What are the main differences between living cells and viruses

Cells are the basic units of life. They can exist by themselves, like bacteria, or apart of a larger organism, like our cells. Viruses are non-living infectious particles that are much smaller then a cell, and need a living host to reproduce. They cannot reproduce outside of a living host cell, nor can they be seen without an electron microscope.  

the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.

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