CBSE Class 9 > Class 9 Notes > Science New NCERT 2026-27 (New Syllabus) > Cheat Sheet: Diversity And Classification
Cheat Sheet: Diversity And Classification
1. Introduction & India as a Biodiversity Hotspot
1.1 Key definitions and terms
| Term | Definition |
|---|---|
| Biodiversity | Variety of living things on Earth; each organism plays a role in ecosystem functioning. |
| Classification | Grouping organisms based on shared traits (body structure, nutrition, cell type, genetics). |
| Endemic species | Species found only in a particular region and nowhere else. |
| Notable Indian endemics | Nilgiri tahr; lion-tailed macaque; Nepenthes khasiana; Neelakurinji. |
| Biodiversity hotspot | A region with many endemic species that has lost a significant portion of original habitat. |
| Biological classification | Organised system to identify, name, and understand relationships among organisms. |
| Chitin | Tough polymer present in insect exoskeletons and fungal cell walls; provides structural strength. |
1.2 India: landscapes and hotspots
| Hotspot | Notes |
|---|---|
| Western Ghats | High endemism; listed as a global biodiversity hotspot overlapping India. |
| Indo-Burma | Includes northeast India; part of global Indo-Burma hotspot. |
| Himalayas | High habitat diversity; included among global hotspots overlapping India. |
| Sundaland (Nicobar Islands) | Includes Nicobar Islands; listed as a global hotspot overlapping India. |
2. Classification: Purpose, Criteria, and Historical Systems
2.1 Criteria for classifying organisms
- External features - body shape, size, structure.
- Mode of nutrition - autotrophic or heterotrophic.
- Internal structures - tissues, organs, skeleton.
- Cell structure - unicellular/multicellular; prokaryote/eukaryote; cell wall presence.
- Ecological role - producer, consumer, decomposer.
- Reproduction - sexual, asexual, or both.
- Genetic similarity - DNA-based relatedness.
2.2 Need for classification
- Organises and systematises the study of living organisms.
- Reveals similarities and differences among organisms.
- Clarifies relationships and interactions among organisms.
- Assists identification and naming of newly discovered organisms.
- Supports biodiversity conservation by identifying threatened organisms.
- Provides a common system for global scientific communication.
2.3 Historical classification systems
| System | Key features |
|---|---|
| Aristotle (4th century BCE) | Artificial habitat-based sorting: land, water, air. |
| Carolus Linnaeus (1758) - Two Kingdoms | Plantae and Animalia; limitations for unicellular organisms and bacteria. |
| Ernst Haeckel (1866) - Three Kingdoms | Added Protista for unicellular microscopic eukaryotes. |
| Herbert F. Copeland (1938) - Four Kingdoms | Separated Monera for prokaryotes; kingdoms: Monera, Protista, Plantae, Animalia. |
| Robert H. Whittaker (1969) - Five Kingdoms | Monera, Protista, Fungi, Plantae, Animalia; based on cell type, cell structure, organisation level, nutrition. |
| Carl Woese (1977) - Three Domains | Domains above kingdoms: Bacteria, Archaea, Eukarya based on genetic (rRNA/DNA) differences. |
2.4 Underlying criteria of Whittaker's system
- Cell type: prokaryote versus eukaryote.
- Cell structure: presence or absence of cell wall and its composition.
- Level of organisation: unicellular versus multicellular.
- Mode of nutrition: autotrophic versus heterotrophic.
