Amoeba proteus is a large unicellular organism that moves over its substrate by sending extensions of its cytoplasm, called pseudopodia, in various directions. The pseudopodia can surround and engulf food by phagocytosis. The leading edge of the amoeba is a clear zone that seems devoid of cytoplasmic organelles; this is called the ectoplasm. The ectoplasm contains large amounts of actin, the contractile protein common in animal muscle cells. The rest of the cytoplasm is called the endoplasm. During amoeboid movement, endoplasm flows forward to fill an extending pseudopodium, and is then converted to ectoplasm just below the plasma membrane. Ectoplasm flows backward around the outside of the cell and is then converted back to endoplasm, a cycle that continues while the amoeba moves. Credit: Henry Mainwaring, Western Carolina University.
