Comprehensive Study Notes on Diversity in Living Organisms

Biodiversity and Fundamentals of Taxonomy

Biodiversity is defined as the diversity of lifeforms. This term specifically refers to the variety of diverse life forms found within a particular geographic region.

Taxonomy is the branch of biology dedicated to the identification, nomenclature (naming), and classification of living organisms. Carolus Linnaeus is officially recognized as the father of taxonomy.

Classification Systems and Hierarchy

Biological classification has evolved through different systems based on the complexity and characteristics of organisms:

Two-Kingdom Classification

Developed by Carolus Linnaeus, this system divided all living organisms into two primary groups:

  1. Plants

  2. Animals

Five-Kingdom Classification

Proposed by Robert H. Whittaker, this system categorizes organisms into five distinct kingdoms based on cellular structure and mode of nutrition:

  1. Monera

  2. Protista

  3. Fungi

  4. Plantae

  5. Animalia

Levels of Classification (Hierarchy)

To provide further detail, organisms are classified into descending levels of specificity:

  • Kingdom

  • Phylum (for animals) or Division (for plants)

  • Class

  • Order

  • Family

  • Genus

  • Species

Example Classification for Humans:

  • Kingdom: Animalia

  • Phylum: Chordata

  • Class: Mammalia

  • Order: Primates

  • Family: Hominidae

  • Genus: Homo

  • Species: Homo sapiens

Basis of Biological Classification

The fundamental criteria used to classify organisms include:

  1. Nucleus Organization: The presence or absence of a defined nucleus.

  2. Structural Organization: The level of cellular organization and the development of specific organs.

  3. Cellular Configuration: The total number and types of cells within the organism.

  4. Mode of Nutrition: How the organism obtains its energy and nutrients.

Kingdom Monera, Protista, and Fungi

Kingdom Monera

  • Cell Type: Prokaryotic.

  • Body Organization: Unicellular.

  • Cell Wall: May or may not possess a cell wall. If present, it is non-cellulosic.

  • Nucleus: Characterized by the absence of a defined nucleus.

  • Mode of Nutrition: Can be Autotrophic (further divided into Chemosynthetic and Photosynthetic) or Heterotrophic (further divided into Saprophytic or Parasitic).

  • Examples: Bacteria, Mycoplasma, and Blue-green algae.

Kingdom Protista

  • Cell Type: Eukaryotic.

  • Body Organization: Unicellular.

  • Cell Wall: Present in some members of the kingdom.

  • Nucleus: A defined nucleus is present.

  • Mode of Nutrition: Both Autotrophic (Photosynthetic) and Heterotrophic varieties exist.

  • Locomotion: Moving is facilitated by hair-like cilia or whip-like flagella in some members.

  • Examples: Amoeba, Paramecium, Euglena.

Kingdom Fungi

  • Cell Type: Eukaryotic.

  • Body Organization: Multicellular.

  • Cell Wall: Present, specifically composed of a complex sugar called chitin.

  • Nucleus: A defined nucleus is present.

  • Mode of Nutrition: Heterotrophic, acting as either Saprophytes (feeding on dead matter) or Parasites.

  • Symbiotic Relationships: Some fungi live in a permanent mutualistic relationship with cyanobacteria (blue-green algae); these composite organisms are called Lichens.

  • Examples: Yeasts, molds, and mushrooms.

Kingdom Plantae: Classification and Characteristics

Kingdom Plantae Overview

  • Cell Type: Eukaryotic.

  • Body Organization: Multicellular, with tissue or organ-level organization.

  • Cell Wall: Present, primarily composed of cellulose.

  • Nucleus: Present.

  • Mode of Nutrition: Autotrophic, performing photosynthesis using chlorophyll.

  • Examples: Various trees and plants.

Classification Criteria for Plants

  1. Plant Body Differentiation: Whether the plant body has well-differentiated, distinct parts (root, stem, leaves).

  2. Vascular System: Presence of specialized tissues (xylem and phloem) for the transport of water and other substances.

  3. Seed Development: The ability to bear seeds and whether those seeds are enclosed within fruit.

Major Plant Groups

1. Algae (Thallophyta)

  • Characteristics: The plant body is not differentiated into roots, stems, or leaves. They are simple, thalloid, autotrophic, and largely aquatic (freshwater and marine). They bear chlorophyll.

  • Types of Algae:

    • Chlorophyceae (Green algae): e.g., Chlamydomonas, Volvox.

    • Phaeophyceae (Brown algae): e.g., Sargassum, Fucus.

    • Rhodophyceae (Red algae): e.g., Gracilaria, Gelidium.

  • Reproduction:

    • Vegetative (by fragmentation).

    • Asexual (by zoospores).

    • Sexual (fusion of two gametes).

  • Economic Importance:

    • Fixation of carbon dioxide (CO2CO_2).

    • Used as food (e.g., Laminaria, Sargassum).

    • Agar is obtained from Gelidium and Gracilaria, used for growing microbes and in ice creams/jellies.

