Completely updated, latest information obtained from scientific researches have been included. The chapter on bioenergetics deals with energy transformations and chemiosmotic theory for ATP formation. A very detailed account of role of light in photosynthesis is discussed in view of the latest findings. Latest scheme of non-cyclic and cyclic photophosphorylation has been explained in detail. Cyanide resistant respiration has been explained in detail. Fat and protein metabolism have been thoroughly updated. The various metabolic processes have been explained with the help of appropriate diagrams. Every chapter has been dealt with in light of recent researches. About 300 new diagrams have been included to make the understanding of the subject easy for the students.