Water as a solvent and carrier
Three of water's most important roles all arise from one property: it dissolves things.
1. An excellent solvent
- It provides the medium for biochemical reactions inside cells
- It is the main component of all extracellular fluids in living things
- It makes it easier for animals to excrete secretions and waste products
Why does this matter so much?
For a chemical reaction to happen, the reacting molecules have to meet each other. Molecules cannot move around inside a solid. Dissolved in water, they move freely and meet.
2. As a transport medium
- As a main component of blood, it transports nutrients, vitamins and hormones to where they are needed
- Because water has high cohesive and adhesive forces, it is transported upwards through the stems of tall plants
Cohesion and adhesion
Cohesion is the force of attraction between water molecules. Adhesion is the force of attraction between water molecules and the molecules of another surface. Together these two forces carry water to the top of a tree many metres tall, with no pump involved.
3. As a respiratory medium
Because oxygen dissolves in water, water matters for the respiration of aquatic organisms. It is how a fish can breathe while staying underwater.