Class 9 › Science › Chapter 12
Patterns in Life: Diversity and Classification
Biodiversity and Indian hotspots, criteria and history of classification, the five kingdoms, plant and animal groups, the taxonomic hierarchy, scientific naming, and threats to biodiversity.
1. Biodiversity and Why It Matters
Biodiversity: the immense variety of living organisms on the Earth, from microscopic organisms to giant trees, living in habitats from the Himalayas to the Andaman coral reefs.
Ecological roles
Keeps nature stable
Microscopic algae release most of our oxygen; fungi and bacteria decompose waste and make soil fertile; birds, bees and bats pollinate; plants make food for nearly all life.
Human needs
Food, shelter, medicine
Humans depend on biodiversity for food, shelter, medicines and livelihoods. Farmers conserved crop varieties with drought tolerance, pest resistance and ability to grow in poor soils, which reduces risk of crop failure and strengthens food security.
- Evolution of diversity: small differences among individuals affected survival and reproduction; over many generations these accumulated and gave rise to new forms of life.
- Biodiversity is studied systematically through classification.
- Indian traditions: Sangam Tinai classification of landscapes and sacred groves preserved local habitats; the Rigveda and Brihat Samhita classified animals by habitat, behaviour and ecological role.
2. India as a Biodiversity Hotspot
Endemic species
Found only in one region
Species restricted to particular regions and not found naturally anywhere else. Indian examples: Nilgiri tahr, lion-tailed macaque, Nepenthes khasiana (pitcher plant), Neelakurinji.
Hotspot
Rich but threatened
A region with a large number of endemic species that has also undergone significant habitat loss. Examples: Western Ghats, Indo-Burma (incl. North East India), Himalayas, Sundaland (incl. Nicobar Islands).
- India's variety of landscapes (mountains, desert, rainforest, plateaus, long coastlines) with different soils and climates supports a wide variety of species.
- Protecting hotspots matters because they support food webs and keep ecosystems healthy.
3. Criteria and Need for Classification
Biological classification: the scientific system of grouping living organisms on the basis of their similarities and/or differences. The same organism can fit into different groups depending on the criterion chosen.
| No. | Criterion | Examples of what is looked at |
|---|---|---|
| 1 | External features | Shape, size, body organisation |
| 2 | Mode of nutrition | Autotrophic or heterotrophic |
| 3 | Internal structures | Skeletal pattern, organs, types of tissues |
| 4 | Cell structure | Unicellular or multicellular; prokaryote or eukaryote; cell wall present or absent |
| 5 | Ecological role | Producer, consumer, decomposer |
| 6 | Reproduction | Asexual and/or sexual |
| 7 | Genetic similarity | Similarity of DNA / inherited features |
- Scientists start with broad, easily visible features and then move to detailed ones. Similar features suggest common ancestry.
- Why classify? (library analogy: books scattered on the floor) It organises study, shows similarities and differences, shows how organisms are related and interact, helps identify and name new organisms, supports conservation of threatened species, and gives scientists worldwide a common system.
- Pakke Tiger Reserve case: about 300 bird species (India has about 1,300) including four hornbills that nest in large old trees and eat specific fruits; hence different hornbills live in different parts of the forest. Losing old trees would threaten them.
4. Classification Systems Over Time
Timeline of classification systems. Each new system fixed a problem in the one before it.
| System | Basis / problem it solved |
|---|---|
| Aristotle (4th c. BCE) | Grouped animals by habitat (land, water, air) and external appearance; limited because it relied only on easily seen features. |
| Two kingdom (Linnaeus, 18th c.) | Plantae: do not move, make own food. Animalia: move, depend on others for food. Confusion over Amoeba, Paramecium, bacteria (move like animals but unicellular). |
| Three kingdom (Haeckel) | Added Protista for unicellular microscopic organisms. |
| Four kingdom (Copeland) | Better microscopes showed bacteria have no true nucleus, unlike amoeba; bacteria placed in Monera. |
| Five kingdom (Whittaker) | Fungi (e.g. mushrooms) do not move like plants and are heterotrophic (absorb nutrients), so placed in separate kingdom Fungi. |
- Classification keeps changing as new tools (microscopes, staining techniques, DNA studies) give new knowledge: science is an ongoing process of reasoning and change.
