Michele Calenzo, age 11, of Utica, New York, for her question:

WHAT DETERMINES HOW TALL YOU WILL BE?

How tall your grandparents and your parents are determines how tall you will be. The same thing is true with other physical characteristics which you have  you have inherited them from your ancestors.

The study of the ways in which physical features are carried from one generation to the next is called heredity. A geneticist is a scientist who studies heredity. He wants to know ways young children and even plants resemble their parents and ways they do not do so.

A young girl may have brown hair and be short like her mother, or she may be tall and have black hair  like her father.

Passing or transmitting of traits from one generation to another  from grandparents to parents, and from parents to grandchildren  is called inheritance. The uniting of an egg cell from the mother with a sperm cell from the father will produce a new individual  a young child, animal or plant.

Why do we ever stop growing? What we call growth is the power the cells of the body have of taking nourishment, becoming larger and of dividing and producing other cells. This power, however, is limited since every kind of cell can grow and multiply only within the limits of its own law  the law of growth.

No matter how much food is eaten, the law of growth prevents any number of cells from becoming more numerous or larger than a given limit. When your body is young, the growth is very active. But when a body grows older, the limit of growth is gradually reached and growth stops.

Today, on the average, we seem to be taller than our ancestors of the Middle Ages. Records also show that those in the services during World War II were taller than those who served during World War I. We all seem to be on our way up.