As water molecules move around in liquid form they constantly make and break hydrogen bonds
Hydrogen bonds make it more difficult for water molecules to escape to become a gas
This makes water a liquid at room temperature, with a much higher boiling point than expected
Because of this, water can:
provide habitats for living things
form a major component of tissues
provide a reaction medium for chemical reactions
provide an effective transport system due to low viscosity
1 of 7
Density
The density of water provides an ideal habitat for living things
Water becomes more dense as it gets colder until about 4 C
From 4 C to freezing, because of its polar nature, the molecules align themselves in a particular structure
This makes ice less dense than water
Because of this:
aquatic organisms have a stable environment
bodies of water are insulated by ice at the top
2 of 7
Solvent
Water is a good solvent for many substances found in living things
These include ionic solutes (salts) or colavent solutes (glucose)
Because water is polar its positive and negative parts are attracted to the positive and negative parts of the solutes
Because of this, water:
forms a major part of tissues (70% of the cytoplasm)
provides a reaction medium, including in the cytoplasm of cells
provides an effective transport system as minerals and ions can be transported around while dissolved
3 of 7
Cohesion and surface tension
The surface of water contracts because the hydrogen bonds make the surface molecules more attracted to the molecules beneath than the air molecules above, demonstrating cohesion
This allows water surface to resist force applied to it, known as surface tension
Because of this:
water can be but transported, such as up xylem tissue
small insects can walk on water, e.g. pond-skaters
4 of 7
High specific heat capacity
The specific heat capacity of a substance is the amount of energy (kJ) needed to raise the temperature of 1kg by 1 C
Water's is relatively high, 4.2 kJ
This means water doesn't heat up or cool down easily
Because of this:
living things have a stable internal environment
aquatic environments are stable
5 of 7
High latent heat of vaporisation
Large amounts of energy are needed for water to evaporate
This is because hydrogen bonds hold the molecules together
Because of this, water can:
cool living things, e.g. through sweat, keeping temperature stable
form a stable environment
6 of 7
Reactant
Water is an important reactant
For example:
photosynthesis
hydrolysis reactions - digestion
Its properties as a reactant don't directly draw on its polarity
Comments
No comments have yet been made