWhen stomata opens\u00a0 water evaporates from the leaf, reducing \u03a8<sub>p<\/sub><span>\u00a0<\/span>and \u03a8<sub>total<\/sub><span>\u00a0<\/span>of the leaf\r\n\r\nThis increases the water potential difference between the water in the leaf and the petiole and allows the\u00a0water to flow from the petiole into the leaf.\r\n<div class=\"wp-block-image\" style=\"text-align: center\">\r\n<figure><\/figure>\r\n<figure class=\"aligncenter size-full is-resized\"><a href=\"https:\/\/organismalbio.biosci.gatech.edu\/files\/2018\/04\/Figure_30_05_02.png\" rel=\"lightbox-0\"><\/a><a href=\"https:\/\/openstax.org\/books\/biology\/pages\/30-5-transport-of-water-and-solutes-in-plants\" target=\"_blank\" rel=\"noopener\">\"Water potential\"<\/a><a href=\"https:\/\/organismalbio.biosci.gatech.edu\/files\/2018\/04\/Figure_30_05_02.png\" rel=\"lightbox-0\"><span>\u00a0by\u00a0<\/span><\/a><a>Open Stax<\/a><a><\/a><a><\/a><a href=\"https:\/\/organismalbio.biosci.gatech.edu\/files\/2018\/04\/Figure_30_05_02.png\" rel=\"lightbox-0\"><span>\u00a0is licensed under\u00a0<\/span><\/a><a href=\"http:\/\/creativecommons.org\/licenses\/by\/4.0\" target=\"_blank\" rel=\"noopener\">CC BY 4.0<\/a><a href=\"https:\/\/organismalbio.biosci.gatech.edu\/files\/2018\/04\/Figure_30_05_02.png\" rel=\"lightbox-0\"><img src=\"https:\/\/organismalbio.biosci.gatech.edu\/files\/2018\/04\/Figure_30_05_02.png\" alt=\"\" class=\"wp-image-8129 aligncenter\" width=\"466\" height=\"418\" \/><\/a><\/figure>\r\n<figure class=\"aligncenter size-full is-resized\"><figcaption class=\"wp-element-caption\"><a href=\"https:\/\/openstax.org\/books\/biology\/pages\/30-5-transport-of-water-and-solutes-in-plants\" target=\"_blank\" rel=\"noopener\">\"Water potential\"<\/a><span>\u00a0by\u00a0<\/span><a>Open Stax<\/a><a><\/a><a><\/a><span>\u00a0is licensed under\u00a0<\/span><a href=\"http:\/\/creativecommons.org\/licenses\/by\/4.0\" target=\"_blank\" rel=\"noopener\">CC BY 4.0<\/a><\/figcaption><\/figure>\r\n<\/div>\r\n<figure class=\"wp-block-embed is-type-video is-provider-youtube wp-block-embed-youtube wp-embed-aspect-16-9 wp-has-aspect-ratio\">\r\n<div class=\"wp-block-embed__wrapper\">\r\n<h2 class=\"lt-bio-1986 editable\">Movement of Water and Minerals in the Xylem<\/h2>\r\nThe water on the surface of mesophyll cells of the leaf\u00a0<span>\u00a0saturates the cellulose microfibrils of the primary cell wall.<\/span>\r\n\r\n<span>The leaf contains many large intercellular air spaces for the exchange of\u00a0 gases.o<\/span>\r\n\r\n<span>When the wet cell wall is exposed to this leaf internal air space the water on the surface of the cells evaporates into the air spaces,<\/span>\r\n\r\n<span>This decreases the thin film on the surface of the mesophyll cells and creates a tension\u00a0<\/span><span>\u00a0on the water in the mesophyll cells <\/span><span>thereby increasing the pull on the water in the xylem vessels.<\/span>\r\n\r\n<span> The xylem vessels and tracheids are structurally adapted to cope with large changes in pressure. <\/span>\r\n\r\n<span>Rings in the vessels maintain their tubular shape. <\/span>\r\n\r\n<span>Small perforations between vessel elements reduce the number and size of gas bubbles that can form via a process called cavitation.<\/span>\r\n\r\n<span>The formation of gas bubbles in xylem interrupts the continuous\u00a0 flow of xylem sap and the the water from base to the top of the plant. This break is termed as embolism.