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Explain The Significance To Organisms of Water As a Transport Medium and Habitat, In Terms Of Its Properties

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Introduction

Essay 2.1.6. : Explain The Significance To Organisms of Water As a Transport Medium and Habitat, In Terms Of Its Properties Water is essential to life, without water life on Earth would not exist. Water is a major component of cells, typically forming between 70 and 95% of the mass of the cell. This means that we are made from approximately 80% of water by mass and some soft bodied creatures such as jellyfish are made up from up to 96% water. Water also provides an environment for organisms to live in, since 75% of the Earth is covered in water. Water is a simple molecule, which is made up of two hydrogen atoms and one oxygen atom, forming H2O. Each hydrogen shares and electron pair with the oxygen to form a covalent bond between hydrogen and oxygen. The oxygen has two unshared electron pairs not involved in bonding. Though, these lone pairs cause two O-H bonds to be at an angle rather than in a straight line, at the angle of 104.5o.The sharing of electrons between the two atoms are uneven; the large number of protons in the oxygen nucleus have a stronger attraction for these shared electrons than the comparatively tiny hydrogen nuclei. This pulls the electrons slightly close to the oxygen nucleus and away from the hydrogen so that the oxygen develops a slight negative charge and the hydrogen's a slight positive charge. ...read more.

Middle

In plants, the most commonly transported substance is sucrose, which is also soluble in water, along the phloem; or in the xylem where water dilates the mineral salts such as nitrates (for growth) and transports them from the roots to the leaves. As well as this water also plays a key role in the metabolic breakdown of such essential molecules as proteins and carbohydrates, called hydrolysis where the molecules are split up. This is essential to animals and plants because it allows them to utilise stored foods that are in long chains by breaking off smaller molecules. Respiration produces water as a by-product, since 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 as a source of hydrogen atoms, which are needed to produce glucose, which is then stored in the plant cells as starch or used for respiration. With out water these two essential reactions would not occur and life would not be able to continue. An important property of water is also its transparency, it allows sunlight to pass through it so aquatic plants can photosynthesise; as well as this it is the main reason life on earth began since life began with organisms which relied on sunlight for photosynthesis. Water has many thermal properties as a temperature stabiliser. Water has a boiling point of 100oC and a melting point at 0oC, this is unusual for a molecule of it's size with ...read more.

Conclusion

The freezing point of water is also decreased by solutes by disrupting the hydrogen bonds. In the cytoplasm, there are many solutes and so the water freezes at a temperature below 0 oC. As water cools, its density increases, though ice floats on water since water is at its most dense at 4 oC which is when its bonds are closes together. When water freezes the lattice arrangement of its structure move apart slightly and it floats on the surface. This allows aquatic life to continue since the layer of ice insulates the water below which stays at 4 oC. Water molecules are highly cohesive because of the hydrogen bonds between the molecules. The cohesive property of water allows plants to pull up water through xylem vessels from the roots to the leaves called the transpiration stream. This also causes the water molecules when they come into contact with air will be held tightly together and the water molecules below them, forming an elastic film known as surface tension. Organisms such as water skaters can move across the surface of the water since they have hydrophobic feet, and a small body mass spread over a large surface area. The surface tension of the water also provides support for plants such as water lilies that rely on water to keep them afloat. Water also has strong hydrostatic forces making it incompressible. This provides support for soft bodied creature such as worms, slugs and jelly fish which therefore due not require a supporting skeletal system also allowing plants to support themselves. ...read more.

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