Physiology of Finfish and Shellfish (2+1)

1.2.1. Introduction

Water is a substance with the chemical formula of H₂O. Its molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions , but it often co-exists on earth with its solid state - ice and gaseous state - water vapor or steam . Water covers 71% of the earth's surface and is vital for all known forms of life . On Earth, it is found mostly in oceans and other large water bodies, with 1.6% of water below ground as ground water and 0.001% in the air as vapor , clouds and precipitation . Oceans hold 97% of surface water, glaciers and polar ice caps 2.4%, and other land surface water such as rivers , lakes and ponds 0.6%. A very small amount of the earth's water is contained within biological bodies and manufactured products. Water is essential to life itself; without water, life on earth would not exist. Water is a major component of cells, typically forming between 70 and 95% of the mass of the cell. This means that we are made from approximately 80% water by mass and some soft bodied creatures such as jellyfish are made of up to 96% water.