Biological Classification

Biological Classification

• Biological classification is the scientific method of arranging living organisms into groups based on similarities and differences in fundamental characteristics.
• It helps us understand the diversity of life, evolutionary relationships, and provides a systematic framework for studying organisms.

Early Attempts at Classification

Aristotle

• Basis of Classification (Plants):
  • Plants were classified as trees, shrubs, and herbs based on external morphology.
• Basis of Classification (Animals):
  • Animals were divided into two groups:
    1. Red-blooded animals
    2. Non-red-blooded animals
• Limitation:
  • This system was simple and based only on superficial characters

Linnaeus

• Contribution:
  • Introduced the Two Kingdom Classification.
• Two Kingdom System:
  1. Kingdom Plantae
  2. Kingdom Animalia

Limitations of the Two Kingdom System

• This system failed to distinguish between:
  • Cell Type: Prokaryotes and eukaryotes
  • Body Organisation: Unicellular and multicellular organisms
  • Mode of Nutrition: Photosynthetic organisms & Non-photosynthetic organisms
  • Problem of Misplacement: Many organisms did not fit properly into either Plantae or Animalia.

Example of Old vs New Understanding

• Old System:
  • Algae, fungi, and bacteria were grouped under plants mainly due to the presence of cell walls.
• New Understanding: Recognises differences such as:
  • Prokaryotic vs eukaryotic organisation
  • Unicellular vs multicellular forms
  • Autotrophic vs heterotrophic nutrition

Need for Better Classification

To overcome earlier limitations, classification needed to consider more reliable characters.

Key Characters Considered:

• Cell structure
• Body organisation
• Mode of nutrition
• Reproduction
• Evolutionary (phylogenetic) relationships

This led to the development of more refined and scientific classification systems.

Intermediate Classification Systems

• Haeckel’s Three Kingdom System:
  • Plantae
  • Protista
  • Animalia
• Copeland’s Four Kingdom System:
  • Monera
  • Protista
  • Plantae
  • Animalia

These systems were improvements but still incomplete.

Five Kingdom Classification by R.H. Whittaker (1969)

This is the most widely accepted system of classification.

Characteristics of the Five Kingdoms

1. Monera: Prokaryotic organisms (bacteria and cyanobacteria).
2. Protista: Unicellular eukaryotes (e.g., Chlamydomonas, Amoeba).
3. Fungi: Heterotrophic organisms with chitin in cell walls.
4. Plantae: Multicellular, autotrophic green plants with cellulose cell walls.
5. Animalia: Multicellular, heterotrophic organisms without cell walls.

Basis of Five Kingdom Classification

• Cell structure
• Body organisation
• Mode of nutrition
• Reproduction
• Phylogenetic relationships (evolutionary history)

Characters	Monera	Protista	Fungi	Plantae	Animalia
Cell type	Prokaryotic	Eukaryotic	Eukaryotic	Eukaryotic	Eukaryotic
Cell wall	Noncellulosic (Polysaccharide + amino acid)	Present in some	Present (chitin)	Present (cellulose)	Absent
Nuclear membrane	Absent	Present	Present	Present	Present
Body organization	Cellular	Cellular	Multicellular/ loose tissue	Tissue & organ level	Tissue/organ/ organ system
Mode of nutrition	Autotrophic (photosynthetic or chemosynthetic) or Heterotrophic (saprophytic/ parasitic)	Autotrophic or Heterotrophic	Heterotrophic (saprophytic/ parasitic)	Autotrophic (photosynthetic)	Heterotrophic (holozoic/ saprophytic, etc.)

Important Clarifications

• Fungi were earlier grouped with plants due to presence of cell wall, but were later separated because:
• They are non-photosynthetic
• Their cell wall is made of chitin, not cellulose

• All prokaryotic organisms were grouped under Monera.

• Unicellular eukaryotes like Chlamydomonas, Amoeba, and Paramecium were grouped under Protista, even though they were earlier placed in different kingdoms.

Special Note

• Viruses are not included in the five kingdom classification because they show both living and non-living characteristics.

