Water Properties: Polarity
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- CHRISTABEL SAMPA
Discuss the assertion that water has several unique properties that make it vital not only for human beings, but for all living organisms to survive.
Water is a normal oxide made of two hydrogen atoms and one oxygen atom. It has a chemical formula of H20 where the ratio of the two different atoms it is made up of two to one ie two atoms of hydrogen and one atom of oxygen covalently bonded to each other. Water is one of the most abundant of the smaller molecules and makes up to 60-90% of the fresh mass of an organism. Survival of all living organisms on earth hence is dependant on water. Therefore it is quite vital to understand the properties of water that makes it important to all living organisms.
Of all the properties of water, polarity can be considered very important as it somehow contributes to almost all the other properties in one way or the other. Water is polar substance because it shows uneven change distribution within its molecule. One part of the water molecule is partially positive and the other is partially negative and this is known as a dipole.
The polarity of water occurs because the oxygen atom in the molecule has greater electron attracting power than hydrogen atoms. Hence, oxygen has a slightly negative charge as compared to the hydrogen atom. The polarity makes water molecules to have weak force of attraction for each other, the opposite charges come together making the molecules behave as though they were sticky like magnets.
The above property enables water posses several unique properties such as:-
High Surface Tension
Surface tension comes about due to forces of attraction between molecules of a liquid at its open boundary surface. In a water molecule however the high surface tension is due to unequal distribution of hydrogen bond at the surface of water. Hydrogen bonds exist between each water molecule of water, but molecules at the surface of liquid water have fewer neighbors and as a result, have greater attraction to the few water molecules that are nearby. The surface tension makes the surface of water slightly difficult to break through thou the interior.
This is very important to living organism such as plants. As the water required for health plants is obtained from the soil which is down the plant, the high surface tension of water enables water to be pulled up a narrow tube by gravity without breaking its surface. “Cohesion of water molecule gives water a high tensile strength which enables water column in xylem elements of stem to be pulled upon to the top of tall trees without breaking.” Jain V.K, 2011:24.
Surface tension is also responsible for the survival of small organisms that are dependent on the water surface as a mode of transport and living. The Basilisk lizards for instance, makes use of the high surface tension of water to accomplish the incredible feat of walking on waters surface. Some insects also are capable of moving on top of water without its surface breaking. Humans are also capable of skipping rocks on water.
However, despite water having a high surface tension, water has a low viscosity. It is capable of sliding over each other easily. This property enables blood to move through thing capillaries and cytoplasm inside cellular boundaries.
in animals, the capillaries are the smallest blood vessels found within the tissues of the body and are the ones that transport blood to larger vessels, for instance during gaseous exchange oxygen from the lungs is delivered to the capillaries around the air sacs to reach the blood inside it which latter is transported to the heart inorder to be pumped to all other blood’s mayor components is water this function of the capillaries is well carried out and animals such as human beings, survive. Therefore the low viscosity of water is important to human survival.
not only what has been mentioned above, but also when molecules of others substances dissolve in mater, they low the surface tension of water and they tend to collect at the interface between the liquid phase and other phases. vermar and ararwal, 1974. this fact make water important in the development of a plasma membrane and aids the movement of molecules between it.
Water is a universal solvent
Water is referred to as a universal solvent as it is able to dissolve a wide range of substances dues to its polarity nature. Water dissolves substances by surrounding charged particles and pulling them into solution. It decreases the electro static interactions between charged substances and increasing yheir solubility.
This property is very important to both plants and animal. According to verma and Agrival 1974:75. “The sol-valency is of great biological importance because all the chemical reactions that take place in the cells, do so in acqueous solution.” these solutions have the solvent water. This simply means that without water, biochemical reactions can not take place.
All water alet acts as a transport medium, it is responsible for the transportation of all dissolved materials in blood such as food substances, gases excretory products and many other essential; and wastes products. in plants, it transports mineral salts and other nutrients to where they are needed.
Water is a solvent for polar substances meaning that it does not dissolve non polar substances. This is of great importance in the formation of membranes and helps to determine the three dimensional properties of molecules of proteins, nucleic acids and their cel structure. Taylaor et al 1997.
The tendency of water to move up a narrow tube against the force of gravity is referred to as capillary action water has a high capillarity action water has s high capillarity. The high capillarity of water is due to its adhesives and cohesive forces.
Cohesion is the mutual attraction between like molecules, water has cohesive properties as the molecules of water attract other water molecules. This is important in the transportation of water through a plant. Mader S. 2010:29 states “because water molecules are cohesive, a tension created that pulls the water column up from the roots.” the roots are anchored in the soil where the plant obtains water from. as the plant continuously transpierce through leaves which are up the plant, the water evaporating is immediately replaced with water molecules from the transport vessels from the roots to leaves.
Adhesion, however, is the attraction between the water molecules and the container in which it is. Adhesion can also be described as the ability of one thing to stick firmly to another. Water is therefore attracted to substances such as cells walls, or glass surface. This is also important to living organisms. In the transport of water to the wall of the vessels also help in preventing the column of water from breaking apart. In general, adhesive and cohesive properties of water work hand in hand in the movement of water from the roots up to the leaves.
Specific heat capacity
Water has a high heat capacity, specific heat capacity is the amount of energy that must added to a unit mass to raise the temperature by one degree, and “the high specific heat capacity of water is due to the hydrogen bonds between the molecules. Water absorbd a lot of heat before it begins to get hot.
The above property is important to organism that line in water such as fish. water organisms do not die due to excess heat and coldness as it take time for water to gain and lose heat, hence the temperature is well maintained for water life. According to Mader 2010:29, “because the temperature of water rises and falls slowly, organisms are better able to maintain their normal internal temperatures and are protected from srapid temperature changes.” most of the chemical reactions in cells take place within a small range of temperature.
Water is idourless, hence transparent. This property is also very important as it enables tight to penetrate through it and reach photosynthetic organalles, the chloroplast inside cells which require sunlight to manufacture food..
Having discussed the above property of water, and this importance to all living organisms, it can be concluded that without water, life on earth is practically impossible as all living organisms depend on water.
Jain V.K. (1974); Fundamentals of plant Physiology, S. Chand and Company Ltd. New Delhi.
Kormondy E.J (1996); Concepts of Ecology, Fourth Edition. Pearson Education New Jersey.
Mader S.S (2010); Biology, tenth Edition. McGraw – Hill Education. Singapore.
Taylor D.J et al (1997); Biological Science 1 and 2 third edition. Camridge University Press. New York.
Verma P.S and Agarwal V.K. (1974); Cell Biology, Genetics, Molecular Biology, Evolution and Ecology, Multicolour edition. Rejendra Ravindra Printer New Delhi.
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