Biophysics is a branch of biology in which the methods and principles of physics are applied to the study of living things. Biophysics grew up in the 20th century alongside the development of electronics. Its tools include the electroencephalograph and the electron microscope, its techniques those of spectroscopy and X-ray diffraction, and its problems the study of nerve transmission (see nerve impulse), bioluminescence, and materials transfer in respiration and secretion, to name but a few.