Mitochondria are enclosed by a double-membrane system made up of an inner and an outer membrane. The space between these two membranes is called (surprise!) the intermembrane space. The inner membrane encloses the interior of the mitochondrion, which is known as the mitochondrial matrix.The inner membrane also forms a large number of folds, called cristae, that extend into the matrix.See Fig.he space between these two membranes is called (surprise!) the intermembrane space. The inner membrane encloses the interior of the mitochondrion, which is known as the mitochondrial matrix. The inner membrane also forms a large number of folds, called cristae, that extend into the matrix. See Fig.
1 The strict definition of relative atomic mass (Ar) is that it equals the average mass of all the isotopic atoms present in the element compared to 1/12th the mass of a carbon-12 atom (relative isotopic mass of 12.0000).
The atomic mass is expressed in units of atomic mass unit, or amu, and consists primarily of the protons and neutrons in the atom's nucleus, making it closely match the mass number of an atom. When an element has two or more isotopes, the atomic weight is expressed as an interval with an upper and lower number. Both atomic masses and atomic weights are determined by mass spectrometry, a technique where electrically charged particles are separated by their masses.