The Living World Notes – Complete Chapter

1. Characteristics of Living Organisms

What defines a Living Organism?

All living organisms show certain defining characteristics that distinguish them from non-living matter. The most important ones are:

1. Growth

Increase in mass AND increase in number
In unicellular organisms: Growth and reproduction are essentially the same thing (G = R)
In multicellular organisms: Growth and reproduction are separate exclusive events (S ≠ R)
Growth is a characteristic of a living organism BUT it is NOT a defining feature alone because non-living things (like crystals, mountains) also show increase in mass
Growth is also reported in non-living things (e.g., crystal growth)

Growth and reproduction are not exclusive to living beings taken individually — but together with other characters, they distinguish life.

2. Reproduction

Asexual Reproduction	Sexual Reproduction
Offspring completely similar to parents	Better mode of reproduction
Does not involve fusion of gametes	Involves fusion of male and female gametes

Modes of Asexual Reproduction:

Mode	Example
Binary Fission	Amoeba, bacteria
Multiple Fission	Plasmodium
Longitudinal Fission	Euglena
Fragmentation	Spirogyra, Planaria
Regeneration	Planaria, Hydra
Budding	Hydra, Yeast
Spore Formation	Fungi

3. Metabolism

The sum total of all chemical reactions occurring inside a cell
Anabolic reactions: Building/synthesis reactions (e.g., Photosynthesis)
Catabolic reactions: Breakdown reactions (e.g., Respiration, Digestion)
Metabolism is THE defining feature of ALL living organisms

Metabolic reactions can occur outside the body too (in vitro / in test tube), but those systems are non-living. So isolated metabolic reactions ≠ life. It is the in vivo integration of all metabolic reactions that defines life.

4. Consciousness / Awareness

The most obvious and most complex defining feature of living organisms
Ability to sense the environment and respond accordingly
Humans are the ONLY organisms known to have self-consciousness (awareness of oneself)
Consciousness is the defining property of living organisms

If a person is on a life-support system — he is not considered truly living (no consciousness), only metabolic reactions are kept running artificially. Example: Brain dead patient.

5. Cellular Structure

All living organisms are made of cells — this is a defining feature
Defining feature = Intrinsic property of metabolism, consciousness, cellular structure

Q

Which is the most defining property of living organisms?
(a) Growth (b) Reproduction (c) Metabolism (d) Consciousness

Ans: (d) Consciousness

While metabolism is a universal feature of all living organisms (even plants and microbes show it), consciousness is considered the most defining and unique property.
Growth is also shown by non-living things (crystals). Reproduction is absent in mules, worker bees — yet they are considered living. Metabolism can occur in vitro too.
Consciousness = ability to sense and respond to environment — this is shown by ALL living organisms and NOT by non-living things → hence it is the most defining property.

Q

Why is growth not considered as a defining feature of living organisms alone?

Ans: Because non-living things also show growth.

Non-living things like mountains grow in size due to deposition of material, crystals grow in size due to addition of molecules from outside.
However, the growth in living organisms is from inside (intrinsic growth, cell division) while in non-living it is from outside (extrinsic growth, material deposition).
So growth alone is not a defining feature — it must be considered together with other characteristics.

Q

A mule is sterile and cannot reproduce. Is it living or non-living? Justify.

Ans: Living

Reproduction is NOT a defining feature of life because many organisms cannot reproduce (mule, worker bees, infertile individuals) yet they are considered living.
A mule shows all other characteristics of life — metabolism, growth, cellular structure, consciousness, response to stimuli → it is a living organism.
This proves that no single characteristic alone defines life — all characters together define living organisms.

2. Diversity in the Living World

Currently about 1.7–1.8 million species are scientifically recorded/identified
Estimated total species on Earth: ~50 million species — most are NOT in scientific record yet
Most stable ecosystem: Ocean (marine ecosystem)

The large number and diversity of organisms makes classification not just convenient but absolutely necessary for systematic study.

3. Classification, Taxonomy & Systematics

Classification

Based on similarities and dissimilarities between organisms
Goal: Group organisms based on common characteristics

Taxonomy

Taxonomy = Branch of science which deals with Characterization, Identification, Classification and Nomenclature of organisms.

Type	Basis
Classical Taxonomy	Based on external/morphological features only
Modern Taxonomy (Neo-taxonomy)	Based on external + internal body features (physiology, biochemistry, genetics etc.)

