TRANSPIRATION AND WATER CONDUCTION ABSRACT Transpiration is the loss of water from a plant in the form of water vapor. Water is absorbed by roots from the soil and transported as a liquid to the leaves via xylem. In the leaves, small pores allow water to escape as a vapor. Of all the water absorbed by plants, less than 5% remains in the plant for growth. This experiment will explain why plants lose so much water, the path water takes through plants, how plants might control for too much water loss to avoid stress conditions, and how the environment plays a role in water loss from plants. I. INTRODUCTION All plants need water, minerals and food. There is a system present in plants called transport system to distribute these substances throughout the body. Water is the most limiting abiotic (non-living) factor to plant growth and productivity, and a principal determinant of vegetation distributions worldwide. Since antiquity, humans have recognized plants' thirst for water as evidenced by the existence of irrigation systems at the beginning of recorded history. Water's importance to plants stems from its central role in growth and photosynthesis, and the distribution of organic and inorganic molecules. Despite this dependence, plants retain less than 5% of the water absorbed by roots for cell expansion and plant growth. The remainder passes through plants directly into the atmosphere, a process referred to as transpiration [ CITATION McE13 \l 1033 ]. According to Titiksha (n.d.), flowering plants have a very well developed system to transport these substances; this system is called vascular system. Vascular system contains two types of tissues, xylem and phloem. Xylem distributes water and phloem distributes food throughout the plants body. Plants need water for photosynthesis, transpiration, transportation and for mechanical function. Minerals are also required by the plants as salts or as ions. Water is absorbed by the roots, for this, roots provide huge surface area, they contain cell sap of higher concentration than the surrounding water and root hair have thin walls. The vascular tissues are present in plant body from the tip of roots up to the leaves, xylem and phloem also joined end to end and form long tubes and phloem cells form long tubes for their functions [ CITATION Titnd \l 1033 ]. II. METHODS AND MATERIALS A. Effect of Some Environmental Factors on Transpiration Rate A.1. Use of an Improvised Potometer Leafy branch from Coleus (mayana) and Muntingia (datiles) were cut off about 2 cm of stem from the base of the shoot. Shoot were transferred to a large beaker of tap water, by making sure the drop of water adheres to the basal cut surface; equally important, it prevents entry of air into the base of the stem. By assembling the improvised photometer by inserting rubber tubing into the delivery end of the buriet, it was filled with distilled water as well as the rubber tubing with the same water by making sure all trapped air bubbles are dislodge. Shoot was inserted with a drop of water on the base to the other end of the rubber tubing, excluding all air from the system, thus the entire system must be completely filled with water. Rubber band was used to tie around the rubber tubing at the plant end to close the set-up since there is the tendency for water to flow out of the rubber tubing while inserting the shoot. The transpiration rate in light and still water, light with fanning, dark and still air, and a normal set-up were determined. A.2. Use of Cobalt Chloride Paper Using cobalt chloride paper is another method of measuring the transpiration rate. This paper is impregnated with cobalt chloride and it is blue when dry and pink when moist. The time it takes for the blue cobalt chloride paper to change to standard pink coloration when the paper is held against a leaf surface can be taken as a comparative measure of transpiration rate. This experiment was held around the DLSU campus by selecting five (5) plants that are growing under the sun and growing under the shade. By ensuring that the leaf was dry, identical pieces of dry cobalt paper was fasten on both leaf surfaces of each selected plants. The leaf was taken from each of the plant species and by putting a small amount of duco cement, strip of small piece of epidermis were examined and observed under the microscope. B. Rise of the Transpiration Stream Two species of plants were used in this experiment. For herbaceous plants, Coleus was used and Muntingia for woody plants. Eighteen (18) leafy stem of both Coleus and Muntingia were immersed quickly under water in 100-mL beaker containing 5 mL of 0.01% eosin. After a half hour, one stem was carefully split longitudinally and the distance travelled by the dye was measured. On the other, a thin cross section of the stem was cut using a razor blade and the location of the dye was examined. III. RESULTS AND DISCUSSION A. Effect of Some Environmental Factors on Transpiration Rate A.1. Use of an Improvised Potometer Plants require a transport system to deliver raw materials for photosynthesis to the leaves and to deliver the sugar made to other parts of the plant for use or storage[ CITATION