Which is not true about plant cell walls? A.) All plants have a primary cell wall
B.) Primary cell walls contain cellulose and hemicellulose
C.) Secondary cell walls are located just outside the primary cell wall
D.) Secondary cell walls occur only in woody plants
E.) Cell walls are penetrated by extensions of cytoplasm that connect adjacent cells’ cytoplasm.

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.