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This is a model of Amoeba,
a relatively large protozoan. Amebas use mobile extensions of the cytoplasm called pseudopodia for movement and food capture. Protozoans that form pseudopodia have two type of cytoplasm, an outer, more viscous portion called the ectoplasm and an inner, more fluid portion called the endoplasm. When a pseudopodium begins to form, a clear space at the leading edge of the pseudopodium called the hyaline cap appears. After this occurs, endoplasm begins to flow into this space, causing the pseudopodium to be pushed forward through the medium. In addition to their locomotor role, pseudopodia can be used to engulf prey in a process known as phagocytosis. Once ingested, food enters a food vacuole where it is digested by enzymes released from lysosomes. Clear areas called contractile vacuoles collect excess water from the surrounding cytoplasm and discharge it to the outside of the body. Also note the darkly stained nucleus, which contains granular chromatin and controls the activities of this unicellular organism. |