Further Advances in Classification

Three-Domain System

• Divides Monera into two separate domains based on molecular studies.
• Leads to six-kingdom type grouping.

Current Status:

• Despite newer systems, the five kingdom classification remains the most commonly taught and used system.

Future of Classification

• Classification systems will continue to evolve as new information about molecular biology, genetics, and evolutionary relationships becomes available.

Kingdom Monera

Bacteria: The Basics

General Nature

• Cell Type:
  • All members of Kingdom Monera are prokaryotic organisms.
• Abundance:
  • Bacteria are the most abundant and widely distributed microorganisms on Earth.
• Habitat: They are found everywhere, including:
  • Soil and water
  • Extreme environments such as hot springs, deserts, snow, and deep oceans
  • On or inside other organisms as parasites

Shapes of Bacteria

1. Coccus: Spherical-shaped bacteria.
2. Bacillus: Rod-shaped bacteria.
3. Vibrium: Comma-shaped bacteria.
4. Spirillum: Spiral-shaped bacteria.

Metabolic Diversity in Bacteria

Bacteria show the greatest metabolic diversity among living organisms.

Autotrophic Bacteria

• Definition: These bacteria synthesise their own food.
• Types:
  1. Photosynthetic Autotrophs:
     • Use sunlight to manufacture food.
     • e.g., cyanobacteria.
  2. Chemosynthetic Autotrophs:
     • Use energy released from oxidation of inorganic substances such as ammonia, nitrites, and nitrates.
     • Play an important role in recycling nutrients like nitrogen, phosphorus, iron, and sulphur.

Heterotrophic Bacteria

• Definition: Depend on other organisms or organic matter for food.
• Types:
  1. Saprophytic – feed on dead organic matter
  2. Parasitic – live on or inside host organisms
  3. Symbiotic – live in association with other organisms (e.g., nitrogen-fixing bacteria)

Major Groups of Kingdom Monera

1. Archaebacteria (Primitive Bacteria)

• Habitats:
  • Found in extreme and harsh environments.
• Cell Wall:
  • Cell wall has a unique structure.
  • Peptidoglycan is absent, which helps them survive extreme conditions.

Major Types of Archaebacteria

1. Halophiles:
   • Salt-loving bacteria found in highly saline environments.
2. Thermoacidophiles:
   • Live in hot and acidic environments such as hot sulphur springs.
3. Methanogens:
   • Obligate anaerobes found in the gut of ruminant animals like cows and buffaloes.
   • Produce methane gas and are responsible for biogas formation.

2. Eubacteria (True Bacteria)

• General Characteristics:
  • Have a rigid cell wall containing peptidoglycan.
  • Many are motile due to presence of flagella.
• Occurrence:
  • Present almost everywhere, including extreme habitats and as parasites.

Classification Based on Nutrition

A. Autotrophic Eubacteria

• Photosynthetic Autotrophs:
  • Include cyanobacteria (blue-green algae).

• Characteristics of Cyanobacteria:
  • Contain chlorophyll a, similar to green plants.
  • Photosynthetic autotrophs.
  • May be unicellular, colonial, or filamentous.
  • Often form blooms in polluted water bodies.
• Nitrogen Fixation:
  • Some cyanobacteria such as Nostoc and Anabaena can fix atmospheric nitrogen.
  • Nitrogen fixation occurs in specialised cells called heterocysts.

B. Chemosynthetic Autotrophs

• Oxidise inorganic substances for energy.
• Play a key role in nutrient cycling in ecosystems.

C. Heterotrophic Eubacteria

• Role as Decomposers:
  • Most heterotrophic bacteria act as decomposers and break down dead organic matter.
• Pathogenic Bacteria: Some cause diseases such as:
  • Cholera
  • Typhoid
  • Tetanus
  • Citrus canker

Economic Importance of Bacteria

• Used in curd formation
• Antibiotic production
• Nitrogen fixation in legume roots

Reproduction in Bacteria

Asexual Reproduction

• Binary Fission:
  • Primary method of reproduction where one cell divides into two.
• Spore Formation:
  • Occurs under unfavourable conditions for survival.

