CBSE Class 11 Biology Revision Notes Chapter 2 Biological Classification
Biological Classification explains how organisms are grouped based on cell structure, body organisation, nutrition, reproduction and evolutionary relationships. In CBSE Class 11 Biology, this chapter covers five kingdoms, bacteria, protists, fungi, viruses, viroids, prions and lichens.
Biological Classification studies how living organisms are arranged into groups based on shared characters. Early systems used simple visible features, but later systems included cell type, cell wall, nutrition, reproduction and phylogenetic relationships.
Use CBSE Class 11 Biology Revision Notes Chapter 2 for 2026–27 to revise two kingdom classification, five kingdom classification, Kingdom Monera, Kingdom Protista, Kingdom Fungi and acellular forms. The chapter also explains why viruses, viroids, prions and lichens are discussed separately.
Key Takeaways
- R.H. Whittaker: Proposed the five kingdom classification in 1969.
- Five kingdoms: Monera, Protista, Fungi, Plantae and Animalia.
- Monera: Includes prokaryotic organisms such as bacteria and cyanobacteria.
- Viruses: Acellular forms with either DNA or RNA, enclosed in a protein coat.
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Biological Classification Class 11 Biology Notes: Meaning and Need
Biological classification is the process of grouping organisms based on similarities and differences. It helps organise the large variety of life forms into clear categories.
Aristotle classified plants as trees, shrubs and herbs. He also grouped animals based on the presence or absence of red blood.
Two Kingdom Classification in Class 11 Biology Chapter 2 Notes
Linnaeus classified organisms into two kingdoms: Plantae and Animalia.
| Kingdom | Included Organisms |
| Plantae | Plants and plant-like organisms |
| Animalia | Animals and animal-like organisms |
This system was easy to understand but had several limitations.
Limitations of Two Kingdom Classification
| Limitation | Explanation |
| Prokaryotes and eukaryotes | Bacteria and plants were grouped together |
| Unicellular and multicellular organisms | Chlamydomonas and Spirogyra were placed together |
| Photosynthetic and non-photosynthetic organisms | Fungi were placed with green plants |
| Cell wall differences | Fungi have chitin, while green plants have cellulose |
| Evolutionary relationships | Phylogenetic links were not properly considered |
The two kingdom system became inadequate because many organisms did not fit clearly into Plantae or Animalia.
Five Kingdom Classification in Biological Classification Class 11 Notes
R.H. Whittaker proposed the five kingdom classification in 1969. The five kingdoms are Monera, Protista, Fungi, Plantae and Animalia.
Basis of Five Kingdom Classification
| Criterion | Meaning |
| Cell structure | Prokaryotic or eukaryotic |
| Body organisation | Cellular, tissue, organ or organ-system level |
| Mode of nutrition | Autotrophic or heterotrophic |
| Reproduction | Asexual or sexual |
| Phylogenetic relationships | Evolutionary relationships |
This system separated prokaryotes from eukaryotes and fungi from green plants.
Five Kingdom Classification Table
| Character | Monera | Protista | Fungi | Plantae | Animalia |
| Cell type | Prokaryotic | Eukaryotic | Eukaryotic | Eukaryotic | Eukaryotic |
| Cell wall | Non-cellulosic | Present in some | Chitin | Cellulose | Absent |
| Nuclear membrane | Absent | Present | Present | Present | Present |
| Body organisation | Cellular | Cellular | Multicellular or loose tissue | Tissue or organ | Tissue, organ or organ system |
| Nutrition | Autotrophic or heterotrophic | Autotrophic or heterotrophic | Heterotrophic | Autotrophic | Heterotrophic |
| Examples | Bacteria | Euglena, Amoeba | Yeast, mushroom | Algae, bryophytes, angiosperms | Humans, insects, fish |
Kingdom Monera in CBSE Class 11 Biology Notes Chapter 2
Kingdom Monera includes bacteria. These organisms are prokaryotic and have no true nucleus.
Bacteria occur almost everywhere. They live in soil, hot springs, deserts, snow, deep oceans and inside other organisms.
