Answer:
Reject some alternative hypothesis.
The source of the animals food
Amoeba acquires it food by endocytosis, that is, a small region in the plasma membrane which ultimately forms a intra-cellular membrane-bound vescicle. It engulfs it food using its pseudopodia (temporary protrusion of the surface of the amoeboid cell used for feeding and movement) and forms a vacuole around it. When the food is already trapped inside, it releases a digestive enzyme to digest it. Intake of liquid particles is pinocytosis (cell drinking) while intake of solid particles is phagocytosis (cell eating).
