Final answer:
A digestive system without the oral cavity and stomach would have disadvantages such as insufficient mechanical and chemical breakdown of food, hindered digestion, and poor nutrient absorption.
Step-by-step explanation:
A digestive system where food enters the small intestine directly without first going through the oral cavity and stomach would have several disadvantages. Firstly, the oral cavity and stomach play important roles in breaking down food mechanically and chemically. Chewing in the oral cavity helps to physically break down food into smaller particles, making it easier to digest. The enzymes present in saliva also begin the chemical breakdown of food. In the stomach, gastric juices and enzymes act on the food particles, further aiding in digestion.
Furthermore, the stomach is an extremely acidic environment, which helps to speed up the actions of enzymes in the digestive process. By bypassing the stomach, the food would miss out on the benefits of the acidic environment, which may hinder the efficiency of digestion.
Overall, an incomplete digestive system without the oral cavity and stomach would result in insufficient mechanical and chemical breakdown of food, potentially leading to poor nutrient absorption and digestion.