<\/span>\r\n\r\n<span>The taller the tree, the greater the tension forces needed to pull water, and the more cavitation events. In larger trees, the resulting embolisms can plug xylem vessels, making them non-functional.<\/span>\r\n<h2 data-type=\"title\">Transportation of Photosynthates<\/h2>\r\n<span>The products of photosynthesis are called photosynthates, which are usually in the form of simple sugars such as sucrose.<\/span>\r\n\r\n<span>Structures that produce photosynthates for the growing plant are referred to as<\/span><strong><span data-type=\"term\" id=\"term-00006\">sources<\/span><\/strong><span>.<\/span>\r\n\r\nThe sugars produced in sources like leaves are delivered to the growing parts of plants through Phloem by a process called <strong>Translocation<\/strong>\r\n\r\n<span>These sugars are delivered to required places such as roots, young shoots, and developing seeds. These structures are\u00a0 called <\/span><strong><span data-type=\"term\" id=\"term-00008\">sinks<\/span><\/strong><span>.<\/span>\r\n\r\n<span> Seeds, tubers, and bulbs can be either a source or a sink, depending on the plant\u2019s stage of development and the season.<\/span>\r\n<h3 data-type=\"title\"><strong>Translocation: Transport from Source to Sink<\/strong><\/h3>\r\nThe mesophyll cells of photosynthesizing leaves produce sugars \/photosynthates such as sucrose.\r\n\r\nThe phloem then\u00a0\u00a0 translocate these to structures where they are used or stored.\r\n\r\nThe photosynthates move through cytoplasmic channels called<strong> plasmodesmata <\/strong>that connect the mesophyll cells and reach phloem sieve-tube elements (STEs) in the vascular bundles.\r\n\r\nFrom the mesophyll cells, the photosynthates are loaded into the phloem STEs through active transport. This is coupled to the uptake of sucrose with a carrier protein called the <strong>sucrose-H<sup>+<\/sup>\u00a0symporter.<\/strong>\r\n<p id=\"fs-idm79174800\">Phloem STEs have reduced cytoplasmic contents.<\/p>\r\nThey are\u00a0 connected by a sieve plate with pores\r\n\r\nThis facilitates pressure-driven bulk flow, or translocation, of phloem sap.\r\n\r\nThe energy for STEs are produced through the metabolic activities of <strong>companion cells\u00a0<\/strong> associated with STEs\r\n\r\n<\/div>\r\n<img src=\"https:\/\/openstax.org\/apps\/archive\/20240506.185246\/resources\/9f487cf9c5ab768c3049abb404118413c83c4137\" alt=\"Illustration shows phloem, a column-like structure that is composed of stacks of cylindrical cells called sieve-tube elements. Each cell is separated by a sieve-tube plate. The sieve-tube plate has holes in it, like a slice of Swiss cheese. Lateral sieve areas on the side of the column allow different phloem tubes to interact.\" width=\"225\" height=\"309\" class=\"aligncenter\" \/>\r\n<p style=\"text-align: center\"><a href=\"https:\/\/openstax.org\/books\/biology\/pages\/30-5-transport-of-water-and-solutes-in-plants\" target=\"_blank\" rel=\"noopener\">\"Pholem\"<\/a><span>\u00a0by\u00a0<\/span><a>Open Stax<\/a><a><\/a><a><\/a><span>\u00a0is licensed under\u00a0<\/span><a href=\"http:\/\/creativecommons.org\/licenses\/by\/4.0\" target=\"_blank\" rel=\"noopener\">CC BY 4.0\u00a0<\/a><\/p>\r\n\r\n<div class=\"wp-block-image\" style=\"text-align: left\">\r\n<figure class=\"aligncenter size-full is-resized\"><figcaption class=\"wp-element-caption\"><span><span><span>The photosynthates are then translocated from the phloem to the nearest sink.