Basic chemistry of a cell Properties of water – – – Life on Earth began in water and evolved there for 3 billion years before spreading onto land. Modern life, even terrestrial life, remains tied to water. All living organisms require water more than any other substance. Human beings for example, can survive for quite for a few weeks without food, but only a week or so without water.
Water is deceptively simple. It is shaped something like a wide V, with its two hydrogen atoms joined to the oxygen atom by single covalent bond. Because oxygen is more electronegative than hydrogen, the electrons of the covalent bonds spend more time closer to oxygen than to hydrogen; in other words, they are polar covalent bonds. The uneven distribution of electrons of water molecules makes it an universal solvent.
In overall, water has four emergent properties: Cohesion 1. Water molecules stay close each other as a result of hydrogen bonding. 2. Although the arrangement of molecules in a sample of liquid water is constantly changing, at any given moment many of the molecules are linked by multiple hydrogen bonds. 3. These linkages make water more structured than most other liquid. 4. Collectively, the hydrogen bonds hold the substance together, a phenomenon called cohesion. 5. Cohesion means the hydrogen bonding between the water molecules that can form a continuous water column against the gravity without breaking. 6. Besides cohesion, water molecules can also perform adhesion between water molecules and cell walls by hydrogen bonds. 7. Both cohesion and adhesion are important in the transport of water in plants.
8. Related to cohesion is surface tension, a measure of how difficult it is to stretch or break the surface of a liquid. 9. At interface of water and air is an ordered arrangement of water molecules, hydrogen-bonded to one another and to the water below. 10. This makes the water behave as though coated with an invisible film. 11. You can observe the surface tension of water by slightly overfilling a drinking glass; the water will stand above the rim. 12. In a more biological example, some animals can stand, walk or run on water without breaking the surface.
Moderation of temperature 1. The ability of water to stabilize temperature stems from its relatively high specific heat capacity. 2. The specific heat capacity of water is 4200 JoC-1kg-1 which means 4200 J of heat energy is required to raise the temperature of 1 kg of water by 1oC . 3. Therefore, water acts as a thermal buffer. 4. The heat of vaporization of water is also high. The high amount of energy required to vaporize water has a wide range of effects. 5. On a global scale, for example, it helps moderate Earth’s climate. 6. On organismal level, water plays an important role in homeostasis. 7. Water acts like a cooling agent. When body temperature deviates from normal range, sweat is produced to cool the body down. The heat energy produced by body can be eliminated by the evaporation of water (sweat) from the surface of skin. Insulation of bodies of water by floating ice 1. Water is one of the few substances that are less dense as a solid than as a liquid. In other word, ice floats in liquid water. 2. At 4oC, the density of water is the greatest. Below this point, water begins to expand and cause the density of water to become lower. 3. A layer of ice on the surface of seas, lakes and ponds during winter prevents the whole volume of water to freeze. Thus, the aquatic organisms can still survive from the insulation of the floating ice.
The solvent of life 1. Water is a versatile solvent which can dissolve many solutes. 2. Therefore, water is a good medium for most of the biochemical reactions. 3. Water can act as a lubricant. Mucus, synovial fluid, pericardial fluid are the examples of lubricants composed mainly of water. 4. Water is a good medium for transport and removal of substances and wastes. 5. Some animals also depend on water to support...
Please join StudyMode to read the full document