    • Space food: Chlorella is used as a food supplement for space travelers.

2. Bryophytes

  • Characteristics: Known as the "Amphibians of the plant kingdom" because they live in both land and water. The body is differentiated into stem and leaf-like structures, but lacks true vascular tissue. They frequent damp, humid, and shaded localities.

  • Reproduction: Vegetative (fragmentation and budding) and Sexual (gamete production).

  • Uses: Succession on bare rocks/soil, food, and Peat (used for fuel and as a packing material).

  • Examples: Liverworts (Marchantia, Riccia) and Mosses (Funaria, Sphagnum).

3. Pteridophyta

  • Characteristics: Known as "botanical snakes" or the "snakes of the plant kingdom." They are cryptogams (do not produce flowers/seeds). They have a differentiated body (leaves, stems, roots) and possess vascular tissues (xylem and phloem).

  • Reproduction: Occurs via spores developed within structures called sporangia.

  • Types: Ferns, Horsetails, and Lycophytes.

  • Examples: Equisetum, Fern, Salvinia.

4. Gymnosperms

  • Characteristics: Seeds are naked (not enclosed in fruits or flowers). They have incomplete vascular tissues. The plant body is a sporophyte differentiated into roots, stems, and leaves. Adaptations to reduce water loss include needle-like leaves, thick cuticles, and sunken stomata.

  • Reproduction: Heterosporous, producing haploid microspores and megaspores. Sporophylls aggregate to form cones or strobili. Cones are unisexual.

  • Special Traits:

    • Mycorrhiza: Association between fungus and roots (e.g., Pinus).

    • Coralloid roots: Roots associated with N2N_2-fixing cyanobacteria (e.g., Cycas).

    • Tallest Gymnosperm: Sequoia sempervirens (Red giant wood).

    • Smallest Gymnosperm: Zamia pygmaea.

    • Living Fossils: Ginkgo.

5. Angiosperms

  • Characteristics: Greek 'angio' (covered) and 'sperma' (seed). Also called flower-bearing plants. Seeds develop inside an ovary, which matures into fruit. The sporophyte is diploid and differentiated into stems, roots, and leaves. They exhibit double fertilization.

  • Reproduction: Heterosporous (pollen grains and megaspores).

  • Size Extremes: Tallest is Australian eucalyptus; smallest is Wolfia.

  • Classification based on Cotyledons:

    • Dicotyledons: Seeds have two cotyledons; leaves have reticulate venation; flowers are tetramerous or pentamerous; possess tap roots (e.g., Bean, gram, pea).

    • Monocotyledons: Seeds have a single cotyledon; leaves have parallel venation; flowers are trimerous; closed, numerous vascular bundles; possess adventitious roots (e.g., Wheat, rice, maize).

Kingdom Animalia: Foundation and Basis of Classification

Kingdom Animalia Overview

  • Cell Type: Eukaryotic.

  • Body Organization: Multicellular (Tissue / Organ / Organ system levels).

  • Cell Wall: Absent.

  • Nucleus: Present.

  • Mode of Nutrition: Heterotrophic (typically Holozoic or Saprophytic).

  • Examples: Fish, insects, humans, birds.

Basis of Classification for Animals

1. Symmetry

  • Bilateral Symmetry: The organism can be divided into identical right and left halves (mirror images) by a single vertical plane.

  • Radial Symmetry: When any plane passing through the central axis of the body divides the organism into two identical halves.

2. Germinal Layers

  • Diploblastic Organization: Cells are arranged in two embryonic layers: an external ectoderm and an internal endoderm.

  • Triploblastic Organization: Cells are arranged in three embryonic layers: ectoderm (external), mesoderm (middle), and endoderm (internal).

3. Coelom (Body Cavity)

  • Acoelomates: Simple organisms possessing no body cavity.

  • Coelomates: Complex organisms with a true cavity lined by mesoderm on all sides.

  • Pseudocoelomates: Organisms possessing a false coelom, characterized by pouches of mesoderm scattered between the endoderm and ectoderm.

Summary Classification of Kingdom Animalia

Animals are divided into Invertebrates (Non-chordata) and Vertebrates (Chordata):

  1. Cellular Level: Porifera.

  2. Tissue Level: Cnidaria, Ctenophora.

  3. Organ/Organ System Level:

    • Acoelomata: Platyhelminthes.

    • Pseudocoelomata: Nematoda.

    • Coelomata: Annelida, Arthropoda, Mollusca, Echinodermata, Chordata.

Classification of Invertebrate Phyla

1. Phylum Porifera

  • Common Name: Sponges.

  • Habitat: Mainly marine.

  • Symmetry: Asymmetrical.

  • Organization: Cellular level; non-motile animals attached to solid supports.

  • Structure: Body has pores called ostia leading to a canal system for water and food circulation. Skeleton is made of calcium carbonate or silica.

