Samacheer Class 7 Science - Basis of Classification

Binomial nomenclature is a universal system of naming organisms that was developed by Carl Linnaeus. As per this system, each organism has two names – the first is the Genus name and the second is the Species name. The genus name is written first and is always capitalized, while the species name is written second and is written in lowercase. Both names are typically written in italics or underlined. For example, the scientific name of humans is Homo sapiens, where Homo is the genus and sapiens is the species. This system provides a standardized way to name organisms across different languages and regions, making scientific communication clear and precise. It helps in organizing and classifying the enormous diversity of life on Earth in a systematic manner.

Kingdom Plantae consists of multicellular eukaryotes that can photosynthesize and produce their own food using sunlight, water, and carbon dioxide. The cells of plants have a rigid cell wall made of cellulose that provides structural support. Plant cells contain chloroplasts where photosynthesis occurs. Plants are generally stationary and cannot move from place to place. Examples of plants include ferns, cone-bearing plants such as pines, and flowering plants such as roses and wheat. Kingdom Animalia consists of multicellular, eukaryotic, and heterotrophic organisms that obtain nutrition by consuming other organisms or organic matter. The cells of animals lack a cell wall and have only a cell membrane, making them flexible. Animals cannot photosynthesize and must obtain energy by consuming food. Unlike plants, animals are mobile and can move from place to place to search for food and escape danger. Examples of animals include invertebrates such as insects and worms, and vertebrates such as fish, birds, mammals, and reptiles. The key differences are that plants are autotrophic with cell walls and are stationary, while animals are heterotrophic without cell walls and are mobile.

Two merits of the Five Kingdom classification are as follows. First, this system of classification is more scientific and natural compared to earlier classification systems because it is based on multiple characteristics of organisms rather than just one or two features. It takes into account the fundamental differences between organisms at the cellular and molecular level. Second, this system of classification clearly indicates the cellular organization of organisms, their mode of nutrition, and the characteristics that reflect the early evolution of life on Earth. By organizing organisms into five kingdoms based on these criteria, it provides a better understanding of how different groups of organisms are related to each other and how life has evolved and diversified over time. This makes it easier for scientists to study and understand the relationships between different organisms.

The five kingdom classification was proposed by R.H. Whittaker in 1969 as an improvement over earlier classification systems. He classified all organisms into five kingdoms on the basis of several important characteristics including cell structure, which distinguishes prokaryotes from eukaryotes; mode of nutrition, which separates autotrophs from heterotrophs; source of nutrition, which differentiates between organisms that obtain energy from sunlight, organic matter, or other organisms; and body organization, which considers whether organisms are unicellular or multicellular. The five kingdoms are Monera, which includes prokaryotic organisms; Protista, which includes simple eukaryotic organisms; Fungi, which includes heterotrophic organisms that decompose organic matter; Plantae, which includes photosynthetic multicellular organisms; and Animalia, which includes multicellular heterotrophic organisms. This classification system provides a more comprehensive and natural grouping of organisms based on their fundamental biological characteristics.

(i) Gaspard Bauhin jn 1623, introduced naming of organisms with two names which is known as Binomial nomenclature, and it was implemented by Carolus Linnaeas in 1753
(ii) Binomial nomenclature an universal system of naming organisms. As per this system, each organism has two names – the first is the Genusname and the second is the Speciesname.
(iii) Genus name begins with a capital letter and Species name begins with a small letter. Example The nomenclature for onion is Allium sativam. Genus name is Allium, species name is sativam.
(iv) Vernacular name is a local name that is familiar for a particular place. Binomial name is an universal name which never changes.
(v) Binomial nomenclature and classification helps scientists to identify any organisms and to place them at a particular hierarchy.

Invertebrates are animals without a backbone. The invertebrates have been classified into various phyla as follows:
S.No
Division
General Characters
1.
Phylum Protozoa
Eg. Amoeba, Euglena p
Microscopic unicellular, pseudopodia, flagella and cilia for locomotion, reproduce by fission or conjugation.
2.
Phylum Porifera
Eg. Leucosolenia, Sycon.
Multicellular organisms with holes in the body. Skeleton formed of spicules, asexual and sexual reproduction.
3.
Phylum Coelenterata Eg. Hydra, Jelly fish.
Multicellular organisms Diploblastic, sessile or free swimming, solitary or colonial, asexual and sexual reproduction
4.
Phylum Platyhelminthes Eg. Planaria, Liver fuke
Acoelomates, parasites inside the body of animals and human beings, mostly hermaphrodite (bisexual).
5.
Phylum Aschelminthes or Nematoda
Eg. Ascaris lumbricoides
Unsegmented body, mostly parasites in human beings and animals, causing diseases, asexual reproduction.
6.
Phylum Annelida Eg. Earthworm, Leech.
Triploblastic, segmented body, mostly hermaphrodite (bisexual and unisexual).
7.
Phylum Arthropoda Eg. Crab, Prawn
Segmented body, thick chitinous cuticle forming an exoskeleton, paired and jointed legs, unisexual exhibits sexual dimorphism.
8.
Phylum Mollusca Eg. Cuttle fish, Snail
Soft bodied, unsegmented, muscular head, foot and visceral mass, mantle, a calcareous shell, sexual reproduction.
9.
Phylum Echinodermata Eg. Starfsh, Sea – Urchin
Exclusively marine, spines and spicules over the body, water vascular system, tube feet, for feeding, respiration and locomotion sexual reproduction.

Kingdom Fungi comprises of unicellular to multicellular organisms which are heterotrophic in their mode of nutrition. They do not contain chlorophyll and cannot photosynthesize, so they must obtain nutrition from other sources. Because of their heterotrophic nature and lack of photosynthetic ability, fungi show multiple modes of nutrition. Saprophytic nutrition involves obtaining nutrition from dead and decaying organic matter, breaking it down into simpler substances that can be absorbed. Examples of saprophytic fungi include Mucor, which grows on bread and other food items. Parasitic nutrition involves obtaining nutrition from living organisms, causing harm to the host organism in the process. An example of a parasitic fungus is Cercospora, which causes leaf spots on plants. Symbiotic nutrition involves obtaining nutrition through a mutually beneficial relationship with another organism, where both organisms benefit from the association. An example of symbiotic fungi is Lichens, which are formed by the association of fungi and algae, where the fungus provides structure and protection while the algae provide food through photosynthesis. These diverse modes of nutrition make fungi essential decomposers in ecosystems.