Peter Milani, age 11, of Pittsburgh, Pennsylvania, for his question:

Do molecules die?

The Green Revolution introduced us to the word "organic". We know very well that it has something to do with living, growing things. We also know that chemicals are made from molecules    and some are called organic chemicals. This gives the idea that molecules might be alive    especially when we know that they often stay only a short while. But those miniature midgets can fool us.

Actually, molecules are not really alive, though they do help to build plants, animals and people. In fact, a living cell cannot possibly live without molecules. A molecule, of course, is a neat package of atoms. It ties itself together with borrowed energy, such as heat or sunlight. Later it may untie its package and set this energy free. Then its separate atoms may be packaged to make different atoms. So molecules form, last a while and then depart. This may fool a person into thinking they are alive    which they are not.

There are at least 525,000 different molecules of assorted shapes and sizes. None of them are big enough for human eyes to see but scientists have all sorts of ways to figure out what they do. We call them chemicals because they are from atoms of the chemical elements. Molecules that are alike tend to attract each other and mass together. Salt crystals are built from molecule packages of sodium and chlorine atoms    all alike. Sugar crystals are molecules made from hydrogen, oxygen and carbon atoms.

Sugar and salt are chemical compounds.. So are other substances that are made from molecules that are all alike. Chemists divide them into two groups    and this also can fool you. About 50,000 of them are called organic chemical compounds. The word "organic" suggests that they are related to growing things. And most of them are, indirectly. Living cells depend on molecules that contain at least one atom of carbon. Organic chemicals have other ingredients, but one of them must be carbon.

The other group is called "inorganic", or "non organic", chemicals. These 25,000 molecules do not depend on the carbon ingredient. Some organic and inorganic chemicals look very much alike. It takes a trained expert to identify them. For  example, sugar and salt look somewhat alike. But one is an organic chemical, the other is inorganic. The salt, with no carbon, is the inorganic chemical. The sugar is an organic chemical because its molecules contain carbon atoms.

Green plants use the energy of sunlight to make atoms into molecules of sugar. Then they use various chemical energies to remodel the sugar into wood and all the other compounds they need to thrive and grow. When we burn the wood, its molecules break apart. This frees the separate atoms    and the energy that tied them in packages goes off as heat. The wood molecules are no more, but their atoms are not harmed. Some of them form other molecules in the air as they escape from the flames.