Main Features of Kingdom Monera
| Feature | Description |
| Cell type | Prokaryotic |
| Nuclear membrane | Absent |
| Cell wall | Usually present |
| Body organisation | Unicellular |
| Nutrition | Autotrophic, heterotrophic or parasitic |
| Reproduction | Mainly by fission |
| Habitat | Soil, water, extreme habitats and living hosts |
Bacteria show high metabolic diversity. Some make their own food, while many depend on dead matter or other organisms.
Shapes of Bacteria
| Shape | Name |
| Spherical | Coccus |
| Rod-shaped | Bacillus |
| Comma-shaped | Vibrio |
| Spiral | Spirillum |
These bacterial shapes are important for identifying and describing bacteria.
Archaebacteria and Eubacteria in Biological Classification
Bacteria are grouped into different types based on structure, habitat and metabolism. Archaebacteria and eubacteria are important groups in Kingdom Monera.
Archaebacteria
Archaebacteria live in extreme habitats. Their cell wall structure differs from other bacteria.
| Type | Habitat | Example or Role |
| Halophiles | Extreme salty areas | Salt-loving bacteria |
| Thermoacidophiles | Hot springs | Survive high temperature and acidity |
| Methanogens | Marshy areas and ruminant gut | Produce methane or biogas |
Methanogens are found in the gut of cows and buffaloes. They help produce methane from animal dung.
Eubacteria
Eubacteria are called true bacteria. They usually have a rigid cell wall and may have flagella if motile.
| Type | Key Feature | Example or Role |
| Cyanobacteria | Have chlorophyll a | Photosynthetic autotrophs |
| Chemosynthetic bacteria | Oxidise inorganic substances | Help recycle nutrients |
| Heterotrophic bacteria | Depend on organic matter | Decomposers, pathogens or useful bacteria |
| Mycoplasma | Lack cell wall | Smallest living cells known |
Cyanobacteria are also called blue-green algae. Some, such as Nostoc and Anabaena, can fix atmospheric nitrogen in specialised cells called heterocysts.
Useful and Harmful Bacteria
| Role | Examples |
| Useful bacteria | Curd formation, antibiotics, nitrogen fixation |
| Harmful bacteria | Cholera, typhoid, tetanus, citrus canker |
| Decomposers | Break down dead organic matter |
| Nutrient cycling | Help recycle nitrogen, phosphorus, iron and sulphur |
Bacteria reproduce mainly by fission. Under unfavourable conditions, some bacteria produce spores.
Kingdom Protista in Class 11 Biology Chapter 2 Notes
Kingdom Protista includes single-celled eukaryotes. Most protists are aquatic.
Protists have a well-defined nucleus and membrane-bound organelles. Some move with cilia or flagella.
Main Features of Kingdom Protista
| Feature | Description |
| Cell type | Eukaryotic |
| Body organisation | Unicellular |
| Habitat | Mostly aquatic |
| Nuclear membrane | Present |
| Movement | Cilia, flagella or pseudopodia in some |
| Reproduction | Asexual and sexual |
| Nutrition | Autotrophic or heterotrophic |
Kingdom Protista forms a link with plants, animals and fungi.
Groups of Protists in Biological Classification Class 11 Biology Notes
Protista includes chrysophytes, dinoflagellates, euglenoids, slime moulds and protozoans.
Chrysophytes
Chrysophytes include diatoms and golden algae. They occur in freshwater and marine environments.
| Feature | Description |
| Examples | Diatoms, golden algae |
| Habitat | Freshwater and marine water |
| Cell wall | Silica-rich walls in diatoms |
| Nutrition | Mostly photosynthetic |
| Importance | Chief producers in oceans |
In diatoms, the cell wall has two overlapping shells like a soap box. Their silica deposits form diatomaceous earth.
Dinoflagellates
Dinoflagellates are mostly marine and photosynthetic. They may appear yellow, green, brown, blue or red due to pigments.
| Feature | Description |
| Habitat | Mostly marine |
| Cell wall | Stiff cellulose plates |
| Flagella | Two flagella |
| Example | Gonyaulax |
| Special feature | Can cause red tides |
Red dinoflagellates may multiply rapidly and form red tides. Toxins released during red tides can kill fish and other marine animals.
