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WATER: its special features and its importance to living organisms

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Introduction

WATER: its special features and its importance to living organisms Water, covering up to 65 percent of the Earth's surface, is the world's largest habitat for animals. Living organisms contain from 60 to 95 percent of water within them. It plays an enormous role in our survival, due to the certain special properties it has. THE STRUCTURE Water is made up of three atoms put together, one oxygen atom and two hydrogen atoms. They are joined together by a covalent bond, a bond where the electrons on the outer shell of two non-metals are shared. All molecules desire a full outer shell, as it gives them stability. The first shell has a maximum of two electrons orbiting it; the second shell and onwards have a maximum of eight electrons. Molecules are able to attain a full outer shell by either losing or gaining electrons. An oxygen atom has eight electrons. This means that the first two electrons orbit the first shell. As the first shell can contain a maximum of two electrons, the remaining six electrons then orbit the second shell. A hydrogen atom only has one electron on its first shell, therefore it only needs to gain one more electron for its outer shell to become full. ...read more.

Middle

The attractive forces mean that a body of water is kept inwards from spreading out, producing a skin on the surface, termed surface tension. Pond skaters distribute their weight across a large area, thus are able to skate on top of the surface layer without the skin breaking. Cohesion is important, because without surface tension, these insects would drown. Adhesion Adhesion differs to cohesion, as it includes the attraction between water as well as other polar molecules. Like cohesion, adhesion is due to water's polarity and the fact that hydrogen bonds connect two polar molecules. This adhesive quality makes water an excellent solvent. We can relate this property to living organisms, because water can then dissolve salts and sugars. Water is able to dissolve any polar substance (whether fully or partially charged) because they surround ions with a hydration shell. In the example of common table salt (sodium chloride), the two ions are separated in water. The sodium, having lost an electron, becomes a cation (positively charged). As a rule, oppositely charged substances attract, and therefore the positive sodium is attracted to the slightly negative oxygen atom of water, and chlorine (the negative anion) is attracted to the slightly positive hydrogen atoms. This means that each ion is then surrounded by water molecules, known as a hydration shell, and it is said to have been dissolved. ...read more.

Conclusion

and a medium for life (e.g. the sheer pressure from the weight of whales is taken off from their fragile organs in the weightless world of water). Freezing I explained earlier that ice is less dense than water, because the water molecules have to spread out before freezing to make room for each to have four hydrogen bonds. This results in ice floating in water. This is important for two reasons. The first is that living organisms living in aquatic environments do not freeze during the winter. The ice forms a cover layer atop a body of water, insulating the water beneath, so that it does not freeze up completely. The temperature underneath the ice is sufficient for some creatures adapted to live in cold temperatures. The second reason of importance is that it allows animals that do not dwell completely in the sea (i.e. polar bears, penguins, walruses, etc.) with a safe, floating area between vast stretches of water. If not for some of these icebergs, even these water-loving animals can drown from exhaustion. In conclusion, water is given far less appreciation than it truly deserves. It is essential for all living organisms as a main constituent for photosynthesis and respiration. Its special properties, uncommon in many other molecules, enable our very survival. 25 September 2002 Nicole Lai 12.4 - 1 - ...read more.

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