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Color coded: Biochemistry of Water

Water is a Polar molecule

  • Because of the high electronegativity of oxygen and the low electronegativity of hydrogen, the oxygen end has a slight negative charge (-), while the hydrogen has a slight positive charge (+).

  • The water molecule’s shape is said to be “bent.”

  • This shape means that one side of the molecule “the hydrogen side” is positive, while the other side “the oxygen side” is negative.

  • The polar water molecules form hydrogen bonds with each other.

  • These bonds affect many of the biologically important properties of water.

Important Properties of Water for Biology

Water has a high specific heat.

Specific heat:The amount of heat needed to change the temperature of 1 gram of a substance by 1 degree.

  • Water’s specific heat is very high due to the hydrogen bonds that hold the water molecules together.

  • Due to its high specific heat, water is excellent for maintaining a constant internal body temperature.

Water is an excellent solvent.

Solvent:The substance dissolving the solute.

  • Water is often referred to as the “Universal Solvent”. This means that water is great for dissolving other materials (solutes).

  • Solutes:The substance being dissolved in the solvent.

  • Due to its polarity, water is best at dissolving salts and polar molecules.

Water has a high heat of vaporization.

Heat of vaporization:The amount of heat needed to convert a liquid to a gas.

  • Due to the many hydrogen bonds which hold water molecules together, the heat of vaporization is very high for water.

  • When the water does eventually evaporate, it carries heat away with it.

Water is cohesive and adhesive

Cohesion:A substance sticking to itself.

Adhesion:A substance sticking to another substance.

  • Due to its polarity, water molecules stick to each other (cohesion) and to other polar molecules (adhesion).

  • This property allows transpiration to move water from the ground, through the plant, and eventually out into the air.

  • Transpiration:The movement of water molecules throughout plants.

Water expands as it freezes

  • The volume of water beings to expand after it cools to temperatures below 4 degrees Celsius.

  • This causes ice to be less dense than liquid water; ice can float on water.

  • This happens because the HYDROGEN bonds force the chains of water molecules further apart as the molecules cool down and slow down; this increased volume causes a decrease in density.

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Color coded: Biochemistry of Water

Water is a Polar molecule

  • Because of the high electronegativity of oxygen and the low electronegativity of hydrogen, the oxygen end has a slight negative charge (-), while the hydrogen has a slight positive charge (+).

  • The water molecule’s shape is said to be “bent.”

  • This shape means that one side of the molecule “the hydrogen side” is positive, while the other side “the oxygen side” is negative.

  • The polar water molecules form hydrogen bonds with each other.

  • These bonds affect many of the biologically important properties of water.

Important Properties of Water for Biology

Water has a high specific heat.

Specific heat:The amount of heat needed to change the temperature of 1 gram of a substance by 1 degree.

  • Water’s specific heat is very high due to the hydrogen bonds that hold the water molecules together.

  • Due to its high specific heat, water is excellent for maintaining a constant internal body temperature.

Water is an excellent solvent.

Solvent:The substance dissolving the solute.

  • Water is often referred to as the “Universal Solvent”. This means that water is great for dissolving other materials (solutes).

  • Solutes:The substance being dissolved in the solvent.

  • Due to its polarity, water is best at dissolving salts and polar molecules.

Water has a high heat of vaporization.

Heat of vaporization:The amount of heat needed to convert a liquid to a gas.

  • Due to the many hydrogen bonds which hold water molecules together, the heat of vaporization is very high for water.

  • When the water does eventually evaporate, it carries heat away with it.

Water is cohesive and adhesive

Cohesion:A substance sticking to itself.

Adhesion:A substance sticking to another substance.

  • Due to its polarity, water molecules stick to each other (cohesion) and to other polar molecules (adhesion).

  • This property allows transpiration to move water from the ground, through the plant, and eventually out into the air.

  • Transpiration:The movement of water molecules throughout plants.

Water expands as it freezes

  • The volume of water beings to expand after it cools to temperatures below 4 degrees Celsius.

  • This causes ice to be less dense than liquid water; ice can float on water.

  • This happens because the HYDROGEN bonds force the chains of water molecules further apart as the molecules cool down and slow down; this increased volume causes a decrease in density.

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