Diversity in Living World — Complete NEET Biology Notes

1. What is Diversity in the Living World?

The Earth contains an enormous variety of organisms that differ in:

Size
Shape
Structure
Habitat
Nutrition
Reproduction
Life processes
Cellular organisation

This variety among living organisms is called biological diversity or biodiversity.

Examples

Organism	Important feature
Bacteria	Microscopic, generally unicellular
Amoeba	Unicellular eukaryote
Mushroom	Multicellular fungus
Mango tree	Multicellular photosynthetic plant
Human	Complex multicellular animal

2. Biodiversity

Biodiversity refers to the variety of living organisms present on Earth.

It can be studied at different levels.

Level	Meaning	Example
Genetic diversity	Variation within a species	Different varieties of mango
Species diversity	Variety of species	Tiger, lion, elephant
Ecosystem diversity	Variety of ecosystems	Forest, desert, pond

3. Biological Classification

Because millions of organisms exist on Earth, studying each organism individually is difficult.

Therefore, organisms are grouped based on their similarities and differences.

This process is called biological classification.

Importance of classification

Makes the study of organisms easier
Helps in identification
Shows similarities and differences
Helps understand evolutionary relationships
Provides a systematic arrangement of organisms

4. Taxonomy

Taxonomy is the science of:

Identification
Nomenclature
Classification

Easy formula

Taxonomy = Identification + Nomenclature + Classification

Identification

Recognition of an organism and determining its correct identity.

Nomenclature

Giving a scientific name to an organism.

Classification

Placing organisms into appropriate groups based on their characteristics.

5. Systematics

Systematics deals with the diversity of organisms as well as their evolutionary relationships.

Difference

Taxonomy	Systematics
Identification, nomenclature and classification	Classification along with evolutionary relationships
More focused on taxonomic study	Broader concept

NEET Point

Systematics considers evolutionary relationships among organisms.

6. Binomial Nomenclature

The system of giving each organism a scientific name consisting of two words is called binomial nomenclature.

It was developed and popularised by Carolus Linnaeus.

Two parts of a scientific name

Genus
Specific epithet

Example

Mangifera indica

Mangifera → Genus
indica → Specific epithet

Another example:

Homo sapiens

Homo → Genus
sapiens → Specific epithet

7. Rules of Binomial Nomenclature

Genus starts with a capital letter.
Specific epithet starts with a small letter.
Scientific names are written in italics when printed.
When handwritten, the two words are underlined separately.
Scientific names are generally derived from Latin or Latinised words.

Example

Printed:

Homo sapiens

Handwritten:

Homo sapiens — each word underlined separately.

8. Why Scientific Names are Necessary

Common names vary from one region or language to another.

Scientific names provide a standard name that can be understood internationally.

Example

The organism commonly called “mango” has the scientific name:

Mangifera indica

This avoids confusion caused by different local names.

9. Taxonomic Categories

Organisms are arranged in a hierarchical system called taxonomic hierarchy.

Main hierarchy

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

From highest to lowest:

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

Memory Trick

K P C O F G S

King Philip Came Over For Good Soup

10. Species

Species is the basic unit of classification.

A species generally consists of organisms that can interbreed under natural conditions and produce fertile offspring.

Examples

Homo sapiens → Human
Panthera tigris → Tiger
Mangifera indica → Mango

NEET Point

Species is the lowest and basic taxonomic category.

11. Genus

A genus contains closely related species having several common characteristics.

Example

Genus Panthera includes:

Panthera tigris → Tiger
Panthera leo → Lion
Panthera pardus → Leopard

Thus, different species can belong to the same genus.

12. Family

A family consists of related genera.

Example

Family Felidae includes genera such as:

Panthera
Felis

Family is a higher category than genus.

13. Order

An order consists of related families.

Example

Order Carnivora includes families such as:

Felidae
Canidae

14. Class

A class consists of related orders.

Example

Class Mammalia includes orders such as:

Primates
Carnivora
Rodentia

15. Phylum

A phylum consists of related classes.

Example

Phylum Chordata includes classes such as:

Mammalia
Aves
Reptilia
Amphibia

Important

In plants, the term Division is commonly used instead of Phylum.

16. Kingdom

Kingdom is a very high taxonomic category containing related phyla or divisions.

Examples:

Kingdom Animalia
Kingdom Plantae

17. Taxonomic Hierarchy — Human Example

Taxonomic category	Human
Kingdom	Animalia
Phylum	Chordata
Class	Mammalia
Order	Primates
Family	Hominidae
Genus	Homo
Species	Homo sapiens

Important Trend

As we move:

Species → Kingdom

Number of organisms increases
Diversity increases
Common characteristics decrease

As we move:

Kingdom → Species

Number of organisms decreases
Similarity increases
Common characteristics increase

18. Taxon

A taxon is a group of organisms placed at any particular rank of the taxonomic hierarchy.