Systematics

Deals with the systematic arrangement of organisms
Includes Phylogeny — evolutionary relationships between organisms
Systematics = Old taxonomy + Phylogeny
Coined by Carolus Linnaeus

Q

What is the difference between Taxonomy and Systematics?

Ans:

Taxonomy deals with identification, characterization, classification and nomenclature of organisms — it focuses on grouping based on similarities and differences.
Systematics is broader — it includes taxonomy AND phylogeny (evolutionary relationships). It systematically arranges organisms considering their evolutionary history.
Formula: Systematics = Old taxonomy + Phylogeny
Both terms were coined by Carolus Linnaeus.

4. Binomial Nomenclature

What is Binomial Nomenclature?

Each organism is given a scientific name with two components: Genus name + Specific epithet
System given by Carolus Linnaeus
First practiced by Gaspard Bauhin in his book "Pinax" — studied by Carolus Linnaeus

Rules of Binomial Nomenclature

Example: Mangifera indica (Mango)
Mangifera = Genus name (first word, written with capital first letter)
indica = Specific epithet (second word, written with small first letter)

Name written in Latin language
When printed → written in italics (e.g., Homo sapiens)
When handwritten → each word separately underlined
First word (Genus) → first letter capital
Second word (specific epithet) → first letter small
Author's name written in short after the name (e.g., Mangifera indica Linn.)
Principle of Priority: The first name given to an individual is the valid name — no other name can replace it as per rules

Important Nomenclature Codes

Code	Full Form	For
ICBN	International Code of Botanical Nomenclature	Plants
ICZN	International Code of Zoological Nomenclature	Animals
ICNB	International Code of Nomenclature for Bacteria	Bacteria
ICNCP	International Code of Nomenclature for Cultivated Plants	Cultivated plants
ICTV	International Committee on Taxonomy of Viruses	Viruses (nomenclature and classification)

Carolus Linnaeus — Key Contributions

Known as Father of Biological Nomenclature (Taxonomy)
Wrote books: Species Plantarum (1753) — for Plants | Systema Naturae (1758) — for Animals

Trinomial Nomenclature

Proposed by Huxley and Strickland
Three names: Genus + Species + Sub-species (for plants: Sub-variety)
Example: Corvus splendens splendens (House crow) — Genus + Species + Sub-species

Q

Scientific name of mango is Mangifera indica. Identify which part represents genus and which represents specific epithet. What language is it written in?

Ans:

In Mangifera indica:
Mangifera = Genus name (first word, first letter capital)
indica = Specific epithet (second word, first letter small)
Language: Latin
When printed: italicized (Mangifera indica) | When handwritten: each word underlined separately

Q

Who gave the system of binomial nomenclature? Who first practiced it?

Ans:

System of binomial nomenclature was given by Carolus Linnaeus.
It was first practiced/proposed by Gaspard Bauhin in his book "Pinax" — Carolus Linnaeus studied this book and popularized the system.
Carolus Linnaeus is called the Father of Biological Nomenclature/Taxonomy and wrote Species Plantarum (1753) and Systema Naturae (1758).

5. Taxonomic Categories (Hierarchy)

Obligate & Intermediate Categories

7 Obligate Categories (compulsory, in order):
Kingdom → Phylum (animals) / Division (plants) → Class → Order → Family → Genus → Species

Mnemonic: King Phillip Came Over For Good Soup

There are also intermediate categories like: Sub-kingdom, Sub-phylum, Sub-class, Sub-order, Sub-family, Sub-genus, Sub-species (these are optional/intermediate categories)

Each Category — Detailed Notes

Species

Term "Species" was coined by John Ray
Biological concept of Species given by Ernst Mayr
Based on Reproductive Isolation — members of same species can interbreed and produce fertile offspring
Species share a common gene pool

Genus

Group of closely related species that also agree in certain common characters
E.g., Potato and Brinjal → different species but belong to same genus Solanum

Family

Assemblage of similar genera (plural of genus)
In plants: characterized on basis of both vegetative and reproductive features
In animals: characterized on basis of similar correlated characters
E.g., Genera Solanum, Petunia and Datura → placed in family Solanaceae
Animal families: Felidae (cats), Canidae (dogs)

Order

Assemblage of various families
In plants: e.g., families Convolvulaceae, Solanaceae → included in Order Polymoniales
In animals: Order Carnivora includes families Felidae (cats) and Canidae (dogs)

Class

Assemblage of related Orders
e.g., Class Mammalia includes Orders Primata, Carnivora etc.

