The carbon containing molecules can then be used

During photosynthesis, plants capture light energy from the Sun to break weak bonds in reactants, such as carbon dioxide and water, and form carbon containing molecules, such as glucose. The carbon containing molecules can then be used: to assemble larger molecules, such as DNA, proteins, and fats.

Explanation:

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.