Examples:

Species is a taxon.
Genus is a taxon.
Family is a taxon.
Kingdom is a taxon.

Remember

Taxonomic category = rank

Taxon = actual group placed at that rank

19. Taxonomical Aids

Tools and resources used for identification, classification and study of organisms are called taxonomical aids.

Major taxonomical aids include:

Herbarium
Botanical gardens
Museums
Zoological parks
Keys
Flora
Manuals
Monographs

20. Herbarium

A herbarium is a collection of dried, pressed and preserved plant specimens mounted on sheets.

Main steps

Collection → Pressing → Drying → Mounting → Labelling → Preservation

Herbarium sheet generally contains

Scientific name
Family
Common/local name
Collection location
Collection date
Collector’s name

Uses

Plant identification
Reference material
Taxonomic research
Comparative studies

NEET Fact

Herbarium = collection of dried, pressed and preserved plant specimens.

21. Botanical Gardens

A botanical garden is a collection of living plants maintained for scientific study, education and conservation.

Uses

Plant identification
Research
Education
Conservation
Study of plant diversity

Difference

Herbarium → Preserved dried plants

Botanical garden → Living plants

22. Biological Museums

Museums contain preserved specimens of plants and animals for study and reference.

Specimens may include

Preserved animals
Insects
Skeletons
Plant specimens
Preserved organisms in containers

Uses

Identification
Study
Teaching
Reference

23. Zoological Parks

Zoological parks or zoos maintain wild animals in protected and controlled conditions.

Uses

Study of animal behaviour
Conservation
Captive breeding
Education
Public awareness

Difference

Botanical garden → Living plants

Zoological park → Living wild animals

24. Key : taxonomical aid

A key is a taxonomical aid used for identifying organisms based on their contrasting characteristics.

Example

Suppose a plant has:

Simple leaves → Option A
Compound leaves → Option B

By repeatedly selecting between contrasting features, the organism can be identified.

Important term

A pair of contrasting statements in a key is called a couplet.

NEET Fact

Key is based on contrasting characters.

25. Flora

Flora is an account of the plants found in a particular geographical area.

Example

A flora describing the plants of a particular state or region.

26. Manual

A manual provides information useful for identifying organisms found in a particular area.

27. Monograph

A monograph is a detailed account of a particular taxon.

Example

A detailed study of a particular genus or family.

28. Five Kingdom Classification

The five-kingdom classification was proposed by R.H. Whittaker in 1969.

The five kingdoms are:

Monera
Protista
Fungi
Plantae
Animalia

Main criteria used

Cell structure
Body organisation
Mode of nutrition
Reproduction
Phylogenetic relationships

29. Kingdom Monera

Monera includes prokaryotic organisms.

Characteristics

Prokaryotic
Mostly unicellular
True nucleus absent
Nuclear membrane absent
Membrane-bound organelles absent
Cell wall generally present
Reproduction mainly asexual
Autotrophic or heterotrophic nutrition

Examples

Bacteria
Cyanobacteria
Archaebacteria
Mycoplasma

30. Kingdom Protista

Protista mainly contains unicellular eukaryotic organisms.

Characteristics

Eukaryotic
Mostly unicellular
True nucleus present
Membrane-bound organelles present
Mostly aquatic
Autotrophic or heterotrophic

Examples

Amoeba
Paramecium
Euglena
Diatoms
Slime moulds

31. Kingdom Fungi

Fungi are eukaryotic heterotrophic organisms.

Characteristics

Eukaryotic
Mostly multicellular
Yeast is unicellular
Cell wall made mainly of chitin
Chlorophyll absent
Heterotrophic
Nutrition generally absorptive
Sexual and asexual reproduction occur

Examples

Fungus	Example
Yeast	Saccharomyces
Bread mould	Rhizopus
Mushroom	Agaricus
Penicillium	Penicillium

32. Kingdom Plantae

Plantae generally includes:

Multicellular organisms
Eukaryotic organisms
Photosynthetic organisms
Chlorophyll-containing organisms
Cell wall-containing organisms
Mainly autotrophic organisms

Examples

Algae
Bryophytes
Pteridophytes
Gymnosperms
Angiosperms

33. Kingdom Animalia

Animalia includes:

Multicellular organisms
Eukaryotic organisms
Heterotrophic organisms
Organisms without cell walls
Generally motile organisms
Organisms with complex body organisation

