AP BIOLOGY

Detailed explanation-1: -Birds with thick gizzards frequently pick up grit-little stones, sand, and small shells. These items collect in the gizzard. When food and digestive juices enter the gizzard, the thick muscles and grit help pulverize the food.

Detailed explanation-2: -The gizzard is the second chamber of the stomach and it consists of very tough muscles. These muscles are used to grind and digest various types of foods. The muscles don’t do this process alone. Many birds pick up small pebbles, sand or grit while they are eating and these items end up in the gizzard.

Detailed explanation-3: -Birds have a glandular stomach, or proventriculus, and muscular stomach or gizzard. The glandular stomach receives food from the esophagus, and secretes mucus, HCl and pepsinogen, similar to what is seen in the mammalian stomach.

Detailed explanation-4: -The gizzards of birds provide another preadaptation for omnivory – a muscular grinding organ can be equally good at grinding animal or plant tissue, provided the bird has sufficient flexibility in food acquisition to ingest both food types.