Class 11 The Living World Notes for NEET – taxonomic hierarchy, binomial nomenclature, ICBN/ICZN & practice MCQs. Free downloadable notes inside.
Diversity in the Living World
- Each different kind of organism = a species.
- Number of species known and described = 1.7 – 1.8 million (NEET fact — remember exact range).
- This range/number of species = Biodiversity.
- New organisms are continuously being identified even in explored areas.
Nomenclature & Identification
| Term | Meaning |
| Nomenclature | Process of giving a scientific name so the organism is known by the same name worldwide |
| Identification | Correct description of the organism so we know exactly what is being named |
Local/common names vary place to place → hence need for standard scientific names.
Codes of Nomenclature
| Code | For |
| ICBN (International Code for Botanical Nomenclature) | Plants |
| ICZN (International Code of Zoological Nomenclature) | Animals |
NEET Note: Current codes are now called ICN (International Code of Nomenclature for algae, fungi & plants) and ICZN — but as per NCERT textbook, remember ICBN & ICZN.
Binomial Nomenclature
- Given by Carolus Linnaeus.
- Example: Mango → Mangifera indica
- Mangifera = genus
- indica = specific epithet
Universal Rules of Nomenclature (Very Important — Direct MCQs)
- Biological names are generally in Latin and written in italics.
- First word = genus, second word = specific epithet.
- When handwritten, both words are separately underlined; when printed, in italics.
- First letter of genus = capital; specific epithet = small letter.
- Name of author appears after specific epithet, in abbreviated form.
- g. Mangifera indica Linn. → first described by Linnaeus.
Classification, Taxonomy & Systematics
| Term | Meaning |
| Classification | Process of grouping organisms into convenient categories based on observable characters |
| Taxa (sing. taxon) | The convenient categories used (e.g., Plants, Animals, Mammals, Dogs) — taxa exist at different hierarchical levels |
| Taxonomy | Process of classification, including characterisation, identification, classification & nomenclature |
| Systematics | Study of diversity + evolutionary relationships among organisms (word from Latin “systema” — used by Linnaeus in Systema Naturae) |
- Basis of modern taxonomy: external + internal structure, cell structure, development process, ecological information.
- Systematics = broader than classification; includes evolutionary relationships.
Taxonomic Categories & Hierarchy (HIGH-YIELD for NEET)
Each category/rank = taxon. All categories together = taxonomic hierarchy.
Hierarchy (Ascending order — MUST MEMORIZE)
Species → Genus → Family → Order → Class → Phylum/Division → Kingdom
- Lower taxa (species) → more common characters shared among members
- Higher taxa (kingdom) → fewer common characters, harder to classify
Species
- Group of individual organisms with fundamental similarities.
- Lowest category in classification (for both plant & animal kingdoms).
- Distinguished from closely related species by morphological differences.
- Human beings: species = sapiens, genus = Homo → Homo sapiens
Genus
- Group of related species with more characters in common vs species of other genera.
- “Aggregates of closely related species.”
- g. Solanum: tuberosum (potato), nigrum, melongena (brinjal)
- g. Panthera: leo (lion), tigris (tiger), pardus (leopard)
Family
- Group of related genera with fewer similarities than genus/species.
- Based on vegetative + reproductive features (in plants).
- Plant e.g.: Solanum, Petunia, Datura → Family Solanaceae
- Animal e.g.: Panthera + Felis → Family Felidae
- Cat & Dog → different families: Felidae and Canidae
Order
- Higher category; assemblage of families with a few similar characters.
- Plant e.g.: Convolvulaceae + Solanaceae → Order Polymoniales
- Animal e.g.: Felidae + Canidae → Order Carnivora
Class
- Includes related orders.
- g.: Order Primata (monkey, gorilla, gibbon) + Order Carnivora (tiger, cat, dog) → Class Mammalia
Phylum / Division
- Phylum (animals): Classes with common features (e.g., presence of notochord, dorsal hollow neural system) → Phylum Chordata
- Division (plants): equivalent term used instead of Phylum
Kingdom
- Highest category.
- All animal phyla → Kingdom Animalia
- All plant divisions → Kingdom Plantae
Master Table (Very frequently asked directly in NEET)
| Common Name | Biological Name | Genus | Family | Order | Class | Phylum/Division |
| Man | *Homo sapiens | *Homo | Hominidae | Primata | Mammalia | Chordata |
| Housefly | *Musca domestica | *Musca | Muscidae | Diptera | Insecta | Arthropoda |
| Mango | *Mangifera indica | *Mangifera | Anacardiaceae | Sapindales | Dicotyledonae | Angiospermae |
| Wheat | *Triticum aestivum | *Triticum | Poaceae | Poales | Monocotyledonae | Angiospermae |
Quick Memory Flow (Mnemonic)
King Philip Came Over For Good Soup
= Kingdom → Phylum → Class → Order → Family → Genus → Species
Important One-Liners for Quick Revision
- Number of species known & described: 1.7 – 1.8 million
- Binomial nomenclature given by: Carolus Linnaeus
- Book by Linnaeus: Systema Naturae
- Plants named under: ICBN
- Animals named under: ICZN
- Lowest taxonomic category: Species
- Highest taxonomic category: Kingdom
- Basis of grouping Felidae & Canidae differently: morphological differences between cat and dog
- Chordata common features: notochord + dorsal hollow nerve cord
NCERT Exercise-Based Concepts to Revise
- Why classify? → To study/manage the huge diversity systematically.
- Why classification systems keep changing? → New info from structure, genetics, evolution keeps updating relationships.
- Correct sequence of taxonomic categories (NCERT Q7): (c) Species → Genus → Order → Phylum — Note: the fully correct complete sequence is Species → Genus → Family → Order → Class → Phylum → Kingdom.
Possible NEET-style MCQs to Practice
- Binomial nomenclature was given by: (a) Whittaker (b) Linnaeus ✓ (c) Darwin (d) Aristotle
- Which pair is correctly matched? (a) Man – Family Hominidae ✓ (b) Housefly – Order Coleoptera ✗ (correct: Diptera)
- The term used for plants instead of “Phylum” is: (a) Class (b) Division ✓ (c) Order (d) Family
- ICZN stands for: International Code of Zoological Nomenclature
- Common features of Phylum Chordata: presence of notochord and dorsal hollow nerve cord