Examples

Earthworm
Fish
Frog
Bird
Human

34. Five Kingdom Classification — Quick Revision

Kingdom	Cell type	Organisation	Nutrition	Example
Monera	Prokaryotic	Mostly unicellular	Auto/Heterotrophic	Bacteria
Protista	Eukaryotic	Mostly unicellular	Auto/Heterotrophic	Amoeba
Fungi	Eukaryotic	Mostly multicellular	Heterotrophic	Mushroom
Plantae	Eukaryotic	Multicellular	Mainly autotrophic	Mango
Animalia	Eukaryotic	Multicellular	Heterotrophic	Human

35. Three-Domain System

Carl Woese proposed the three-domain system based largely on molecular comparisons, particularly ribosomal RNA.

The three domains are:

Archaea
Bacteria
Eukarya

Important

Both Archaea and Bacteria are prokaryotic, whereas Eukarya contains eukaryotic organisms.

36. Archaea

Archaea are prokaryotic organisms with characteristics distinct from typical bacteria.

Many archaea are found in extreme environments.

Major groups

Methanogens
Extreme halophiles
Thermoacidophiles

37. Methanogens

Methanogens are archaea capable of producing methane.

Example

Methanobacterium

They occur in anaerobic environments, including the digestive tract of ruminants.

Importance

Methanogens contribute to biogas production.

NEET Fact

Methanogens → Archaea → Methane production

38. Extreme Halophiles

These archaea can survive in environments containing extremely high concentrations of salt.

Example habitat

Highly saline environments.

39. Thermoacidophiles

These organisms can survive in environments with:

High temperature
High acidity

They are examples of extremophilic archaea.

40. Eubacteria

Eubacteria are commonly called true bacteria.

Characteristics

Prokaryotic
Unicellular
Cell wall generally present
Different shapes
Autotrophic or heterotrophic

41. Common Bacterial Shapes

Shape	Name
Spherical	Coccus
Rod-shaped	Bacillus
Comma-shaped	Vibrio
Spiral	Spirillum

Easy memory

Coccus → Circle-like

Bacillus → Rod

Vibrio → Comma

Spirillum → Spiral

42. Cyanobacteria

Cyanobacteria are photosynthetic prokaryotes.

They were traditionally called blue-green algae, but they are actually bacteria.

Characteristics

Prokaryotic
Photosynthetic
Chlorophyll-a present
Unicellular, colonial or filamentous
Some can fix atmospheric nitrogen

Examples

Nostoc
Anabaena

Heterocysts

Some cyanobacteria possess specialised cells called heterocysts, which are associated with nitrogen fixation.

NEET Fact

Cyanobacteria = photosynthetic prokaryotes

43. Mycoplasma

Mycoplasma are very small prokaryotic organisms.

Most important characteristic

Cell wall is absent.

Therefore, their shape can be variable.

NEET Fact

Mycoplasma = organisms without a cell wall

44. Viruses

Viruses are acellular infectious entities and are fundamentally different from cellular organisms.

Structure

A typical virus contains:

Nucleic acid + Protein coat

The protein coat is called the capsid.

Genetic material

A virus contains either:

DNA
or
RNA

Characteristics

Acellular
No independent cellular metabolism
Obligate intracellular parasites
Replicate inside living host cells
Outside the host, they can remain inert

Examples

Bacteriophage
Influenza virus
Tobacco mosaic virus
HIV

45. Virus — Important NEET Concept

Viruses show a unique relationship between living and non-living characteristics.

Outside host

They can behave like non-living particles.

Inside host

They replicate using the host’s cellular machinery.

Therefore, viruses are generally described as obligate intracellular parasites.

46. Viroids

Viroids are infectious agents smaller and simpler than viruses.

Characteristics

Consist of small circular RNA
Protein coat absent
Mainly known to cause diseases in plants

Difference

Virus	Viroid
DNA or RNA	Small circular RNA
Protein coat present	Protein coat absent
More complex	Simpler

NEET Fact

Viroid = naked infectious RNA

47. Lichens

Lichens represent a symbiotic association between an alga and a fungus.

Algal partner

Performs photosynthesis
Provides food

Fungal partner

Provides shelter
Helps in water and mineral absorption

Importance

Lichens are sensitive to air pollution and can therefore act as indicators of air pollution.

