SYSTEM LEVEL-an association of organs that have a common function; the major systems in the human body include digestive, nervous, endocrine, circulatory, respiratory, urinary, and reproductive. There are two types of cells that make up all living things on earth: prokaryotic and eukaryotic. Prokaryotic cells, like bacteria, have no 'nucleus', while eukaryotic cells, like those of the human body, do. So, a human cell is enclosed by a cell, or plasma, membrane. Enclosed by that membrane is the cytoplasm (with associated organelles) plus a nucleus. Cell, or Plasma, membrane-encloses every human cell. 1  Structure - 2 primary building blocks include protein (about 60% of the membrane) and lipid, or fat (about 40% of the membrane).