The cytoplasm (cell fluid) is viscous, and any internal structure that it might have in terms of barriers or compartments is obscured by densely packed ribosomes, although some scientists believe that compartments do exist.

The fluid is a 20% protein solution in water, containing ions and small molecules and serving as a pool or reservoir for the small metabolites of the cell.

It contains the enzymes for all cell processes other than respiration and the light reactions of photosynthesis.

These processes include glycolysis, glucose synthesis, various other syntheses, and DNA replication and transcription.