The Journey of a Water Drop Bushra Shaikh 8C

What are the stages of the water cycle?  Evaporation/Evapotranspiration: When the water from the ground evaporates to the atmosphere, evapotranspiration is when the water from the plants evaporates from the leaves. These can be from vents, volcanoes and fog.  Condensation: When the moisture from the ground makes contact with the particles in the atmosphere to from water droplets.  Precipitation: The process when the droplets of water from the atmosphere come down on earth in forms of rain, snow, sleet, hail etc.  Infiltration: The process where the water gets stored in places like groundwater storage or can just escape from springs, seepage and rivers.

What does the water do when it gets into a plant? There are three stages of which the water goes through: - Root - Stem - Leaves

Root First the water is collected through the piliferous region of the root, this is where the youngest parts of the root hairs are. This is a region that has a group of epidermal tissue projection to increase surface area. This allows the plants maximum intake of water. These hairs die off but are replaced by new growth regularly. The water is absorbed through the epidermal tissue through osmosis. A process where the water is moved from a region of higher concentration to a region of lower concentration. The concentration gradient indicates the different in the concentration of solutes in a solution between the two regions. To be more specific, “water molecules diffuse too, but in living things water often diffuses across a membrane.” (Schmoop, 2013)

Cohesion and Adhesion So how does the water keep moving exactly? One of the characteristics of water is water tension. This means that water has a bond, like a chain. So if water is pulled through one end then the other end also comes along. So when water transpires, (not evaporating because the water is going from a living organism)and is drawn out the water throughout the rest of the plant is pulled. This is the engine running the flow of water and this is why water continuously moves throughout the plant. Cohesion and adhesion is where we get into detail. Cohesion is a bond between to similar molecules whereas adhesion is a bond between two different molecules. The hydrogen bonds in the molecules (of the water) make them stick together (cohesion) and when the hydrogen molecules form bonds with carbohydrates this forms adhesion. The connection it has with this particular subject can be determined through the cohesion tension theory. This theory says that when water is drawn out through transpiration the water in the xylem is pulled towards it(adhesion). The water flows consistently due to water tension and cohesion between the hydrogen molecules present in water.

Stem Next the water goes through the stem, the part that supports the plant. There are two types of stems xylem and phloem. The xylem is the vascular tissue of the plant. It distributes water and dissolved minerals to all parts of the plant. The xylem also contributes greatly in the replacement of water lost during photosynthesis and transpiration. Sometimes the water moves us due to root pressure capillary action. Root pressure occurs due to too much water intake during low transpiration in the plant. So if the root absorbs too much water form the moist soil the water is pushed up because there is too much and some of it needs to transpire. Furthermore, when the water increases the sap in the xylem moves to the tip of the leaves and causes guttation (when the sap forms drops on the tips of the leaves).

Leaves The leaves help the water transpire. Transpiration occurs faster during when there is more light or temperature. Subsequently the heat motivates the stomata of the leaves to open more. The stomata are miniscule pores on the outer layer of the leaf that control the vapor passing in and out of the plant. Another reason that the stomata are essential to plants because they also uptake the gas needed for photosynthesis. Due to this stomata are mostly open during the day, when photosynthesis occurs. Although, there are certain types of plants called Crassulacean Acid Metabolism which do photosynthesis at night! Therefore, their stomata can also open at night! CAM plants are mostly desert plants, like here in Qatar. Also, the drier and windier the environment is the more transpiration occurs.

… Furthermore (about leaves, in a diagram will appear to have several different layers, each responsible for a different job if not an interdependent one. After the cuticle and the epidermis there is the palisade. The palisade contributes mainly to photosynthesis and consists of parenchyma cells. After this there is the mesophyll (meaning leaf), most photosynthesis takes place in the palisade mesophyll, which is efficiently located under the epidermis at the top portion of the leaf. Different leaves are adapted to their environments in different ways. There may be leaves that are a different shape for example a long leaf or a compound leaf. Sometimes there are even leaves of different colors like red and pink!

Why does water need to move consistently through a plant?  To keep the plant alive, continuously supplying it with hydration and nutrients.  To keep the flow of the water going the water needs to consistently be moving throughout the plant, if the plant gets too much water it will rot and die.  Water is also incorporated into the cells, a percentage of the cells are actually water.  Water is needed to activate photosynthesis, water helps reacts with carbon dioxide to form the building blocks needed for plant’s cell using the energy extracted from the sunlight.

Bibliography  "Adhesion and Cohesion of Water." Adhesion and Cohesion Water Properties, USGS Water Science School. USGS, Web. 23 Mar  "The Water Cycle.", U.S. Geological Survey (USGS) Water Science School. USGS, Web. 23 Mar  Scully, Lizzy. "How Water Moves Through Plants." EHow. Demand Media, 15 Apr Web. 23 Mar  Shmoop Editorial Team. "Transportation in the Plant - Shmoop Biology" Shmoop.com. Shmoop University, Inc., 11 Nov Web. 23 Mar  "Plant Water Regulation - Adaptation Tutorial." Plant Water Regulation. Biology-Online.org, Web. 23 Mar  "Concentration Gradient." - Definition from Biology-Online.org. Biology-Online.org, Web. 23 Mar  Shmoop Editorial Team. "Leaf Structure - Shmoop Biology" Shmoop.com. Shmoop University, Inc., 11 Nov Web. 25 Mar  "Transport in Plants." Transport in Plants. N.p., n.d. Web. 25 Mar