1. The Living World – NCERT PUC I YEAR NOTES

The Living World – NCERT PUC I YEAR NOTES

Introduction to Biology & The Living World

Definition:
Biology is the science of life forms and living processes.

Early Human Perspective:
Early humans could easily perceive the difference between inanimate (non-living) matter and living organisms. Out of a sense of awe or fear, they often deified some inanimate matter (like the wind, sea, and fire) as well as some plants and animals.

Historical Progress:
Societies that held an anthropocentric (human-centered) view of biology made limited progress in biological knowledge.

Need for Systematics:
The systematic and monumental description of life forms became necessary, leading to the creation of detailed systems of identification, nomenclature, and classification.

Evolutionary Relationships:
The biggest spin-off of these systematic studies was the recognition that all living organisms share similarities both horizontally (among present-day organisms) and vertically (with organisms that ever lived on this earth).

Conservation:
This revelation of relatedness humbled mankind and sparked cultural movements for the conservation of biodiversity.

Ernst Mayr (1904 – 2004) – “The Darwin of the 20th Century”

Awards and Recognition

Recognized as one of the 100 greatest scientists of all time, he was awarded the three prizes widely regarded as the “Triple Crown of Biology”:

• The Balzan Prize in 1983.
• The International Prize for Biology in 1994.
• The Crafoord Prize in 1999.

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Introduction & What is Living

• Definition: Biology is the science of life forms and living processes.
• Perception of Life: Early humans could easily perceive the difference between inanimate (non-living) matter and living organisms. They often deified some inanimate objects (like the wind, sea, and fire) as well as certain plants and animals out of a sense of awe or fear.
• What is living?: When asking “what indeed is life?”, there are two implicit questions:
  1. A technical question: Seeks an answer to what living is as opposed to the non-living.
  2. A philosophical question: Seeks an answer to what the purpose of life is (which scientists do not attempt to answer).
• Systematic Studies: Societies that held an anthropocentric (human-centered) view of biology made limited progress. The need for systematic descriptions out of necessity led to detailed systems of identification, nomenclature, and classification.

Diversity in the Living World

• Biodiversity:
  • This refers to the number and types of organisms present on earth. 
  • The number of species that are known and described currently ranges between 1.7-1.8 million.
• Nomenclature (Naming):
  • Nomenclature is the standardized process of assigning scientific names to living organisms.
  • Because local names vary from place to place, there is a need to standardize the naming of living organisms so that a particular organism is known by the same name all over the world.
• Identification:
  • Recognition of the identity or essential characters of an organism is called Identification.
  • Nomenclature is only possible when an organism is described correctly and we know what organism the name is attached to. This process is called Identification.

International Codes

Binomial Nomenclature & Rules

The system of providing a scientific name with two components is called Binomial nomenclature, a system developed by Carolus Linnaeus that is practiced globally.

Each name has two components: the Generic name and the specific epithet.

For example, the scientific name of mango is Mangifera indica, where Mangifera represents the genus and indica represents the specific epithet.

Universal Rules of Nomenclature

• Biological names are generally in Latin and written in italics. They are Latinised or derived from Latin irrespective of their origin.
• The first word in a biological name represents the genus while the second component denotes the specific epithet.
• Both words in a biological name, when handwritten, must be separately underlined, or printed in italics to indicate their Latin origin.
• The first word denoting the genus starts with a CAPITAL LETTER while the specific epithet starts with a small letter.
• The name of the author who first described the species appears after the specific epithet in an abbreviated form. (e.g., Mangifera indica Linn.)

Classification, Taxa & Systematics

Classification

It is the process by which anything is grouped into convenient categories based on some easily observable characters.

Taxa

The scientific term for these categories is taxa (singular: taxon). Taxa can indicate categories at very different levels (e.g., ‘Plants’, ‘Wheat’, ‘Animals’, ‘Mammals’, and ‘Dogs’ are all taxa).

Taxonomy

The process of characterization, identification, classification, and nomenclature of all living organisms into different taxa based on their characteristics. 

Basis of Modern Taxonomy

External and internal structure, along with cell structure, developmental process, and ecological information.

Systematics

Derived from the Latin word ‘systema’ (meaning systematic arrangement of organisms). 

Systematics is the branch of biology that studies the diversity of life and the evolutionary relationships between organisms.

Linnaeus used Systema Naturae as the title of his publication.

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Taxonomic Categories & Hierarchy

Concept of Taxonomic Categories

Classification is not a single step process but involves a hierarchy of steps where each step represents a rank or category. Since this category is a part of the overall taxonomic arrangement, it is called a taxonomic category, and all categories together constitute the taxonomic hierarchy.

Taxon

Each category, referred to as a unit of classification, represents a rank and is commonly termed as a taxon (plural: taxa). These represent distinct biological entities, not merely morphological aggregates.

Taxonomic Hierarchy Sequence

The common categories in ascending order are:

Species → Genus → Family → Order → Class → Phylum or Division → Kingdom

1. Species

• Definition: A group of individual organisms with fundamental similarities.
• Identification: One species is distinguished from closely related species based on distinct morphological differences.
• Examples: In Mangifera indica (mango), Solanum tuberosum (potato), and Panthera leo (lion)- the words indica, tuberosum, and leo represent the specific epithets (species).

2. Genus

• Definition: Comprises a group of related species which has more characters in common in comparison to species of other genera. They are aggregates of closely related species.
• Examples: Potato and brinjal belong to the genus Solanum. Lion (Panthera leo), leopard (P. pardus), and tiger (P. tigris) belong to the genus Panthera. Cats belong to the genus Felis.

3. Family

• Definition: A group of related genera with a lesser number of similarities as compared to genus and species.
• Basis of Classification: Families are characterised on the basis of both vegetative and reproductive features of plant species.
• Examples: The genera Solanum, Petunia, and Datura are placed in the plant family Solanaceae. The animal genera Panthera (lion, tiger, leopard) and Felis (cats) are placed in the family Felidae. Dogs are placed in a separate family, Canidae.

4. Order

• Definition: Higher taxonomic categories are identified based on the aggregates of characters. An order is the assemblage of families which exhibit a few similar characters.
• Examples: Plant families like Convolvulaceae and Solanaceae are included in the order Polymoniales (mainly based on floral characters). The animal families Felidae (cats) and Canidae (dogs) are included in the order Carnivora.

5. Class

• Definition: This category includes related orders.
• Examples: Order Primata (comprising monkey, gorilla, and gibbon) and order Carnivora (tiger, cat, dog) are both placed together in class Mammalia.

6. Phylum / Division

• Definition: Classes comprising animals with common features constitute the next higher category called Phylum. In the case of plants, classes with a few similar characters are assigned to a higher category called Division.
• Examples: Classes of fishes, amphibians, reptiles, birds, and mammals are grouped into Phylum Chordata based on common features like the presence of a notochord and a dorsal hollow neural system.

7. Kingdom

• Definition: The highest category. All animals belong to Kingdom Animalia, and all plants belong to Kingdom Plantae.
• Key Trend: As we go higher from species to kingdom, the number of common characteristics goes on decreasing. Lower taxa share more characteristics. Higher categories make it more difficult to determine relationships to other taxa at the same level.

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Important Classifications to Memorize (Table 1.1)

Also Read : Excercise QUESTION and ANSWERS from PYQs and Biology Question Banks

Read NCERT CHAPTER : The Living World