Euglenoids
Euglenoids are mostly freshwater organisms found in stagnant water. They have a flexible protein-rich layer called pellicle.
| Feature | Description |
| Habitat | Freshwater, stagnant water |
| Cell wall | Absent |
| Outer covering | Pellicle |
| Flagella | One short and one long flagellum |
| Nutrition | Photosynthetic in sunlight, heterotrophic without sunlight |
| Example | Euglena |
Euglenoids have pigments similar to those found in higher plants.
Slime Moulds
Slime moulds are saprophytic protists. They move over decaying twigs and leaves and feed on organic material.
| Feature | Description |
| Nutrition | Saprophytic |
| Feeding | Engulf organic matter |
| Aggregation | Plasmodium |
| Unfavourable conditions | Form fruiting bodies with spores |
| Spore dispersal | Air currents |
Their spores have true walls and can survive adverse conditions for many years.
Protozoans
Protozoans are heterotrophic protists. They may live as predators or parasites.
| Group | Movement or Feature | Example |
| Amoeboid protozoans | Pseudopodia | Amoeba, Entamoeba |
| Flagellated protozoans | Flagella | Trypanosoma |
| Ciliated protozoans | Cilia | Paramoecium |
| Sporozoans | Infectious spore-like stage | Plasmodium |
Plasmodium causes malaria. Trypanosoma causes sleeping sickness.
Kingdom Fungi in CBSE Class 11 Biology Revision Notes Chapter 2
Kingdom Fungi includes heterotrophic organisms with chitin in their cell wall. Fungi show great diversity in structure and habitat.
Mushrooms, yeast, bread mould and Penicillium are fungi. Some fungi are useful, while others cause diseases.
Main Features of Kingdom Fungi
| Feature | Description |
| Cell type | Eukaryotic |
| Cell wall | Chitin and polysaccharides |
| Body | Usually filamentous |
| Nutrition | Heterotrophic |
| Food absorption | Absorb soluble organic matter |
| Reserve food | Glycogen and oils |
| Reproduction | Vegetative, asexual and sexual |
Except yeast, most fungi are filamentous. Their thread-like structures are called hyphae. A network of hyphae is called mycelium.
Types of Fungal Nutrition
| Type | Meaning |
| Saprophytic | Feed on dead organic matter |
| Parasitic | Feed on living organisms |
| Symbiotic | Live in association with another organism |
Fungi may live with algae as lichens. They may also live with roots of higher plants as mycorrhiza.
Reproduction in Fungi
| Type | Methods |
| Vegetative reproduction | Fragmentation, fission, budding |
| Asexual reproduction | Conidia, sporangiospores, zoospores |
| Sexual reproduction | Oospores, ascospores, basidiospores |
Sexual reproduction in fungi involves plasmogamy, karyogamy and meiosis.
| Step | Meaning |
| Plasmogamy | Fusion of protoplasms |
| Karyogamy | Fusion of two nuclei |
| Meiosis | Formation of haploid spores |
In ascomycetes and basidiomycetes, a dikaryotic stage may occur. This stage has two nuclei per cell and is called dikaryophase.
Classes of Kingdom Fungi in Class 11 Biology Chapter 2 Notes
Fungi are classified based on mycelium, spore formation and fruiting bodies.
Phycomycetes
| Feature | Description |
| Habitat | Aquatic habitats, decaying wood, moist places |
| Mycelium | Aseptate and coenocytic |
| Asexual spores | Zoospores or aplanospores |
| Sexual spore | Zygospore |
| Examples | Mucor, Rhizopus, Albugo |
Rhizopus is commonly called bread mould. Albugo is a parasitic fungus found on mustard.
Ascomycetes
| Feature | Description |
| Common name | Sac fungi |
| Body | Mostly multicellular, rarely unicellular |
| Mycelium | Branched and septate |
| Asexual spores | Conidia |
| Sexual spores | Ascospores |
| Fruiting body | Ascocarp |
| Examples | Aspergillus, Penicillium, Neurospora, yeast |
Yeast is unicellular. Neurospora is used in biochemical and genetic studies.
