Watery World
Water, water, everywhere,
Nor any drop to drink.
As said by Samuel Coleridge in "The Rhyme of the Ancient Mariner" water is everywhere. Our planet's name - Earth - cannot be taken for face value because in reality the "Earth" is covered by more than 70% water. To be exact there is approximately 326 million cubic miles of water on Earth. In order to appreciate and envisage such an enormous amount you have to put it into perspective. Out of all the water on Earth, only 0.3% of it is usable by humans. The other 99.7% is unusable in oceans, seas, ice and the atmosphere. And even out of that 0.3%, most of it is out of our reach.
But what is water? Water is a substance whose molecule is made from two 1hydrogen atoms and one 16oxygen atom (H20) and that is in a liquid state at room temperature. It boils at 100ºC and melts at 0ºC. Water is probably the fundamental reason for sustenance of life on Earth. Every living thing depends on it to survive which is why water is so important. As well as being essential to life, water also has many other uses. Some of these include being a very good solvent, for washing or even as habitats and environments. Water's abundance and requirements towards life already make it special but there are even more properties of water as a result of the hydrogen bonds between water molecules that make water an ideal constituent of living things.
The structure of water molecules is unique. The two hydrogen atoms that are bonded to the oxygen atom are 105º apart and all three atoms carry slight charges. The oxygen atom has a ???charge and the hydrogen atoms both carry a ?+ charge. The significance of this is that it makes water molecules dipolar. This affects the bonding between molecules because the charges cause one hydrogen atom to attract to the oxygen in another molecule. This produces hydrogen bonding through attraction. Although individual bonds are weak, collectively they form important forces that hold water molecules together. This makes water a much more stable substance than would otherwise be the case.
Due to the hydrogen bonding and the increased strength of attraction, more energy is required to separate water molecules from each other. Water has an unusually high specific heat capacity (SHC). The SHC of a substance is the amount of energy required to raise the temperature of one gram of the substance by 1 Kelvin. In the case of water, its SHC is 4.2 J g-1 k-1. Therefore it requires more heat than expected to convert liquid water into vapour. Water is heated and cooled more slowly than expected so in effect it buffers sharp temperature changes. This ability aids life because it assists in keeping the body temperature constant. Homeostasis is the maintenance of a constant internal environment so water helps the homeostasis of body temperature. A normal human body temperature is 37ºC and so the water in the body will be at that temperature too. Therefore if the living environment changes to either extreme, hot or cold, then the water will take longer to adapt from the body temperature to the temperature of the environment. So this provides a better resistance to fluctuations in environments and increases length of survival. A similar principal is evident in other mammals too. For example in the arctic, home of polar bears, when the atmospheric temperature drops then the bears can move into the water. This may seem strange since the water is freezing cold anyway but it would be warmer than the temperature outside and would stay constant because there is such a great mass of water there.
Water, water, everywhere,
Nor any drop to drink.
As said by Samuel Coleridge in "The Rhyme of the Ancient Mariner" water is everywhere. Our planet's name - Earth - cannot be taken for face value because in reality the "Earth" is covered by more than 70% water. To be exact there is approximately 326 million cubic miles of water on Earth. In order to appreciate and envisage such an enormous amount you have to put it into perspective. Out of all the water on Earth, only 0.3% of it is usable by humans. The other 99.7% is unusable in oceans, seas, ice and the atmosphere. And even out of that 0.3%, most of it is out of our reach.
But what is water? Water is a substance whose molecule is made from two 1hydrogen atoms and one 16oxygen atom (H20) and that is in a liquid state at room temperature. It boils at 100ºC and melts at 0ºC. Water is probably the fundamental reason for sustenance of life on Earth. Every living thing depends on it to survive which is why water is so important. As well as being essential to life, water also has many other uses. Some of these include being a very good solvent, for washing or even as habitats and environments. Water's abundance and requirements towards life already make it special but there are even more properties of water as a result of the hydrogen bonds between water molecules that make water an ideal constituent of living things.
The structure of water molecules is unique. The two hydrogen atoms that are bonded to the oxygen atom are 105º apart and all three atoms carry slight charges. The oxygen atom has a ???charge and the hydrogen atoms both carry a ?+ charge. The significance of this is that it makes water molecules dipolar. This affects the bonding between molecules because the charges cause one hydrogen atom to attract to the oxygen in another molecule. This produces hydrogen bonding through attraction. Although individual bonds are weak, collectively they form important forces that hold water molecules together. This makes water a much more stable substance than would otherwise be the case.
Due to the hydrogen bonding and the increased strength of attraction, more energy is required to separate water molecules from each other. Water has an unusually high specific heat capacity (SHC). The SHC of a substance is the amount of energy required to raise the temperature of one gram of the substance by 1 Kelvin. In the case of water, its SHC is 4.2 J g-1 k-1. Therefore it requires more heat than expected to convert liquid water into vapour. Water is heated and cooled more slowly than expected so in effect it buffers sharp temperature changes. This ability aids life because it assists in keeping the body temperature constant. Homeostasis is the maintenance of a constant internal environment so water helps the homeostasis of body temperature. A normal human body temperature is 37ºC and so the water in the body will be at that temperature too. Therefore if the living environment changes to either extreme, hot or cold, then the water will take longer to adapt from the body temperature to the temperature of the environment. So this provides a better resistance to fluctuations in environments and increases length of survival. A similar principal is evident in other mammals too. For example in the arctic, home of polar bears, when the atmospheric temperature drops then the bears can move into the water. This may seem strange since the water is freezing cold anyway but it would be warmer than the temperature outside and would stay constant because there is such a great mass of water there.