3. Five-Kingdom Details, Plant Groups, and Animal Phyla
3.1 Five kingdoms - distinguishing features
| Kingdom | Distinguishing feature |
|---|---|
| Monera | Unicellular prokaryotes; genetic material not enclosed in a nucleus. |
| Protista | Unicellular eukaryotes with membrane-bound nucleus; varied cell walls or none. |
| Fungi | Eukaryotic mostly multicellular organisms with external digestion via mycelium and reproduction by spores. |
| Plantae | Multicellular autotrophic eukaryotes with cellulose cell walls; primary producers. |
| Animalia | Multicellular heterotrophic eukaryotes; movement and complex behaviour; chordates possess a notochord. |
3.2 Plantae: major groups
| Group | Key trait |
|---|---|
| Thallophyta (Algae) | Undifferentiated thallus; no true root, stem, or leaf; mostly aquatic or persistently wet. |
| Bryophyta | Require water for fertilisation; possess rhizoids but no true roots, stems, or leaves. |
| Pteridophyta | Vascular tissue present (xylem and phloem); true roots, stems, leaves; no seeds. |
| Gymnosperms | Naked seeds exposed on cones; reproduction without water for fertilisation. |
| Angiosperms | Flowers and fruits; efficient pollination and seed dispersal; most species-rich plant group. |
3.3 Monera notes
- Cyanobacteria are photosynthetic prokaryotes that released oxygen into the atmosphere ~2.5 billion years ago.
- Stromatolites are layered rock formations preserving ancient cyanobacteria; found in Rajasthan and Madhya Pradesh.
3.4 Fungi-specific terms
| Term | Definition |
|---|---|
| Mycelium | Network of fine fungal threads that absorb digested nutrients. |
| Saprophyte | Organism that feeds on dead organic matter, recycling nutrients. |
3.5 Animalia: invertebrate phyla and key traits
- Porifera - Habitat: marine; Organisation: cellular; Skeleton: none.
- Cnidaria - Habitat: fresh and marine water; Organisation: tissue; Skeleton: none.
- Platyhelminthes - Habitat: water or inside host; Organisation: organ; Skeleton: none.
- Nematoda - Habitat: soil, water, or inside host; Organisation: organ system; Skeleton: none; two body openings.
- Annelida - Habitat: moist soil or water; Organisation: organ system; Skeleton: none; segmented body.
- Arthropoda - Habitat: land and water; Organisation: organ system; Skeleton: exoskeleton.
- Mollusca - Habitat: water or moist land; Organisation: organ system; Skeleton: shell (external in many).
- Echinodermata - Habitat: marine; Organisation: organ system; Skeleton: endoskeleton.
3.6 Protochordates and vertebrates
- Protochordates - Notochord present at some life stage; not developed into vertebral column.
- Vertebrates - Notochord replaced by vertebral column; five groups: fish, amphibians, reptiles, birds, mammals.
4. Adaptations, Hierarchy, Naming, Fossils, and Threats
4.1 Adaptations as evolutionary outcomes
- Structural changes that improved survival and reproduction were passed to descendants and accumulated over generations.
4.2 Hierarchical classification
| Level | Sequence |
|---|---|
| Hierarchy | Kingdom → Phylum → Class → Order → Family → Genus → Species |
4.3 Scientific naming: binomial nomenclature and rules
| Rule | Description |
|---|---|
| Binomial format | Two parts: genus name first, species name second. |
| Capitalisation | Genus name begins with a capital letter; species name is lowercase. |
| Formatting | Written in italics when printed; underlined when handwritten. |
| Genus | Groups closely related species that share key features. |
| Species | Group of individuals similar enough to interbreed and produce fertile offspring. |
4.4 Fossils and named contributors
| Term / Name | Details |
|---|---|
| Fossils | Preserved remains or imprints in sedimentary rock; older layers contain simpler organisms; provide a timeline of life's history. |
| Birbal Sahni | Studied fossil plants; founded the Birbal Sahni Institute of Palaeosciences (BSIP) in Lucknow. |
| Purple Frog - Nasikabatrachus sahyadrensis | Species name derived from Sahyadri Hills; rediscovered in 2003; belongs to an ancient amphibian lineage. |
| Sangai deer | Exclusive to Loktak Lake phumdis; declared extinct in 1951 and rediscovered in 1953; listed as endangered on the IUCN Red List. |
4.5 Biodiversity under threat
- Main threats: pollution, deforestation, overexploitation, climate change.
- Consequences: loss of species triggers further losses among dependent organisms.
- Conservation priority: protect hotspots and endemic-rich habitats because losses there are irreplaceable.
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