Intracellular digestion

[1] However, to obtain energy from its outside environment, cells must not only retrieve molecules from their surroundings but also break them down.

In detail, a phagocyte's duty is obtaining food particles and digesting it in a vacuole.

This kind of intracellular digestion occurs in many unicellular protozoans, in Pycnogonida, in some molluscs, Cnidaria and Porifera.

[3] Heterophagic intracellular digestion has an important job which is to break down all molecules that are brought into a cell by endocytosis.

[4] Most organisms that use intracellular digestion belong to Kingdom Protista, such as amoeba and paramecium.