Basidiomycetes
| Feature | Description |
| Common forms | Mushrooms, bracket fungi, puffballs |
| Mycelium | Branched and septate |
| Asexual spores | Generally absent |
| Vegetative reproduction | Fragmentation |
| Sexual spores | Basidiospores |
| Fruiting body | Basidiocarp |
| Examples | Agaricus, Ustilago, Puccinia |
Agaricus is mushroom. Puccinia causes rust disease.
Deuteromycetes
| Feature | Description |
| Common name | Imperfect fungi |
| Sexual stage | Not known in many members |
| Asexual spores | Conidia |
| Mycelium | Septate and branched |
| Role | Decomposers, saprophytes or parasites |
| Examples | Alternaria, Colletotrichum, Trichoderma |
Many deuteromycetes help in mineral cycling by decomposing litter.
Kingdom Plantae in Biological Classification Class 11 Notes
Kingdom Plantae includes eukaryotic organisms with chlorophyll. Their cell wall is mainly made of cellulose.
| Feature | Description |
| Cell type | Eukaryotic |
| Cell wall | Cellulose |
| Nutrition | Mostly photosynthetic |
| Main pigment | Chlorophyll |
| Groups included | Algae, bryophytes, pteridophytes, gymnosperms, angiosperms |
| Life cycle | Alternation of generations |
Some plants are partially heterotrophic. Bladderwort and Venus fly trap are insectivorous plants. Cuscuta is a parasitic plant.
Kingdom Animalia in CBSE Class 11 Biology Notes Chapter 2
Kingdom Animalia includes multicellular, eukaryotic and heterotrophic organisms. Their cells do not have cell walls.
| Feature | Description |
| Cell type | Eukaryotic |
| Body | Multicellular |
| Cell wall | Absent |
| Nutrition | Holozoic |
| Food reserve | Glycogen or fat |
| Growth | Definite growth pattern |
| Movement | Most animals show locomotion |
| Reproduction | Mostly sexual |
Animals directly or indirectly depend on plants for food. Higher animals have sensory and neuromotor mechanisms.
Viruses, Viroids, Prions and Lichens in Biological Classification
Viruses, viroids, prions and lichens are not placed in Whittaker’s five kingdom classification. They are discussed separately because they do not fit neatly into the five kingdoms.
Viruses
Viruses are non-cellular organisms. They remain inert outside a living cell but multiply inside a host cell.
| Feature | Description |
| Structure | Nucleic acid enclosed in protein coat |
| Genetic material | DNA or RNA |
| Protein coat | Capsid |
| Capsid units | Capsomeres |
| Nature | Obligate parasites |
| Outside host | Inert crystalline form |
No virus has both DNA and RNA. Plant viruses usually have single-stranded RNA. Bacteriophages usually have double-stranded DNA.
Viral Diseases and Symptoms
| Host | Examples |
| Humans | Mumps, smallpox, herpes, influenza, AIDS |
| Plants | Mosaic formation, leaf rolling, curling, yellowing, vein clearing, dwarfing |
Dmitri Ivanowsky recognised microbes causing tobacco mosaic disease. M.W. Beijerinck used the term virus for the infectious agent.
Viroids
Viroids are smaller than viruses. They contain free RNA and lack a protein coat.
| Feature | Description |
| Discovered by | T.O. Diener |
| Disease | Potato spindle tuber disease |
| Structure | Free RNA |
| Protein coat | Absent |
Viroids have low molecular weight RNA.
Prions
Prions are infectious agents made of abnormally folded proteins.
| Feature | Description |
| Composition | Abnormally folded protein |
| Disease in cattle | Bovine spongiform encephalopathy |
| Common name | Mad cow disease |
| Human disease | Creutzfeldt-Jakob disease |
Prions are linked with certain infectious neurological diseases.
Lichens
Lichens are symbiotic associations between algae and fungi.
| Component | Name | Role |
| Algal component | Phycobiont | Prepares food |
| Fungal component | Mycobiont | Provides shelter, water and minerals |
Lichens are good pollution indicators because they do not grow in polluted areas.