Genetic Recombination (Primitive Sexual Processes)

• DNA Transfer:
  • Not a true sexual reproduction.
• Occurs through:
  1. Transformation – uptake of DNA from surroundings
  2. Transduction – DNA transfer via bacteriophages
  3. Conjugation – direct transfer of DNA between bacteria

Mycoplasma

General Characteristics:

• Cell Wall:
  • Absent, making them pleomorphic (variable in shape).
• Size:
  • Smallest living cells.
• Oxygen Requirement:
  • Can survive without oxygen (anaerobic).
• Antibiotic Resistance:
  • Resistant to antibiotics like penicillin that act on cell wall synthesis.
• Mode of Life:
  • May live as saprophytes or parasites on plants, animals, and humans.
• Special Name:
  • Mycoplasma are also called the “jokers of the plant kingdom” due to their unusual nature.

Key Points

• Kingdom Monera includes all prokaryotic organisms.
• Archaebacteria are adapted to extreme environments due to unique cell wall structure.
• Eubacteria show maximum metabolic diversity.
• Cyanobacteria are photosynthetic and some fix atmospheric nitrogen.
• Bacteria play both beneficial and harmful roles in nature.

Kingdom Protista

Overview

• Definition:
  • Kingdom Protista includes all single-celled eukaryotic organisms.
• Habitat:
  • Most protists are aquatic and are found in freshwater or marine environments.
• Basic Features:
  • Cells have a well-defined nucleus.
  • Membrane-bound organelles are present.
  • Some protists possess locomotory structures like flagella or cilia.
• Reproduction:
  • Reproduce both asexually and sexually.
  • Sexual reproduction involves cell fusion and zygote formation.
• Evolutionary Significance:
  • Protists show characteristics similar to plants, animals, and fungi.
  • They act as an evolutionary link among these kingdoms.
• Nutritional Diversity: Protists may be:
  • Photosynthetic
  • Heterotrophic
  • Parasitic
  • Saprophytic
  • Mixotrophic
• Food Reserve:
  • May include starch, glycogen, paramylon, chrysolaminarin, or fats.

Major Groups of Kingdom Protista

1. Chrysophytes

• Includes:
  • Diatoms
  • Golden algae (desmids)
• Habitat:
  • Found in freshwater as well as marine environments.
• General Characteristics:
  • Microscopic organisms.
  • Float passively in water currents as plankton.
  • Most are photosynthetic.
• Ecological Importance:
  • Diatoms are the chief producers in oceans.
• Cell Wall Structure:
  • Diatoms have two thin overlapping silica shells.
  • Shells fit together like a soap box.
  • Silica walls are indestructible.
• Economic Importance:
  • Accumulated silica shells form diatomaceous earth.
  • Used for polishing materials.
  • Used in filtration of oils and syrups.

2. Dinoflagellates

• Habitat:
  • Mostly marine and photosynthetic.
• Colour Variation:
  • May appear yellow, green, brown, blue, or red due to different pigments.
• Cell Wall:
  • Outer surface has stiff cellulose plates.
• Locomotion: Two flagella present:
  1. One longitudinal
  2. One transverse (lying in a furrow)
• Special Phenomenon:
  • Some species like Gonyaulax multiply rapidly and cause red tides.
  • Toxins released during red tides can kill marine animals.
• Additional Feature:
  • Some dinoflagellates show bioluminescence and are called “night lights”.

3. Euglenoids

• Habitat:
  • Freshwater, commonly in stagnant water bodies.
• Cell Covering:
  • Cell wall absent.
  • Body covered by a flexible, protein-rich layer called pellicle.
• Locomotion: Two flagella present:
  1. One long
  2. One short
• Mode of Nutrition:
  • Photosynthetic in presence of sunlight.
  • Heterotrophic in absence of sunlight.
• Photosynthetic Pigments:
  • Same as those found in higher plants.
• Example: Euglena.