5. Five Kingdom Classification
Four criteria of the five kingdom system: cell type (prokaryote / eukaryote), level of organisation (unicellular / multicellular), cell structure (cell wall present / absent) and mode of nutrition (autotrophic / heterotrophic).
Decision tree for the five kingdoms (Whittaker, 1969).
| Kingdom | Cell type | Organisation | Cell wall | Nutrition | Examples |
|---|---|---|---|---|---|
| Monera | Prokaryote | Unicellular | Present in many | Autotrophic or heterotrophic | Bacteria, cyanobacteria |
| Protista | Eukaryote | Unicellular | Absent, or cellulose | Autotrophic or heterotrophic | Amoeba, Paramecium, Euglena |
| Fungi | Eukaryote | Mostly multicellular | Chitin | Heterotrophic (absorb nutrients) | Mushroom, yeast, Aspergillus |
| Plantae | Eukaryote | Multicellular | Cellulose | Autotrophic | Mosses, ferns, pine, rose |
| Animalia | Eukaryote | Multicellular | Absent | Heterotrophic | Ant, frog, bird, human |
- Viruses are acellular, show life activity only inside a host cell, and have no cellular organisation, so they do not fit in any of the five kingdoms (a limitation of the system).
6. Kingdoms Monera, Protista and Fungi
Monera
Unicellular prokaryotes
Bacteria and cyanobacteria. Found everywhere (soil, water, air, hot springs, even inside humans). Some are pathogens; many are useful (Lactobacillus, Rhizobium). Gut bacteria of ruminants help make biogas; some bacteria break down oil, pesticides, sewage. Cyanobacteria are autotrophs.
Protista
Unicellular eukaryotes
Single-celled eukaryotes with no cell wall, or a cellulose wall. Live in water or moist places; some autotrophic, some heterotrophic, some decomposers. Link in aquatic food chains; some produce oxygen, others are food for small animals.
Fungi
Mostly multicellular eukaryotes
Cell wall of chitin. Absorb nutrients from dead matter through fine filaments forming a mycelium. Mostly saprophytes (decomposers); some symbiotic or parasitic. Reproduce by spores; grow best in warm, moist conditions.
- Cyanobacteria were among the first organisms to make oxygen by photosynthesis (about 2.5 billion years ago); ancient cyanobacteria are found as fossils in stromatolites.
- Ram Bux Singh ('Father of Modern Biogas') set up India's first scientifically designed biogas plant (1957, Ramnagar, Sitapur, U.P.).
- Fungi examples: yeast (unicellular but placed in fungi because of its chitin wall), Aspergillus and Penicillium (enzymes, antibiotics), mushrooms (macroscopic). Without fungi, decay of dead matter would be greatly reduced.
- Hay infusion (grass + pond water, covered with muslin, kept for a week) is used to see protists under a microscope; wear lab coat, mask and gloves because it smells bad.
7. Kingdom Plantae
Plantae: multicellular, autotrophic eukaryotes whose cells have a rigid cellulose cell wall. Divided into five classes: Thallophyta, Bryophyta, Pteridophyta, Gymnosperm, Angiosperm.
| Class | Key features | Advantage | Challenge | Examples |
|---|---|---|---|---|
| Thallophyta (algae) | Simple undifferentiated body (thallus); mostly aquatic or moist habitats; direct exchange of gases, water, nutrients | Simple body suits survival and dispersal in water | Cannot live on land | Spirogyra |
| Bryophyta | First step to land; some differentiation; rhizoids; no vascular tissue; need water for reproduction | Adapted to moist land ('amphibians' of plants) | Always need moisture | Moss, Marchantia |
| Pteridophyta | True roots, stems, leaves; xylem and phloem; no seeds; need water for reproduction | Live on land; transport water and food to all parts | Reproduction needs water | Ferns |
| Gymnosperm | Needle/scale-like leaves; seeds naked (on cones); fertilisation without water | Suited to cold, dry regions; seeds protect embryo | Seeds not covered by fruits | Pine, cycas |
| Angiosperm | Flowers and fruits; seeds enclosed in fruits; most complex body | Flowers attract pollinators; fruits aid seed dispersal; most diverse group | Depends on pollination agents; complex tissues | Gulmohar, pea, mango |
- Word meanings: thallos = undifferentiated body, bryon = moss, pteris = feather, gymnos = naked, angeion = vessel, spermos = seed.
