Transportation of Water in Plants

1. Transportation of Water in Plants • By Arsalaan Muhammad • 8a • E-portfolio Project

2. So what basically happens: • In every plant, water moves from the ground, through the roots, up the stem, enters the leaves, and finally exits from the plant through the leaves and repeats. In the following slide show, you will find out what how water is transported through a plant. This is fun waiting to be seen!

3. It all starts at the roots • The water and any other Soluble nutrients disseminate in through the roots to the xylem and then are distributed where needed in the plant. Root hairs help absorb the water and others nutrients in the soil. From here, there is a process called osmosis, which is when water moves from a region of higher concentration to one of lower concentration.

4. Parts of the roots • The outer layer of the root is the epidermis. This region produces root hairs which project into the soil increasing surface area for uptake of water. • Below the epidermis is the cortex. Cortical cells are highly permeable to water and dissolved solutes. • Below the cortex is a thin layer called the endodermis. The endodermis controls flow of water and minerals within the plant. • At the centre of the root is the stele. This region contains the vascular tissues (the xylem and phloem) surrounded by a layer of cells called the pericycle. The remainder of the stele is the vascular cambium. These cells are able to divide to form new xylem and phloem increasing the size of the roots.

5. So what are the Xylem and Phloem?

6. What causes the water to go up the plant? • The answer to this is the Root Pressure and Capillary Action. • Root Pressure: Water moves up through a plant because of root pressure and capillary action. Root pressure occurs during times when transpiration is low but the soil is very moist, and the roots absorb too much water. Because the water accumulates in the plant, a slight root pressure is created that pushes the xylem sap to the tips or edges of leaves, where it forms drops (the process is called guttation). • Capillary action: During capillary action, water rises up the walls of the thin, porous xylem tube as a result of the forces of adhesion, cohesion and surface tension. Xylem tubes are made of cellulose, to which water molecules stick.

7. Next Part of the Journey- Reaching the Xylem • The water moves across the root from the hair cell to the xylem by three different pathways: • apoplast pathway - water passes through the cell walls and from the wall of one cell to the wall of an adjacent cell • symplast pathway - water moves through the cytoplasm and from the cytoplasm of one cell into the cytoplasm of the next cell via the plasmodesmata- (a narrow thread of cytoplasm that passes through the cell walls of adjacent plant cells and allows communication between them.) • vacuolar pathway - water passes from the vacuole of one cell into the vacuole of the next cell • Water is not completely free to move from the root hair cell to the xylem. • The apoplastic pathway is blocked when it reaches the endodermis because the endodermal cells have a waxy, waterproof layer which prevents the further passage of water through the wall. This waxy layer is called the Casparian strip and is shown in the diagram below. • The Casparian strip allows the endodermis to regulate the quantity of water entering the xylem.

8. In the xylem • Once in the xylem, water with the minerals that have been deposited in it (as well as occasional organic molecules supplied by the root tissue) move up in the vessels and tracheids. At any level, the water can leave the xylem and pass to supply the needs of other tissues. At the leaves, the xylem passes into the petiole and then into the veins of the leaf. Water leaves the finest veins and enters the cells of the spongy (temporarily stores the sugars and amino acids synthesized in the palisade mesophyll) and palisade layers. Here some of the water may be used in metabolism, but most is lost in transpiration.

9. Cohesion and Adhesion Theory • Cohesion: The cohesion theory is when water molecules are strongly attracted to each. Cohesion is whereby the driving force of transport is transpiration, that is, the evaporation of water from the leaf surfaces. Water molecules cohere (stick together), and are pulled up the plant by the tension, or pulling force, exerted by evaporation at the leaf surface. • Adhesion is when water molecules adhere or stick to the walls of the xylem. When unequal distribution of ions go across the membrane, solutes move along the concentration gradient. when unequal distribution of ions go across the membrane, solutes move along the concentration gradient. This is called diffusion.