4. Slime Moulds

• Mode of Nutrition:
  • Saprophytic, feeding on decaying organic matter.
• Movement:
  • Creep along decaying leaves and twigs, engulfing organic material.
• Aggregation:
  • Forms plasmodium (a large, single-celled, multinucleate mass) under suitable conditions.
• Reproduction:
  • During unfavourable conditions, plasmodium forms fruiting bodies.
  • Fruiting bodies produce spores.
• Spores:
  • Have true cell walls.
  • Highly resistant.
  • Can survive adverse conditions for many years.
  • Dispersed by air currents.
• Example: Physarum

5. Protozoans

• General Nature:
  • All protozoans are heterotrophic.
  • Live as predators or parasites.
  • Considered primitive relatives of animals.

Classification Based on Locomotion

1. Amoeboid Protozoans:
   • Move using pseudopodia (false feet).
   • Found in freshwater, seawater, or moist soil.
   • Some are parasitic.
   • Marine forms may have silica shells.
   • Example: Amoeba, Entamoeba
2. Flagellated Protozoans:
   • Move using flagella.
   • May be free-living or parasitic.
   • Cause several diseases.
   • Example:
     • Trypanosoma – causes sleeping sickness
     • Leishmania donovani – causes kala-azar
     • Giardia intestinalis – causes giardiasis
3. Ciliated Protozoans:
   • Aquatic and actively moving.
   • Move using numerous cilia.
   • Have a gullet for ingestion of food.
   • Show nuclear dimorphism:
     1. Macronucleus – controls metabolism and growth
     2. Micronucleus – involved in reproduction
   • Example: Paramecium
4. Sporozoans:
   • All are endoparasites.
   • Locomotory organs absent.
   • Have an infectious spore-like stage in life cycle.
   • Example: Plasmodium – causes malaria

Key Points

• Kingdom Protista includes unicellular eukaryotes.
• They show maximum diversity in nutrition and structure.
• Protists connect plant, animal, and fungal kingdoms evolutionarily.
• Some protists are ecologically beneficial, while others cause serious diseases.

Kingdom Fungi

Overview

• Nature:
  • Fungi constitute a unique kingdom of heterotrophic organisms.
• Diversity:
  • They show great diversity in form, structure, and habitat.
• Common Examples:
  • Mushrooms and toadstools
  • Fungi growing on moist bread and rotten fruits
  • Yeast – unicellular fungus used in bread and beer making
  • Penicillium – source of antibiotics
  • Puccinia – causes wheat rust

Habitat

• Occurrence: Fungi are cosmopolitan and are found in:
  • Air
  • Water
  • Soil
  • On plants and animals
• Environmental Preference:
  • They grow best in warm and humid conditions.

Nutrition

Mode of Nutrition: All fungi are heterotrophic.

• Saprophytes:
  • Absorb nutrients from dead and decaying organic matter.
• Parasites:
  • Depend on living hosts for nutrition.
• Symbionts:
  • Live in association with other organisms.

Examples of Symbiosis:

1. Lichens – association between fungi and algae
2. Mycorrhiza – association between fungi and plant roots

Reserve Food Material: Glycogen

Structure

• Body Organisation:
  • Most fungi are filamentous (except yeast).
• Hyphae:
  • Long, slender, thread-like structures forming the body.
• Mycelium:
  • A network of hyphae forms the mycelium.

Types of Hyphae:

1. Coenocytic Hyphae: Continuous tubes with many nuclei and no cross walls.
2. Septate Hyphae: Hyphae divided by cross walls (septa) forming distinct cells.

Cell Wall Composition: Made of chitin and polysaccharides.

Reproduction in Fungi

Fungi reproduce by vegetative, asexual, and sexual methods.

• Vegetative Reproduction:
  • Fragmentation
  • Fission
  • Budding
• Asexual Reproduction: Occurs by spores such as:
  1. Conidia
  2. Sporangiospores
  3. Zoospores
• Sexual Reproduction: Occurs by spores such as:
  1. Oospores
  2. Ascospores
  3. Basidiospores

Sexual Cycle in Fungi

• Plasmogamy:
  • Fusion of protoplasm between two cells or gametes.
• Karyogamy:
  • Fusion of two nuclei.
• Meiosis:
  • Occurs in the zygote, producing haploid spores.