<\/span><\/span><\/span>The phloem sap is an aqueous solution \u00a0containing 30 percent sugar, minerals, amino acids, and plant growth regulatorsThe high percentage of sugar decreases \u03a8<sub>s,<\/sub><span style=\"font-size: 1em\">\u00a0<\/span><span style=\"font-size: 1em\">This decreases the total water potential .<\/span><span style=\"font-size: 1em\">Therefore water to moves by osmosis from the adjacent xylem into the phloem tubes, thereby increasing pressure. <\/span><span style=\"font-size: 1em\">This increase in total water potential causes the bulk flow of phloem from source to sink .<\/span><span style=\"font-size: 1em\">As the sucrose concentration in the sink cells has been metabolized for growth, or converted to polymers such as starch ( for storage)\u00a0 or cellulose (for structural integrity) .<\/span><span style=\"font-size: 1em\">\u00a0Unloading at the sink end of the phloem tube occurs by either diffusion or active transport . <\/span><span style=\"font-size: 1em\">Water diffuses from the phloem by osmosis and is then transpired or recycled via the xylem back into the phloem sap.<\/span><img src=\"https:\/\/openstax.org\/apps\/archive\/20240506.185246\/resources\/328680818e492e6a7171cbae39e3d751231cb263\" alt=\" Illustration shows the transpiration of water up the tubes of the xylem from a root sink cell. At the same time, sucrose is translocated down the phloem to the root sink cell from a leaf source cell. The sucrose concentration is high in the source cell, and gradually decreases from the source to the root.\" width=\"302\" height=\"409\" class=\"aligncenter\" \/>\r\n<p style=\"text-align: center\"><a href=\"https:\/\/openstax.org\/books\/biology\/pages\/30-5-transport-of-water-and-solutes-in-plants\" target=\"_blank\" rel=\"noopener\">\"Pholem\"<\/a><span>\u00a0by\u00a0<\/span><a>Open Stax<\/a><a><\/a><a><\/a><span>\u00a0is licensed under\u00a0<\/span><a href=\"http:\/\/creativecommons.org\/licenses\/by\/4.0\" target=\"_blank\" rel=\"noopener\">CC BY 4.0\u00a0<\/a><\/p>\r\n\r\n<div class=\"textbox shaded\">Watch the video from <a class=\"yt-simple-endpoint style-scope yt-formatted-string\" href=\"https:\/\/www.youtube.com\/@fuseschool\" style=\"text-align: initial;font-size: 1em\">FuseSchool - Global Education\u00a0<\/a><\/div>\r\n&nbsp;\r\n<div id=\"container\" class=\"style-scope ytd-channel-name\">\r\n<div id=\"text-container\" class=\"style-scope ytd-channel-name\">\r\n\r\n[embed]https:\/\/youtu.be\/QXdujo4PZ7c?si=3jdtkHx6knQHABgT[\/embed]\r\n\r\n<\/div>\r\n<\/div>\r\n<\/figcaption><\/figure>\r\n<\/div>\r\n<figure class=\"wp-block-embed is-type-video is-provider-youtube wp-block-embed-youtube wp-embed-aspect-16-9 wp-has-aspect-ratio\">\r\n<div class=\"wp-block-embed__wrapper\">\r\n\r\n<span>[h5p id=\"46\"]<\/span>\r\n\r\n<\/div><\/figure>\r\n<\/figure>\r\n&nbsp;","rendered":"<p>Transport of <span>nutrients, gasses, water, and waste is essential for all living organisms . This is made possible through the process of diffusion in some small plants and animals while carried out by organized\u00a0 transport systems in larger plants and animals.<\/span><\/p>\n<p><span>The structure of plant roots, stems, and leaves facilitates the transport of water, nutrients, and products of photosynthesis throughout the plant.