I. ERNST MAYR (1904-2004)
Harvard University — Alexander Agassiz Professor of Zoology Emeritus
| DETAIL | FACT |
|---|---|
| Born | 5 July 1904, Kempten, Germany |
| Known as | 'The Darwin of the 20th century' ⭐ |
| Institution | Harvard University — Alexander Agassiz Professor of Zoology Emeritus |
| Career span | Nearly 80 years |
| Key contribution | Made origin of species diversity the central question of evolutionary biology |
| Species concept | Pioneered the currently accepted definition of a biological species ⭐ |
| Research areas | Ornithology, Taxonomy, Zoogeography, Evolution, Systematics, History & Philosophy of Biology |
| Died | Age 100, in 2004 |
"TRIPLE CROWN OF BIOLOGY"
| PRIZE | YEAR |
|---|---|
| Balzan Prize | 1983 |
| International Prize for Biology | 1994 |
| Crafoord Prize | 1999 |
Ernst Mayr is known as 'The Darwin of the 20th century'. He pioneered the currently accepted definition of biological species (biological species concept).
II. WHAT IS LIVING? — DEFINING CHARACTERISTICS
A UNIQUE FEATURES OF LIVING ORGANISMS
Listed in NCERT:
- Growth
- Reproduction
- ⭐⭐ Metabolism
- Ability to sense environment (consciousness)
- Ability to mount a suitable response
- Self-organisation
- Ability to self-replicate
- Interact with environment
- Emergence (properties that arise at higher levels of organisation)
B CAN ANY SINGLE FEATURE DEFINE 'LIVING'? — ANALYSIS
1. GROWTH
| FEATURE | LIVING ORGANISMS | NON-LIVING |
|---|---|---|
| Growth occurs? | Yes | Yes — Mountains, Boulders, Sand mounds also grow |
| Mechanism | By cell division (intrinsic) | By accumulation of material (extrinsic) |
| TYPE | GROWTH MECHANISM |
|---|---|
| Multicellular organisms | Grow by cell division |
| Unicellular organisms | Growth & reproduction are synonymous ⭐ (increase in cell number = reproduction) |
NEET 2016: In unicellular organisms (bacteria, Amoeba, unicellular algae), reproduction is synonymous with growth (both involve increase in number of cells). Growth ALONE cannot define living — non-living things also grow!
Growth alone cannot define living — non-living things (mountains, boulders, sand mounds) also grow (by accumulation of material).
2. REPRODUCTION
- Many organisms do NOT reproduce:
- Mules (sterile hybrid)
- Sterile worker bees
- Infertile human couples
3. METABOLISM (THE DEFINING FEATURE)
Definition: Sum total of all chemical reactions occurring in the body
| STATEMENT | DETAIL |
|---|---|
| Defining feature? | YES — metabolism is the defining feature of ALL living organisms without exception ⭐⭐ |
| Occurs where? | In vivo (inside living body) — defines living |
| In vitro? | Isolated metabolic reactions in vitro (test tube) are NOT living things but are surely living reactions ⭐ |
NEET 2011: Metabolism = defining feature of all living organisms without exception. Isolated metabolic reactions in vitro = NOT living things but ARE living reactions. No organism exists that lacks metabolism. Even organisms that don't reproduce (mules, worker bees) still have metabolism. That's why metabolism, not reproduction, is the all-inclusive defining feature.
4. CONSCIOUSNESS
| TYPE | FOUND IN |
|---|---|
| Consciousness (sense & respond) |
All living organisms — defining feature of living |
| Self-consciousness | Only Human Beings — unique to humans ⭐ |
NEET 2011: Self-consciousness = defining property of HUMAN BEINGS only. Consciousness = defining property of ALL living organisms.
5. GENETIC LINKAGE
- ⭐ All living organisms — present, past and future — are linked to one another by the sharing of common genetic material, but to varying degrees.
