Diversity in Living Organisms
Contents
- Biodiversity & Classification
- Taxonomy & Linnaeus
- Hierarchy of Classification
- Five Kingdom Classification
- Kingdom Monera
- Kingdom Protista
- Kingdom Fungi
- Kingdom Plantae
- Kingdom Animalia
- Vertebrata – Classes
- Binomial Nomenclature
Biodiversity & Classification
Biodiversity means different forms of living organisms or a variety of life forms found in a particular region. The branch of science dealing with identification, naming and classification of organisms is called systematics or taxonomy.
Classification enables us to study organisms conveniently, reveals inter-relationships between groups, and helps establish evolutionary tendencies.
Artificial vs. Natural Classification
- Artificial classification (Aristotle) — based on one or few arbitrarily chosen criteria (habitat, habit). Drawback: grouped unrelated organisms; separated related ones.
- Natural classification — based on multiple characters, from broad groups down to smallest units, reflecting true evolutionary relationships.
- Phylogenetic classification — based on evolutionary relationships of organisms.
Taxonomy & Carolus Linnaeus
Carolus Linnaeus (1707–1778), a Swedish scientist, is called the father of Taxonomy. He introduced binomial nomenclature and published Systema Naturae (1735), classifying all known organisms.
History of Kingdom Classifications
| Classification | Proposed By | Kingdoms |
|---|---|---|
| Two Kingdom | Carolus Linnaeus, 1758 | Plantae, Animalia |
| Three Kingdom | Ernst Haeckel | + Protista |
| Four Kingdom | Copeland | + Monera |
| Five Kingdom | R.H. Whittaker, 1969 | Monera, Protista, Fungi, Plantae, Animalia |
Hierarchy of Classification (Linnaean)
| Category | Description & Example |
|---|---|
| Species | Lowest; individuals that can interbreed. Pisum sativum (pea). |
| Genus | Closely related species. Dog & wolf → Canis. |
| Family | Related genera. Cat & lion → Felidae. |
| Order | Assemblage of families with common characters. |
| Class | Related orders. Rats, camels, monkeys → Chordata. |
| Phylum/Division | Classes with same specific characters. |
| Kingdom | Highest category — Plantae, Animalia. |
Five Kingdom Classification (Whittaker, 1969)
| Kingdom | Organisation | Prokaryotic/Eukaryotic | Cell Wall | Nutrition |
|---|---|---|---|---|
| Monera | Unicellular | Prokaryotic | Some have, some don't | Autotrophic & Heterotrophic |
| Protista | Unicellular | Eukaryotic | Some have, some don't | Autotrophic & Heterotrophic |
| Fungi | Multicellular | Eukaryotic | Chitin | Heterotrophic |
| Plantae | Multicellular | Eukaryotic | Cellulose | Autotrophic |
| Animalia | Multicellular | Eukaryotic | Absent | Heterotrophic |
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Kingdom Monera
- Mostly unicellular; cyanobacteria are filamentous.
- No definite nucleus — circular dsDNA not enclosed by nuclear envelope (prokaryotes).
- No membrane-bound organelles (except ribosomes).
- Cell wall generally present; single-stranded flagella in many.
- Nutrition: autotrophic or heterotrophic.
Groups within Monera
- True bacteria: Cocci, Diplococci, Bacilli, Spirilli, Vibrio.
- Actinomycetes: Unicellular, branched, filamentous — Streptomycetes, Mycobacterium.
- Cyanobacteria (Blue-green algae): Nostoc, Anabaena (N₂ fixation), Oscillatoria, Trichodesmium (red colour of sea).
- Mycoplasma: Mycoplasma pneumoniae.
- Archaebacteria: Methanogens, Halophiles, Thermoacidophiles.
Kingdom Protista
- Mostly aquatic; typically eukaryotic with distinct plasma membrane.
- Contain membrane-bound organelles (mitochondria, plastids, Golgi, ER, ribosomes).
- DNA: linear dsDNA complexed with proteins in chromosomes; nucleolus present.
- Motile forms use pseudopodia, flagella or cilia.
Three Major Groups
- Protistan algae (plant-like): Dinoflagellates, Diatoms, Euglena, Chlamydomonas, Volvox.
- Protozoa (animal-like): Amoeba, Entamoeba, Paramecium, Trypanosoma, Plasmodium.
- Slime moulds (fungus-like): Physarum, Dictyostelium.
Kingdom Fungi
- Thalloid, unicellular or multicellular, filamentous/mycelial. Single filament = hypha; cluster = mycelium.
- Cell wall of chitin (tough complex sugar).
- Lack chlorophyll — heterotrophic (saprotrophic or parasitic).
- Reserve food: glycogen and oil drops.