<\/span><\/p>\n<div class=\"textbox shaded\"><a href=\"https:\/\/ncstate.pressbooks.pub\/introbio181\/chapter\/plant-transport\/\" title=\"Plant transport\">Click on the link to the Chapter on Plant transport from the\u00a0 pressbook on Introductory Biology : Ecology, Evolution and Biodiversity\u00a0 to understand about plant tissues<\/a><\/div>\n<p>&nbsp;<\/p>\n<p>The\u00a0\u00a0<span> xylem is the tissue primarily responsible for movement of water and the phloem for the transport of\u00a0 nutrients and photosynthetic products. <\/span><\/p>\n<p><span>Plants are able to transport water from their roots up to the tips of their tallest shoot through<\/span><\/p>\n<ul>\n<li><span>\u00a0water potential, <\/span><\/li>\n<li><span>evapotranspiration, and <\/span><\/li>\n<li><span>stomatal regulation\u00a0<\/span><\/li>\n<\/ul>\n<p>As we had discussed about\u00a0 transpiration and stomatal regulation in previous chapters we will focus on water potential.<\/p>\n<h2 class=\"wp-block-heading\">Water Transport from Roots to Shoots<\/h2>\n<p id=\"fs-idm67889584\"><strong>Water potential<\/strong><span>\u00a0<\/span>is a measure of the<span>\u00a0<\/span><em>potential energy<\/em><span>\u00a0<\/span>in water.\u00a0It is based on potential water<span>\u00a0<\/span><em>movement<span>\u00a0<\/span><\/em>between two systems. It is\u00a0the difference in potential energy\u00a0 at atmospheric pressure and ambient temperature\u00a0 between any given water sample and pure water .<\/p>\n<p>\u00a0Water potential is denoted by the Greek letter \u03a8 (<em data-effect=\"italics\">psi<\/em>)<\/p>\n<p>and is unit od water potential is <span data-type=\"term\">megapascals<\/span><span>\u00a0<\/span>(MPa).<\/p>\n<p>The potential of pure water (\u03a8<sup>pure H2O<\/sup>) is ignored and considered\u00a0 as zero .<\/p>\n<p>Water potential is calculated using the equation<\/p>\n<p>\u03a8 system= \u03a8 total= \u03a8s + \u03a8p +\u03a8g +\u03a8m<\/p>\n<p>Water potential can be positive or negative,<\/p>\n<p>\u03a8 system<span style=\"font-size: 1em;text-align: initial\">= \u03a8s + \u03a8p, where <\/span><\/p>\n<p><span style=\"font-size: 1em;text-align: initial\">\u03a8s = solute potential, and \u03a8p = pressure potential.<\/span><\/p>\n<p>Addition of solutes decreases the water potential and vice- versa.<\/p>\n<p>While addition of pressure increases the water potential and vice-versa.<\/p>\n<p>Water always moves from a region of high to low water potential until equilibrium is reached.<\/p>\n<p>The water potential at a plant\u2019s roots is predicted to be\u00a0 higher than the water potential in each leaf and the water potential of the lef is predicted to be higher than the water potential in the atmosphere.<\/p>\n<p>This fact enables water to continuously move through the plant from the soil to the air without equilibrating<\/p>\n<p>Mathematically: \u03a8<sup>soil<\/sup>\u00a0must be &gt; \u03a8<sup>root<\/sup>\u00a0&gt; \u03a8<sup>stem<\/sup>\u00a0&gt; \u03a8<sup>leaf<\/sup>\u00a0&gt; \u03a8<sup>atmosphere<\/sup>.<\/p>\n<p>&nbsp;<\/p>\n<h1>The<span>\u00a0<\/span><strong>solute potential (\u03a8<\/strong><sub><strong>s<\/strong><\/sub><strong>)<\/strong><\/h1>\n<p>This is also called osmotic potential,<\/p>\n<p>The solute potential of pure water is 0.<\/p>\n<p>Further it is to be recollected that as solute concentration increases the water potential decreases.<\/p>\n<p>The high concentration of solutes in the cytoplasm of the plant cell makes the solute potential of the plant cell to be negative.