Answer:
mass
Explanation:
the chemical formula for water is H20 which means every molecule of water has 2 atoms of hydrogen and one atom of oxygen. Here comes the key part. from the periodic table of elements one sees that one mole of hydrogen atoms weight 1 gram while one mole of oxygen weights 16 grams.
Have plasma membrane, DNA, ribosome, and cytoplasm.
I would say energy myself, and this is because energy plays a key role in all of these. With trophic levels energy is being transferred amongst the levels. Food chain's is a map of how the energy is passed along the chain. Food web is a web of how energy is transferred, and this is why I would say energy is a keyword.
