Eukaryotic cells ingest molecules from the extracellular space by a process called endocytosis. In endocytosis, a portion of the plasma membrane bends inwards to surround an incoming molecule and then buds off to form a transport vesicle. The transport vesicle carries the molecules into the cytosol for fusion with other intracellular organelles, such as endosomes or lysosomes. Following fusion with the lysosome, the ingested material can be degraded with the help of lysosomal enzymes. On the other hand, some endocytosed molecules must be released in the cell for utilization. Endocytosis enables cells to uptake nutrients, certain proteins, and a variety of soluble molecules. Some specialized cells, such as phagocytes, also engulf cell debris, foreign particles, or organisms, like bacteria or protozoa as a part of the host's defense mechanism. This type of endocytosis is known as phagocytosis.