<\/p>\n<p>Water will move from the soil into a plant\u2019s root cells via osmosis until the water potential in the plant root cells is lower than the water potential of the water in the soil.<\/p>\n<p>Further plants can metabolically change their solute potential by adding or removing \u00a0solute molecules to increase water uptake from the soil during drought conditions.<\/p>\n<h1><strong>Pressure potential<\/strong><span>\u00a0<\/span>(\u03a8<sub>p<\/sub>)<\/h1>\n<p>This is also called turgor potential,<\/p>\n<p>It may be positive or negative.<\/p>\n<p>Positive pressure or compression increases \u03a8<sub>p<\/sub>, while\u00a0 negative pressure or vacuum decreases \u03a8<sub>p<\/sub>.<\/p>\n<p>The turgor pressure produced because of the rigid cell wall creates positive pressure inside cells and can be as high as\u00a0\u00a01.5 MPa in a well-watered plant.<\/p>\n<p>Plant cells can modify pressure potential by the process of osmosis and by changing the\u00a0 \u03a8<sub>s<\/sub><span>\u00a0<\/span><\/p>\n<p>If cytoplasmic solute concentration is increased\u00a0\u00a0 then \u03a8<sub>s<\/sub><span>\u00a0<\/span>will decline and water will move into the cell by osmosis.<\/p>\n<p>This causes \u03a8<sub>p<\/sub><span>\u00a0<\/span>to increase.<\/p>\n<p>The opening and closing of stomata also regulates\u00a0\u03a8<sub>p<\/sub><span>\u00a0<\/span><\/p>\n<p>When stomata opens\u00a0 water evaporates from the leaf, reducing \u03a8<sub>p<\/sub><span>\u00a0<\/span>and \u03a8<sub>total<\/sub><span>\u00a0<\/span>of the leaf<\/p>\n<p>This increases the water potential difference between the water in the leaf and the petiole and allows the\u00a0water to flow from the petiole into the leaf.<\/p>\n<div class=\"wp-block-image\" style=\"text-align: center\">\n<figure><\/figure>\n<figure class=\"aligncenter size-full is-resized\"><a href=\"https:\/\/organismalbio.biosci.gatech.edu\/files\/2018\/04\/Figure_30_05_02.png\" rel=\"lightbox-0\"><\/a><a href=\"https:\/\/openstax.org\/books\/biology\/pages\/30-5-transport-of-water-and-solutes-in-plants\" target=\"_blank\" rel=\"noopener\">&#8220;Water potential&#8221;<\/a><a href=\"https:\/\/organismalbio.biosci.gatech.edu\/files\/2018\/04\/Figure_30_05_02.png\" rel=\"lightbox-0\"><span>\u00a0by\u00a0<\/span><\/a><a>Open Stax<\/a><a><\/a><a><\/a><a href=\"https:\/\/organismalbio.biosci.gatech.edu\/files\/2018\/04\/Figure_30_05_02.png\" rel=\"lightbox-0\"><span>\u00a0is licensed under\u00a0<\/span><\/a><a href=\"http:\/\/creativecommons.org\/licenses\/by\/4.0\" target=\"_blank\" rel=\"noopener\">CC BY 4.0<\/a><a href=\"https:\/\/organismalbio.biosci.gatech.edu\/files\/2018\/04\/Figure_30_05_02.png\" rel=\"lightbox-0\"><img decoding=\"async\" src=\"https:\/\/organismalbio.biosci.gatech.edu\/files\/2018\/04\/Figure_30_05_02.png\" alt=\"\" class=\"wp-image-8129 aligncenter\" width=\"466\" height=\"418\" \/><\/a><\/figure>\n<figure class=\"aligncenter size-full is-resized\"><figcaption class=\"wp-element-caption\"><a href=\"https:\/\/openstax.org\/books\/biology\/pages\/30-5-transport-of-water-and-solutes-in-plants\" target=\"_blank\" rel=\"noopener\">&#8220;Water potential&#8221;<\/a><span>\u00a0by\u00a0<\/span><a>Open Stax<\/a><a><\/a><a><\/a><span>\u00a0is licensed under\u00a0<\/span><a href=\"http:\/\/creativecommons.org\/licenses\/by\/4.0\" target=\"_blank\" rel=\"noopener\">CC BY 4.0<\/a><\/figcaption><\/figure>\n<\/div>\n<figure class=\"wp-block-embed is-type-video is-provider-youtube wp-block-embed-youtube wp-embed-aspect-16-9 wp-has-aspect-ratio\">\n<div class=\"wp-block-embed__wrapper\">\n<h2 class=\"lt-bio-1986 editable\">Movement of Water and Minerals in the Xylem<\/h2>\n<p>The water on the surface of mesophyll cells of the leaf\u00a0<span>\u00a0saturates the cellulose microfibrils of the primary cell wall.