= Cytoplasm
{wiki}
The <cytoplasm> is the material inside a <cell membrane> but outside the <cell nucleus>, when one is present. It includes the <cytosol>, the <organelles> suspended in it, and other structures; it is not just a name for the liquid. In a <prokaryote>, which has no <cell nucleus>, the <nucleoid> and <ribosomes> are within the <cytoplasm>. See https://openstax.org/books/biology-2e/pages/4-3-eukaryotic-cells[Clark, Douglas and Choi, Biology 2e, 4.3: cytoplasm and cytosol] and https://openstax.org/books/biology-2e/pages/4-2-prokaryotic-cells[Clark, Douglas and Choi, Biology 2e, 4.2: prokaryotic organization].
\Image[/eukaryotic-cell-compartments.png]
{title=<Cell nucleus>, <cytosol> and <organelles> in a nucleated <eukaryotic> <biological cell>}
{description=Original schematic: the pale blue region represents <cytosol>, while the surrounding <cytoplasm> also includes the depicted <mitochondrion> and <ribosomes>. The <cell nucleus> and <cell nucleolus> are excluded from the <cytoplasm>. A <nuclear pore complex> provides a route across the double <nuclear envelope>. Dimensions and component counts are illustrative; many structures are omitted.}
Try classifying four positions in the diagram. A point in the pale blue region belongs to both <cytosol> and <cytoplasm>. A point inside the <mitochondrion> belongs to an <organelle> included in the <cytoplasm>, but not to the surrounding <cytosol>. A point on a free <ribosome> belongs to the <cytoplasm>, but the <ribosome> itself is not <cytosol>. A point inside the <cell nucleus> belongs to neither <cytoplasm> nor <cytosol>. These distinctions prevent the misleading inference that everything outside the <cell nucleus> shares one undivided liquid environment.
The usefulness of the <cytoplasm> is this combination of shared surroundings and specialized structures: <enzymes> in the <cytosol> carry out many steps of <metabolism>, while <organelles> maintain their own internal conditions. A soluble <protein> made by a free <ribosome> may work in the <cytosol> or be transported elsewhere, including into the <cell nucleus>. Cellular organization therefore combines separation with exchange, rather than assigning each <protein> permanently to its place of synthesis. See https://www.ncbi.nlm.nih.gov/books/NBK26932/[Alberts et al., Molecular Biology of the Cell (2002): traffic between nucleus and cytosol].
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