- Asexual reproduction by spores; sexual by gamete fusion.
Examples: Yeast (Saccharomyces), mushroom (Agaricus campestris), Rhizopus, Penicillium, Aspergillus.
Kingdom Plantae
Multicellular eukaryotes with chlorophyll for photosynthesis. Cell wall of cellulose; large central vacuole; mostly non-motile; indefinite growth.
Division: Thallophyta
Most primitive plants; no differentiation into root, stem, leaves (thalloid). Predominantly aquatic; no vascular system; single-celled reproductive organs.
- Algae: Aquatic or terrestrial; autotrophic; unicellular to multicellular. Examples: Nostoc, Anabaena, Ulothrix, Spirogyra, Ulva, Chara.
- Fungi (within Thallophyta): Heterotrophic; chitin cell wall; parasitic or saprotrophic. Examples: Rhizopus, Saccharomyces, Agaricus, Aspergillus, Penicillium.
- Lichens: Symbiotic relationship between algae (phycobiont) and fungi (mycobiont). Grow on rocks, tree trunks. Examples: Parmelia, Alectoria.
Division: Bryophyta
Simplest non-vascular land plants; amphibians of the plant kingdom (need water for life cycle). Main plant body is gametophyte (haploid). No xylem/phloem.
Examples: Funaria (moss), Riccia, Marchantia.
Division: Pteridophyta (First Vascular Plants)
Sporophyte (diploid); true roots, stem, leaves; xylem and phloem present. Flowers and seeds absent. Male sex organs: antheridia; female: archegonia.
Examples: Lycopodium, Selaginella, Equisetum, Marsilea, Azolla, Pteridium (fern).
| Feature | Bryophytes | Pteridophytes |
|---|---|---|
| Plant body | Gametophyte (haploid) | Sporophyte (diploid) |
| Differentiation | Thallus/foliose; no true roots, stem, leaves | True roots, stem and leaves |
| Attachment | Rhizoids | True roots |
| Vascular tissue | Absent | Present |
Division: Gymnosperms
Vascular, perennial, evergreen, woody plants. Ovules are naked (not enclosed in ovaries). After fertilisation, ovules become seeds (not enclosed in fruits). Sporophylls form cones (separate male and female).
Examples: Cycas, Pinus, Ephedra.
Division: Angiosperms (Flowering Plants)
Seeds enclosed within fruits (developed from ovary). Embryo has plumule, radicle and cotyledons. Two sub-groups based on number of cotyledons:
| Feature | Dicotyledons | Monocotyledons |
|---|---|---|
| Cotyledons | Two | One |
| Leaf venation | Reticulate | Parallel |
| Vascular bundle | Open, in a ring | Closed, scattered |
| Root system | Tap root | Fibrous |
| Flower parts | Pentamerous or tetramerous | Trimerous |
| Examples | Pea, Gram, Mustard | Wheat, Rice, Maize |
Kingdom Animalia – Non-Chordates
Multicellular, eukaryotic, no chlorophyll, no cell wall. Nutrition by ingestion. Reproduction mostly sexual. Growth stops at adult stage.
- Mostly marine; sessile; radial symmetry or asymmetrical.
- Cellular level of organisation (simplest multicellular animals; no tissues/organs).
- Body perforated by pores (Ostia); single opening = osculum; canal system.
- Hard outside skeleton of spicules; no mouth/digestive cavity/anus.
- Asexual by budding/gemmules; sexual by ova and spermatozoa.
- Aquatic; two-layered body (tissue level of organisation); radial symmetry.
- Single body cavity with one aperture (mouth); no anus.
- Stinging cells: cnidoblasts. Tentacles present.
- Both asexual and sexual reproduction.
- Marine, transparent, radial symmetry; 8 ciliated comb plates for locomotion.
- Bilaterally symmetrical; dorsoventrally flattened; no segmentation.
- First animals with 3 germ layers (triploblastic); no true coelom.
- Excretion by flame cells (protonephridia); mostly hermaphrodite.
- Cylindrical; bilaterally symmetrical; triploblastic; unsegmented; tough cuticle.
- Body cavity = pseudocoelom (not lined by mesoderm); straight one-way alimentary canal.
- Sexes generally separate; mostly parasitic.
- Soft, elongated, bilaterally symmetrical; body divided into metameres (segmentation = metamerism).
- Locomotory appendages: parapodia, setae/chaetae.
- True coelom; complete alimentary canal; closed circulatory system.
- Excretion by metanephridia.
Largest phylum (~900,000 species).
- Segmented body grouped into cephalothorax + abdomen, or head + thorax + abdomen (tagmatization).
- Exoskeleton of chitin; jointed legs; haemocoel (open circulatory system).