<\/span><\/p>\n<p><span>The leaf contains many large intercellular air spaces for the exchange of\u00a0 gases.o<\/span><\/p>\n<p><span>When the wet cell wall is exposed to this leaf internal air space the water on the surface of the cells evaporates into the air spaces,<\/span><\/p>\n<p><span>This decreases the thin film on the surface of the mesophyll cells and creates a tension\u00a0<\/span><span>\u00a0on the water in the mesophyll cells <\/span><span>thereby increasing the pull on the water in the xylem vessels.<\/span><\/p>\n<p><span> The xylem vessels and tracheids are structurally adapted to cope with large changes in pressure. <\/span><\/p>\n<p><span>Rings in the vessels maintain their tubular shape. <\/span><\/p>\n<p><span>Small perforations between vessel elements reduce the number and size of gas bubbles that can form via a process called cavitation.<\/span><\/p>\n<p><span>The formation of gas bubbles in xylem interrupts the continuous\u00a0 flow of xylem sap and the the water from base to the top of the plant. This break is termed as embolism.<\/span><\/p>\n<p><span>The taller the tree, the greater the tension forces needed to pull water, and the more cavitation events. In larger trees, the resulting embolisms can plug xylem vessels, making them non-functional.<\/span><\/p>\n<h2 data-type=\"title\">Transportation of Photosynthates<\/h2>\n<p><span>The products of photosynthesis are called photosynthates, which are usually in the form of simple sugars such as sucrose.<\/span><\/p>\n<p><span>Structures that produce photosynthates for the growing plant are referred to as<\/span><strong><span data-type=\"term\" id=\"term-00006\">sources<\/span><\/strong><span>.<\/span><\/p>\n<p>The sugars produced in sources like leaves are delivered to the growing parts of plants through Phloem by a process called <strong>Translocation<\/strong><\/p>\n<p><span>These sugars are delivered to required places such as roots, young shoots, and developing seeds. These structures are\u00a0 called <\/span><strong><span data-type=\"term\" id=\"term-00008\">sinks<\/span><\/strong><span>.<\/span><\/p>\n<p><span> Seeds, tubers, and bulbs can be either a source or a sink, depending on the plant\u2019s stage of development and the season.<\/span><\/p>\n<h3 data-type=\"title\"><strong>Translocation: Transport from Source to Sink<\/strong><\/h3>\n<p>The mesophyll cells of photosynthesizing leaves produce sugars \/photosynthates such as sucrose.<\/p>\n<p>The phloem then\u00a0\u00a0 translocate these to structures where they are used or stored.<\/p>\n<p>The photosynthates move through cytoplasmic channels called<strong> plasmodesmata <\/strong>that connect the mesophyll cells and reach phloem sieve-tube elements (STEs) in the vascular bundles.<\/p>\n<p>From the mesophyll cells, the photosynthates are loaded into the phloem STEs through active transport. This is coupled to the uptake of sucrose with a carrier protein called the <strong>sucrose-H<sup>+<\/sup>\u00a0symporter.<\/strong><\/p>\n<p id=\"fs-idm79174800\">Phloem STEs have reduced cytoplasmic contents.