Digestive Systems of Other Animals

Protozoa, such as amoeba, do not have a digestive system because their body consists of a single cell. Nutrients are absorbed across the entire surface of the cell. The amoeba captures food particles, forming food vacuoles around them. It is in these vacuoles that food is digested with the help of enzymes.

Hydra also does not have differentiated digestive organs. Its body consists of two layers of cells - ectoderm and endoderm. Digestion is carried out by endoderm cells. Food enters through the mouth into the internal cavity, where it is digested.

Planaria have a primitive digestive system consisting of a mouth, pharynx and a branched stomach. However, there is no anus. Digestion occurs both inside the cells and in the stomach cavity.

The earthworm already has a complete digestive system with a mouth and anus. It includes the pharynx, esophagus, stomach, and intestines. Digestion is mainly extracellular.

In vertebrates, the digestive system became significantly more complex, with the addition of new organs such as the liver and pancreas. But the principle of its structure remained the same from fish to humans. Digestive chemistry and enzymes are also very similar between animals at different levels of organization.

Thus, in the process of evolution, the digestive system gradually became more complex from the simplest to the higher animals, acquiring increasing differentiation of organs and the efficiency of the processes of digestion and assimilation of food.