C SUMMARY — WHICH FEATURE DEFINES LIVING?
| FEATURE | DEFINES LIVING? | WHY / WHY NOT |
|---|---|---|
| Growth | ❌ Not exclusively | Non-living things also grow |
| Reproduction | ❌ Not all-inclusive | Mules, sterile worker bees, infertile humans don't reproduce |
| Metabolism | ✅ YES — ALL-INCLUSIVE ⭐⭐ | No exception; all living organisms exhibit metabolism |
| Consciousness | ✅ Yes (for all living) | All living organisms can sense & respond |
| Self-consciousness | Only for humans | Unique to Homo sapiens |
III. BIODIVERSITY
Definition: The number and types of organisms present on earth
| FACT | DETAIL |
|---|---|
| Known & described species | 1.7 – 1.8 million ⭐ |
| New organisms | Continuously being identified in new and old areas |
IV. NOMENCLATURE
Definition: The process of standardising the naming of living organisms such that a particular organism is known by the same name all over the world
PREREQUISITES
- Organism must be correctly described first (identification)
- Then a scientific name is assigned
INTERNATIONAL CODES
| CODE | FULL NAME | FOR |
|---|---|---|
| ICBN | International Code for Botanical Nomenclature | Plants |
| ICZN | International Code of Zoological Nomenclature | Animals |
- Scientific names ensure each organism has only one name.
- Ensure the name has not been used for any other known organism.
BINOMIAL NOMENCLATURE
Definition: System of providing a name with two components — given by Carolus Linnaeus ⭐
| COMPONENT | POSITION | EXAMPLE (MANGIFERA INDICA) |
|---|---|---|
| Generic name (Genus) |
First word | Mangifera |
| Specific epithet (Species) |
Second word | indica |
UNIVERSAL RULES OF NOMENCLATURE
| RULE | DETAIL |
|---|---|
| Language | Generally in Latin; Latinised or derived from Latin |
| Print format | Written in ITALICS (when printed) |
| Handwritten format | Both words SEPARATELY UNDERLINED ⭐ |
| First word (Genus) | Starts with CAPITAL letter |
| Second word (specific epithet) |
Starts with SMALL letter |
| Author name | Appears after the specific epithet, in abbreviated form |
NEET 2019: Binomial nomenclature = two components: Generic name + Specific epithet; given by Carolus Linnaeus; name of author appears after specific epithet. When HANDWRITTEN, the two words are separately underlined (not written in italics — italics is for PRINT only)!
V. TAXONOMY & SYSTEMATICS
A CLASSIFICATION
Definition: The process by which anything is grouped into convenient categories based on some easily observable characters
- Scientific term for these categories = Taxa (singular: Taxon)
- Taxa can indicate categories at very different levels (e.g., 'Plants', 'Wheat', 'Animals', 'Mammals', 'Dogs' — all are taxa but at different levels)
B TAXONOMY
BASIS OF MODERN TAXONOMIC STUDIES
- External structure (morphology)
- Internal structure (anatomy)
- Structure of cell (cytology)
- Development process (embryology/ontogeny)
- Ecological information
PROCESSES BASIC TO TAXONOMY
| PROCESS | DETAIL |
|---|---|
| Characterisation | Describing the features |
| Identification | Recognising the organism |
| Classification | Grouping into categories |
| Nomenclature | Giving standardised scientific names |
C SYSTEMATICS
Definition: The study of kinds and diversity of organisms and the relationships among them
| FEATURE | DETAIL |
|---|---|
| Word origin | Latin word 'systema' = systematic arrangement of organisms |
| Linnaeus's publication | 'Systema Naturae' ⭐ |
| Scope | Includes identification, nomenclature, classification + takes into account evolutionary relationships |
VI. TAXONOMIC CATEGORIES & HIERARCHY
A KEY DEFINITIONS
| TERM | DEFINITION |
|---|---|
| Taxonomic category | A rank or category; part of overall taxonomic arrangement |
| Taxonomic hierarchy | All categories together constitute the taxonomic hierarchy |
| Taxon (pl. Taxa) | Each category = a unit of classification = a rank |
B THE HIERARCHY (ASCENDING ORDER)
Taxonomic Hierarchy — Lowest to Highest:
SPECIES → GENUS → FAMILY → ORDER → CLASS → PHYLUM/DIVISION → KINGDOM
RE-NEET 2026 — Direct: Correct ascending order of taxonomic categories:
Species → Genus → Family → Order → Class → Phylum → Kingdom
RE-NEET 2026 — Direct: Genus represents a group of closely related SPECIES (not families, individuals or populations).
