endoplasma

Endoplasma, in traditional cell biology, refers to the inner, more granular portion of the cytoplasm found in some cells, notably certain protozoa such as amoebae. It is contrasted with the outer clear layer known as the ectoplasm. The endoplasm is typically denser and contains a higher concentration of solutes and organelles, giving it a more granular appearance under light microscopy. It houses most of the cell’s cytoplasmic machinery, including mitochondria, ribosomes, and various vesicles.

In many organisms, the endoplasm plays a central role in storage and digestion. During phagocytosis or feeding, food vacuoles form within the endoplasm where ingested material is transported and broken down. The region also serves as a reservoir for nutrients and enzymes necessary for metabolic processes. The distinction between endoplasm and ectoplasm often corresponds to functional zones, with the ectoplasm supporting locomotion and shape maintenance.

The endoplasm is usually more dynamic than the peripheral cytoplasm, participating in cytoplasmic streaming and the redistribution of organelles as the cell moves or changes its state. This movement helps distribute nutrients, organelles, and signaling molecules to where they are needed.

In modern cell biology, the term endoplasm is largely historical or descriptive, and broader discussions typically refer to the cytoplasm as a whole. It should not be confused with the endoplasmic reticulum, a separate membrane-bound organelle network involved in protein and lipid synthesis. See also cytoplasm, ectoplasm, amoeba, and endoplasmic reticulum.