Variety of species have evolved on the earth over time.
Classification of the myriad of organisms was difficult for the biologists.
Researchers proposed different categories to classify living things. Ernst Haeckel, Robert Whittaker and Carl Woese are some whose contributions are notable.
Whittaker classified living organisms into five kingdoms.
The classification is based on cell structure, mode, and source of nutrition and body design. This is accepted by modern taxonomy. They are:
Kingdom Monera (Prokaryotic bacteria and blue green algae).
Kingdom Plantae (Multicellular green plants and advanced algae).
Kingdom Animalia (Multicellular animals)
CHARACTERSITCS OF FIVE KINGDOMS
Kingdom Monera (Prokaryotes)
Organisms that belong to this category do not have a defined nucleus or organelles. Also, they do not show any multi-cellular body designs. So, this kingdom comprises of unicellular organisms with a prokaryotic cell organization.
Cell wall may or may not be present in them.
They get nutrition either by synthesizing their own food (autotrophic) or from their environment (heterotrophic).
This group includes microbes, viz bacteria, they are prokaryotes and many are autotrophs. Many bacteria are motile (e.g, Escherichia coli) and contain one or more flagella.
Kingdom Protista (or Protoctista)
This group includes many kinds of unicellular eukaryotic organisms such as unicellular algae, protozoans and unicellular fungi. Some of these of organisms use appendages, such as hair-like cilia.
Their mode of nutrition is either autotrophic or heterotrophic.
Phylum Protozoa
They are Unicellular (one-celled or single-celled) and mostly aquatic (fresh water or marine) animals.
Protozoans are Solitary or colonial, free living or parasitic or symbiotic.
Their Body is naked or covered by pellicle or hard shells.
Body shape of these animals may be irregular, spherical, oval, elongated or flattened.
Cytoplasm is differentiated into outer ectoplasm and inner endoplasm.
They can be Uninucleate, binucleate or multinucleate.
Locomotion is by finger-like pseudopodia, flagella or cilia.
Nutrition is mostly heterotrophic.
They reproduce asexually by binary fission, multiple fission, and sexually by conjugation.
Kingdom Fungi
These are Simple non-green plants which are not photosynthetic. Their mode of nutrition is through their environment viz, They are heterotrophic.
They are eukaryotic organisms which may be unicellular or multicellular.
Fungi have a cell wall which consists of a mixture of chitin and cellulose. Chitin is a tough complex sugar. Lichens
There are some fungal species that live in permanent mutually dependent relationships with the blue green algae. This relationship is called symbiotic and such fungal species are called lichens
The fungus absorbs water and mineral matter and supplies it to the algae. The algae, in turn, prepares food and supplies it to the fungus.
Lichens are slow-growing coloured patches on rocks and, bark of tree-trunks.
Kingdom Plantae
Except for some primitive relatives of algae, kingdom Plantae includes multicellular organisms.
These are eukaryotes, that is, each cell in these organisms has a nucleus and membrane bound cellular organelles.
Each cell is surrounded by Cellulose – containing cell wall.
A mature plant commonly possesses a single large central vacuole bound by tonoplast (membrane).
Reserve food of plants is starch and some plant species have oil as their reserve food like the seed of castor plant.
All the plant cells are surrounded by double membrane covered cell organelles, called plastids. Some plastids possess photosynthetic pigments (chlorophyll) and are called chloroplasts.
Plants have the ability to synthesize their own food with the help of chlorophyll present in the chloroplasts. These chloroplasts help the plants to perform photosynthesis. So, the mode of nutrition in plants is autotrophic.
Due to the presence of growing points, growth in plants is generally indefinite.
Body form of the plants is irregular due to presence of branches.
The plant kingdom is a vast group and so it is further classified into subgroups based on the following three criteria:
Plant body– whether the body has well-differentiated structures or not.
Vascular system-whether the plant has vascular system for transportation of substances or not
Seed formation– whether the plant bears flowers and seeds or not; if it does, then whether it is enclosed within fruits or not.
Kingdom Animalia
Animals are eukaryotes with no cell wall.
The mode of nutrition for Animals is heterotrophic and holozoic (= ingestive) type. In most animals, an internal alimentary canal is present for extra-cellular or intracellular digestion and absorption. Also, Digestion is intracellular in primitive animals. The undigested matter is thrown out.
Unlike plants, growth of animals is limited and stops after reaching maturity.
Except for some lower forms, animals generally possess a definite shape, size and symmetry.
Most animals are mobile. Locomotion helps them obtain food and other necessities (e.g, dwelling, mate). Sponges and cnidarians (e.g, Hydra, Obelia, corals), however, are mobile (e.g, tentacles in Hydra and flagella of choanocytes in sponges).
Movements occur in animals with the help of a muscular system. Information is conveyed to different parts of the body by nervous system which also provides stimulus to muscles for contraction.
Animals have organization of cellular, tissue, organs and organ system level.