KEY RULES
| DIRECTION | COMMON CHARACTERISTICS | SPECIFICITY |
|---|---|---|
| Species → Kingdom (ascending) |
DECREASE ⭐ | Less specific |
| Kingdom → Species (descending) |
INCREASE | More specific |
PLANT vs ANIMAL TERMINOLOGY
| LEVEL | PLANTS | ANIMALS |
|---|---|---|
| Sub-kingdom level | Division | Phylum |
SUFFIXES FOR PLANT CLASSIFICATION (Frequently Asked)
| TAXONOMIC LEVEL | SUFFIX | EXAMPLE |
|---|---|---|
| Order | -ales | Polymoniales, Sapindales, Poales |
| Family | -aceae | Solanaceae, Anacardiaceae, Poaceae |
Species is the lowest category; Kingdom is the highest category in the taxonomic hierarchy.
In plants, Phylum (animals) is replaced by Division.
Higher taxa (ascending) have fewer common characters (less specific). Lower taxa have more common characters (more specific).
C EACH CATEGORY EXPLAINED
1. SPECIES (LOWEST CATEGORY)
- A group of individual organisms with fundamental similarities
- Distinguished from closely related species by distinct morphological differences
- ⭐ Lowest category for all organisms (both plants and animals)
| ORGANISM | SCIENTIFIC NAME | GENUS | SPECIFIC EPITHET |
|---|---|---|---|
| Mango | Mangifera indica | Mangifera | indica |
| Potato | Solanum tuberosum | Solanum | tuberosum |
| Lion | Panthera leo | Panthera | leo |
| Tiger | Panthera tigris | Panthera | tigris |
| Human | Homo sapiens | Homo | sapiens |
| Brinjal | Solanum melongena | Solanum | melongena |
| Black nightshade | Solanum nigrum | Solanum | nigrum |
• Same genus can have more than one specific epithet (e.g., Panthera leo, P. tigris, P. pardus)
2. GENUS
• Comprises a group of related species which share more characters in common compared to species of other genera
| GENUS | INCLUDES SPECIES |
|---|---|
| Solanum | Potato (tuberosum), Brinjal (melongena), nigrum |
| Panthera | Lion (leo), Leopard (pardus), Tiger (tigris) |
| Felis | Cats |
3. FAMILY
- A group of related genera with still less number of similarities compared to genus & species
- Characterised on basis of both vegetative and reproductive features (in plants)
| FAMILY | GENERA INCLUDED | COMMON FEATURE |
|---|---|---|
| Solanaceae | Solanum, Petunia, Datura | Floral characters |
| Felidae | Panthera (lions, tigers, leopards), Felis (cats) | Cat-like features |
| Canidae | Dogs | Dog-like features |
4. ORDER
- Assemblage of families which exhibit a few similar characters
- Higher category → fewer similar characters compared to family level
| ORDER | FAMILIES INCLUDED | BASIS |
|---|---|---|
| Polymoniales (plants) |
Convolvulaceae, Solanaceae | Mainly floral characters ⭐ |
| Carnivora (animals) |
Felidae, Canidae | Carnivorous habit |
5. CLASS
• Includes related orders
| CLASS | ORDERS INCLUDED | EXAMPLES |
|---|---|---|
| Mammalia | Primata (monkey, gorilla, gibbon) + Carnivora (tiger, cat, dog) + others | All mammals |
| Insecta | Diptera (housefly) + many others | All insects |
6. PHYLUM (ANIMALS) / DIVISION (PLANTS)
• Includes related classes
| PHYLUM | CLASSES INCLUDED | COMMON FEATURES |
|---|---|---|
| Chordata | Fishes, Amphibians, Reptiles, Birds, Mammals | Presence of notochord and dorsal hollow neural system |