<\/p>\n<p>They are\u00a0 connected by a sieve plate with pores<\/p>\n<p>This facilitates pressure-driven bulk flow, or translocation, of phloem sap.<\/p>\n<p>The energy for STEs are produced through the metabolic activities of <strong>companion cells\u00a0<\/strong> associated with STEs<\/p>\n<\/div>\n<p><img decoding=\"async\" src=\"https:\/\/openstax.org\/apps\/archive\/20240506.185246\/resources\/9f487cf9c5ab768c3049abb404118413c83c4137\" alt=\"Illustration shows phloem, a column-like structure that is composed of stacks of cylindrical cells called sieve-tube elements. Each cell is separated by a sieve-tube plate. The sieve-tube plate has holes in it, like a slice of Swiss cheese. Lateral sieve areas on the side of the column allow different phloem tubes to interact.\" width=\"225\" height=\"309\" class=\"aligncenter\" \/><\/p>\n<p style=\"text-align: center\"><a href=\"https:\/\/openstax.org\/books\/biology\/pages\/30-5-transport-of-water-and-solutes-in-plants\" target=\"_blank\" rel=\"noopener\">&#8220;Pholem&#8221;<\/a><span>\u00a0by\u00a0<\/span><a>Open Stax<\/a><a><\/a><a><\/a><span>\u00a0is licensed under\u00a0<\/span><a href=\"http:\/\/creativecommons.org\/licenses\/by\/4.0\" target=\"_blank\" rel=\"noopener\">CC BY 4.0\u00a0<\/a><\/p>\n<div class=\"wp-block-image\" style=\"text-align: left\">\n<figure class=\"aligncenter size-full is-resized\"><figcaption class=\"wp-element-caption\"><span><span><span>The photosynthates are then translocated from the phloem to the nearest sink.<\/span><\/span><\/span>The phloem sap is an aqueous solution \u00a0containing 30 percent sugar, minerals, amino acids, and plant growth regulatorsThe high percentage of sugar decreases \u03a8<sub>s,<\/sub><span style=\"font-size: 1em\">\u00a0<\/span><span style=\"font-size: 1em\">This decreases the total water potential .<\/span><span style=\"font-size: 1em\">Therefore water to moves by osmosis from the adjacent xylem into the phloem tubes, thereby increasing pressure. <\/span><span style=\"font-size: 1em\">This increase in total water potential causes the bulk flow of phloem from source to sink .<\/span><span style=\"font-size: 1em\">As the sucrose concentration in the sink cells has been metabolized for growth, or converted to polymers such as starch ( for storage)\u00a0 or cellulose (for structural integrity) .<\/span><span style=\"font-size: 1em\">\u00a0Unloading at the sink end of the phloem tube occurs by either diffusion or active transport . <\/span><span style=\"font-size: 1em\">Water diffuses from the phloem by osmosis and is then transpired or recycled via the xylem back into the phloem sap.<\/span><img decoding=\"async\" src=\"https:\/\/openstax.org\/apps\/archive\/20240506.185246\/resources\/328680818e492e6a7171cbae39e3d751231cb263\" alt=\"Illustration shows the transpiration of water up the tubes of the xylem from a root sink cell. At the same time, sucrose is translocated down the phloem to the root sink cell from a leaf source cell. The sucrose concentration is high in the source cell, and gradually decreases from the source to the root.