Biology/Water term paper 12303

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Water is the most important substance in our evolution and our daily lives. Without water,

life as we know it would not have been possible. This essay will examine the water molecule

in order to ascertain how it brought about Earth's thriving ecosystem and how important it

is to us today.

Each water molecule consists of one oxygen atom and two hydrogen atoms. The oxygen atom (or the apex of the water molecule) bears a slight electronegative charge while hydrogen

possesses a more positive one. Because opposite charges attract, the water molecules are drawn together. When an oxygen atom is linked to a neighboring molecule's hydrogen atom, a bond called a hydrogen bond is formed. In an ice crystal the hydrogen bonds to give the shape of the crystal so that the grid of molecules surrounds relatively to large spaces. In a liquid form, water has no such spaces; so ice is less dense and will float on liquid water. If not for this, great bodies

of water would freeze from the bottom up without the insulation of a top layer of ice and

all life in the water would die.

The water molecule is a very small one but because of its unique properties it behaves like

a larger one. The bonds between water molecules are so strong that water resists changes in

its state (Solid, liquid, gas); thus water has a higher melting point and a higher boiling

point than another molecule of similar size. If water followed the example of other

molecules its size it would have a boiling point of -75øC and a freezing point of -125øC4.

This would mean that, on Earth, water would be a gas all of the time and life would not be

possible.

When heat is applied to solid water, some hydrogen bonds get so much kinetic energy that

they break and the ice melts. Liquid water does not necessarily have all four hydrogen bonds

present at all times but it must retain some of them. All plant life on Earth benefits from the ability of water to make a hydrogen bond with another substance of similar electronegative charge. Cellulose, the substance that makes up cell walls and paper products, is a hydrophilic substance ("water-loving"). It interacts with water but, unlike other hydrophilic substances, it will not dissolve in it. Cellulose can form strong hydrogen bonds with water molecules. This explains why a paper towel will "wick" water upwards when it comes in with it. Each water molecule will make a hydrogen bond with cellulose and pull another water molecule up from down below and so on.

Without this feature, plants would find it more difficult to transport water up their stems to the leaves in order to make food through photosynthesis.

Water has a very high heat capacity. Most of the heat introduced to water is used not to set

water molecules in motion (giving them kinetic energy and causing their temperature to

rise), but to move hydrogen atoms around between neighboring oxygen atoms. If all of this

heat was used solely to warm the water, living cells would boil in their own heat. Every

action in a living cell releases some heat. If the heat was not dissipated by the water, all

living things would cook themselves.

In conclusion, it is apparent that water is the most important substance ever to have been

created because it is so vital to our race. Its weird properties aid all living things to

survive in the scheme of nature on our planet Earth.

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