BBCnd \l 1033 ]. The uptake of water can be measured using a potometer. Under normal circumstances, the rate of water uptake gives a measure of the rate of transpiration. A simple potometer is a piece of capillary tubing to which a plant has been connected. The water uptake is measured by recording the time taken for a bubble in the tube to move a set distance [ CITATION BBCnd \l 1033 ]. The potometer is set up underwater to avoid unwanted air bubbles in the xylem of the plant which may disrupt the transpiration stream. All joints are sealed with rubber band to make it as airtight as possible [ CITATION BBCnd \l 1033 ]. Water evaporates through the many stomata on the leaf surface; the rate of transpiration is directly related to the surface area. This was done with different set-ups. Testing the light intensity was the first method by using lamp set at different distances from the plant. Next is using wind speed by using fan to create different wind speeds by placing the plant shoot and photometer in front of the fan. Another method was placing it in dark place by putting a black bag in the set-up and the last is the control set-up where it was placed in a normal room temperature. Light Plants transpire more rapidly in the light than in the dark. This is largely because light stimulates the opening of the stomata. Light also speeds up transpiration by warming the leaf. Temperature Plants transpire more rapidly at higher temperatures because water evaporates more rapidly as the temperature rises due to the increased kinetic energy of the water molecules. At 30°C, a leaf may transpire three times as fast as it does at 20°C. Wind, when there is no breeze, the air surrounding a leaf becomes increasingly humid thus reducing the rate of transpiration. When a breeze is present, the humid air is carried away and replaced by drier air. So a steep diffusion gradient is maintained. Humidity The rate of diffusion of any substance increases as the difference in concentration of the substances in the two regions increases. When the surrounding air is dry, diffusion of water out of the leaf goes on more rapidly [ CITATION Siynd \l 1033 ]. Table 1. Effects of Different Factors on the Rate of Transpiration Factor Temperature Humidity Effect Increased Decreased Explanation Evaporation and diffusion are faster at higher temperatures Humidity decreases the concentration gradient between the Wind speed Increased inside and outside of the leaf – this reduces transpiration Moving air removes water vapor, increasing the rate of Light Increased diffusion of water vapor from the leaf The stomata open wider to allow more carbon dioxide into intensity the leaf for photosynthesis Table 2. Comparison of the Transpiration Rate of Two Species Using an Improvised Potometer Set-up. Treatment Control Dark/Still air Wind Light Transpiration Rate (vol/unit time) Coleus Muntingia 1 mL 0.1 mL 1 mL 0.5 mL 3.5 mL 0.5 mL 3 mL 1.5 mL Figure A (Wind Treatment) FigureB (Dark/Still Air Treatment) Figure C (Setting-up the experiment) A.2. Use of Cobalt Chloride Paper Cobalt chloride, CoCl2, is a fascinating compound that changes color in response to humidity. As humidity increases, cobalt chloride changes color from sky blue to purple to pink. Such striking changes in color make cobalt chloride useful as a humidity indicator in weather instruments[ CITATION Ame06 \l 1033 ]. According to American Chemistry (2006), if we could examine blue cobalt chloride solid with an extremely powerful microscope, we would see a repeating, threedimensional pattern of cobalt and chlorine atoms, known as a crystal structure. This regular, repeating internal arrangement of atoms is the reason that individual grains viewed through a magnifying lens, for example, look like tiny crystals. As the humidity increases, and water is absorbed by CoCl 2, the crystal structure rearranges itself to make room for water molecules. First, two water molecules surround each cobalt atom, forming the dihydrate, which is "chemistry speak" for "two water molecules." Cobalt chloride dihydrate is purple[ CITATION Ame06 \l 1033 ]. The hydration reaction may be represented by the following chemical reaction: Source: https://chlorine.americanchemistry.com Table 3. Comparison of the transpiration rate of plants growing under the sun and shade using cobalt cgloride paper. Plant Species Time it takes for cobalt No. of Stomates chloride paper to change Under the sun Lantana Sword Fern San Francisco 7 minutes 9 minutes 9 minutes 149 185 115 Under the shade Palm Oregano Santan 19 minutes 13 minutes 15 minutes 265 204 263 Figure D Leaves on the upper part in figure D were observed under the sun, while the leaves on the lower part were observed in shaded places. B. Rise of the Transpiration Stream Transpiration is the evaporation of water at the surfaces of the spongy mesophyll cells in leaves, followed by loss of water vapor through the stomata [ CITATION BBCnd \l 1033 ]. Water moves through the xylem vessels in a continuous transpiration stream: root → stem → leaf According to BBC (n.d.), transpiration produces a tension or ‘pull’ on the water in the xylem vessels by the leaves. Water molecules are