| Arthropoda | Insecta and others | Jointed appendages |
• In plants: Classes with similar characters → Division (e.g., Angiospermae)
7. KINGDOM (HIGHEST CATEGORY)
| KINGDOM | INCLUDES |
|---|---|
| Kingdom Animalia | All animals from various phyla |
| Kingdom Plantae | All plants from various divisions |
D HOUSEFLY CLASSIFICATION (MUST MEMORISE)
| CATEGORY | HOUSEFLY |
|---|---|
| Common Name | Housefly |
| Biological Name | Musca domestica |
| Genus | Musca |
| Family | Muscidae |
| Order | Diptera ⭐ |
| Class | Insecta ⭐ |
| Phylum | Arthropoda |
NEET 2016, 2021, 2023: Housefly → Order Diptera, Class Insecta, Genus Musca. This is among the most frequently asked classification questions!
E COMPLETE CLASSIFICATION TABLE — FOUR KEY ORGANISMS
| CATEGORY | MAN | HOUSEFLY | MANGO | WHEAT |
|---|---|---|---|---|
| Biological Name | Homo sapiens | Musca domestica | Mangifera indica | Triticum aestivum |
| Genus | Homo | Musca | Mangifera | Triticum |
| Family | Hominidae | Muscidae | Anacardiaceae | Poaceae |
| Order | Primata | Diptera | Sapindales | Poales |
| Class | Mammalia | Insecta | Dicotyledonae | Monocotyledonae |
| Phylum / Division | Chordata | Arthropoda | Angiospermae | Angiospermae |
| Kingdom | Animalia | Animalia | Plantae | Plantae |
MANGO — QUICK FACTS (Frequently Asked)
| DETAIL | ANSWER |
|---|---|
| Family | Anacardiaceae |
| Order | Sapindales |
| Fruit type | Drupe (from monocarpellary superior ovary; one-seeded) |
VII. PHOTOPERIOD & REPRODUCTION
NEET 2016 Trap: Photoperiod DOES affect reproduction in seasonal breeders (both plants and animals). This is TRUE — many organisms reproduce only in certain seasons influenced by day length.
VIII. RAPID REVISION — ALL KEY FACTS AT A GLANCE
TABLE 1: DEFINING FEATURES SUMMARY
| FEATURE | STATUS | REASON |
|---|---|---|
| Growth | ❌ Not exclusive | Non-living things (mountains, boulders) also grow |
| Reproduction | ❌ Not all-inclusive | Mules, sterile worker bees, infertile humans don't reproduce |
| Metabolism | ✅ ALL-INCLUSIVE defining feature ⭐⭐ | No exception — all living organisms show metabolism |
| Consciousness | ✅ Defining for all living | All living organisms can sense & respond |
| Self-consciousness | Only humans | Unique to Homo sapiens |
| In vitro metabolic reactions | Not living things | But they ARE living reactions |
TABLE 2: NOMENCLATURE RULES
| RULE | DETAIL |
|---|---|
| System | Binomial nomenclature by Carolus Linnaeus |
| Components | Generic name (Genus) + Specific epithet (Species) |
| Language | Latin (Latinised) |
| Italics | |
| Handwritten | Separately underlined |
| Genus | Capital letter |
| Specific epithet | Small letter |
| Author | After specific epithet, abbreviated |
| Codes | ICBN (plants); ICZN (animals) |
TABLE 3: TAXONOMIC HIERARCHY — ASCENDING ORDER
Complete Hierarchy:
Species → Genus → Family → Order → Class → Phylum/Division → Kingdom
| DIRECTION | COMMON CHARACTERISTICS | SPECIFICITY |
|---|---|---|
| Species → Kingdom (ascending) | Decrease | Less specific |
| Kingdom → Species (descending) | Increase | More specific |
