Which part of the mouth secretes enzymes that prepare the food for digestion in the stomach? teeth tongue salivary glands pancreas?

The correct answer is salivary glands.
 Salivary glands are exocrine glands which means that they release their product onto epithelial structure by the duct. There are three major types of salivary glands in humans: parotid, submandibular, and sublingual as well as hundreds of minor salivary glands. Beside the function of digestion (secrete the enzyme amylase, which hydrolyses starch into maltose and dextrin) those glands have a protective role 

Mitochondria produce atp, a high energy compound. atp is used for all sorts of enzyme-mediated reactions, such as making proteins/nucleotides/etc, certain compounds cross the cell membrane, muscles move, etc.  without this source of energy, a cell will die. it will not be able to repair itself, defend against pathogens, etc.