Cytoplasm

Definition

The entire contents of a cell enclosed by the plasma membrane, comprising the cytosol (the aqueous, gel-like matrix), organelles, and cytoplasmic inclusions, but excluding the nucleus in eukaryotes. In arthropods, cytoplasmic organization varies markedly among cell types: oenocytes contain abundant cytoplasm rich in lipids and enzymes for cuticular hydrocarbon synthesis; hemocytes show cytoplasmic granules or filopodia depending on immune function; and nurse cells in insect ovaries transfer cytoplasmic contents including ribosomes and mRNAs to developing oocytes. The cytoplasm serves as the medium for metabolic reactions, intracellular transport, and cytoskeletal dynamics.

Etymology

From Greek kytos (hollow vessel, cell) + plasma (something molded, formed substance)

Example

In the fat body cells of a caterpillar, the cytoplasm becomes densely packed with lipid droplets and glycogen granules during feeding phases, then mobilizes these reserves during metamorphosis when the larval tissues are reorganized.

Synonyms

• cell substance
• protoplasm (historical, now imprecise)

Related Terms

• Cytosol
• organelle
• nucleoplasm
• cytoskeleton
• cytoplasmic streaming
• endoplasm
• ectoplasm

Usage Notes

Specialists distinguish cytoplasm (the entire compartment) from cytosol (the soluble, non-organelle fraction). In older literature, 'protoplasm' conflated cytoplasm and nucleoplasm; modern usage reserves cytoplasm for the extra-nuclear material. In arthropod histology, cytoplasmic texture and staining properties help identify cell types and functional states. Some texts use 'endoplasm' and 'ectoplasm' for inner and outer cytoplasmic zones, particularly in protozoa and certain insect secretory cells.