In some fungi (ascomycetes and basidiomycetes), an intermediate dikaryotic stage (n + n) is present before karyogamy.

Major Classes of Fungi

1. Phycomycetes

• Habitat:
  • Aquatic environments
  • Moist and damp places
  • Obligate parasites on plants
• Mycelium:
  • Aseptate and coenocytic.
• Asexual Reproduction:
  • Zoospores – motile
  • Aplanospores – non-motile
• Sexual Reproduction:
  • Zygospore formed by fusion of gametes.
• Examples:
  • Mucor
  • Rhizopus (bread mould)
  • Albugo

2. Ascomycetes (Sac-fungi)

• Forms:
  • Mostly multicellular
  • Some unicellular forms like yeast
• Nature:
  • Saprophytic
  • Decomposers
  • Parasitic
  • Coprophilous (growing on dung)
• Mycelium:
  • Branched and septate.
• Asexual Reproduction:
  • Conidia produced on specialised structures called conidiophores.
• Sexual Reproduction:
  • Ascospores produced inside sac-like structures called asci.
  • Asci are arranged in fruiting bodies called ascocarps.
• Examples:
  • Aspergillus
  • Penicillium
  • Claviceps
  • Neurospora
• Special Points:
  • Neurospora is widely used in biochemical and genetic research.
  • Morels and truffles are edible fungi and considered delicacies.

3. Basidiomycetes

• Forms:
  • Mushrooms
  • Bracket fungi
  • Puffballs
• Habitat:
  • Soil
  • Logs and tree stumps
  • Living plants as parasites
• Mycelium:
  • Branched and septate.
• Asexual Reproduction:
  • Usually absent.
  • Vegetative reproduction by fragmentation is common.
• Sexual Reproduction:
  • Basidiospores produced on club-shaped structures called basidia.
  • Basidia are arranged in fruiting bodies called basidiocarps.
• Examples:
  • Agaricus (mushroom)
  • Ustilago (smut)
  • Puccinia (rust fungus)

4. Deuteromycetes (Imperfect fungi)

• Nature:
  • Only asexual or vegetative stages are known.
  • Sexual stage is absent or not yet discovered.
• Reproduction:
  • Asexual reproduction by conidia.
• Mycelium:
  • Septate and branched.
• Ecological Role:
  • Saprophytes
  • Parasites
  • Major decomposers involved in mineral cycling.
• Examples:
  • Alternaria
  • Colletotrichum
  • Trichoderma

Reclassification: Once the sexual stage is discovered, members are reassigned to ascomycetes or basidiomycetes.

Key Points

• Fungi are heterotrophic organisms with chitinous cell walls.
• They play crucial roles as decomposers, parasites, symbionts, and industrial organisms.
• Reproduction involves complex life cycles with distinct spores.
• Kingdom Fungi is divided into four major classes based on mycelial structure and reproduction.

Class	Habitat / Nature	Mycelium	Asexual Reproduction	Sexual Reproduction	Examples
Phycomycetes	Aquatic, moist places, plant parasites	Aseptate, coenocytic	Zoospores (motile), aplanospores (non-motile)	Zygospore (fusion of gametes)	Mucor, Rhizopus (bread mould), Albugo
Ascomycetes	Mostly saprophytic, decomposers, parasitic, coprophilous	Branched, septate	Conidia (on conidiophores)	Ascospores (in asci within ascocarps)	Penicillium, Aspergillus, Claviceps, Neurospora, Morels, Truffles
Basidiomycetes	Soil, logs, tree stumps, living plants (parasites)	Branched, septate	Rare; vegetative reproduction by fragmentation	Basidiospores (on basidia within basidiocarps)	Agaricus (mushroom), Ustilago (smut), Puccinia (rust fungus)
Deuteromycetes	Saprophytes, parasites, decomposers	Septate, branched	Conidia	None known; reclassified when sexual stage identified	Alternaria, Colletotrichum, Trichoderma

