3.1 Chemical elements and water

Most frequently occurring chemical elements
The most frequently occurring chemical elements in living things are carbon, hydrogen, oxygen, and nitrogen.

Other elements needed by living organisms

A variety of other elements are needed by living organisms including sulfur, calcium, phosphorus, iron and sodium.

Roles of the other elements

Sulfur - component of some amino acids.

Calcium - constituent of bones.

Phosphorous - component of nucleotides in DNA and RNA.

Iron - a role in oxygen transport in animal blood.

Sodium - a role in nerve impulses in animals.

Structure of water molecules (mrothery.co.uk)

Thermal, cohesive and solvent properties of water

Thermal Properties: Heat Capacity - large amounts of energy are needed to raise its temperature and break hydrogen bonds which means that water has a large heat capacity.

Thermal Properties: Boiling Point - the boiling point of water is high and in order to change it from liquid to gas, the hydrogen bonds must be broken.

Thermal Properties: Cooling Effect of Evaporation - water can evaporate at temperatures below boiling point, but hydrogen bonds must be broken; the heat energy needed to break the bonds is taken from the liquid water which cools it down.

Cohesion - water molecules are able to stick to each other due to hydrogen bonding.

Solvent - due to the polarity of water, many substances are able to dissolve in water; inorganic particles with + or - charges dissolve (ex Na ions), organic substances with polar molecules dissolve (ex glucose), enzymes.

Relationship between the properties of water and its uses in living organisms

Thermal Properties: Cooling Effect of Evaporation - evaporation of water from leaf of plant and human skin has cooling effect, therefore water acts as a coolant.

Thermal Properties: Boiling Point - water below boiling point almost everywhere on the earth, therefore water is a medium for metabolic reactions.

Thermal Properties: Heat Capacity - blood, mainly composed of water, can carry heat from warmer parts of body to cooler part, here, water acts as a transport medium.

Solvent - most chemical reactions in living organisms take place with all substances dissolved in water, it allows many substances to be carried dissolved in water, here, water is a transport medium.

Cohesion - strong pulling forces can be exerted to suck columns of water up to trees, water columns rarely break, here, water is used as a transport medium.