As I have mentioned, neighbouring water molecules are attracted to one another. Molecules at the surface of liquid water have fewer neighbours and as a result, have a greater attraction to the few water molecules that are nearby. This stronger attraction is called surface tension, which makes the surface of the liquid slightly more difficult to break through in. When a small object that would normally sink in water, is placed carefully on the surface, it can remain suspended on the surface due to surface tension. Incredibly, some animal such as Basilisk lizard makes use of the high surface tension of water to walk on the surface of water! The Basilisk cannot actually walk on water; rather, it runs on water, moving its feet before they break through the surface and sink down. Water forms spherical droplets which have the maximum inner area and least surface area when in contact with a hydrophobic material. This cohesive property of water is also very necessary as it allows the xylem vessels in the plants to pull up water from the roots to the leaves.
Water is a good solvent, although it cannot dissolve the molecules that aren’t also polar or ionic, such as glass pieces, permanent ink, etc. For example, ionic substances such as sodium chloride are made up of positively and negatively charged ions. Although these ionic attractions require a large amount of energy to break, it becomes much easier when put together with water molecules. Oxygen atoms (negatively charged) in the water molecules will cluster around the positive sodium ions Na+ and hydrogen atoms (positively charged) will cluster around the negative chloride ions Cl-, causing the attraction between the Na+ and Cl- ions to be weakened and separated. This is how the water molecules act as a solvent. Many non-polar substances are made soluble in water by use of detergents and soaps, both of which are large molecules with a polar end and a non-polar end. The polar end is attracted to the polar water molecule, whereas the non-polar part is attracted to the non-polar greasy dirt. Covalently bonded molecules such as glucose and sucrose can be dissolved in water as well, because the polar hydroxyl groups (-OH) in its structure forms hydrogen bonds with the water separating the molecules from each other.
Water's properties as a solvent, cohesive and adhesive property are vital to life as most biochemical reactions such as respiration, blood plasma, and transpiration stream in xylem. Water as a solvent is also why cell cytoplasm contains about 90% water. The adhesive quality of water is related with capillary action, which can be seen in the experiment of placing a straw into a glass of water. When we place a straw into a glass of water, the water 'climbs' up the straw. What is happening is that the water molecules are attracted to the straw molecules. When one water molecule moves closer to the straw molecules the other water molecules (which are cohesively attracted to that water molecule) also move up into the straw. Capillary action is limited by gravity and the size of the straw. The thinner the straw or tube the higher up capillary action will pull the water. Plants take advantage of capillary action to pull water from into them, so that they can be able to use water and support themselves. Transpiration is the evaporation of water into the atmosphere from the leaves and stems of plants. They can deliver nutrients to their leaves by transpiration stream, and at last the water is evaporated through stomata and the evaporation can cool down the plant as well. The capillary action also works for the water to move through the tiny blood vessels in our bodies as well.
When water freezes it’s density increases and the hydrogen bonding gets to take on a more latticed formation as ice. Water is at its maximum density at 4°C (39F), and at this temperature ice layers start to float on the surface of water, insulating the water below such as ponds and lakes. Water also works as a natural insulator for itself; therefore the aquatic life under the water can be continued.
Homeostasis in our body happens due to water since it also has many thermal properties as a temperature stabiliser. Water has a high specific heat capity, meaning that it takes quite a lot of thermal energy to raise the temperature of water (it takes 4.2 J to raise 1g of water by 1°C. An important fact is, once warm it cools slowly, which is essential to life where internal body temperature must be kept at a constant degrees. Water is not only used to maintain warmth but also necessary to cool the body. Because hydrogen bonding is reasonably strong, it takes 2Kj of energy to break the large number of bonds and turn 1g of water to vapour. Because water takes up much thermal evergy for evaporation, animals including humans use this property by using excess body heat to evaporate water from skin surfaces so that excess body heat energy will be transferred into the environment with only a small amount of water used. This includes such as what we call sweating and panting. Water also has a high latent heat of fusion from solid to liquid. Because water requires 300J per 1g of ice to melt into form water, water stays liquid. This is essential for the cells because cytoplasm is made of a high percentage of water as I have mentioned before, and once a cell is frozen it will be seriously damaged. The freezing point of water is also lowered by chemical solute. It is contained in cytoplasm to keep water not to be frozen; therefore the cells are protected until the temperature gets extremely cold.
As water has a high specific heat capacity, large volumes of water do not fluctuate greatly in temperature. You might have learnt in geography lesson that more heat energy needed to raise or cool the temperature of water or sea. This is why aquatic environment is slow to change temperature and bulky organisms have stable temperatures. Reasonably stable temperature allows the organisms under the water to be survived in deep water, and great aquatic environment change is less likely to happen because of the heat capacity of water. Also, it is a reason why it is cooler on summer and warmer on winter in the areas that are near to the sea.
Water is vital for hydrolysis in animal and plants, because water splits up molecules. The use of water allows them to utilize stored long-chain foods, which need to be broken smaller. Respiration, and photosynthesis requires the use of water as well. Firstly, respiration produces water as a by-product. A large amount of energy is produced by oxidising hydrogen, which contains so much energy it is an explosive gas, into water. Photosynthesis uses water, because hydrogen atoms are needed to produce glucose. Glucose is then stored as starch in the plant cells for later use, or used for respiration as well. We need to be aware that photosynthesis required water, and produces oxygen which is also vital for animal’s lives.
Without water these to most important reactions for life would not have occurred at all and life would not be able to evolve or continue on earth. An important property of water is also it's transparency, it allows sunlight to pass through it so aquatic plants can photosynthesis and on a larger scale, very importantly it allowed life on earth to begin, since life started in the oceans with small organisms which relied on sunlight for the reaction photosynthesis to take place! Water is also vital for creatures such as jellyfish, slugs and worms because these creatures have no skeletal system and water is necessary to provide support for their body. The human brain is composed of 70% water, as is skin, blood is 82% water, and the lungs are nearly 90%t water. Such Animals, and especially plants also need water to fill their plant cells to become turgid, so that they can support themselves.
The substance called water seemed to be so much simple and ordinary, however, writing this essay helped me to realize interesting property and qualities of water. Because of the hydrogen bonding, water is a good solvent, adhesive and cohesive. Water as a solvent allows from transport and transpiration system of animals and plants, to useful inventions such as soaps. Water works as an insulator because when it freezes the ice layers float on the water insulating the water below, with less change in temperature caused by heat capacity to make suitable aquatic environment. It also helps our body to maintain constant temperature because it has properties as a temperature stabiliser. Cohesive and adhesive property of water is vital for the transpiration stream and blood plasma to travel through the xylem and phloem vessels and blood vessels as well to transport water and nutrients. Finally, Photosynthesis and Respiration requires the use of water, because of its unique physical and chemical properties. In conclusion, water is the most important and unique substance on the earth since it has very wide range of biological, chemical, and physical properties that are vital for every life beings to live and continue. Without the presence of water, a single cell would not have survived and the life would not take place on this planet.
