Which of the following statements are correct regarding sea urchin gastrulation? -The stomoderm develops into the mouth after connecting to the mesoderm
-The pools of cell formed from the blastula are germ layers
-The flattening of the mesoderm and endoderm occurs before cells are differentiated
-The movement of primary mesenchyme cells occur at the animal poll
(can pick more than one correct statement)

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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.