10. The leaves (main parts) • Leaves have xylem and phloem tubes. • The epidermis is on the outside to protect the leaf. The epidermal layer of a leaf protects the tissues which lie between them and also help in the process of gaseous exchange. • The palisade mesophyll (photosynthesis cell) have chloroplast which have green substance called chlorophyl. • Spongy mesophyll protects the epidermis. They are more rounded and are not as tightly packed as palisades. They contain less chlorophyll. • Stomata's connect to air spaces between mesophyll. Carbon dioxide travels through stomata at the bottom of the leaf. • Light energy which chloroplast creates turns carbon dioxide and water to create glucose and oxygen • Photosynthesis takes place in chloroplasts in leaves which absorbs sunlight. Photosynthesis is the process by which plants convert energy from the sun. • Plants use sugar to make starch, fats and proteins.

11. Transpiration • Once the water reaches the xylem it moves upwards as a result of transpiration. So basically, transpiration is kind of evaporation. Leaves have openings called stomata which are guard cells which open and close. They only respond to light, meaning that the plant doesn’t transpire as much at night. Stomata's circulate carbon dioxide from the air for photosynthesis to enter the leaf as well as regulate the amount of water in the leaf. In the process, water evaporates from the leaf. Transpiration cools plants and allows large amounts of nutrients and water to shoots. • The formula for photosynthesis: • carbon dioxide + water (+ light energy) → glucose + oxygen = • 6 CO2 + 6 H2O → C6H12O6 + 6 O2

12. Bibliography • Walker Keenan. "Gymnosperms." 2009. Web. 20 Mar. 2011. <http://sharon-taxonomy2009-p2.wikispaces.com/Gymnosperms>. • "Transport of Water and Minerals in Plants." 16 Dec. 2010. Web. 18 Mar. 2011. <http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/X/Xylem.html>. • Ridwan. "TRANSPORTATION IN PLANTS." Scribd. Web. 23 Mar. 2011. <http://www.scribd.com/doc/4801010/TRANSPORTATION-IN-PLANTS>. • Water Transport in Plants. "Water Transport in Plants." Nick's Pages - Mostly Biology. Web. 23 Mar. 2011. <http://www.nicksnowden.net/Module_2_Biology_pages/water_transport_in_plants.htm>. • "SparkNotes: Plants: Essential Processes: Water Transport." SparkNotes: Today's Most Popular Study Guides. Web. 23 Mar. 2011. <http://www.sparknotes.com/biology/plants/essentialprocesses/section1.html>. • Holbrook, N. M., M. J. Burns, and C. B. Field. "Negative Xylem Pressures in Plants: A Test of the Balancing Pressure Technique." Science 270 (1995): 1183–1192. • Raven, Peter H., Ray F. Evert, and Susan E. Eichhorn. Biology of Plants, 6th ed. New York: W. H. Freeman and Company, 1999. • Taiz, Lincoln, and Eduardo Zeiger. Plant Physiology, 2nd ed. Sunderland, MA: Sinauer Associates, 1998. • "Water Movement in Plants - Biology Encyclopedia - Cells, Body, Function, Process, Used, Structure, Molecules, Energy." Biology Reference. Web. 23 Mar. 2011. <http://www.biologyreference.com/Ve-Z/Water-Movement-in-Plants.html>. • "Water in Plants - Biology Online." Life Science Reference - Biology Online. Web. 23 Mar. 2011. <http://www.biology-online.org/11/8_water_in_plants.htm>.http://www.youtube.com/watch?v=DpFU-NkKUqg • Scully, Lizzy. "How Water Moves Through Plants | EHow.com." EHow | How To Do Just About Everything! | How To Videos & Articles | EHow.com. Web. 23 Mar. 2011. <http://www.ehow.com/how-does_4912679_how-water-moves-through-plants.html>.

