The Living World Biology Notes - Properties of Living Organisms, Taxonomy, Binomial Nomenclature, Taxonomic Categories and Taxonomic Aids

• Life is a unique, complex organization of molecules, expressed through chemical reactions which lead to growth, development, responsiveness, adaptation & reproduction.
• A living organism is a self-replicating, evolving, and self-regulating interactive system capable of responding to external stimuli.

Properties of Living Organisms

1. Growth

• It is the increase in number & mass of cells by cell division.
• In plants, growth continues throughout their lifespan.
• In animals, growth is only up to a certain age. However, cell division occurs to replace lost cells.
• Basically, growth is the increase in mass & size. Thus non-living objects also grow (surface accumulation of material). So growth is not a defining property of living organisms.
• In living organisms, growth is from inside.

2. Reproduction

• It is the production of progeny having features similar to those of parents.
• Organisms reproduce asexually and sexually.
• In unicellular organisms, growth & reproduction are the same because they reproduce by cell division.
• Many organisms do not reproduce (e.g., mules, worker bees, infertile human couples, etc.). Hence, reproduction is not a perfect defining property of living organisms.

3. Metabolism

• It is the sum total of all biochemical reactions taking place inside a living system.
• It is the defining feature of living organisms.
• Metabolic reactions can be demonstrated outside the body in cell-free systems. Isolated metabolic reactions in vitro are not living things but are living reactions.

4. Cellular Organization

• Organisms are made up of one or more cells.
• It is the defining feature of living organisms.

5. Consciousness

• It is the ability of organisms to sense their environment and respond to environmental stimuli (like light, water, temperature, other organisms, chemicals, pollutants, etc).
• All organisms are ‘aware’ of their surroundings. So, it is the defining property of living organisms.
• Humans are the only organisms having self-consciousness.

Diversity in the Living World

• The number and types of organisms present on Earth refer to biodiversity.
• The number of species described is 1.7-1.8 million.

Taxonomy

• Taxonomy is the study of identification, classification & nomenclature of organisms.

Systematics

• Systematics (Latin ‘systema’ = systematic arrangement) deals with evolutionary relationships among organisms.

Systema Naturae

• Systema Naturae is a book written by Linnaeus.

Basic Processes of Taxonomy

• Characterization: Understanding of characters of organisms such as external & internal structure, cell structure, development process, ecological information, etc.
• Identification: Correct description of the organism to enable naming.
• Classification: Grouping of organisms into convenient categories (taxa) based on characters.
• Nomenclature (naming): Standardization of names so an organism is known by the same name worldwide.

• The system of naming with two components is called Binomial nomenclature. It was proposed by Linnaeus.
• Botanical names are based on the rules in International Code for Botanical Nomenclature (ICBN).
• Zoological names are based on International Code for Zoological Nomenclature (ICZN).

Universal Rules of Binomial Nomenclature

• Scientific names are in Latin or Latinised and written in italics. When handwritten, they are underlined separately.
• The first word is the genus name (Generic name) and the second word is the species name (specific epithet).
  • E.g., Homo sapiens - Homo represents the genus name, and sapiens represents the species name.
• The Genus name starts with a capital letter, and the species name starts with a small letter.
• The name of the author (in abbreviated form) appears at the end of the biological name.
  • E.g., Mangifera indica Linn. indicates this species was first described by Linnaeus.

Taxonomic Categories

• Classification involves a hierarchy of steps, where each step represents a taxonomic category (rank).
• All categories together constitute a taxonomic hierarchy.
• A group of organisms occupying a particular category is called a taxon (pl. taxa). E.g., Class Mammalia.
• Each category or taxon represents a unit of classification.

Taxonomic Hierarchy in Ascending Order

• Species: A group of closely related organisms capable of interbreeding to produce fertile offspring. It is the lowest category.

  Common name	Generic name	Specific epithet
  Mango	Mangifera	indica
  Potato	Solanum	tuberosum
  Nightshade	Solanum	nigrum
  Brinjal	Solanum	melongena
  Lion	Panthera	leo
  Tiger	Panthera	tigris
  Leopard	Panthera	pardus
  Modern man	Homo	sapiens

• Genus: An aggregate of closely related species.
  • Potato, nightshade, and brinjal are species of genus Solanum.
  • Lion, leopard, and tiger are species of genus Panthera. It differs from genus Felis (genus of cats).
• Family: A group of closely related genera.
  • Genus Solanum, Petunia, and Datura belong to Family Solanaceae.
  • Genus Panthera and Felis belong to Family Felidae.
• Order: An assemblage of related families.
  • Families Convolvulaceae and Solanaceae belong to Order Polymoniales.
  • Families Felidae and Canidae belong to Order Carnivora.
• Class: An assemblage of related orders.
  • Orders Primata, Carnivora, etc., belong to class Mammalia.
• Phylum (Division in case of plants): An assemblage of related classes.
  • Classes Amphibia, Reptilia, Aves, Mammalia, etc., come under phylum Chordata.
• Kingdom: The assemblage of related phyla. It is the highest category.
  • E.g., Kingdom Plantae, Kingdom Animalia.

Organisms with Their Taxonomic Categories

Taxonomic Aids

a. Herbarium

• It is a store house (repository) of plant specimens that are dried, pressed and preserved on sheets and are arranged according to universally accepted classification.
• Herbarium sheets are labelled with information about date and place of collection, English, local and botanical names, family, collector’s name etc.

b. Botanical Gardens

• These are specialized gardens having collections of living plants for reference and identification.
• Each plant is labelled with its botanical name and family.

Famous botanical gardens:

• Royal Botanical Garden at Kew (England).
• Indian Botanical Garden, Howrah (India).
• At National Botanical Research Institute, Lucknow (India).

c. Biological Museum

• It is a collection of preserved plants and animals for study and reference.
• A museum contains:
• Specimens preserved in preservative solutions in containers or jars.
• Preserved dry specimens of plants and animals.
• Insects preserved in insect boxes after collecting, killing and pinning.
• Stuffed larger animals like birds and mammals.
• Collections of animal skeletons.

d. Zoological Parks (Zoos)

• These are the places where live wild animals are kept in protected environments under human care.
• It helps to learn about their food habits and behaviour.

e. Key

• It is an analytical method of identification of organisms based on similarities and dissimilarities.
• It is based on the contrasting characters generally in a pair called couplet.
• Each couplet has two opposite options. Of these, only relevant option is accepted and other is rejected.
• Each statement in the key is called a lead.

Flora, Manuals, Monographs & Catalogues

• Flora: Actual account of habitat and distribution of plant species of a given area.
• Manuals: The record that contains information for identification of names of species found in an area.
• Monographs: The records that contain information on any one taxon.
• Catalogue: Alphabetical list of species.