Kingdom Plantae

Overview

• Nature:
  • Kingdom Plantae includes eukaryotic, chlorophyll-containing, photosynthetic organisms commonly called plants.
• Special Cases:
  • Some plants are partially heterotrophic.
  • Insectivorous plants trap insects to supplement nutrition.
  • Parasitic plants depend completely on host plants.
• Examples:
  • Insectivorous plants: Bladderwort, Venus flytrap
  • Parasitic plant: Cuscuta

Cell Structure

• Cell Type:
  • Eukaryotic cells.
• Cell Wall:
  • Present, mainly made of cellulose.
• Cell Organelles:
  • Chloroplasts are present and carry out photosynthesis.

Major Groups of Plants

1. Algae: Simple, mostly aquatic plants.
2. Bryophytes: Mosses and liverworts.
3. Pteridophytes: Ferns and their relatives.
4. Gymnosperms: Conifers and cycads; naked seeds.
5. Angiosperms: Flowering plants; seeds enclosed within fruits.

Life Cycle in Plants

• Phases in Life Cycle:
  • Diploid sporophytic phase.
  • Haploid gametophytic phase.
• Alternation of Generations:
  • The sporophytic and gametophytic phases alternate.
  • The dominance and dependency of these phases vary among different plant groups.

Kingdom Animalia

Overview

• Nature:
  • Multicellular, heterotrophic, eukaryotic organisms.
• Cell Structure::
  • Cells lack cell walls.
  • Food is stored as glycogen or fat.
• Dependence on Plants:
  • Animals depend directly or indirectly on plants for food.

Key Characteristics

• Mode of Nutrition:
  • Holozoic nutrition by ingestion of food.
• Growth Pattern:
  • Definite growth pattern.
  • Animals grow into adults with a specific shape and size.
• Physiological Features:
  • Higher animals show advanced sensory and neuromotor mechanisms.
• Locomotion:
  • Most animals are capable of movement.

Reproduction in Animals

• Type:
  • Sexual reproduction.
• Process:
  • Copulation between male and female.
  • Followed by embryological development.

Viruses, Viroids, Prions, and Lichens

Viruses

• Nature:
  • Acellular (non-cellular) organisms.
  • Metabolically inert outside a living host cell.
  • Become active only inside host cells.
• Living or Non-living:
  • Considered borderline between living and non-living due to lack of cellular organisation.
• Discovery and Contributions:
  • Dmitri Ivanowsky (1892): Discovered viruses while studying tobacco mosaic disease.
  • M.W. Beijerinek (1898): Described viruses as “contagium vivum fluidum” (infectious living fluid).
  • W.M. Stanley (1935): Crystallised viruses, showing they are mainly protein in nature.

Structural Organisation

• Genetic Material:
  • Either RNA or DNA, never both.
• Protein Coat:
  • Genetic material is enclosed within a protein coat called capsid.
• Capsomeres:
  • Capsid is made of smaller subunits called capsomeres.
• Nature:
  • Viruses are nucleoproteins.

Types of Viruses

• Plant viruses:
  • Usually single-stranded RNA.
• Animal viruses:
  • May have single-stranded RNA, double-stranded RNA, or double-stranded DNA.
• Bacteriophages:
  • Viruses that infect bacteria.
  • Usually have double-stranded DNA.

Mode of Life

• Parasitism:
  • Viruses are obligate parasites.
  • They hijack host cell machinery for replication, often killing the host cell.

Diseases Caused

• In Humans:
  • Mumps
  • Smallpox
  • Herpes
  • Influenza
  • AIDS
• In Plants:
  • Mosaic formation
  • Leaf rolling and curling
  • Yellowing and vein clearing
  • Stunted growth

Viroids

• Discovery:
  • T.O. Diener (1971).
• Nature:
  • Smaller than viruses.
  • Consist only of free RNA.
  • Lack a protein coat.
• Disease Caused:
  • Potato spindle tuber disease.
• Special Feature:
  • RNA has very low molecular weight.