Phylum (animals) / Division (plants)

Group of related Classes
e.g., Phylum Chordata includes all vertebrates

Kingdom

Largest unit of classification
Has the maximum number of individuals and least number of common characters

⚡ KEY CONCEPT

As we go from Species → Kingdom (ascending order): Common characters decrease, Number of individuals increases
As we go from Kingdom → Species (descending order): Common characters increase, Number of individuals decreases
Lower the taxon → more common characters shared within that taxon

Example — Classification of Humans

Category	Human	Housefly	Mango
Kingdom	Animalia	Animalia	Plantae
Phylum/Division	Chordata	Arthropoda	Angiospermae
Class	Mammalia	Insecta	Dicotyledonae
Order	Primata	Diptera	Sapindales
Family	Hominidae	Muscidae	Anacardiaceae
Genus	Homo	Musca	Mangifera
Species	sapiens	domestica	indica

Q

As we move from species to kingdom in taxonomic hierarchy, the number of common characteristics:
(a) Increases (b) Decreases (c) Remains same (d) First increases then decreases

Ans: (b) Decreases

As we go from Species → Kingdom (ascending hierarchy), we include more and more diverse organisms.
Species shares maximum common characters (same species = same morphology, physiology, gene pool).
Kingdom includes all organisms — animals, plants — they share minimum common characters (just eukaryotic multicellularity for Animalia, for example).
So going Species → Kingdom: common characters decrease, number of individuals increases.

Q

Potato, tomato, brinjal belong to which family?
(a) Solanaceae (b) Malvaceae (c) Fabaceae (d) Rosaceae

Ans: (a) Solanaceae

Potato (Solanum tuberosum), Tomato (Solanum lycopersicum), Brinjal/Eggplant (Solanum melongena) — all belong to genus Solanum.
The genus Solanum, along with Petunia and Datura, is placed in family Solanaceae.
This family is characterized by 5 petals (pentamerous flowers), alternate leaves, and berry/capsule type fruits.

6. Taxonomic Aids

Taxonomic studies require correct identification and classification of organisms. These studies use the following aids:

Herbarium

A store house of collected plant specimens that are dried, pressed and preserved on sheets
Specimens are poisoned to kill insects (by chemicals like mercuric chloride/HgCl₂)
Information recorded: date and place of collection, habitat, local name, botanical name, collector's name
Standard size of herbarium sheet: 41 × 29 cm (approximately A3 size)
Provides accurate identification in taxonomy

Botanical Gardens (Living Herbarium)

Ex-situ conservation (conservation outside natural habitat)
Specialized gardens with collection of living plants for reference
Each plant is labelled with its botanical/scientific name and its family

Famous Botanical Gardens:
• Royal Botanical Garden, Kew (England) → "Botanical Capital of the World"
• Central Botanical Garden, Puri, Kolkata (India)
• National Botanical Research Institute (NBRI), Lucknow, India

Zoological Parks (Zoo) & Museum

Zoological Parks: Ex-situ conservation in which live animals are kept in human care, provided conditions similar to natural habitat. Plays significant role in study of animal behaviour.
Largest/Finest zoo in India: National Zoological Park, New Delhi
Museum: Place where preserved plant and animal specimens are kept. Larger animals are stuffed and then preserved. Insects are kept in boxes. Specimens are poisoned to prevent decay.
National Museum of Natural History: Smithsonian Institution, Washington D.C.

Zoological Parks are Ex-situ conservation but animals are kept alive (unlike museum where specimens are preserved/dead).

Taxonomic Key

An analytical tool used for identification of plants and animals based on similarities and dissimilarities
Keys are based on contrasting characters — each statement in key is called a Lead
Each lead has two contrasting statements — choosing one leads to the next step until identification is complete
Keys are important taxonomic aids for identification of plants and animals on basis of similarities and differences

Flora, Fauna, Manuals and Catalogues

Aid	What it contains	Key Point
Flora	Information about plants present in a particular area — includes habitat, distribution of plants	Flora of India written by T.K. Maheshwari. Contains information about one taxon.
Fauna	Information about animals of a particular area	Complement to Flora for animals
Manual	Complete listing and alphabetical arrangement + description to help in identification of plants growing in a particular area	Provides aid in identification and description of various species
Catalogue	Alphabetical arrangement of species found in a particular area	Simple reference list
Monograph	Contains information about ONE taxon only	In-depth study of single group

Q

What is the difference between Herbarium and Botanical Garden? Both are related to plants — then how are they different?