- Respiration by gills, trachea, or book-lungs.
- Soft, unsegmented; body in three regions: head, visceral mass, ventral foot.
- Mantle secretes calcareous shell; respiration by ctenidia (gills).
- Marine; radial symmetry in adults; no head; mesodermal exoskeleton of calcareous spines.
- True coelom; peculiar tube feet for locomotion; sexes separate.
Three distinctive characters present at some stage:
- Notochord — solid, unjointed rod (persists in lower chordates; replaced by vertebral column in higher ones).
- Dorsal hollow nerve cord
- Pharyngeal gill slits
Sub-Phylum Vertebrata – Five Classes
Class Cyclostomata (Agnatha)
Most primitive vertebrates; jawless; circular suctorial mouth; cartilagenous skeleton; two-chambered heart (1 auricle + 1 ventricle); external fertilisation.
Examples: Petromyzon (lamprey), Myxine (hagfish).
Class Pisces (Fish)
Exclusively aquatic; scales; respiration by gills; cold-blooded; two-chambered heart; external fertilisation.
| Feature | Chondrichthyes (Cartilaginous) | Osteichthyes (Bony) |
|---|---|---|
| Skeleton | Cartilaginous throughout | Bony in adult |
| Mouth | Ventral | Terminal |
| Tail fin | Heterocercal (asymmetric) | Homocercal (symmetric) |
| Gills covered? | No (naked) | Yes (operculum) |
| Swim bladder | Absent | Usually present |
| Fertilisation | Internal | External |
| Examples | Sharks, rays, Scoliodon | Labeo, Hippocampus, Anabas |
Class Amphibia
Live on land and water; first vertebrates to invade land; cold-blooded; smooth moist skin; two pairs of pentadactyl limbs; respiration by gills, lungs, skin and bucco-pharyngeal cavity; three-chambered heart (2 auricles + 1 ventricle); no marine forms.
Examples: Rana tigrina (frog), Bufo (toad), Hyla (tree frog), Salamandra.
Class Reptilia
First vertebrates fully adapted to dry land; cold-blooded; horny epidermal scales (keratin); internal fertilisation; cleidoic eggs with calcareous shells; heart incompletely four-chambered (2 auricles + partly divided ventricle); 12 pairs of cranial nerves.
Examples: Hemidactylus (wall lizard), Python, Naja (cobra), Testudo (tortoise), Crocodiles, Gavialis (gharial).
| Feature | Amphibia | Reptilia |
|---|---|---|
| Skin | Smooth and moist | Dry and cornified |
| Scales | Absent | Present |
| Claws | Absent | Present |
| Heart | 3-chambered | Incompletely 4-chambered |
| Fertilisation | External | Internal |
Class Aves (Birds)
Forelimbs modified into wings; feathers cover body; bony but spongy/light endoskeleton; beak present; teeth absent; respiration by lungs; four-chambered heart; warm-blooded.
Examples: Columba (pigeon), Struthio (ostrich), Pavo (peacock), Corvus (crow). Flightless birds: Ostrich (Africa), Rhea (S. America), Kiwi (New Zealand), Emu (Australia), Penguin.
Class Mammalia
Primarily terrestrial; hair covers body; mammary glands (milk production); mostly viviparous (except Platypus, Echidna — oviparous); lungs for respiration; four-chambered heart; warm-blooded; two pairs of pentadactyl limbs.
Examples: Macropus (kangaroo), bat, Rattus (rat), Felis (cat), Panthera (lion, tiger, leopard), Elephas (elephant), Balaena (whale), Macaca (monkey), Homo sapiens (human).
| Feature | Invertebrata | Vertebrata |
|---|---|---|
| Notochord | Absent | Present at some stage |
| Nerve cord | Solid and ventral | Hollow and dorsal |
| Heart position | Dorsal (if present) | Ventral |
| Vascular system | Open or closed | Closed |
| Haemoglobin | Dissolved in plasma (if present) | In red blood corpuscles |
| Pharyngeal gill slits | Absent | Present |
| Post-anal tail | Absent | Present |
Binomial Nomenclature
Proposed by Carolus Linnaeus (1753). Each organism receives two names: first = genus (capital letter), second = species (small letter). Governed by ICBN (plants) and ICZN (animals).
Conventions
- Genus name begins with a capital letter; species name begins with a small letter.
- Printed in italics; when handwritten, genus and species are underlined separately.
- Scientific names are based on Latin and accepted internationally.
| Organism | Scientific Name |
|---|---|
| Human | Homo sapiens |
| Common frog | Rana tigrina |
| Pea | Pisum sativum |
| Mango | Mangifera indica |
| Lion | Panthera leo |
| Wheat | Triticum vulgare |
| Rice | Oryza sativa |