cohesive so water is pulled up through the plant. The transpiration stream has several functions. These include 1) transporting mineral ions 2) providing water to keep cells turgid in order to support the plant 3) providing water to leaf cells for photosynthesis and 4) keeping the leaves cool by evaporation. Table 4. Comparison of Water Movement During Transpiration of Coleus and Muntingia. Plant Species Distance travelled Coleus (cm) 5.5 5.0 4.0 18.0 18.0 16.0 Muntingia Time lapsed (min.) Rate of transport 45 45 40 45 45 40 (cm/min.) 0.12 0.11 0.10 0.4 0.4 0.4 IV. CONCLUSION Transpiration is the evaporation of water from the surface of leaf cells in actively growing plants. This water is replaced by additional absorption of water from the soil leading to a continuous column of water in the plant's xylem. The process of transpiration provides the plant with evaporative cooling, nutrients, carbon dioxide entry and water to provide plant structure. Rates of transpiration depend on the water potential gradient from the soil to the atmosphere and the resistances to its movement through the plant. Water enters the root and travels through the cortex and endodermal layers of cells to reach the xylem where water ascends to the leaf where, if not used in the plant, evaporates. If water loss is greater than water uptake, air bubbles can form in the xylem. Plants reduce water loss by closing their stomata, developing thick cuticles, or by possessing leaf hairs to increase the boundary layer. Stomata are quick to respond to environmental cues to protect the plant from losing too much water, but still allowing in enough carbon dioxide to drive photosynthesis [ CITATION Ste04 \l 1033 ]. REFERNCES AmericanChemistry. (2006). Cobal chloride: colorful moisture detector. BBC. (n.d.). Transport system in plants. McElrone, A. J., Choat, B., Gambetta, G. A., & Brodersen, C. R. (2013). Water uptake and transport in vascular plants. Nature Education Knowledge . Siyavula. (n.d.). Life Science Grade 10. Sterling, T. D. (2004). Transpiration - water movement through plants. Titiksha. (n.d.). Plant - absorption, conduction, rise of cell sap and transportation. A NEEDLE IN THE HAYSTACK: SERACHING FOR NEW MEDICINES IN THE RAIN FOREST More than two thirds of the world's plant species are found in the tropical rainforests; plants that provide shelter and food for rainforest animals as well as taking part in the gas exchanges which provide much of the world's oxygen supply. Rainforest plants live in a warm humid environment that allows an enormous variation rare in more temperate climates. The video presented the search of possible species of plant in a tropical rain forest for the possible cure of cancer and HIV. The scientists went to different tropical countries in Asia particularly Indonesia, Malaysia, and a remote place in Palawan, Philippines. Since there is a diverse species of plant in the rain forest, scientist has been pulling out all the stops to get the possible medicinal plant to be tested by the researcher at University of Illinois, Chicago (UIC) where they conducted the experiment in testing the pulverized parts of the specific plant by observing the effect on each virus. According to Desai, et al., cancer is the second leading cause of death worldwide. Although great advancements have been made in the treatment and control of cancer progression, significant deficiencies and room for improvement remain. A number of undesired side effects sometimes occur during chemotherapy. Natural therapies, such as the use of plant-derived products in cancer treatment, may reduce adverse side effects. Currently, a few plant products are being used to treat cancer. However, a myriad of many plant products exist that have shown very promising anti-cancer properties in vitro, but have yet to be evaluated in humans. Further study is required to determine the efficacy of these plant products in treating cancers in humans. On the other hand, the acquired immunodeficiency syndrome (AIDS) is a result of human immunodeficiency virus (HIV) infection which subsequently leads to significant suppression of immune functions. AIDS is a significant threat to the health of mankind, and the search for effective therapies to treat AIDS is of paramount importance. Several chemical anti-HIV agents have been developed. However, besides the high cost, there are adverse effects and limitations associated with using chemotherapy for the treatment of HIV infection. Thus, herbal medicines have frequently been used as an alternative medical therapy by HIV positive individuals and AIDS patients (Wu, Attele, Zhang & Yuan, 2001). They were able to find specific specie of plant that treats those diseases but it needs a further study to prove that it really kills the virus. Traditional systems of medicine continue to be widely practiced on many accounts. Population rise, inadequate supply of drugs, prohibitive cost of treatments, side effects of several synthetic drugs and development of resistance to currently used drugs for infectious diseases have led to increased emphasis on the use of plant materials as a source of medicines for a wide variety of human ailments.
