The correct answer is option A: Presence or absence of a well defined nucleus.R.H. Whittaker (1969) proposed the five kingdom system, namely Monera, Protista, Fungi, Plantae and Animalia.
He delimited the kingdoms using five criteria:
(i) Complexity of cell structure
(ii) Complexity of body organisation
(iii) Mode of nutrition
(iv) Ecological life cycle, which includes the mode of reproduction
(v) Phylogenetic relationships
Thus the system is based on the mode of reproduction, the mode of nutrition and the complexity of body organisation.
The mere presence or absence of a well defined nucleus was not used by Whittaker as a separate criterion of classification.
Hence, the five kingdom system is not based on the presence or absence of a well defined nucleus.
