Prokaryotic and Eukaryotic Cells
Living organisms are made of either prokaryotic or eukaroytic cells - two major kinds of cells, which can be distinguished by structural organization.
Cytoplasm - Entire region between the nucleus and cell membrane.
Cytosol - Semi-fluid medium found in the cytoplasm.

Cell Size Limitations
Size ranges of cells:
Range of cell size is limited by metabolic requirements (the energy and chemical reactions needed to sustain life). The lower the limits are probably determined by the smallest size with:
  • Enough DNA to program metabolism
  • Enough ribosomes, enzymes and cellular components to sustain life and reproduce.

The upper limits of size are imposed by the surface area to volume ration. As a cell increases in size, its volume grows proportionately more than its surface area.
  • The surface area of the plasma membrane must be large enough for the cell volume, in order to provide an adequate exchange surface for oxygen, nutrients and wastes.

Advantages of Compartmental Organization
The largest eukaryotic cell has a thousand times the volume of the smallest prokaryotic cell, but only a hundred times the surface area. Eukaryotic cells compensate for the small surface area to volume ration by having internal membranes which:
  • Partition the cell into compartments.
  • Have unique lipid and protein compositions depending upon their specific functions.
  • May participate in metabolic reactions since many enzymes are incorporated directly into the membrane.
  • Provide localized environmental conditions necessary for specific metabolic processes.
  • Sequester reaction, so they may occur without interference from incompatible metabolic processes elsewhere in the cell.