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MHT-CET : Biology Entrance Exam

MHT - CET : Biology - Classification Page 1

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 Introduction:

 

  1.  Taxonomy A branch of science that deals with identification, naming and classification of plants as well as animals is called taxonomy.
  2. Importance of taxonomy
    a. Collective study of organisms.
    b. Identification scheme for organisms.
    c. Universally accepted scientific names.
    d. Classifying and putting the plants and animals into definite group.
    e. Evolutionary relationship.

 

 

Concept of Species

 

  1. 'Species' is regarded as the basic unit of classification.
  2. Species: Groups of interbreeding natural populations which are reproductively isolated from other groups, are called species.

 

 

Various Taxa and Categories

 

  1. Classification includes a hierarchical system of different ranks, with 'kingdom' at the top and 'species' at the bottom.
  2. Categories: All the ranks of classification are called categories.
  3. Taxon: All the members of a category belong to one taxon.
  4. Various categories used in classification, from the bottom to the top, are:
    1. Species: It is the smallest unit. The potentially interbreeding group.
    2. Genus: Group of closely related species.
    3. Family: Group of closely related genera.
    4. Order/Cohort: Group of closely related families.
    5. Series: Group of closely related orders.
    6. Subclass: Group of closely related series.
    7. Class: Group of closely related sub - classes.
    8. Subdivision: Group of closely related classes.
    9. Division: Group of closely related subdivisions.
    10. Kingdom: Group of closely related divisions.
  5. Units of classification:

1.      Species: The species is the smallest unit of classification. The species refers to a group of plants or animals which have close resemblance with one another in their morphological characters and breed freely among themselves. For example, all banyan trees belong to the species bengalensis while all pipal trees belong to the species religiosa. John Ray was first to use the term species.

2.      Genus: The genus is a unit of classification higher than the species. The genus is a group of related species which show resemblance in their reproductive characters but differ in their vegetative characters. For example, banyan and pipal are two different species belonging to the same genus Ficus.

3.      Family: The family is a unit of classification higher than the genus. The family is a collection of genera (singulargenus) showing similar reproductive characters. For example, Hibiscus and Sida are two different genera showing resemblance in their floral characters belonging to the same family, Malvaceae.

4.      Cohort or Order: The cohort or order is a unit of classification higher than the family. A group of closely related families forms a cohort or order. For example, families Malvaceae and Tiliaceae belong to the same cohort (order) Malvales.

5.      Class: The class is a broad unit of classification which includes all related subclasses. For example, class Dicotyledonae consists of subclasses like Polypetalae, Gamopetalae and Apetalae.

6.      Division or Phylum: The division or phylum (for animals) is the largest unit of classification. The division consists of closely related classes. For example, division Angiospermae includes classes like Dicotyledonae and Monocotyledonae.

 

 

Hierarchical Levels of Classification

 

Classification of Hibiscus plant according to the hierarchical levels of classification.

Kingdom
Plantae - Multicellular autotroph.

Division
Spermatophyta - Seed producing plant.

Sub
-division Angiospermae - Ovules enclosed inside ovary.

Class
Dicotyledonae - Two cotyledons in the embryo.

Sub
-class Polypetalae - Petals of flowers are free.

Series
Thalamiflorae - Distinct thalamus, hypogynous flower.

Order
Malvales - Monadelphous stamens, axile placentation.

Family
Malvaceae - Stipulate leaves, Reniform anthers.

Genus
Hibiscus - Epicalyx present, capitate stigma.

Species
rosa - sinensis - Flower stalk presents (pedicel), long staminal tube.

 

 

Binomial Nomenclature

 

  1. Carlous Linnaeus was a Swedish botanist who established a naming system consisting of two words called binomial nomenclature.
  2. The first part of the name indicates genus while the second part indicates species. Example: For the mango plant, the binomial nomenclature is Mangifera indica Linn, where Mangifera is genus, the indica is species and Linn is the short form of the name of scientist Linnaeus who discovered it.
  3. Importance of Binomial Nomenclature
    a. Simple, meaningful, standard and universally accepted names.
    b. Helps in identification and grouping of organisms in any part of the world.

 

 

Principles of Classification:

 

  1. Taxonomy makes use of information from all the branches of biology such as morphology, cytology, phylogeny, molecular biology, etc.
  2. Morphological Criteria: Plants with identical morphological characters are grouped together.
  3. Phylogenetic Considerations: Phylogeny is evolutionary history. According to phylogeny, each group of plants is a product of modifications of different characters. If plants resemble each other, then they are of common origin.
  4. Numerical Taxonomy: Resemblance in characters is considered to be the index of closeness while differences indicate separation of plants into different groups.
  5. Chemotaxonomy: Here, the plants are classified according to their chemical composition into different groups. If two species are identical in their chemical substances, then they are closely related.

 

Carolus Linnaeus:

  1. Professor of Botany and Medicine.
  2. Father of taxonomy.
  3. Life span:1707 - 1781.
  4. Swedish Naturalist, studied at the university of Lund.
  5. Identified and described 5,900 species of plants and 4,200 species of animals.
  6. Introduced binomial nomenclature and artificial system of classification based on sexual characteristics, viz., stamens and carpels.
  7. Books:(1)Genera Plantarum (2)Species Plantarum.

 

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