Biophysics is the application of the principles of physics (the science that deals with matter and energy) to explain and explore the form and function of living things. The most familiar examples of the role of physics in biology are the use of lenses to correct visual defects and the use of X rays to reveal the structure of bones.
Computerized axial tomography (CAT scan): An X-ray technique in which a three-dimensional image of a body part is put together by computer using a series of X-ray pictures taken from different angles along a straight line.
Electron microscope: A microscope that uses a beam of electrons to produce an image at very high magnification.
Laser: A device that uses the movement of atoms and molecules to produce intense light with a precisely defined wavelength.
Magnetic resonance imaging (MRI): A technique for producing computerized three-dimensional images of tissues inside the body using radio waves.
Positron-emission tomography: A technique that involves the injection of radioactive dye into the body to produce three-dimensional images of the internal tissues or organs being studied.
Ultracentrifuge: A machine that spins at an extremely high rate of speed and that is used to separate tiny particles out of solution, especially to determine their size.
X ray: A form of electromagnetic radiation with an extremely short wavelength that is produced by bombarding a metallic target with electrons in a vacuum.
X-ray diffraction: A technique for studying a crystal in which X rays directed at it are scattered, with the resulting pattern providing information about the crystal's structure.
Principles of physics have been used to explain some of the most basic processes in biology such as osmosis, diffusion of gases, and the function of the lens of the eye in focusing light on the retina. (Osmosis is the movement of water across a membrane from a region of higher concentration of water to an area of lower concentration of water. Diffusion of gases is the random motion of gas particles that results in their movement from a region of higher concentration to one of lower concentration.)
The understanding that living organisms obey the laws of physics—just as nonliving systems do—has had a profound influence on the study of biology. The discovery of the relationship between electricity and muscle contraction by Luigi Galvani (1737–1798), an Italian physician, initiated a field of research that continues to give information about the nature of muscle contraction and nerve impulses. Galvani's discovery led to the development of such instruments and devices as the electrocardiograph (to record the electrical impulses that occur during heartbeats), electroencephalograph (to record brain waves), and cardiac pacemaker (to maintain normal heart rhythm).
Medical technology in particular has benefited from the association of physics and biology. Medical imaging with three-dimensional diagnostic techniques such as computerized axial tomography (CAT) scanning, magnetic resonance imaging (MRI), and positron-emission tomography (PET) has permitted researchers to look inside living things without disrupting life processes. Today, lasers and X rays are used routinely in medical treatments.
The use of a wide array of instruments and techniques in biological studies has been advanced by discoveries in physics, especially electronics. This has helped biology to change from a science that describes the vital processes of organisms to one that analyzes them. For example, one of the most important events of this century—determining the structure of the DNA molecule—was accomplished using X-ray diffraction. This technique has also been used to determine the structure of hemoglobin, viruses, and a variety of other biological molecules and microorganisms.
The ability to apply information discovered in physics to the study of living things led to the development of the electron microscope and ultracentrifuge, instruments that have revealed important information about cell structure and function. Other applications include the use of heat and pressure sensors to obtain information about bodily functions under a variety of conditions. This application of the principles of physics to biology has been of great value in the space program.