The ‘lock’ and ‘key’ theory of enzyme structure and function was proposed by
a)	Morgan	b)	Robertson	c)	Brown	d)	Fischer

(d)

Emil Fisher (1894) proposed ‘lock and key’ theory to explain the mechanism of enzyme action. According to this theory, the active sites of enzyme have a specific geometric shape wherein the substrate molecule get fitted to form enzyme-substrate complex. This is like the fitting of a key to a particular lock.