PROCARYOTES TO EUCARYOTES
Procaryotes are the simple, unicellular organisms which do not have well defined nucleus, whereas eucaryotes are the complex;multicellular organisms with well defined nucleus. Procaryotes were originated about three and a half billion years ago, whereas eucaryotes originated about one and a half billion years ago. Thus, it appears that eucaryotes evolved later than the procaryotes. But in biochemical details the procaryotes and eucaryoteb are very similar. Therefore, we can say that they have a common origin. Eucaryotes, like procaryotes. have the same biochemical pathways for respiration both anaerobic and aerobic and for photosynthesis. The eucaryotes not only attained larger size and complex structure but also developed into multicellular organisms. Earlier each form of cell which was thought as an autonomous arid self-sufficient unit, gradually became dependent on each other in larger organisnis leading to division of labour within organisms. This type of cooperation between cells eventually led to the development of higher forms of life as they exist today.