- Trend from algae to angiosperms: dependence on water decreases as plants evolve transport tissues, then seeds, then flowers.
- Lichens (patthar ke phool): symbiosis of an autotrophic alga (makes food) and a heterotrophic fungus (gives protection). They are bioindicators of air quality, used as spice, medicine and dye; some are poisonous.
- Leaves can be grouped as monocots or dicots by shape and venation.
8. Kingdom Animalia: Non-chordates (Invertebrates)
Animalia: multicellular, heterotrophic eukaryotes without cell wall; show locomotion, rapid response to stimuli and coordinated behaviour. Major criterion: presence or absence of a notochord (flexible rod-shaped structure) → non-chordata (invertebrata) and chordata.
| Phylum | Level of organisation | Key features | Habitat | Skeleton | Examples |
|---|---|---|---|---|---|
| Porifera | Cellular | Pores let water flow through; no tissues or organs; fixed in one place | Marine water | None | Sponges |
| Cnidaria | Tissue | Tentacles catch prey; single opening for food intake and waste | Fresh and marine water | None | Hydra, jellyfish, coral |
| Platyhelminthes (flatworms) | Organ | Bilateral symmetry; flattened body; single opening; hooks and suckers in parasites | Water / inside host | None | Planaria, tapeworm |
| Nematoda (roundworms) | Organ system (digestive) | Cylindrical body; two openings (mouth and anus) | Soil / water / inside host | None | Roundworm |
| Annelida | Organ system | Segmented body, body cavity, muscles, nerve cord | Moist soil / water | None | Earthworm |
| Arthropoda | Organ system | Jointed appendages, segmented body, hard external skeleton (protection, less water loss, supports muscles) | Land / water | Exoskeleton | Insects, crabs, spiders |
| Mollusca | Organ system | Soft body with head, muscular foot; often a protective shell | Water / moist land | Exoskeleton (shell) | Snail, squid, octopus |
| Echinodermata | Organ system | Spiny skin; internal skeleton of calcium carbonate (without notochord) | Marine water | Endoskeleton | Starfish, sea urchin |
- Trend: from sponges to echinoderms, body organisation becomes more complex (cells → tissues → organs → organ systems), improving feeding, movement and protection but often adding new challenges.
- Why the phylum order matters: cnidarians and flatworms have a single body opening; roundworms are the first with two openings.
- Parasitic worms enter through contaminated water and food; wash hands, keep good hygiene, eat well-cooked food and drink boiled or filtered water.
9. Protochordates and Vertebrates
Protochordates
First notochord
Possess a notochord at least once in life (e.g. Amphioxus). A primitive type of chordate; show the transition from invertebrates to vertebrates.
Vertebrates
Animals with a backbone
Have a vertebral column that supports the body and protects the brain and spinal cord. Five groups: fish, amphibians, reptiles, birds, mammals (based on habitat use, body covering and reproduction).
Adaptations: structure helps survival
Fish: fins and gills for moving and breathing in water.
Birds: feathers and hollow bones make flight possible.
Camel / polar bear: fat storage, thick fur for extreme conditions.
Mammals: mammary glands improve survival of the young.
- Healthy, diverse forests act as barriers to disasters: mangroves reduced damage in the 1999 Orissa super cyclone, forest diversity lowers risk of Kyasanur Forest Disease (monkey fever) in the Western Ghats, and soil microbes break down pollutants.
10. Hierarchy of Classification
Taxonomic ladder
Kingdom → Phylum → Class → Order → Family → Genus → Species
Classification of the tiger (sub-phylum Vertebrata lies between phylum and class).
| Level | Tiger | Pea plant |
|---|---|---|
| Kingdom | Animalia | Plantae |
| Phylum | Chordata | Magnoliophyta |
| Class | Mammalia | Magnoliopsida |
| Order | Carnivora | Fabales |
| Family | Felidae | Fabaceae |
| Genus | Panthera | Pisum |
| Species | P. tigris | P. sativum |
- Each lower group is part of the group above it; at each lower level organisms share more common features and groups have fewer members.
- It works like an address: it helps scientists identify, compare and study organisms accurately.
