Hello There!
METABOLISM - In an organism, the metabolism converts food into energy. Another important thing it does is it gives you the energy you need every day in life.
CATABOLISM - This is the break down of molecules that are very small. Cells need nutrients because inside them, they contain energy. Catabolic reactions release the energy and then makes all the different substances available.
ANABOLISM - This is the building of organic compounds. Complex molecules are synthesized from molecules that are way more basic.