Prions

• Nature:
  • Infectious agents made of abnormally folded proteins.
• Resistance:
  • Not destroyed by proteases, nucleases, UV radiation, or heat.
• Diseases Caused:
  • Bovine Spongiform Encephalopathy (BSE) – mad cow disease
  • Creutzfeldt–Jakob Disease (CJD) – human variant

Lichens

• Nature:
  • Symbiotic association between algae and fungi.
• Components:
  1. Phycobiont: Algal partner, autotrophic, prepares food.
  2. Mycobiont: Fungal partner, heterotrophic, provides shelter and absorbs water and minerals.
• Pollution Indicator:
  • Lichens do not grow in polluted areas.
  • Their presence indicates clean air.

Key Points

• Plants are autotrophic eukaryotes showing alternation of generations.
• Animals are heterotrophic, multicellular organisms with advanced organisation.
• Viruses show both living and non-living features.
• Viroids and prions are simpler infectious agents.
• Lichens represent mutualistic symbiosis and act as bioindicators.

Chapter Summary

Early Classification Systems

• Aristotle:
  • First proposed biological classification.
  • Based plants and animals on simple morphological characters.
• Linnaeus:
  • Introduced the Two Kingdom Classification.
  • All organisms were placed into Plantae and Animalia.

Five Kingdom Classification

• Proposed By:
  • R. H. Whittaker (1969).
• Five Kingdoms:
  1. Monera
  2. Protista
  3. Fungi
  4. Plantae
  5. Animalia
• Basis of Five Kingdom Classification:
  1. Cell structure
  2. Body organisation
  3. Mode of nutrition
  4. Reproduction
  5. Phylogenetic (evolutionary) relationships

Kingdom Monera

• Members: Bacteria and related prokaryotes.
• Key Features:
  • Prokaryotic organisms.
  • Found in all types of habitats.
  • Show maximum metabolic diversity.
• Nutrition:
  • Autotrophic (photosynthetic or chemosynthetic).
  • Heterotrophic (saprophytic or parasitic).

Kingdom Protista

• Members: Single-celled eukaryotes.
• Examples:
  • Chrysophytes
  • Dinoflagellates
  • Euglenoids
  • Slime moulds
  • Protozoans
• Key Features:
  • Well-defined nucleus.
  • Membrane-bound organelles present.
  • Mostly aquatic.
• Reproduction:
  • Asexual reproduction.
  • Sexual reproduction through cell fusion and zygote formation.

Kingdom Fungi

• General Nature:
  • Eukaryotic and heterotrophic organisms.
• Habitat and Nutrition:
  • Show great diversity in structure and habitat.
  • Mostly saprophytic; some parasitic or symbiotic.
• Reproduction:
  • Asexual reproduction by spores.
  • Sexual reproduction involving specialised spores.

• Major Classes of Fungi
  1. Phycomycetes
  2. Ascomycetes
  3. Basidiomycetes
  4. Deuteromycetes

Kingdom Plantae

• Members: All eukaryotic, chlorophyll-containing plants.
• Major Groups:
  1. Algae
  2. Bryophytes
  3. Pteridophytes
  4. Gymnosperms
  5. Angiosperms
• Key Features:
  • Autotrophic and photosynthetic.
  • Cell wall made of cellulose.
• Life Cycle:
  • Shows alternation of generations.
  • Haploid gametophytic phase alternates with diploid sporophytic phase.

Kingdom Animalia

• Members: Multicellular, eukaryotic, heterotrophic organisms.
• Key Features:
  • Cell wall absent.
  • Holozoic mode of nutrition.
  • Well-developed sensory and neuromotor mechanisms in higher forms.
• Reproduction:
  • Mostly sexual reproduction.

Special Groups Not Included in Five Kingdom System

• Viruses:
  • Acellular and obligate parasites.
• Viroids:
  • Infectious RNA molecules without protein coat.
• Lichens:
  • Symbiotic association between algae and fungi.

Final Note

• The five-kingdom classification provides a scientific and evolutionary framework for understanding the diversity of living organisms.
• However, entities like viruses, viroids, and lichens do not fit neatly into this system and are studied separately.