Biochemistry

Water is a chemical substance with the chemical formula H2O. Its molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state, water vapor or steam.

Water covers 70.9% of the Earth's surface,[1] and is vital for all known forms of life.[2] On Earth, it is found mostly in oceans and other large water bodies, with 1.6% of water below ground in aquifers and 0.001% in the air as vapor, clouds (formed of solid and liquid water particles suspended in air), and precipitation.[3]Oceans hold 97% of surface water, glaciers and polar ice caps 2.4%, and other land surface water such as rivers, lakes and ponds 0.6%. A very small amount of the Earth's water is contained within biological bodies and manufactured products.

Water on Earth moves continually through a cycle of evaporation or transpiration (evapotranspiration),precipitation, and runoff, usually reaching the sea. Over land, evaporation and transpiration contribute to the precipitation over land.

Clean drinking water is essential to human and other lifeforms. Access to safe drinking water has improved steadily and substantially over the last decades in almost every part of the world.[4][5] There is a clear correlation between access to safe water and GDPper capita.[6] However, some observers have estimated that by 2025 more than half of the world population will be facing water-based vulnerability.[7] A recent report (November 2009) suggests that by 2030, in some developing regions of the world, water demand will exceed supply by 50%.[8] Water plays an important role in theworld economy, as it functions as a solvent for a wide variety of chemical substances and facilitates industrial cooling and transportation. Approximately 70% offreshwater is consumed by agriculture.[9]

Water is a polar molecule (this means that the distribution of charges through the molecule isn't even). The hydrogen atoms have partially positive charges (δ +) and the oxygen atoms have partially negative charges (δ -). These charges form very strong bonds between molecules of water (Hydrogen - oxygen) called hydrogen bonds. A covalent bond is formed between the oxygen (group 6) and two hydrogen atoms (group 1).

Property:

Reason/ explanation:

Application:

High specific heat capacity

Specific heat capacity is the amount of energy that it takes to raise the temperature of 1kg of a substance by 1 degree. Temperature relates to the amount of kinetic energy that the molecules within a substance have. As there are very strong hydrogen bonds between the water molecules, it takes a lot of energy to break them. As a result of these strong hydrogen bonds, more of the energy goes into breaking them rather than raising the temperature of the water. Therefore the amount of energy needed to raise the temperature of 1kg of water by 1 degree is relatively high so it has a high specific heat capacity.

The high specific heat capacity is why water has a high boiling point and is a water at room temperature.

Water in our bodies works as a temperature buffer. This means that it keeps our bodies as close to 37 degrees most of the time. This is because if, for example the temperature of the surrounding environment increases or the rate of respiration rises à exercise, then the temperature of our bodies does not increase. (There is a high percentage of water in our bodies). A constant body temperature is important for homeostasis to stop our enzymes from denaturing.

Latent heat of evaporation

In a body of water, some molecules are moving faster than others because they have more kinetic energy. Some of these molecules have enough kinetic energy to leave the body of water. As this water leaves the body of water it takes a lot of the energy from the total body of water with it (as they are taking kinetic energy with them and therefore the temperature of the body of water falls).

This is why water evaporates in the sun after it has rained even though the water isn't boiling.

This process is important in bodies of animals because the evaporation of sweat helps to cool down the body.

It is also has effect on the leaves in plants as it removes water from leaves.

Strong Cohesion

Cohesion Is when molecules attract to each other (because of the partial charges of the hydrogen and oxygen atoms). In a body of water, all of the molecules are attracted to each other, however, the uppermost molecules only have forces from beneath. Therefore, the uppermost molecules are pulled further down and closer together (laterally).

This creates surface tension on a large body of water.

These strong attractions are important in the xylem as it allows water to flow in a continuous stream so the water can be taken up from root to leaf.

Important solvent.

As water is a polar molecule, it is therefore an important solvent. This is because the partially positive and negative charges attract atoms in other molecules causing them to separate and therefore dissolve. à When substances are dissolved in water they are free to move around and react with other molecules.

Metabolic processes (i.e. respiration or photosynthesis) which are essential for any life can only happen when reactants are dissolved in water. For example the movement of Oxygen into our blood.

Density

When water freezes it turns to ice, which is less dense than when it is a liquid. This is because the hydrogen bonds formed are slightly further apart (due to the polarity) than that distance in water. This produces a giant, rigid open structure where every oxygen atom is at the centre of a tetrahedral arrangement (surrounded by hydrogen atoms).

The lower density as a solid is why ice floats on water and doesn't sink.

Adhesion

The cohesive forces of water are related to the property of strong adhesion. Adhesion is the attraction between water molecules and other molecules - these forces can sometimes be stronger than cohesion.

When water is within charged surfaces, for example the type that are found on the inside of a capillary tube, the water 'climbs' up the tube. This is because the water molecules are attracted to the charges on the insides of the capillary walls more than they are to each other.

The buffer is the medium through which the current flows. In the electrophoresis chamber, the anode and cathode are separated and the gel is placed between them. In order to close the circuit and generate the voltage which causes the migration, the entire chamber is filled with a conductive buffer. It is actually possible to perform electrophoresis without a buffer; however this requires a specially made electrophoresis chamber. In these chambers the electrodes actually contact the top and bottom of the gel eliminating the need for a conductive buffer to close the circuit.

SDS PAGE electrophoresis uses buffer not primarily as a conductor but for holding a desired pH, dissipating heat and providing SDS in excess in the case of denaturing gels. A gel would run without a buffer as the gel itself is a conductor but the currents involved would heat it to the point of decomposition. Also the volume of liquid in a gel does not allow for an adequate pH buffering system. Holding a pH is extremely important for reproducibility especially in native gels as the pH can change the charge on the peptide. It is true some gels do not require buffer but these are rare cases like isoelectric focusing.
the primary application of the buffer would be to conduct electricity,to form a closed circuit

White light form the sun is made up of :-

Red, Orange, Yellow, Green, Blue, Indigo and Violet colored light (as you see in a rainbow)

When this white light hits a leaf, all the colors exceptGreen are absorbed by the pigments in the leaf. The Green light is not absorbed and this is reflected to your eyes so that leaves appear green.