Ruthie Belknap, age 9, of Orlando, Fla., for her question:

WHAT IS BIOPHYSICS?

Biophysics is the science that uses the tools and methods of the physicist to study living things. Biophysics has been largely responsible for many discoveries about the physiology, or body functions, of man and other organisms.

Biophysics uses the principle of diffusion, a basic part of physics, to explain the interchange of gases between lungs and blood, and between blood and cells.

Biophysicists are interested in physical activities such as muscle movements, breathing and chewing. Osmosis is a biophysical activity of great importance in the physiology of living things.

Biophysicists study the effect of temperature, light, sound, pressure and other forces on living things.