what are the merits and demerits of two kingdom classification and five kingdom classification?
Merits and Demerits of Two kingdom classification
1) Plants and animals were divided into two kingdoms not abruptly but based upon specific characters.
2) It initiated systematic methods to classify the living organisms. More and more characters were, later, taken into consideration for development of better methods.
- There was no distinction between eukaryotes and prokaryotes. For example- bacteria which lack nuclear envelope & cytoplasmic organelles but still they are placed in kingdom plantae.
- It kept photosynthetic and non photosynthetic organism together in plant kingdom. For example- Fungi which lack chlorophyll and are saprotrophic still placed in kingdom plantae.
- There are some organism which neither fall into plant or animal kingdom, like lichens.
- There are some organisms which have the characters of both plants & animals like euglena, chlamydomonas so can be placed in any kingdom.
- Unicellular plants like diatoms and animals like protozoans which have same level of organization and reproduce by fission but they are placed in different knigdoms.
Five kingdom classification
(i) It explains the relationship among organisms with regard to levels of organization and mode of nutrition.
(ii) It explains evolutionary trend indicating gradual evolution of complex organisms from simpler ones.
(iii) Better placement of certain controversial groups like Cyanobacteria, fungi, Euglena etc.
(iv) Separation of kingdom Fungi from plants seems to be justified as fungi bear own type of structural, physiological as well as biochemical characters.
(i) The position of virus is not clear.
(ii) Kingdom Protista includes organisms having diverse form, structure and life cycle, hence does not seem to be proper grouping.
(iii) Some organisms included under Protista (e.g. Dinoflagellates) are not eukaryotic rather mesokaryotic.
(iv) Slime moulds placed under Protista differ considerably from the rest of protists.