Hill reaction The release of oxygen from isolated illuminated chloroplasts when suitable electron acceptors (e.g. potassium ferricyanide) are added to the surrounding water. The reaction was discovered by Robert Hill (1899–1991) in 1939; the electron acceptors substitute for NADP⁺, the natural acceptor for the light-dependent reactions of photosynthesis.

Hill reaction A reaction, discovered by Robert Hill in 1939, in which isolated chloroplasts produce oxygen and hydrogen when illuminated in the presence of an oxidizing agent (e.g. a ferric salt).