NEET Fact

Lichen = Alga + Fungus

48. Prokaryotic vs Eukaryotic Cells

Feature	Prokaryotic	Eukaryotic
True nucleus	Absent	Present
Nuclear membrane	Absent	Present
Membrane-bound organelles	Absent	Present
Ribosomes	70S	80S in cytoplasm
Example	Bacteria	Amoeba, plants, animals

49. Autotrophic vs Heterotrophic Nutrition

Autotrophic	Heterotrophic
Organism produces its own organic food	Obtains food from other sources
Photosynthesis or chemosynthesis may occur	Various modes of nutrition
Green plants	Animals
Cyanobacteria	Fungi

Examples

Green plant → Autotrophic

Human → Heterotrophic

Mushroom → Heterotrophic

50. Plants vs Animals

Feature	Plants	Animals
Cell wall	Present	Absent
Chlorophyll	Present in green plants	Absent
Nutrition	Mainly autotrophic	Heterotrophic
Locomotion	Generally absent	Generally present
Vacuoles	Usually large	Usually smaller/temporary

51. Important Scientists and Contributions

Scientist	Major contribution
Carolus Linnaeus	Binomial nomenclature
R.H. Whittaker	Five-kingdom classification
Carl Woese	Three-domain system

52. NEET One-Liners

Basic unit of classification → Species
Science of identification, nomenclature and classification → Taxonomy
Study of diversity and evolutionary relationships → Systematics
Binomial nomenclature → Carolus Linnaeus
Five-kingdom classification → R.H. Whittaker
Three-domain system → Carl Woese
Scientific name → Genus + Specific epithet
Dried and preserved plant specimens → Herbarium
Living plant collection → Botanical garden
Wild animals under protected conditions → Zoological park
Identification based on contrasting characters → Key
Fungal cell wall → Chitin
Typical bacterial cell wall → Peptidoglycan-containing
Mycoplasma → Cell wall absent
Lichen → Alga + fungus
Viroid → Naked infectious RNA
Virus → Acellular infectious entity
Cyanobacteria → Photosynthetic prokaryotes
Methanogens → Archaea
Three domains → Archaea, Bacteria, Eukarya

53. Taxonomic Hierarchy — Quick Revision

Kingdom

↓

Phylum / Division

↓

Class

↓

Order

↓

Family

↓

Genus

↓

Species

Direction of increasing similarity

Kingdom → Species

Similarity increases

Diversity decreases

Number of organisms decreases

54. Most Important NEET Facts

1. Species

Basic unit of classification.

2. Taxonomy

Identification + Nomenclature + Classification

3. Systematics

Includes evolutionary relationships.

4. Binomial nomenclature

Scientific name consists of Genus + specific epithet.

5. Herbarium

Dried, pressed and preserved plant specimens.

6. Botanical garden

Living collection of plants.

7. Key

Based on contrasting characters.

8. Whittaker

Proposed five-kingdom classification in 1969.

9. Woese

Proposed three-domain system.

10. Mycoplasma

Cell wall absent.

11. Fungi

Cell wall mainly contains chitin.

12. Cyanobacteria

They are prokaryotes, not true algae.

13. Lichen

Algal partner + fungal partner.

14. Viroid

Small infectious RNA without a protein coat.

15. Virus

Obligate intracellular parasite.

16. Archaea

Include methanogens, extreme halophiles and thermoacidophiles.

55. Final NEET Rapid Revision Map

Diversity in Living World

→ Biodiversity

→ Classification

→ Taxonomy

→ Systematics

→ Binomial Nomenclature

→ Taxonomic Categories

→ Taxonomic Hierarchy

→ Taxonomical Aids

→ Herbarium

→ Botanical Garden

→ Museum

→ Zoological Park

→ Key

→ Flora

→ Manuals

→ Monographs

→ Five Kingdom Classification

→ Monera

→ Protista

→ Fungi

→ Plantae

→ Animalia

→ Three Domains

→ Archaea

→ Bacteria

→ Eukarya

→ Viruses

→ Viroids

→ Lichens

56. Ultra-Short NEET Revision

Species → Basic unit

Genus → Group of related species

Family → Group of related genera

Order → Group of related families

Class → Group of related orders

Phylum → Group of related classes

Kingdom → Group of related phyla

Herbarium → Dried plant specimens

Botanical garden → Living plants

Zoo → Living wild animals

Key → Contrasting characters

Monera → Prokaryotes

Protista → Mostly unicellular eukaryotes

Fungi → Chitinous cell wall

Plantae → Mainly autotrophic

Animalia → Heterotrophic, no cell wall

Archaea → Distinct prokaryotic domain

Cyanobacteria → Photosynthetic bacteria

Mycoplasma → No cell wall

Virus → Acellular infectious entity

Viroid → Naked RNA

Lichen → Alga + fungus