Water—The Essence of Life - Water in Ecosystems and Habitats

Water is known as the 'Universal Solvent' because it can dissolve more substances than any other liquid, which is essential for transporting nutrients in ecosystems.

Aquatic habitats are divided into Freshwater (rivers, lakes, ponds) and Marine (oceans, seas). Marine water contains high salinity, approximately $3.5\%$.

Hydrophytes (aquatic plants) have special adaptations such as waxy coatings to prevent rotting and air-filled tissues (aerenchyma) to stay afloat. A common example is the Lotus ($Nelumbo\ nucifera$).

Aquatic animals have adaptations like gills to extract dissolved oxygen ($O_2$) from water and streamlined bodies to reduce friction while swimming.

Water is a vital reactant in photosynthesis, where plants convert light energy into chemical energy: $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$.

The distribution of water on Earth is roughly $97\%$ saltwater and $3\%$ freshwater, of which only about $1\%$ is accessible for human use.