Biology >> The Living World

The Living World

1. Meaning of LIFE and Characteristics of 'Living Beings'

Life can be defined as a complex and unique organisation of molecules which is expressed by various chemical interactions exhibiting the phenomena of life and responding to stimulations and showing other characteristic features as self-controlled, duplication of characters, growth and evolution. But in truth, we cannot keep confine the definition of life to these few words. We can say an object or a body is alive if it exhibits the following characteristics:

  • Growth: All living organisms grow internally by the ingestion or intake of substances from the environment and transforming it into cell substances. Growth in living beings is an irreversible process. This type of growth which happens from the inside is called intussusceptions.
  • Size and shape: Living organisms have definite shape and size by which they can be distinguished from each other as well as from non-living objects.
  • Cellular organisation: Living organisms possess a working organization system at the cellular level, tissues, organ and organ systems to carry out the different functions in a co-ordinate manner.
  • Reproduction: Living beings replicate themselves. They reproduce, i.e., they produce their own kind and increase the number of individuals of their species which they do for the continuation of their species. This may happen by asexual, sexual or vegetative methods.
  • Response to stimuli: Living beings respond to external stimuli or abrupt or gradual changes in the environment such as heat, light, moisture, touch etc. and react against it.
  • Metabolism: Living organisms take in suitable food materials from their environment which are then digested inside the body and utilised to produce energy which is vital for all the life processes of the organism. All the biochemical processes like nutrition, respiration, excretion etc. going within the body are collectively called metabolism.
  • Locomotion and movement: All the animals show movement in one way or the other and some plant species too show movement in response to light or other external stimulus.
  • Life Cycle: Living organisms follow a definite pattern of life cycle. The same steps are apparent in the life cycle of all the individuals of a particular species.

2. Nomenclature of Living Organisms:

Nomenclature refers to the assigning of names to organisms to avoid confusion and help in proper study of the organism. Every organism has a common name which is obviously different in all parts of the world as people in different parts of the world speak a variety of languages. Hence, to avoid confusion, a scientific name is necessary which can be recognised worldwide.

Carolus Linnaeus was the first biologist to develop a rule for the naming of living organisms. In 1735, he suggested this system in which every organism was given a name consisting of two parts – generic name and specific name. This proposal was approved by the International Botanical Congress. Several restrictions and modifications were set but the basis of nomenclature proposed by Linnaeus remains unchanged. These rules' governing the naming of plants is embodied in a code known as International Code of Botanical Nomenclature and that for animals is known as International Code of Zoological Nomenclature formulated by International Zoological Congress.

Eg: Tiger: Panthera tigris
  Mango: Mangifera indica

Note: Sometimes, a third word indicating the sub-species is also added to the name which is termed Trinomial nomenclature. For example, the scientific name of Cauliflower is Brassica oleracea botrytis.

3. Rules of Binomial Nomenclature:

  1. The name should be in Latin or derivatives of Latin.
  2. The name should always be in italics.
  3. The generic name should begin with a capital letter and the specific name with a small letter.
  4. The name should generally be limited to 12 letters.
  5. The author's name should be suffixed in Roman letters.
  6. A name cannot be repeated.
  7. The name should indicate the feature of the organism.
  8. It must be easily pronounceable.
  9. The Taxonomist who wants to name a plant or animal should submit the diagnosis of the organism in Latin to the International Botanical or Zoological Congress. The author should follow the rules of nomenclature and publish his account in standard journal. The proposed name will be valid only if the International Congress recognizes this as a valid publication and approves the diagnosis.
  10. The author should also send the specimen as type-specimen for preservation in some famous museums and herbaria.

4. Taxonomic hierarchy and Taxonomic categories:

For the ease of classification, the organisms (both plants and animals) are put in certain groups called taxons (sing. Taxa). The process of classification and grouping of organisms into different taxa is called Taxonomy. The scientific study and the classification of organisms with the goal of reconstructing their evolutionary history and relationships are called systematics. In short, Systematics is taxonomy combined with Phylogeny. Hierarchy is a systematic framework of classification with sequence of groups at different levels in which each group except the lowest includes one or subordinate groups.

The prevailing system of Taxonomic Hierarchy (from larger to smaller taxa) is:
Kingdom → Phylum/Division→ Class → Order → Family → Genus → Species

Species: It is the lowest category of classification, comprising closely related individuals with similar morphological, anatomical, biochemical and cytological characters. It can be described as a group of population capable of breeding among themselves and sharing a common gene pool. E.g. Sativum, leo, tigris, sapiens, etc.

Genus: It is a broader category compared to species and comprises of several species having certain similarities of characters

Eg. Solanum (comprising of species - tuberosum, nigrum, melongena etc.), Panthera (comprising of specie - tigris, leo, etc.)

Family: It comprises of several related genera bearing certain similar characteristics. For example, Solanaceae (includes genera – solanum, petunia, Datura, Atropa etc.), Felidae (includes genera – Panthera, Felis, etc.)

Order: It is a group of related families. Example: Polymoniales (includes families – Convolvulaceae, Solanaceae, etc.), Carnivora (includes families like Felidae and Canidae)

Class: It is a group of several related orders. Example: Dicotyledonae (includes orders like sapindales and polymoniales), Mammalia (includes orders like Primata, Carnivora)

Phylum/Division: Phylum is a group of several classes for animals. Example: Chordata (includes mammalian, reptilian, aves, amphibian and pisces)

Division is for plant classes. Example: Angiospermae (includes dicots and monocots)

Kingdom: It is the highest category comprising of related phylum or divisions. Example: Kingdom Animalia, Plantae, Monera, etc.

5. Taxonomical Aids:

  1. Herbarium: It is a place where plant specimens are collected, dried, pressed, and preserved on sheets of dimensions 41×29 cm with information about their identity, date and place of collection, collector’s name, etc. Their main purpose is accurate identification and α-taxonomic research on the basis of morphological research and for quick reference.
  2. Botanical Gardens: Contains a vast array of plants collected from different locations for ready reference. The botanical name and family name is labelled into each plant (ex-situ conservation). Examples are: Royal Botanical Garden, Kew, England; Indian Botanical Garden, Kolkata, India.
  3. Museum: Museums contains collection of preserved (dead) specimen of plants and animals for study and reference. Common methods are stuffing (medium size animals), pinning (insects), skeleton display (large animals).
  4. Zoological Parks: Contains animal species collected from their natural habitat and kept for public display and study of food habits and behaviour in a protected environment (ex-situ conservation). Kruger, South Africa is the largest Zoo in the world.
  5. Taxonomic Key: It is used for identification of plants and animals based on similarities and differences. A key consists of group characters, sub-group characters and individual characters. By eliminating irrelevant characters and choosing only the most relevant character, one can descend from group characters into individual characters that help in identifying the species. It is a set of contrasting characters known as a couplet. For example: to identify a plant species we may consider the following couplets –

    i. (a) Flowering (b) Non-flowering
    ii. (a) Tap root system (b) Fibrous root system
  6. f. Other aids:
    i. Flora – contains the actual account of habitat and distribution of plants of a given area.
    ii. Manuals – these are complete listings and description of plants growing in a particular area.
    iii. Monographs – they contain information on only one taxon.
    iv. Catalogues – Alphabetical arrangement of species along with their features.



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