Answer:
1. Many vertebrates have teeth, and chewing (mastication) breaks up food into small particles, expanding its surface and mixes it with fluid secretions, which makes it possible to digest. Teeth are located in the mouth of animals, where the digestive process initiates.
2. The stomach, which resembles a bag-like shape, can either fold up when empty and expand like a balloon when it fills up with food. By doing this, the area of activity of the gastric juice is expanded, increasing the efficiency of the digestion. Food enters the stomach from the esophagus.
3. The villi and microvilli present in the epithelial wall of the small intestine, are fingerlike projections that greatly enhance the surface area of the small intestine. In humans, this surface area is 300 square meters and it is over this large surface that the products of digestion are absorbed.