Millie Thompson, age 13, of Meridian, Miss., for her question:
HOW DOES GROWTH TAKE PLACE?
Growth is an increase in size. All living things grow. Every living organism consists of cells. Each individual starts life as a single cell.
The cell takes in materials and builds them into protoplasm, the living substance of which the cell itself is made. Thus, the single cell grows from within. This cell can multiply and divide to form other cells. The process of building, multiplying and dividing is growth. Growth continues until the organism is fully developed.
As the cells grow, they also change in character. Some grow into the tissues that form skin. Others grow into muscle tissues. Still others form body organs such as the heart, lungs and liver.
This growth and organization of the cells into specific structures is called differentiation. This process of differentiation follows definite rules. The seed of a redwood always grow into a redwood tree are not into an oak tree or carnation. A dog’s tail always grows at the base of its spine, not between its ears.
The rules of differentiation are called heredity. The new cell from which an individual grows contains the hereditary traits that influence certain chemical and physical processes in the cell to make it grow into the correct individual.
Other kinds of regulators are also produced by the cells. As growth proceeds, certain cells develop that produce specific substances that influence. and regulate the further development of the organism. These substances are called hormones and are found both in plants and in animals.
Among the higher vertebrates, or animals with backbones, the single tiny cell develops and steadily grows into a form that resembles the adult at birth.
When animals are provided with the proper food, their growth depends or. heredity and on hormones produced by certain of the body’s glands.
When a baby is born, he is growing very fast. The rapid rate of growth continues for the first part of the baby’s life. Both boys arid girls grow most rapidly during the first two years of their lives. Then, their growth rate becomes gradually slower until they reach adolescence
For two years during adolescence, boys and girls suddenly grow rapidly again. This is what some people call the “adolescent spurt” in height growth.
Adolescent boys usually exhibit this spurt in growth between the ages of 13 and 15 and a half years. Their gain in height often ranges from four to 12 inches. But the fastest rate of growth in boys may take place any time between the ages of 12 and 17.
The adolescent growth spurt in girls usually starts about two years earlier than in boys. Their maximum growth rate is somewhat less than that of boys.
Most healthy human beings stop growing some time between the ages of 18 and 30. Ususally, a person is tallest when he is about 20 years old.