Classification of Living Organisms
* A process of gradual and progressive change or development in characteristics is known as evolution.
* Organisms are grouped at various levels: Kingdom, Phylum for animals or Division for plants, class, Order, Family, Genus, and species.
* Kingdom Protista includes unicellular eukaryotic organisms, the simplest of the eukaryotes.
* Kingdom Monera consists of prokaryotic cell consisting of bacteria, small one – celled organisms.
* Kingdom Fungi are eukaryotic organisms which lack chlorophyll. They have to depend on other sources for their nourishment.
* Kingdom Plantae are multi cellular eukaryotic with cell walls. They use chlorophyll for photosynthesis.
* Kingdom Animalia includes all organisms which are heterotrophic, multi cellular eukaryotic without cell walls.
Diversity in Living Organisms – The Plant Kingdom
* Bryophytes do not have true leaves and roots or special tissues for the transportation of nutrient and water. For example – Moss.
* Pteridophytes have well – differentiated plant body and vascular tissues. For example – Ferns.
* Gymnosperms bear naked seeds and are usually perennial, evergreen and woody. For example – Pines.
* Angiosperms are highly evolved plants with flowers, fruit and covered seeds.
* Plant embryos in Angiosperms are made of Cotyledons.
* Monocots are Angiosperms with a single Cotyledon. For example – Corn.
* Dicots are Angiosperms with two Cotyledon. For example – Bean
Biological Classification System
* The first classification were made to identify organisms that were useful to an for food, shelter and clothing.
* Aristotle devised the first scientific method of classification.
* Later, Carl Linnaeus came up with the two kingdom system of classification.
* All plants were put in the Kingdom plantae while all animals were put in the Kingdom Animalia.
* In 1969, R.H. Whittaker proposed a Five kingdom Classification system. Three more kingdoms: Monera, Protista and Fungi classifation were added to the existing kingdoms of Plantae and Animalia.
* The main criteria that Whittaker used for this classification system were cell structure, thallus organisation, mode of nutrition, reproduction and phylogenetic relationships.
Kingdom Monera
* Bacteria are the sole members of kingdom Monera.
* Different bacteria synthesise their food in different ways.
* Based on their shape, bacteria can be classified into four types: spherical coccus, rod – shaped bacillus, comma – shaped vibrium and spiral sprillum.
* Bacteria reproduce by fission. They can also reproduce sexually by a primitive
* DNA transfer from one bacterium to another.
* Eubacteria like cyanobacteria are the true bacteria.
* There are also special bacteria called archaebacteria that live in extreme conditions.
* Mycoplasmas are the bacteria that do not have a cell wall.
Kingdom Protista
* All unicellular eukaryotes come under Kingdom Protista.
* Members of this kingdom are primarily aquatic.
* Some protests also have a flagella or a cilium.
* They reproduce both asexually through cell fusion and sexually via zygote formation.
* Chrysophytes , dianoflagellates, euglenoids, slime moulds and protozoans are some examples of protists.
* Chrysophytes include diatoms and golden algae.
* Dianoflagellates are colourful protists found both in marine and fresh water.
* Euglenoids have two flagella, one short and the other long one.
* Slime moulds are saprophytic protists.
* There are four types of protozoans: amoeboid protozoans, flagellated protozoans, ciliated protozoans and sporozoans.
Kingdom Plantae and Animalia
* Kingdom Plantae comprises all eukaryotic, chlorophyll – containing organism called plants.
* Plant cells are characterised by the presence of a cell wall, which is made up of cellulose.
* Most plants are autotrophs, but they can be insectivorous and parasites as well.
* Plants have two alternate phases on their life cycle: the diploid sporophytic and the haploid gametophytic phases.
* The phenomena of alteration of sexual and asexual forms in the lifecycle is referred to as “alternation of generation”.
* Kingdom Animalia comprises only heterotrophic, multicellular eukaryotic organisms.
* Animal cells have no cell wall.
* Animals reproduce sexually after a male and a female copulate, is followed by embryological development.
* Most animals are motile.
Algae
* Algae are simple, thalloid, chlorophyll – bearing autotrophic organisms found in fresh and marine water, moist stones, soil and wood.
* Algae can be unicellular, colonial or filamntous.
* Based on the type of pigment and the type of stored food we can classify algae into Chlorophyceae, Phaeophyceae and Rhodophyceae.
* Chlamydomonas, Volvox, Spirogyra, are some members of the class Chlorophyceae.
* Class Phaeophyceae includes Ectocarpus, Dictyota, and Laminaria.
