Physical and chemical properties of water important for life
Water is a vital inorganic molecule
Life could not exist on this planet without water. It is important due to following two reasons
Physical and chemical properties of water molecule provide the ability to render its vitality.
Water molecule is a small, bipolar and angular molecule (104.5°)
Polarity is an uneven charge distribution within a molecule. Hence in water molecule one pole is slightly positive and the other end is slightly negative. This condition is known as dipole. Due to this dipolarity water molecules have weak attraction for each other. This weak attractions are known as hydrogen bonds.
Main functions of water
Other functions of water
| Property | Role | Example |
| Liquid at room temperature | Medium of protoplasm | · Major component in protoplasm is H2O |
| Polarity | Powerful solvent | · Most of the materials of a cell are dissolved in protoplasm & cell sap
· Metabolic reactions take place in an aqueous medium in a cell |
| Chemical property | Reactant in some biochemical processes | · Photosynthesis
6CO2+6H2O → C6H12O6 + 6O2 · Hydrolysis Starch + H2O → Maltose |
| High adhesive and cohesive forces. | Maintenance of turgor in cells | · Cell enlargement
· mechanical support in herbaceous plants · Turgor movements · Movement of guard cells · Blooming of flowers |
| Transport and absorption of materials in organisms | · Translocation and ascent of sap
· Absorption of water and minerals from soil solution. |
|
| High surface tension | Provides habitats for some aquatic insects | · Water skaters |
| High specific heat capacity | Water resists to change its temperature when a considerable amount of heat is absorbed or lost | · Maintain the body temperature of poikilotherms within a narrow range |
| High latent heat of vaporization | Cooling the body surfaces | · Sweating
· Transpiration |
| High latent heat of fusion | A lot of heat should be dissipated for water bodies to freeze | · Water will not freeze easily within the cells and in water bodies. |
| Anomalous expansion of volume on freezing | Water bodies will not freeze solid. Ice forms on top and liquid water remains at the bottom | · Aquatic organisms are capable of surviving during winter. |
| Transparency | Allowing penetration of light | · Allows to grow aquatic plants and algae in a considerable depth in water bodies. |
Importance of water for life
Due to cohesion between water molecules, water and dissolved substances such as minerals and nutrients transport through vascular tissues, xylem and phloem against gravity
Due to adhesion between water molecules and cell walls also helps in conduction of water and dissolved substances
Due to the high specific heat, water will function as thermal buffer in living system and aquatic bodies during the temperature fluctuations on earth
Due to the high heat of vaporization, with the minimum loss of water an organism can loss much heat energy. Therefore body surface of an organism maintained as cool surface
Eg- evaporation of sweat from human skin keeps the body temperature at the constant level. Prevent from over heating
Transpiration in plants keeps the plant body surface and prevent from becoming too warm in the sunlight
Water can stretch maximum within a small area. This ability is given to water molecules, due to cohesion between the water molecules. Therefore in an aquatic system, upper surface water molecules are attracted by lower surface molecules and forms a water film. Small insects eg. Water skaters can walk on the surface of a pond.
Generally increase of the temperature of any substances reduces its density and decrease of the temperature of any substances increases its density. But for water when the temperature falls below 4°C it begins to freeze and forms a crystalline lattice called an ice cubes which increases the valence of few molecules of water and decreases its density. Therefore water has the maximum density at 4°C. Ice floats on the surface of water bodies. It is important in Polar Regions, organisms in the aquatic water bodies can survive during the winter.
This ability is given to water due to its polarity. Any polar molecules can dissolve in water because water molecules surround each of the solute molecules and form hydrogen bond with them. Solubility depends on the polarity. No need to be ionic to dissolve.
In some biochemical processes water is used as a reactant
In these reactions, water molecules act as hydrogen donors.
carbohydrates proteins,lipids and nucleic acids notes?