To classify something as living, we evaluate specific biological processes. However, NCERT strictly distinguishes between a characteristic feature (common to living things but can have exceptions or apply superficially to non-living things) and a defining feature (present in all living organisms without any exception).
The Five Core Features of Life
- Growth: An increase in mass and twin characteristics of growth: increase in mass and increase in number of individuals.
- Non-Living Exception: Mountains, boulders, and sand dunes grow by accumulation of material on their surface (extrinsic growth). Living organisms grow from the inside (intrinsic growth). Hence, growth is NOT a defining feature.
- Reproduction: The production of progeny possessing features more or less similar to those of parents.
- Exceptions: Mules, sterile worker bees, and infertile human couples do not reproduce. Yet, they are alive. Hence, reproduction is NOT a defining feature.
- Metabolism: The sum total of all chemical reactions occurring in a body. No non-living object exhibits metabolism. It can be demonstrated outside the body in a cell-free system (in vitro)—where the reaction is living, but the isolated reaction itself is not an organism. Hence, metabolism IS a defining feature.
- Cellular Organization: The architectural structural unit of an organism. Cells assemble to form tissues and organs. Hence, cellular organization IS a defining feature.
- Consciousness: The ability of an organism to sense their surroundings or environment and respond to these environmental stimuli (physical, chemical, or biological). All organisms, from prokaryotes to complex eukaryotes, show consciousness. Human beings are the only organisms with self-consciousness. Hence, consciousness IS a defining feature.
- Intrinsic growth (from inside) is seen only in living beings.
- Isolated metabolic reactions in vitro are not living things but surely living reactions.
Important NCERT Points
2. Diversity in the Living World & Nomenclature
The number of species that are known and described ranges between 1.7–1.8 million. This refers to biodiversity. To handle this vast number, we must standardize the naming of living organisms such that a particular organism is known by the same name all over the world. This process is called nomenclature.
Before naming, we must accurately describe the organism so we know what organism the name is attached to. This is identification.
Global Nomenclature Code Bodies
ICBN: International Code for Botanical Nomenclature (for plants)
ICZN: International Code for Zoological Nomenclature (for animals)
3. Rules of Binomial Nomenclature
Introduced by Carolus Linnaeus, every scientific name has two components: the Generic name (Genus) and the Specific epithet (Species).
The Four Golden Rules (Direct NCERT Extractions)
Biological names are generally in Latin and written in italics. They are Latinized or derived from Latin irrespective of their origin.
The first word represents the genus while the second word denotes the specific epithet.
When handwritten, both words are separately underlined, or printed in italics to indicate their Latin origin.
The genus name starts with a capital letter while the specific epithet starts with a small letter.
Example: Scientific name of Mango is written as Mangifera indica. If the author’s name is included, it appears after the specific epithet in an abbreviated form: Mangifera indica Linn. (indicating Linnaeus discovered. this species)
4. Taxonomic Categories & Hierarchy
Classification is not a single-step process but involves a hierarchy of steps where each step represents a rank or category. The aggregate of all categories constitutes the taxonomic hierarchy. Each category, referred to as a unit of classification, represents a rank and is commonly termed as taxon (plural: taxa).
5. Taxonomical Aids: Quick Reference Guide
Taxonomical aids are techniques, procedures, and stored information useful in identification and classification of organisms.
Herbarium: A storehouse of collected plant specimens that are dried, pressed, and preserved on sheets. Sheets carry a label providing information about date, place of collection, English, local, and botanical names, family, and collector’s name. It serves as a quick referral system.
Botanical Gardens: Specialized gardens containing collections of living plants for reference. Famous locations include Kew (England), Indian Botanical Garden (Howrah), and National Botanical Research Institute (Lucknow).
Museums: Established in educational institutes. Have collections of preserved plant and animal specimens for study. Insects are preserved in insect boxes after collecting, killing, and pinning. Larger animals are usually stuffed and preserved.
Zoological Parks (Zoos): Places where wild animals are kept in protected environments under human care, allowing us to learn about their food habits and behavior.
Key: Used for identification of plants and animals based on similarities and dissimilarities. The keys are based on contrasting characters generally in a pair called a couplet. Each statement in the key is called a lead. Keys are generally analytical in nature.
10. FAQ Section
Q1: What is the basic unit of classification?
A1: Species is the fundamental and lowest basic unit of classification in the taxonomic hierarchy.
Q2: Why is growth not considered a defining feature of life?
A2: Because non-living structures like crystals and sand dunes grow in size through surface accretion of external material. Living organisms must grow internally.
Q3: What are the twin characteristics of growth?
A3: According to NCERT, increase in body mass and increase in the total number of individuals are defined as twin features of growth.
Q4: What is a couplet in a biological taxonomic key?
A4: A couplet refers to a pair of contrasting choices or statements used during step-by-step specimen identification within analytical keys.
Q5: Name the scientists who introduced the binomial nomenclature method.
A5: Carolus Linnaeus standardized and popularized the binomial nomenclature system for globally naming organisms.
Q6: What is the full form of ICBN?
A6: ICBN stands for the International Code for Botanical Nomenclature, governing scientific naming for plants.
Q7: What does the term 'Linn' signify at the end of a biological name?
A7: It indicates that the particular species was originally described and cataloged by Carolus Linnaeus.
Q8: Why are scientific names written in italics?
A8: Printing names in italics displays their classical Latin origin, ensuring uniformity across international scientific communities.
Q9: What information does a herbarium sheet label carry?
A9: It includes the date and location of collection, local/English/botanical names, taxonomic family name, and the individual collector's name.
Q10: How does a key help in taxonomy?
A10: It helps identify unknown specimens by presenting sequential pairs of matching or contrasting statements (leads) that eliminate unrelated groups.
Q11: What is self-consciousness? Who exhibits it?
A11: Self-consciousness is the advanced awareness of one's own mental state and identity. Human beings are the only organisms that possess it.
Q12: What is a taxon?
A12: A taxon represents any concrete rank or level within the biological framework of classification, such as Genus, Order, or Class.
Q13: What are the three components of taxonomy?
A13: Characterization/Identification, Nomenclature, and systematic Classification form the main core pillars of taxonomy.
Q14: What is the difference between an order and a family?
A14: An order is a broader category that groups together multiple closely related families exhibiting common features.
Q15: Why are museums considered taxonomical aids?
A15: They provide preserved actual physical specimens of species, serving as educational models for detailed morphological research.