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Properties of Water

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Water Water is by far the most abundant component of organisms. Like all living organisms, humans depend on water and it makes up 60-70% of the human body, or about 40 litres, of which 25 litres are inside the cells and 15 litres outside (12 litres in tissue fluid, and 3 litres in blood plasma). A loss of 4 litres may cause hallucinations; a loss of 8-10 litres may cause death. About 1.5 litres a day are lost through breathing, sweating, and in faeces, and the additional amount lost in urine is the amount needed to keep the balance between input and output. In temperate climates, people cannot survive more than five or six days without water; this is reduced to two or three days in a hot environment. Often overlooked by many as the most important substance the body needs, water is involved in every aspect of maintaining the human body from forming nucleic acids in it to transporting various substances around it. The root of these special characteristics lies in the properties of water itself. The Properties of Water This liquid is such a good solvent that almost anything will dissolve into it and it is therefore known as the universal solvent. Its properties as a solvent depend on the fact that it is a polar molecule. ...read more.


If the human body needs to cool, water is itself lost as sweat. When the water in the sweat evaporates, it cools the skin. Water molecules are attracted to other water molecules. This is because the oxygen end of water has a negative charge and the hydrogen end has a positive charge. The hydrogen atoms of one water molecule are attracted to the oxygen from other water molecules. This attractive force (also known as hydrogen bonding) is what gives water its cohesive properties. These cohesive properties also give water the ability to travel through vessels and to the top of tree trunks. If these forces were weaker, then trees would not grow to be as tall as they are. Because of the cohesion, water also has the highest surface tension of any liquid except mercury. Sometimes insects walk on water - it is because of surface tension. Hydrogen bonds are holding the molecules of water together, forming a surface "skin" that an insect can walk on (if it spreads its weight out over the surface). Surface tension is responsible for water sticking together in small drops. As a water droplet falls, it stays together until it hits the surface. This is because the hydrogen bonding is keeping water together until it becomes a certain size at which point gravity overcomes the attractive forces between the molecules and the droplet 'splits' apart. ...read more.


The kidneys help to maintain the balance with ultrafiltration, where any excess of substances, including water, are removed from the body. In the nephrons, inside the kidney, a high pressure is built up which squeezes water, urea, ions and sugars out of the blood and into the bowman's capsule. As the substances flow along the nephrons, useful quantities are reabsorbed back into the blood. At this point, most of the water will be reabsorbed but there will be a little excess left over which will come out of the nephron, into the ureter and down to the bladder as urine. During this process, the water will also act as a transporting agent for the urea and the other waste products. Another important reaction which involves water is respiration. The aim of respiration is to provide energy for the body to use. In this instance, the glucose is oxidised to produce energy, as well as carbon dioxide and water. Because of the aim of this process, water can be labelled a by-product or a useless product but it is actually very important that water can be produced. If water was not available, then it is possible that oxygen gas would be produced which would instantly kill humans (because the body would think that the person has cut themselves, which is why there will be oxygen gas, and the body would form a scab along all blood vessels, stopping all the processes of life). ...read more.

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Here's what a teacher thought of this essay

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This essay starts well with some clear explanation, but is rather confused in places, and towards the end contains lots of information that isn't really relevant.

To improve it needs to:

- Discuss the density of ice relative to liquid water
- Discuss some biological reactions that actually need water (e.g. hydrolysis)
- Discuss water's role in transport.

Marked by teacher Rebecca Lewis 24/09/2012

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