11. Scientific Naming: The Binomial System
Binomial nomenclature: universal system of naming organisms introduced by Carolus Linnaeus (18th century). Every organism has a two-part scientific name (genus + species) in Latin or a Latinised form. Common names vary by region (tiger / bagh / puli / tigre), causing confusion.
| Common name | Scientific name | Genus | Species |
|---|---|---|---|
| Tiger | Panthera tigris | Panthera | tigris |
| Lion | Panthera leo | Panthera | leo |
| Mango | Mangifera indica | Mangifera | indica |
| Pea | Pisum sativum | Pisum | sativum |
Rules for writing scientific names
1. Two parts: genus first, then species.
2. Genus begins with a capital letter; species is in small letters.
3. Italics when printed, underlined when handwritten.
- Genus: groups closely related species with common features (tiger and lion are both Panthera, the 'roaring cats').
- Species: a group of similar individuals capable of interbreeding and producing offspring.
- New species may be named after the place of discovery or a scientist, e.g. Purple frog Nasikabatrachus sahyadrensis (Sahyadri Hills, discovered 2003).
12. Three Domains, Fossils and Biodiversity Under Threat
Three domains
Carl Woese, 1977
Based on DNA comparison: Bacteria, Archaea, Eukarya. Showed that microscopic life is far more diverse than believed.
Fossils
Evidence of change
Preserved remains of plants and animals in rock, sand and mud layers. Older layers hold simpler organisms, newer layers more complex forms. Birbal Sahni studied fossil plants and founded BSIP, Lucknow.
Threats
Human activities
Pollution, deforestation, overuse of resources and climate change reduce biodiversity. If one species disappears, others that depend on it may also decline.
- Sangai deer (endemic to Manipur) lives on phumdis (floating grasslands) in Loktak lake; declared extinct in 1951, rediscovered 1953, now on the IUCN Red List as phumdis degrade: habitat loss is the main danger.
13. Quick Revision
| Concept | Key point |
|---|---|
| Biodiversity | Variety of life; keeps ecosystems stable; basis of food security |
| Endemic species / hotspot | Found only in one region / many endemic species + high habitat loss |
| Classification criteria | Cell type, organisation, cell wall, nutrition (five kingdom basis) |
| Five kingdoms | Monera, Protista, Fungi, Plantae, Animalia (Whittaker, 1969) |
| Plant classes | Thallophyta → Bryophyta → Pteridophyta → Gymnosperm → Angiosperm |
| Animal split | Notochord absent (invertebrates) vs present (chordates) |
| Vertebrate groups | Fish, amphibians, reptiles, birds, mammals |
| Hierarchy | Kingdom, Phylum, Class, Order, Family, Genus, Species |
| Binomial name | Genus (capital) + species (small), italics / underlined |
| Three domains | Bacteria, Archaea, Eukarya (Woese, 1977) |
Remember
Cell wall material
Fungi: chitin · Plants: cellulose · Protista: none or cellulose · Animals: none.
Remember
Key firsts
Porifera: no tissues · Cnidaria: tissues · Platyhelminthes: bilateral symmetry · Nematoda: two body openings · Annelida: segmentation · Arthropoda: jointed legs.
Common mistakes:
• Placing yeast (unicellular) in Protista; it is a fungus (chitin wall).
• Saying gymnosperms have no seeds; they have naked seeds (not in fruits).
• Confusing bryophytes (no vascular tissue) with pteridophytes (xylem and phloem).
• Writing scientific names without italics/underline, or with a capital species name.
• Calling echinoderms chordates; they have an internal skeleton but no notochord.
• Putting viruses into a kingdom; they are acellular and outside the five kingdoms.
• Thinking classification is only naming; it also shows relationships and helps conservation.
• Placing yeast (unicellular) in Protista; it is a fungus (chitin wall).
• Saying gymnosperms have no seeds; they have naked seeds (not in fruits).
• Confusing bryophytes (no vascular tissue) with pteridophytes (xylem and phloem).
• Writing scientific names without italics/underline, or with a capital species name.
• Calling echinoderms chordates; they have an internal skeleton but no notochord.
• Putting viruses into a kingdom; they are acellular and outside the five kingdoms.
• Thinking classification is only naming; it also shows relationships and helps conservation.