Cell biologists have introduced radioactively labeled carbohydrates, fats, and amino acids to living cells, allowed time for cell metabolism, and then placed the cells in a blender and separated out the various cell organelles from the cytoplasm. They found the radioactive molecules could soon be detected as part of various cellular compounds, although the visible cell structures appeared unchanged. Which of the following is the best conclusion based on this information?
a) these "food" molecules are used only for energy.
b) most cell components are constantly being broken down and rebuilt.
c) radioactivity was transferred from the introduced molecules to the resident table molecules.
d) molecules diffuse at random through the cytoplasm and into cell organelles.