13. Glossary • Abscisic Acid  -  The best known of the inhibitor hormones; inhibits growth and prolongs dormancy. • Acid Growth Hypothesis  -  Explains phototropism by suggesting that increased acidity in the walls of certain cells (stimulated by the hormone auxin) increases their flexibility and expandability, so that more water can diffuse into the cells and cause cell elongation. • Active Transport  -  Movement of substances across cell membranes that requires energy expenditure on the part of the cell; contrasts with passive diffusion, or osmosis. • Apoplast  -  The pathway from the root surface to the core by which water moves along cell walls and through intercellular spaces, bypassing the cells themselves. • Auxin  -  One in a class of plant hormones that stimulates (among other things) cell elongation, secondary tissue growth, and fruit development. • Cytokinin  -  One in a class of plant hormones that promotes cell division and tissue growth. • Day-Neutral Plant  -  Plant in which blooming is not affected by photoperiod, so that flowering occurs independently of the duration of day and night. • Ethylene  -  A plant hormone that controls fruit ripening and promotes senescence (aging). • Florigen  -  Name given to the hypothetical hormone that might control flowering in plants. • Gibberellin  -  One of a class of plant hormones that stimulates stem elongation, germination, and conversion of the embryonic food source into usable sugars. • Gravitotropism  -  Reaction of a plant to gravity; a stem grows against gravity, roots toward gravity. • Hormone  -  A hormone is a chemical that affects the ways in which an organism functions; it is produced in one part of the plant body but, by traveling to target cells throughout the body, affects many other parts as well. • Inhibitor  -  One in a class of plant hormones that inhibits growth and prolongs dormancy in buds and seeds. • Leaf Abscission  -  Hormone-stimulated leaf loss; caused by the formation of a weak, thin-walled abscission layer at the base of the leaf. • Long-Day Plant  -  Plant in which blooming is affected by photoperiod so that flowering occurs when the hours of darkness in a 24-hour photoperiod fall below a certain level. • Osmosis  -  The passive diffusion of water across a membrane. Osmotic concentration refers to the concentration of solutes (dissolved substances) in the water; when the osmotic concentrations of two regions differ, water will flow from the area of low concentration to the area of high concentration. In contrast, the solutes themselves will flow from areas of high osmotic concentration to areas of low osmotic concentration. • Phloem  -  Vascular tissue composed of cells that are living at maturity; transports the products of photosynthesis throughout the plant body. • Photoperiodism  -  An organism's response to the length of day and night within a 24-hour period (photoperiod); in many plants, this phenomenon determines when flowering will occur. • Photosynthesis  -  The process by which plants and other autotrophic organisms convert light energy into vital organic materials. • Phototropism  -  The growth of a plant toward a light source, resulting from the rapid elongation of cells on the dark side of the plant; stimulated by auxin. • Phytochrome  -  Pigment in leaves that allows them to measure the duration of day and night. • Pressure Flow  -  The mechanism by which sugars are transported through the phloem, from sources to sinks; dependent upon the high turgor pressure of sources and the low turgor pressure of sinks. • Root Hair  -  An outgrowth of a plant root that provides an increased surface area for the absorption of water and dissolved minerals from the soil. • Short-Day Plant  -  Plant in which blooming is affected by photoperiod so that flowering occurs when the hours of darkness in a 24-hour photoperiod rise above a certain level. • Sieve Element  -  A living conductive cell of phloem. • Sink  -  Regions of the plant, such as growing tissues, that are in need of nutrients; characterized by low turgor pressure. • Source  -  Nutrient-rich region, such as a leaf, that supplies sugars for the rest of the plant; characterized by high turgor pressure. • Symplast  -  The pathway from the root surface to the core by which water enters the root hair membrane and travels through the cytoplasm of adjacent cells, via channels that connect their contents. • Target Cell  -  A cell that receives hormone signals. • TATC  -  Transpiration-Adhesion-Tension-Cohesion; the mechanism by which scientists theorize that fluids are pulled upward through the xylem (driven by transpiration, the evaporation of water from the leaf, and the cohesion between water molecules). • Thigmotropism  -  Reaction of a plant to touch; results from differential cell elongation. • Transpiration  -  The process by which a plant loses water to its environment through evaporation. • Tropism  -  Long-term growth of a plant toward or away from a stimulus as a result of differential cell elongation. • Turgor Movement  -  Relatively rapid, easily reversible plant movement, occurring in response to a stimulus, that results from changes in turgor pressure in certain plant cells. • Turgor Pressure  -  The force that the contents of a plant cell exert on the cell wall after the osmotic entry of water into the cell. • Vascular System  -  Mechanism of internal water and nutrient transport, made up of the vascular tissues xylem and phloem, that is characteristic of tracheophytes. • Vascular Tissue  -  A conductile component (either xylem or phloem) of the system that transports food and nutrients throughout the plant body. • Water Potential  -  The pressure that causes water to move across a membrane; water always moves naturally from areas of higher water potential to those of lower water potential. • Xylem  -  Vascular tissue composed of cells that are dead at maturity; transports water and dissolved minerals upwards from the roots to the shoot.