Ans:

Herbarium: Plant specimens are collected, dried, pressed, and preserved on herbarium sheets (dead specimens). Used as a reference for identification and taxonomy. Standard sheet size = 41 × 29 cm.

Botanical Garden: Called "Living Herbarium" — plants are alive and growing. Each plant labelled with botanical name. Serves as ex-situ conservation. Examples: Kew Gardens (England), Central Botanical Garden (Kolkata).

Key difference: Herbarium = dead/preserved specimens | Botanical Garden = living plants

Q

Which botanical garden is called the "Botanical Capital of the World"?
(a) Central Botanical Garden, Kolkata (b) NBRI, Lucknow (c) Royal Botanical Garden, Kew, England (d) Ooty Botanical Garden

Ans: (c) Royal Botanical Garden, Kew, England

Royal Botanical Garden at Kew, England is internationally recognized as the "Botanical Capital of the World."
It has one of the largest collections of living plants from around the world.
In India: Central Botanical Garden is at Puri/Kolkata, and NBRI is at Lucknow — both are important but not called "Botanical Capital of the World."

Q

What is a taxonomic key? How is it used in identification?

Ans:

A taxonomic key is an analytical tool based on contrasting characters used for identification of plants and animals.
It works through a series of paired contrasting statements called leads. Each lead presents two options — the user selects one that matches the organism, which leads to the next lead, and so on, until the organism is identified.
It is one of the most important taxonomic aids because it allows systematic identification of unknown organisms based on observable characters (morphological, anatomical etc.) without needing expert knowledge every time.

Q

Flora provides information about plants in a particular area. Flora of India was written by whom?
(a) Gaspard Bauhin (b) T.K. Maheshwari (c) Carolus Linnaeus (d) Ernst Mayr

Ans: (b) T.K. Maheshwari

Flora = Reference book containing information about plants present in a particular area, including habitat and distribution.
Flora of India was written by T.K. Maheshwari.
Flora contains info about one taxon only (as per notes: "Keys contain information about only one taxon").
Carolus Linnaeus wrote Species Plantarum & Systema Naturae | Gaspard Bauhin wrote "Pinax" | Ernst Mayr gave biological concept of species.

7. Quick Revision — Important Points

All Must-Remember Facts

Fact	Detail
Most defining feature of life	Consciousness (ability to sense + respond to environment)
Universal feature of all living organisms	Metabolism (in vivo)
Not a defining feature alone	Growth (non-living also grow) \| Reproduction (mules don't reproduce)
No. of species scientifically recorded	1.7–1.8 million
Estimated total species on Earth	~50 million
Most stable ecosystem	Ocean
Father of Taxonomy / Biological Nomenclature	Carolus Linnaeus
First practiced Binomial Nomenclature	Gaspard Bauhin (book: Pinax)
Species concept (biological)	Ernst Mayr — based on Reproductive Isolation
Term "Species" coined by	John Ray
Trinomial Nomenclature proposed by	Huxley and Strickland
Herbarium sheet size	41 × 29 cm
Botanical Capital of the World	Royal Botanical Garden, Kew, England
Finest zoo in India	National Zoological Park, New Delhi
Flora of India	Written by T.K. Maheshwari
Species Plantarum (1753)	Plants — Carolus Linnaeus
Systema Naturae (1758)	Animals — Carolus Linnaeus
Solanaceae family genera	Solanum, Petunia, Datura
Carnivora order families	Felidae (cats) + Canidae (dogs)
Herbarium and Botanical Garden	Both = Ex-situ conservation

Asexual Reproduction Modes — Quick Table

Mode	Organisms
Binary Fission	Amoeba, Bacteria, Paramecium
Multiple Fission	Plasmodium (malarial parasite)
Longitudinal Fission	Euglena
Fragmentation	Spirogyra (alga), Planaria
Regeneration	Planaria, Hydra
Budding	Hydra (animal), Yeast (fungus)
Spore Formation	Fungi, some bacteria

The Living World – Complete Notes