BIOLOGICAL CLASSIFICATION CLASS 11TH NOTES

 

BIOLOGICAL CLASSIFICATION NOTES

 

 

vAristotle was the first to classify plants into trees, shrubs, and herbs based on simple morphological characters. Later, Linnaeusintroduced two-kingdom classification-: the Plantae and Animaliakingdoms. A need was felt to further classify the kingdoms in terms of its characteristics.           R.H. Whittaker came up with five kingdom classification in 1969.

They are: Monera, Protista, Fungi, Plantae, and Animalia. His basis of classification was cell structure, thallus organisation, mode of nutrition, reproduction and phylogenetic relationships.

Ø  Kingdom Monera: It has bacteria as its member. Based on shape bacteria are of four types: Spherical coccus, Rod-shaped Bacillus, Comma- shaped Vibrium and the Spiral Spirillum.

• Archaebacteria Bacteria live in harsh habitats. They have different cell wall structures.
• Eubacteria
• It is also called ‘true bacteria’. Its features are a rigid cell wall and if it is motile then it has a flagellum. Few examples of Eubacteria are:

Cyanobacteria have chlorophyll similar to green plants and are photosynthetic autotrophs. They can be unicellular, colonial, filamentous, marine or terrestrial algae.

• Autotrophic bacteria break down inorganic substances and release energy for their ATP production.
• Bacteria are decomposers and have a crucial effect on humans. 
• They are the tiniest living cell and lack a cell wall? They can survive without oxygen.

Ø  Kingdom Protista: It contains all the single-celled eukaryotes. It has a well-defined nucleus and other membranes- bound organelles. They reproduce through cell fusion and zygote formation. Below are some examples of Protista:

• Chrysophytes

Microscopic organisms live in fresh as well as marine water. Diatoms and golden algae are examples of it.

• Dinoflagellates

Marine and photosynthetic, they have stiff cellulose. E.g. Gonyaulax.

• Euglenoids

Have pellicles (protein-rich layers) making their body flexible. They can be both photosynthetic as well as heterotrophs. E.g. Euglena.  

• Slime Moulds

Saprophytic protists feed on decaying twigs and leaves. They can transform into both plasmodium and fruiting bodies bearing spores. 

• Protozoans
• Live as predators and parasites and are heterotrophs. Four categories of protozoans:
• With the help of pseudopodia move and catch prey. 
• Have flagella and can be free-living or parasitic. 
• Ciliated possess thousands of cilia and a cavity that opens on the cell surface. In their life cycle include an infectious spore-like stage.

Ø  Kingdom Fungi: These heterotrophic organisms are filamentous except unicellular yeast. They have hyphae which are a long thread-like structure. Their cell walls consist of chitin and polysaccharides. They can be saprophytes (living on dead organisms), parasites (depending on living organisms) and symbionts (as lichens and mycorrhiza). They reproduce through fragmentation, fission, and budding. Their reproduction cycle includes three steps: Plasmogamy, karyogamy, and meiosis.

Based on the characteristics, this kingdom is divided into the following types:

• Phycomycetes
• Occur in water, decayed woods or as plant parasites. Their mycelium can be aseptate or coenocytic. Reproduction takes place through zoospores or aplanospores. E.g. Mucor, Albugo.
• Ascomycetes
• Are unicellular or multicellular and are saprophytic, decomposers, parasitic or coprophilous. Their mycelium is branched and separate. They are also called sac- fungi. E.g. Aspergillus and Neurospora.
• Basidiomycetes
• Live in soil, on wood, or as parasites on plant bodies. Their mycelium is branched and separate. Their vegetative reproduction takes place by fragmentation. E.g. Agaricus and Puccinia.
• Deuteromycetes
• Are known as imperfect fungi. They reproduce through spores called conidia. Their mycelium is branched and separate. They are parasites, saprophytes or decomposers. E.g. Alternaria and Trichoderma.

Ø  Kingdom Plantae: These eukaryotic chlorophyll-containing organisms are partially heterotrophic or parasitic. The plant cell predominantly contains chloroplasts and their cell wall is made of cellulose. This kingdom includes algae, bryophytes, angiosperms, etc. Diploid sporophytic and haploid gametophytes are the two stages of the plant life cycle.

Ø  Kingdom Animalia: These multicellular heterotrophic eukaryotic organisms lack cell walls. Plants are their main source of food. Their nutrition pattern is holozoic and they reproduce through embryological development. They have definite phases of growth and are most capable of locomotion.

ü  Viruses, Viroids and Lichens: These organisms are not included in Whittaker’s kingdom classification. The Viruses are non-cellular organisms and have an inert crystalline structure. The term ‘virus’ was coined by Pasteur. The virus contains proteins or either RNA or DNA. Viroids were discovered by T.O. Diener in 1971. These infectious agents contain free RNA and lack any protein coat.

ü  Viroids are smallest self replicating particles.

ü  Lichens live in a symbiotic association with algae and fungi. Their autotrophic algal component is called phycobiont and their heterotrophic fungal component is called mycobiont. Decrease in lichen population of an area is indicative of water pollution.