Quick Comparison of Five Kingdoms for Class 11 Biology Chapter 2 Notes
| Kingdom | Cell Type | Cell Wall | Nutrition | Example |
| Monera | Prokaryotic | Present, non-cellulosic | Autotrophic or heterotrophic | Bacteria |
| Protista | Eukaryotic | Present in some | Autotrophic or heterotrophic | Euglena |
| Fungi | Eukaryotic | Chitin | Heterotrophic | Mushroom |
| Plantae | Eukaryotic | Cellulose | Autotrophic | Mango plant |
| Animalia | Eukaryotic | Absent | Heterotrophic | Human |
This table is useful for revising the main differences between the five kingdoms.
Important Terms from Biological Classification Class 11 Notes
| Term | Meaning |
| Biological classification | Grouping organisms based on similarities |
| Two kingdom classification | Classification into Plantae and Animalia |
| Five kingdom classification | Whittaker’s classification into five kingdoms |
| Prokaryotic cell | Cell without a true nucleus |
| Eukaryotic cell | Cell with a true nucleus |
| Cyanobacteria | Blue-green algae |
| Diatomaceous earth | Silica-rich deposits of diatom cell walls |
| Red tide | Red appearance of sea due to rapid dinoflagellate growth |
| Mycelium | Network of fungal hyphae |
| Dikaryophase | Stage with two nuclei per fungal cell |
| Capsid | Protein coat of a virus |
| Capsomeres | Small subunits of capsid |
| Phycobiont | Algal component of lichen |
| Mycobiont | Fungal component of lichen |
NCERT-Based Exam Points
- Aristotle classified plants into trees, shrubs and herbs.
- Linnaeus proposed the two kingdom classification.
- The two kingdoms were Plantae and Animalia.
- R.H. Whittaker proposed five kingdom classification in 1969.
- The five kingdoms are Monera, Protista, Fungi, Plantae and Animalia.
- Bacteria are the sole members of Kingdom Monera.
- Bacteria may be cocci, bacilli, vibrio or spirilla.
- Archaebacteria survive in extreme habitats.
- Methanogens help in biogas production.
- Cyanobacteria have chlorophyll a.
- Diatoms have silica-rich cell walls.
- Dinoflagellates can cause red tides.
- Euglenoids have a pellicle.
- Slime moulds form plasmodium.
- Protozoans include amoeboid, flagellated, ciliated forms and sporozoans.
- Fungal cell walls contain chitin.
- Fungal hyphae form mycelium.
- Plantae includes chlorophyll-containing eukaryotes.
- Animalia includes multicellular heterotrophs without cell walls.
- Viruses contain either DNA or RNA.
- Viroids lack a protein coat.
- Lichens have phycobiont and mycobiont.
Useful Links for Class 11 Biology Revision Notes
| Section | Useful Links |
| Revision Notes | CBSE Class 11 Biology Revision Notes |
| Syllabus | CBSE Class 11 Biology Syllabus |
| NCERT Solutions | NCERT Solutions Class 11 Biology |
| Sample Papers | CBSE Sample Papers for Class 11 Biology |
| Important Questions | Important Questions Class 11 Biology |
| NCERT Books | NCERT Books for Class 11 Biology |
FAQs (Frequently Asked Questions)
The five kingdoms are Monera, Protista, Fungi, Plantae and Animalia. R.H. Whittaker proposed this classification in 1969 using cell structure, body organisation, nutrition, reproduction and phylogenetic relationships.
Two kingdom classification did not separate prokaryotes from eukaryotes, unicellular organisms from multicellular organisms, or fungi from green plants. It grouped many unrelated organisms together under Plantae or Animalia.
Archaebacteria live in extreme habitats and have a different cell wall structure. Eubacteria are true bacteria with a rigid cell wall and, in motile forms, flagella. Cyanobacteria are examples of eubacteria.
Viruses are acellular and do not have a cellular structure. They remain inert outside a host cell and replicate only inside living cells, so they are discussed separately from the five kingdoms.
Lichens are symbiotic associations between algae and fungi. The algal component, called phycobiont, prepares food. The fungal component, called mycobiont, provides shelter, water and minerals.