Genus–differentia definition (Photo credit: Wikipedia)
Diversity in Living OrganismsCLICK HERE FOR DIAGRAMS
1) Every living organism is unique and this uniqueness is the basis of the vast diversity
displayed by the organisms in our world.
2) This huge diversity is the result of evolution, which has occurred over millions of years.
3) The massive biological diversity can only be studied by classification i.e. arranging
organisms into groups based on their similarities and differences.
4) Different characteristics are used to determine thehierarchy of classification.
5) The primary characteristics that determine the broadest divisions in classification are
independent of any other characteristics. The secondary characteristics depend on the
primary ones.
6) Prokaryotic or eukaryotic cell organization is the primary characteristic of classification,
since this feature influences every detail of cell design and capacity to undertake
specialized functions.
7) Being a unicellular or multicellular organism formsthe next basic feature of classification
and causes huge differences in the body design of organisms.
8) The next level of classification depends on whether the organism is autotrophic or
heterotrophic. Further classification depends on the various levels of organization of the
bodies of these organisms.
9) The evolution of organisms greatly determines theirclassification.
10) The organisms who evolved much earlier have simple and ancient body designs whereas
the recently evolved younger organisms have complexbody designs.
11) Older organisms are also referred to as primitive or lower organisms whereas the younger
organisms are also referred to as advanced or higher organisms.
12) The diversity of life forms found in a region is biodiversity.
13) The region of mega-diversity is found in the warm and humid tropical regions of the Earth.
14) Aristotle classified organisms depending on their habitat.
15) Robert Whittaker proposed the five-kingdom scheme of classification, based on the cell
structure, nutrition and body organization of the organisms.
16) The main characteristics considered in the five-kingdom scheme of classification are:
i) Presence of prokaryotic or eukaryotic cells.
ii) If eukaryote, whether the organism is unicellular or multicellular.
“Monophyletic tree of organisms”. Ernst Haeckel: Generelle Morphologie der Organismen, etc. Berlin, 1866. (Photo credit: Wikipedia)
iii) Whether the cells possess or lack cell wall and whether they can prepare their own
food.
17) The categories or taxa used in the classification of organisms are kingdom,
phylum/division, class, order, family, genus and species. The smallest unit of classification
is species whereas the highest unit is kingdom.
18) The 5 kingdoms proposed by Whittaker are Monera, Protista, Fungi, Plantae and Animalia.
Carl Woese further divided Monera into Archaebacteria and Eubacteria.
19) Prokaryotic one-celled organisms such as bacteria, cyanobacteria and mycoplasma are
included in Monera.
20) Monerans show either autotrophic or heterotrophic nutrition. Cell wall may be present or
absent.
21) Unicellular eukaryotic organisms such as protozoans, unicellular algae and diatoms are
grouped under Protista. They may be autotrophic or heterotrophic and may use
appendages for locomotion.
22) Fungi, such as yeast and mushrooms, include heterotrophic, eukaryotic organisms, which
are normally saprophytes. Their cell walls are composed of chitin.
23) Lichens are symbiotic associations of certain fungiwith blue green algae.
24) Multicellular, autotrophic eukaryotes possessing cell wall are included under kingdom
Plantae.
25) Classification of plants is done at three levels onthe basis of
i) Presence or absence of well-differentiated body
ii) Presence or absence of vascular tissue
iii) Ability to bear seeds, which could be naked orenclosed in fruits.
26) The important divisions of Plantae are Thallophyta, Bryophyta, Pteridophyta,
Gymnospermae and Angiospermae.
27) Thallophytes, Bryophytes and Pteridophytes possess inconspicuous reproductive organs
and are called Cryptogams. Gymnosperms and Angiosperms are grouped under
Phanerogamae, since they possess well-differentiated, seed producing reproductive
tissues.
28) Thallophytes (or algae) are the simplest plants lacking well-differentiated body design.
E.g. – Spirogyra.
29) Bryophytes, such as moss and Riccia, show differentiated plant body lacking vascular
tissue.
30) Plants grouped under Pteridophyta show well-differentiated plant body with vascular
tissues for conduction. E.g. Ferns.
31) Gymnosperms, for e.g. pines and deodar, are phanerogams bearing naked seeds.
32) In Angiosperms/flowering plants, the seeds are enclosed in fruits.
33) Cotyledons are present in the embryos of seeds.
34) Monocot plants possess seeds with single cotyledons whereas dicots are plants with 2
cotyledons in seeds.
35) Monocots show fibrous root system, parallel venation of leaves and flowers with three (or
multiple of three) petals.
36) Tap root system, reticulate venation of leaves and flowers with five (or multiple of five)
petals are features of dicots.
37) Organisms grouped under Animalia are eukaryotic, multicellular, heterotrophic and lacking
cell walls.
38) Animals are further divided into ten groups – Porifera, Coelenterata, Platyhelminthes,
Nematoda, Annelida, Arthropoda, Mollusca, Echinodermata, Protochordata and Vertebrata.
39) In Porifera, also called sponges, the body is perforated by numerous pores and shows
cellular level of organization. In addition, a hard exoskeleton and canal system are
present. Sponges are non-motile. E.g. – Sycon.
40) Coelenterates are radially symmetrical and show a cavity called coelenteron between
epidermis and gastrodermis. Some like Hydra aresolitary forms whereas others like corals
live in colonies.
41) Platyhelminthes includes the flat worms which are bilaterally symmetrical, dorsoventrally
flattened, triploblastic and acoelomate. They may be free-living (e.g. Planaria) or parasitic
(e.g. tape worm).
42) The body of nematode worms is cylindrical, bilaterally symmetrical, triploblastic and
pseudocoelomate. They are usually parasitic. E.g. Ascaris.
43) Annelids are triploblastic, bilaterally symmetrical with true coelom and found in diverse
habitats. Segmentation and extensive organ differentiation is seen. E.g. Earthworm and
Nereis.
44) The largest phylum of animal kingdom, Arthropoda, contains triploblastic, bilaterally
symmetrical and segmented animals. These animals possess jointed legs and open
circulatory system. E.g. Butterfly, centipede, crab, spider.
45) In phylum Mollusca, (e.g. snail and Octopus) organisms show bilateral symmetry, soft
body, open circulatory system and reduced coelom.
46) Echinodermata includes spiny skinned organisms with calcareous skeleton. They are
triploblastic, coelomate, marine and free-living. Water vascular system is an important
feature. Starfish and Holothuriaare examples of this phylum.
47) All chordates have a notochord, dorsal nerve cord and paired pharyngeal gill
slits/pouches. Also they are triploblastic, coelomic and bilaterally symmetrical.
48) Vertebrates and Protochordates are grouped under Chordata.
49) The Protochordates possess notochord at some or the other stage of their life, e.g.
Balanoglossus, Amphioxus.
50) Vertebrates show true vertebral column and endoskeleton. Complex body organization
and differentiation is seen.
51) The five classes of vertebrates are Pisces, Amphibia, Reptilia, Aves and Mammalia.
52)The endoskeleton in fish may be cartilaginous or bony.
53) Mammary glands produce milk in mammals to nourish the young ones.
54) Binomial nomenclature, developed by Carolus Linnaeus, uses two names to identify an
organism. The first name is the generic name beginning with a capital letter whereas the
second name is the species name which begins with asmall letter.
55) Binomial nomenclature makes it possible to identify every species of organisms in the
astounding diversity of life present in our planet.
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