12.2: Water in the Body
Water is essential for living things to survive because all the chemical reactions within a body take place in a solution of water. An animal’s body consists of up to 80% water. The exact proportion depends on the type of animal, its age, sex, health and whether or not it has had sufficient to drink. Generally animals do not survive a loss of more than 15% of their body water.
In vertebrates almost 2/3rd of this water is in the cells ( intracellular fluid ). The rest is outside the cells ( extracellular fluid ) where it is found in the spaces around the cells ( tissue fluid ), as well as in the blood and lymph.
Diagram 12.1 - Water in the body