* These species, commonly termed as brown algae, are mostly found in brackish or salt water.
* Rhodophyceae is another class of algae whose members include Polysiphonia,
* Gracilaria and Gelidium, often called red algae.
Bryophytes
* Bryophytes are plants that usually grow in damp, humid and shaded localities.
* The plant body is thallus – like and is either prostrate or erect, and is attached to the substratum by unicellular or multicellular rhizoids.
* Bryophytes have both male and female multicellular sex organs.
* The male sex organ is called the antheridia and it produces biflagellate antherezoids.
* The female organ is called the archegonium and produces a single egg.
* Bryophytes are of two types – liverworts and mosses.
* Liverworts grow in moist and shady environs.
* Liverworts reproduce both asexually and sexually.
* Moss is another type of bryophyte.
* Mosses reproduce vegetatively and sexually.
Pteridophytes
Pteridophytes are plants that:
* Flourish in a damp, cool and shady habitat although some species also grow in sandy – soil conditions
* Possess vascular tissues – xylem and phloem
* The main plant body is a sporophyte and is differentiated into organs such as roots, stem and leaves.
* Sporophyte bears sporangia, which germinate into a prothallu – a structure that bears antheridia and archegonia.
* An antherozoid fuses with the egg in the archegonium to form a zygote.
* The Sporophytic phase is the dominant phase in the lifecycle of Pteridophytes.
Gymnosperms
* Gymnosperms are plants in which the ovules are not enclosed by an ovary wall and remain exposed both pre and post – fertilisation.
* The seeds that develops from the ovules post – fertilisation. too are uncovered or naked.
* Most gymnosperms have tap roots.
* The stems of a gymnosperms can be branched or unbranched and the leaves compound or simple.
* The reproductive structure of gymnosperms is called a strobilus or cone.
* Gymnosperms have both male and female strobili.
* Fertilisation occurs when the pollen grains. released from the microsporangium, are carried by the air currents and come in contact with the opening of the ovules.
Angiosperms
* Angiosperms are plants in which the ovules are not naked but present inside the flowers.
* Reproduction in angiosperms takes place through stamen and pistil, the male and female sex organs in the plant’s flowers.
* The stamen consists of two parts – filament and anther.
* The pistil consists of the stigma at the tip followed by the style in the middle and an ovary at the base.
* The embryo – sac has a three – celled egg apparatus consisting of one egg cell, two synergids, three antipodal cells and two polar nuclei.
* During pollination, one male gamete fuses with the egg cell to produce a zygote, while the other gamete fuses with the diploid secondary nucleus to produce the triploid primary endosperm nucleus or PEN.
Basic of Animal Classification
* Animals are classified on the basic fundamental features such as level of organisation, symmetry, cell organisation, nature of coelom, segmentation and notochord.
* Level of organisation is the first basic fundamental features by which animals are classified. There are four main types of cell patterns: cellular, tissue, organ and organ system.
* Some animals are asymmetrical, some have radial symmetry and many exhibit bilateral symmetry.
* In animal, there are two types of cell organisation – disploblastic and triploblastic.
* According to the nature of coelom, animals are classified as, coelomates, acoelomates and pseudocoelomates.
* Animals are also classified on the basis of segmentation.
* The most important feature for animals classification is the classification is the presence absence of a notochord.
* Hemichordates are a small group of worm – like marine animals with cylindrical body divided into proboscis, collar and trunk.
* Phylum Chordata includes animals which possess a notochord either throughout or during early embryonic life.
* Phylum Chordata is divided into three subphyla: Urochordata or Tunicata, Cephalocahordata and.
* Subphyla Urochordata and Cephalochlordata are also referred to as protochordates.
* Urochordata have a notochord only in the larval tail, while Cephalocahordata have a persistent notochord, which extends from head to tail region.
* Vertebrates possess a notochord during the embryonic period, which is later replaced by a cartilaginous or bony Vertebral column.
Vertebrates
* All Vertebrates are chordates but all chordates are not Vertebrates.
* Cyclostomates are the most primitive chordates, without jaws and are ectoparasites on fish.
* Chondricthyes are marine and freshwater fish with a bony endoskeleton and a persistant notochord.
* Osteichthyes are marine and freshwater fish with a bony endoskeleton and streamlined body.
* Amphibians have adapted to both land and water.
* Reptiles are characterised by the presence of dry and cornified skin.
* Birds are warm – blooded animals and have feathers on their bodies.
* Mammals have mammary glands, hair on their skin and are warm – blooded animals.