Over their couple billion of years of evolution, eukaryotic (complex) cells have developed numerous organelles, or subcomponents, which perform specialized tasks to increase the overall effectiveness or adaptability of the cell. The most obvious is the nucleus, within which is the nucleolus, the epicenter of the cell where the genetic material can be found. The nucleus protects the genes (masters of the body) from degeneration from various sources such as invading viruses or energetic solar radiation. The nucleus is usually the largest of organelles in the cell, though sometimes second to large vacuoles.

The second most famous of the organelles is probably the mitochondria. The mitochondria is the only organelle that itself contains some genetic material, likely a vestige from an era when the mitochondria was an independent organism. Mitochondria serve the function of power plants for the cell, taking NADH and NADPH and converting it into energy in the form of ATP via oxidative phosphorylation. NADH and NADPH can be found floating around in the bloodstream, but must be converted to ATP for the cell's machinery to be able to use it. There are around 2,000 mitochondria in a typical eukaryotic cell, which take up about 20% of its total volume.

Another prominent specimen among the organelles are the ribosomes, an extremely important component of the cell. It is made up of 65% ribosomal RNA and 35% ribosomal proteins. The ribosomes, about 20 nm in diameter, are responsible for building all the proteins that make up the human body. The nucleolus of the cell sends out tiny molecules called messenger RNA to tell the ribosomes what to build. The ribosomes use transfer RNA to bring them amino acids, which they string together into the long polypeptides we know as proteins. These smaller molecules floating in the intracellular medium are generally not considered organelles.

Other organelles, some only found in plants, include plastids (chroloplasts being the most famous), which conduct photosynthesis, the endoplasmic reticulum, which modifies new proteins and lipids, the Golgi apparatus, which sorts and modifies proteins, the vacuole, which mediate storage and homeostasis, and dozens more minor organelles. All of these float in the soup of cytoplasm, the fluid which fills the cell. The structure of the cell is largely dictated by the cytoskeleton, which is made up of fibrous proteins.