Water Drop Journey in Plants Done By: Omar Ibrahim Grade: 8B
General Idea • Have you ever heard of the term “osmosis”? What about “water concentration gradient”? We all know that plants absorb water, and nutrients, from the soil by the roots, and transport the water to the leaves in order to carry the process of making glucose, photosynthesis, which is made by water, sunlight, carbon dioxide, and chlorophyll, but did we ever know how does a water drop move inside a plant in exact details? Or even what happens to a water drop when it falls from the sky, enters the plant, and leave it again? This is what I will explain in this presentation.
Precipitation • To begin with, water falls from the clouds by a process called precipitation. What does precipitation mean? Precipitation is the water released from clouds in the form of rain, frozen rain, sleet, hail, or snow. Precipitation is the mean that starts the whole water drop journey. After falling from clouds, these water drops land on Earth to become part of the groundwater in the soil, or little ponds or lakes might be formed from the falling water droplets.
Roots Absorption of Water • As we know, the absorption of water is carried out by the plant’s roots, but what part exactly takes in the water? Most of the water absorbed by the roots is absorbed by an area in the roots called piliferous region, also called the root-hair layer and made of hundreds of projections of the epidermal tissue. The piliferous region is the most area in the root in which the water absorption happens in, since this region has the largest amount of root hairs in the whole plant. Since the root hairs are narrow walled, the surface area of the water absorption increases. Water enters the roots by a process called osmosis, in which water is transferred from where there is a higher water potential to where there is a lower water potential.
Inside the Roots and Upwards • After entering the root hairs, water moves to a vascular tissue, called xylem, which transports water and nutrients from the roots to the leaves, in order to carry out the essential process of photosynthesis. Where can we find xylem inside the plant? The vascular tissue, xylem, is found a central column, surrounded by the endodermis, the innermost layer of the cortex that forms a sheath around the vascular tissue of the roots and some stems. The endodermis is covered by the cortex parenchyma cells. The parenchyma is the fundamental tissue of plants, which is composed of thin-walled cells that has the ability to divide.
Inside the Roots and Upwards (Continuing) • The water movement inside the plant continues when the water concentration gradient is established. Water concentration gradient is the graduated difference in concentration of water per unit distance through a solution, and since the roots have a higher concentration of water molecules than the leaves, water moves from the roots to the leaves by cell-by-cell transport. Water passes from one cell to another either through the cell wall, cytoplasm, or the vacuole. This whole process inside the root hairs and inside the xylem is called Transpiration-Adhesion-Tension-Cohesion (TATC). Water moves from the soil all the way up to the stems and then to the leaves to carry photosynthesis and get more food for the plant, glucose, in order to survive.
Inside the Xylem • The concentration of water inside the xylem that happens across the cortex results in producing something called the root pressure, also known as guttation, which is pressure exerted in the roots of plants which results from osmosis, pushing the water outside the plant, if part of the plant was removed. Root pressure is considered one of the means that force water to move upwards inside the plant, instead of heading downwards, and following the gravitational force.
Structure of Xylem • Xylem is known in the plant to be narrow, long, and hollow. Xylem also consists of dead material, and doesn’t consist of any living material. Xylem is impregnated, soaked, with bands of lignin, an organic substance that acts as a binder for the cellulose fibers in plants and wood, and adds strength to stop vessels from collapsing.
Water in Leaves and Leaf Structure • After water reaches the plant’s leaves, it is now time for water to share in making photosynthesis. This process requires absorbing CO2, water, light energy, and using chlorophyll, which is found in the green organelle responsible for photosynthesis called chloroplast. What type of leaves can make absorption of light more flowing? Broad leaves are the best leaves for light absorption, since they are thin, wide, and flat. This also makes it easier for CO2 to enter the plant through the stomata, small openings that enable exchange of gas. Water, light energy, and CO2 meet together in the leaves, and make the process of photosynthesis, converting light energy to chemical energy, which is glucose.
Water in Leaves and Leaf Structure (Continuing) • After producing glucose from the process of photosynthesis, it is now time for the water to be lost, transpiration or evaporation, to return back to the environment and form a new cloud. Water can be lost when also photosynthesis is still happening, since the stomata have two guard cells, one to “open” the stomata, and one to “close” it, and while the carbon dioxide is taken in by the stomata, water might accidentally be lost. In most broad-leaved plants, the amount of stomata is found higher at the back of the leaf, enabling a fewer amount of water to transpire, evaporate, from the plant.
Out and Away! • As transpiration takes place, water diffusing into the air spaces from the spongy mesophyll cells takes its place. After being lost, water evaporates and reaches the sky. After this step, all the water droplets combine together, becoming more condense and making large, thick clouds in the air, and this process is called condensation. Finally, the water falls down again, precipitation, as snow, rain, frozen rain, sleet, or hail.
Water Drop Journey Video • This is a very brief video that I found on the Internet that explains the concept of the water droplet’s journey inside a plant. • The link to this video is: http://www.youtube.com/watch?v=QYbg4lQ-iaU
Bibliography • http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artmar00/watermvt.html • http://www.sparknotes.com/biology/plants/essentialprocesses/section1.html • http://static5.depositphotos.com/1032749/417/i/950/depositphotos_4171029-Water-drop-on-leaves.jpg • http://2.bp.blogspot.com/-MnmheO4MuOY/TyRcbN8EtYI/AAAAAAAAAxQ/mcR6kk5lvGQ/s1600/rain1.jpg • http://ga.water.usgs.gov/edu/watercycleprecipitation.html • http://botanydictionary.org/piliferous-layer.html • http://www.microscopy-uk.org.uk/mag/imgmar00/roothair.jpg • http://faculty.uca.edu/johnc/RootHairsRadish.jpg
Bibliography • http://www.thefreedictionary.com/endodermis • http://content.answcdn.com/main/content/img/McGrawHill/Encyclopedia/images/CE498100FG0010.gif • http://www.thefreedictionary.com/concentration+gradient • http://www.chaosscience.org.uk/sites/default/files/xylem_5.jpg • http://www.sbs.utexas.edu/mauseth/weblab/webchap9secretory/web9.3-1.jpg • http://dictionary.reference.com/browse/parenchyma
Bibliography • http://www.biology-online.org/dictionary/Lignin • http://www.thefreedictionary.com/root+pressure • http://lavonardo.net/wp/wordpress/wp-content/uploads/2009/03/guttation.jpg • http://www.extension.org/mediawiki/files/6/6d/Guttation.jpg • http://chenected.aiche.org/wp-content/uploads/2010/11/lignin_h-1024x647.jpg • http://micro.magnet.fsu.edu/cells/chloroplasts/images/chloroplastsfigure1.jpg
Bibliography • http://images.kish.in/2011/03/stomata2.jpg • http://waynesword.palomar.edu/images/stomat2b.jpg • http://www.youtube.com/watch?v=QYbg4lQ-iaU • http://www2.puc.edu/Faculty/Gilbert_Muth/phot0023.jpg • http://www.historyforkids.org/scienceforkids/physics/weather/pictures/clouds.jpg