BIOLOGY Volume 1 - A Guide to General Biology - 2004

5. CELLS

5.10. Cell Structures

5.10.2. Cytoplasm

The living contents of Eukaryotic Cells consist of The Nucleus and Cytoplasm, which together form the "protoplasm". The cytoplasm is composed of an aqueous ground substance and a variety of embedded Organelles. In addition, it contains various inclusions, such as insoluble metabolic end products and reserve nutrients.

The soluble part of the cytoplasm, or its ground substance, fills the space between Cell organelles. It contains a network of very fine protein filaments (Section 5.10.7), but otherwise appears transparent and structureless when viewed under an Electron microscope. Water accounts for approximately 90% of its composition. Dissolved within this water are all the essential Biomolecules. Ions and small molecules—namely salts, sugars, Amino Acids, Fatty acids, NUCLEOTIDES, Vitamins, and dissolved gases—form true solutions. Large molecules, such as Proteins, form colloidal solutions. A solution is termed colloidal when the solute molecules are relatively large (see Appendix 1, Vol. 3). A colloidal solution can exist as either a sol (fluid) or a gel (viscous); the outer layers of the cytoplasm often have a consistency closer to that of a gel.

The cytoplasmic ground substance is not merely a storage site for biomolecules. It is also the site of several metabolic processes, most notably Glycolysis.

When we manage to observe living cytoplasm, one thing that immediately stands out is its high activity—the intense movement of organelles, particularly Mitochondria.