Richard Dorin, age 14, of Redwood City, California, for his question:

What basic features distinguish plants from animals?

The more things change, the more they remain the same. This old conundrum is a package of subtle wisdom. It is profound enough to be translated thus. The more differences we discover the more similarities we discover. In this case, it applies to today's question.

Biologists have identified more than a million living organisms and it is doubtful that they have discovered half of them. They have classified them in two major groups   the Plant Kingdom and the Animal Kingdom. This classification was established generations ago when scientists approached the study of nature with brash and rather cocksure convictions. Modern scientists have learned that nature's profound wisdom is too flexible to be fitted into simple, set rules devised by the human mind. They know enough to allow for loopholes in nature's schemes, to expect bridges between their hard and fast classifications. They know enough to be baffled. When they are wise, they keep their minds open like students, eager to learn from nature, the greatest of all teachers.

All this leads to the topic in today's question. It is true that we can divide most of the known species of life into plants and animals. But nature herself may not abide by this man made system. Let's keep in mind that our classifications were devised for human convenience and that the wisdom and diversity of nature are, at present, beyond the full grasp of the human mind. We can note a number of basic features found in molt animals. But biologists of the future may require a midway kingdom for many of the single celled protist organisms.

    Anybody can note different fundamental features in an elm and an elk; and nobody assumes that the crow is related to the crocus. The elm and the crocus are permanently rooted in the ground. The elk and the crow can, and indeed they must, move freely around. Motion appears to be a basic difference. But plants bow to the wind and move as they slowly grow. They also scatter seeds, moving their offspring to new locations. What's more, the adult sponge, which is an animal, remains fixed to one spot like a rooted plant. The big¬gest plants grow larger and live longer than any animal. But this rule does not apply to smaller plants. What's more, certain one celled plants and animals both may be immortal.

In the matter of supporting themselves, making a living, the differences are quite marked. Most, but not all plants contain green chlorophyll to use sunlight for making basic food from air and water. Their roots absorb other nourishment from chemicals dissolved in ground water. Unlike most animals, they cannot hunt and devour chunks of whole food. But all animals must digest their food, separate and liquify its nutrients. The living cells of both plants and animals must be served a liquid diet and both need oxygen to perform their wondrous chemical activities.

It seems that not one of these distinctions is a hard and fast rule. But nevertheless they are useful: guidelines for distinguishing most plants from most animals. And, strange to say, as we probe each different feature, it leads us to ponder a dozen similarities. A wise student regards the exceptions to the general rules as challenges to explore the overlapping, the interdependence and the living web of relationships in the planetary scheme of nature. Directly or indirectly, every life form needs all the others and all of them need the resources of the earth.