why did Margulis and Schwartz modified Whittaker scheme?
Whittaker proposed the classification scheme in 1959. This scheme was based on the level of organization of the organism (unicellular and multicellular), as well as nutrition strategy (heterotrophic, and photosynthetic). As a result, Whittaker's classification comprised five kingdoms comprising Animals, Fungi, Plants, Protists, and Prokaryotes. However, one of the limitations of the classification was that unicellular and multicellular algae were separated into two kingdoms - Protists and Plants, though these organisms possess many similarities. As a result, Margulis and Schwartz modified Whittaker's scheme to eliminate the limitations and to unite related algae into one kingdom. They suggested that multicellular algae should be placed into the Protist kingdom that was renamed to the Protoctist kingdom.