Cytoplasm

The cytoplasm is the contents of the cell enclosed by the plasma membrane, excluding the nucleus. In eukaryotic cells it consists of the cytosol—the jelly‑like fluid—and the organelles and inclusions suspended in it, together with the cytoskeleton. The nucleus is not part of the cytoplasm.

Cytosol is a viscous, water‑based solution containing ions, nutrients, small molecules, and soluble enzymes. It hosts most metabolic pathways, including glycolysis, and serves as the site of many enzymatic reactions. The cytoskeleton, a network of protein filaments, provides structural support, helps maintain cell shape, and enables movement and intracellular organization.

Organelles within the cytoplasm include mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, and various vesicles. In plant cells, chloroplasts and vacuoles are also present. The nucleus, while surrounded by its own membrane, is excluded from the cytoplasm.

Functions of the cytoplasm include supporting metabolism, energy production, and protein synthesis (on cytosolic ribosomes and on ribosomes attached to the endoplasmic reticulum). It also mediates intracellular transport through motor proteins that move along cytoskeletal tracks, participates in signal transduction, and contributes to cell division and spatial organization. The cytoplasm helps maintain cellular homeostasis by regulating the distribution of ions and metabolites.

Dynamics within the cytoplasm are continual and organized, with mixing and flow that distribute organelles and nutrients. Cytoplasmic streaming occurs in some plant cells, aiding rapid intracellular transport.