THE HUMAN DIGESTIVE SYSTEM Introduction:- Animal required water, oxygen, simple sugar, amino acids, fatty acids, vitamins and many other inorganic and organic substances. These substances except water and oxygen are rare in the natural environment and are not directly available to the organisms. In nature, these substances are available in the form of fats, protein, starch, vitamin, and minerals. In these substances, vitamin and minerals are not able to use without break down and digested into simple molecules such as amino acid, sugars and fatty acid for that purpose animals have a specific system to digest complex molecules into simple molecules called The Digestive System. Digestive System Function Digestion in Buccal Cavity OR Digestion in Mouth/ Oral Cavity:- There are three functions of the oral cavity in digestion. (i) Selection of food (ii) Grinding or Mastication (iii) Lubrication and digestio