AP BIOLOGY

Detailed explanation-1: -The proventriculus (also known as the true stomach) is the glandular stomach where digestion primarily begins. Hydrochloric acid and digestive enzymes, such as pepsin, are added to the feed here and begin to break it down more significantly than the enzymes secreted by the salivary glands.

Detailed explanation-2: -The gizzard performs the same function as mammalian teeth, grinding and disassembling the food, making it easier for the digestive enzymes to break down the food. In most birds the gizzard contains sand grains or small rocks to aid the grinding process.

Detailed explanation-3: -The crop stores food temporarily and starts the digestion process before it enters the stomach. It is a thin-walled pouch at the base of the esophagus where birds can store food before it is sent the rest of the way to the stomach.

Detailed explanation-4: -The stomach of birds has two chambers: the proventriculus, where gastric juices are produced to digest the food before it enters the stomach, and the gizzard, where the food is stored, soaked, and mechanically ground.