1. The Properties of Water

2. Water is a polarised molecule

3. Cohesion Hydrogen bonds link water molecules together;
Creates 'skin' on surface of water (surface tension)

4. Transparency Underwater plants can photosynthesise;
Hunters and hunted can see each other.

5. Solvent Property Principles:
Many substances can form hydrogen bonds with water and therefore dissolve eg sugars;
Other substances form ions in water and dissolve, e.g. sodium chloride (salt) forms sodium ions Na+ and chloride ions Cl-.
Value to organisms:
Watery habitat dissolves ions that can be absorbed by organism;
Soluble excretory products eg urea, can be removed;
Substances can be transported around an organism in its circulatory system and within cells in the cytoplasm.

6. Thermal Property: Specific Heat Capacity
Principle:
Water requires a lot of heat energy to change it’s temperature.
Value to organisms:
Habitat - the temperature remains fairly steady even though air temperatures can change widely eg alligators can keep warmer at night by remaining in water.
Heat transport - blood can transfer heat from hot regions of the body to cooler regions for temperature regulation.

7. Thermal Property - Freezing
Principles:
Water freezes at °C;
Ice is less dense than water;
Water at 4°C is denser and so sinks.
Value to organisms
Ice floats and insulates the water below;
The denser water at 4°C allows animals e.g. fish, to survive at the bottom of a lake.

8. Thermal Property - Evaporation
Principles
Water requires a high input of energy to break the hydrogen bonds and turn it from
the liquid state to the vapour state.
Evaporation of water off the surface of an organism allows it to lose heat.
Value to organisms
Plants in deserts increase transpiration when in danger of over-heating;
Mammals sweat for thermoregulation.