TABLE 4: SUFFIXES FOR PLANT CLASSIFICATION
| LEVEL | SUFFIX | EXAMPLE |
|---|---|---|
| Order | -ales | Polymoniales, Sapindales |
| Family | -aceae | Solanaceae, Anacardiaceae |
TABLE 5: TAXONOMY vs SYSTEMATICS
| FEATURE | TAXONOMY | SYSTEMATICS |
|---|---|---|
| Includes | Characterisation, Identification, Classification, Nomenclature | All of taxonomy + evolutionary relationships |
| Linnaeus publication | — | 'Systema Naturae' |
| Word origin | Greek: taxis (arrangement) + nomos (law) | Latin: systema (systematic arrangement) |
TABLE 6: IMPORTANT SCIENTIFIC NAMES
| COMMON NAME | SCIENTIFIC NAME | KEY TAXONOMIC DETAIL |
|---|---|---|
| Man | Homo sapiens | Class Mammalia, Order Primata |
| Housefly | Musca domestica | Order Diptera, Class Insecta |
| Mango | Mangifera indica | Family Anacardiaceae, Order Sapindales |
| Wheat | Triticum aestivum | Family Poaceae, Order Poales |
| Potato | Solanum tuberosum | Family Solanaceae |
| Brinjal | Solanum melongena | Family Solanaceae |
| Lion | Panthera leo | Family Felidae |
| Tiger | Panthera tigris | Family Felidae |
| Leopard | Panthera pardus | Family Felidae |
| Cat | Felis sp. | Family Felidae |
TABLE 7: FAMILY-LEVEL GROUPINGS
| FAMILY | GENERA / SPECIES INCLUDED |
|---|---|
| Solanaceae | Solanum, Petunia, Datura |
| Felidae | Panthera (lion, tiger, leopard), Felis (cat) |
| Canidae | Dog |
| Hominidae | Homo (human) |
| Muscidae | Musca (housefly) |
| Anacardiaceae | Mangifera (mango) |
| Poaceae | Triticum (wheat) |
IX. COMMON EXAM TRAPS — QUICK REFERENCE
| TRAP / QUESTION | CORRECT ANSWER |
|---|---|
| What is the defining feature of ALL living organisms? | Metabolism ⭐ |
| Is reproduction a defining feature of living? | No — mules, sterile worker bees, infertile humans don't reproduce |
| Can non-living things grow? | Yes — mountains, boulders, sand mounds |
| In unicellular organisms, growth = ? | Reproduction (synonymous processes) |
| Are in vitro metabolic reactions living things? | No — but they ARE living reactions |
| Self-consciousness is unique to? | Human beings only |
| Consciousness is a feature of? | All living organisms |
| Who gave binomial nomenclature? | Carolus Linnaeus |
| Who gave the biological species concept? | Ernst Mayr |
| Housefly order? | Diptera |
| Housefly class? | Insecta |
| Plants use which suffix for order? | -ales |
| Plants use which suffix for family? | -aceae |
| Division (plants) = ? (animals) | Phylum |
| Higher taxa → common characters? | Decrease |
| Lower taxa → common characters? | Increase |
| Linnaeus's publication title? | Systema Naturae |
| Mango family? | Anacardiaceae |
| Mango order? | Sapindales |
| Convolvulaceae & Solanaceae grouped in which order? | Polymoniales (based on floral characters) |
| Species is which level of category? | Lowest category in both plants & animals |
| Kingdom is which level? | Highest category |
| Handwritten biological names — italics or underlined? | Separately UNDERLINED (italics = print only) |
| Author name appears where? | After specific epithet |
| Does photoperiod affect reproduction? | Yes — in seasonal breeders (both plants & animals) |