\" width=\"302\" height=\"409\" class=\"aligncenter\" \/><br \/>\n<a href=\"https:\/\/openstax.org\/books\/biology\/pages\/30-5-transport-of-water-and-solutes-in-plants\" target=\"_blank\" rel=\"noopener\">&#8220;Pholem&#8221;<\/a><span>\u00a0by\u00a0<\/span><a>Open Stax<\/a><a><\/a><a><\/a><span>\u00a0is licensed under\u00a0<\/span><a href=\"http:\/\/creativecommons.org\/licenses\/by\/4.0\" target=\"_blank\" rel=\"noopener\">CC BY 4.0\u00a0<\/a><\/p>\n<p>Watch the video from <a class=\"yt-simple-endpoint style-scope yt-formatted-string\" href=\"https:\/\/www.youtube.com\/@fuseschool\" style=\"text-align: initial;font-size: 1em\">FuseSchool &#8211; Global Education\u00a0<\/a><\/figcaption><\/figure>\n<\/div>\n<p>&nbsp;<\/p>\n<div id=\"container\" class=\"style-scope ytd-channel-name\">\n<div id=\"text-container\" class=\"style-scope ytd-channel-name\">\n<p><iframe id=\"oembed-1\" title=\"Xylem and Phloem - Part 3 - Translocation - Transport in Plants | Plants | Biology | FuseSchool\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/QXdujo4PZ7c?feature=oembed&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<\/div>\n<\/div>\n<\/figure>\n<figure class=\"wp-block-embed is-type-video is-provider-youtube wp-block-embed-youtube wp-embed-aspect-16-9 wp-has-aspect-ratio\">\n<div class=\"wp-block-embed__wrapper\">\n<p><span><\/p>\n<div id=\"h5p-46\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-46\" class=\"h5p-iframe\" data-content-id=\"46\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Passive Transport\"><\/iframe><\/div>\n<\/div>\n<p><\/span><\/p>\n<\/div>\n<\/figure>\n<p>&nbsp;<\/p>\n","protected":false},"author":1,"menu_order":4,"template":"","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_uf_show_specific_survey":0,"_uf_disable_surveys":false,"pb_show_title":"on","pb_short_title":"Transport of water ,mineral and assimilates","pb_subtitle":"Transport of water ,mineral and assimilates","pb_authors":["malathi"],"pb_section_license":"cc-by-sa"},"chapter-type":[],"contributor":[62],"license":[54],"class_list":["post-231","chapter","type-chapter","status-publish","hentry","contributor-malathi","license-cc-by-sa"],"aioseo_notices":[],"part":32,"_links":{"self":[{"href":"https:\/\/pressbooks.justwrite.in\/interactive-biology-secondary\/wp-json\/pressbooks\/v2\/chapters\/231","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.justwrite.in\/interactive-biology-secondary\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.justwrite.in\/interactive-biology-secondary\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.justwrite.in\/interactive-biology-secondary\/wp-json\/wp\/v2\/users\/1"}],"version-history":[{"count":46,"href":"https:\/\/pressbooks.justwrite.in\/interactive-biology-secondary\/wp-json\/pressbooks\/v2\/chapters\/231\/revisions"}],"predecessor-version":[{"id":2081,"href":"https:\/\/pressbooks.justwrite.in\/interactive-biology-secondary\/wp-json\/pressbooks\/v2\/chapters\/231\/revisions\/2081"}],"part":[{"href":"https:\/\/pressbooks.justwrite.in\/interactive-biology-secondary\/wp-json\/pressbooks\/v2\/parts\/32"}],"metadata":[{"href":"https:\/\/pressbooks.justwrite.in\/interactive-biology-secondary\/wp-json\/pressbooks\/v2\/chapters\/231\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.justwrite.in\/interactive-biology-secondary\/wp-json\/wp\/v2\/media?parent=231"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.justwrite.in\/interactive-biology-secondary\/wp-json\/pressbooks\/v2\/chapter-type?post=231"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.justwrite.in\/interactive-biology-secondary\/wp-json\/wp\/v2\/contributor?post=231"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.justwrite.in\/interactive-biology-secondary\/wp-json\/wp\/v2\/license?post=231"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}