  • Reproduction: Hermaphrodite; asexual (fragmentation) and sexual (gametes).

  • Examples: Sycon, Spongilla, Euspongia.

2. Phylum Coelenterata (Cnidaria)

  • Characteristics: Aquatic (mostly marine), sessile or free-swimming, radially symmetrical, diploblastic, tissue-level organization.

  • Structure: Skeleton in corals is made of calcium carbonate.

  • Body Forms:

    • Polyp: Sessile and cylindrical.

    • Medusa: Umbrella-shaped and free-swimming.

  • Examples: Hydra, Adamsia, Aurelia (Jellyfish).

3. Phylum Ctenophora

  • Common Name: Sea walnuts or comb jellies.

  • Characteristics: Marine, radially symmetrical, hermaphrodite, diploblastic, tissue-level organization. They possess bioluminescence.

  • Locomotion: Facilitated by comb plates.

  • Reproduction: Sexual means only.

  • Examples: Pleurobrachia, Ctenoplana.

4. Phylum Platyhelminthes

  • Common Name: Flatworms.

  • Characteristics: Bilaterally symmetrical, triploblastic, acoelomate, tissue/organ level organization. Body is dorso-ventrally flattened.

  • Parasitic Features: Mostly endoparasites with hooks and suckers.

  • Excretion: Done via flame cells (osmoregulation and excretion).

  • Examples: Planaria (free-living), Liver fluke (parasitic).

5. Phylum Nematoda (Aschelminthies)

  • Common Name: Roundworms.

  • Characteristics: Bilaterally symmetrical, triploblastic, pseudocoelomate, dioecious, organ-system level organization. Body is cylindrical; alimentary canal is complete.

  • Diseases: Known parasitic worms causing elephantiasis (filarial worms).

  • Examples: Ascaris (Roundworm), Wuchereria, Hookworm. Females are typically longer than males.

6. Phylum Annelida

  • Characteristics: Triploblastic, metamerically segmented, coelomate, organ-system level, bilateral symmetry.

  • Locomotion: Longitudinal and circular muscles; Nereis has parapodia for swimming.

  • Excretion: Accomplished by nephridia.

  • Examples: Nereis (dioecious), Earthworm and leeches (monoecious).

7. Phylum Arthropoda

  • Note: Largest phylum in Kingdom Animalia, including insects.

  • Body Structure: Bilaterally symmetrical, triploblastic, segmented, coelomate. Body consists of a Head, Thorax, and Abdomen. Features jointed appendages and a chitinous exoskeleton.

  • Circulation & Excretion: Open circulatory system; excretion via Malpighian tubules.

  • Nutrition/Reproduction: Mostly oviparous and dioecious.

  • Examples: Prawn, Scorpion, Cockroach, Housefly, Butterfly, Spider.

8. Phylum Mollusca

  • Note: Second largest animal phylum.

  • Characteristics: Terrestrial or aquatic, organ-system level, bilaterally symmetrical, triploblastic, coelomate.

  • Structure: Body is unsegmented, covered by a calcareous shell. Contains a distinct head, muscular foot for locomotion, and a visceral hump.

  • Excretion: Kidney-like organs.

  • Examples: Pila (Apple snail), Octopus, Pearl oyster.

9. Phylum Echinodermata

  • Characteristics: Endoskeleton of calcium carbonate. Triploblastic, coelomate, dioecious, organ-system level organization.

  • Symmetry: Radial in adults, but bilateral in larvae.

  • Water Vascular System: Uses tube feet for locomotion, respiration, and food transport.

  • Reproduction: Sexual with external fertilization.

  • Examples: Asterias (Starfish), Sea urchin.

10. Phylum Hemichordata (Protochordata)

  • Characteristics: Bilaterally symmetrical, triploblastic, coelomate, organ-system level. Cylindrical body composed of an anterior proboscis, a collar, and a long trunk.

  • Systems: Open circulatory system; respiration via gills; excretion via proboscis gland.

  • Examples: Balanoglossus, Saccoglossus.

Phylum Chordata and Subphylum Vertebrata

Phylum Chordata Characteristics

All chordates possess the following features at some stage in their development:

  1. Notochord

  2. Dorsal nerve cord

  3. Triploblastic germ layers

  4. Paired gill pouches

  5. Coelomate body cavity

Subphylum Vertebrata Overview

Vertebrates possess a true vertebral column and internal skeleton. Characteristics include:

  • Bilateral symmetry, triploblastic, coelomic, and segmented bodies.

  • Ventral muscular heart.

  • Kidneys for excretion/osmoregulation.

  • Paired appendages (fins or limbs).

  • The notochord present during the embryonic period is replaced by a bony vertebral column in adults.

  • Rule: All vertebrates are chordates, but not all chordates are vertebrates.

Metabolic Classifications

  • Warm-blooded (Homoiothermous): Organisms that maintain a constant body temperature regardless of external surroundings (e.g., humans).

  • Cold-blooded (Poikilothermous): Organisms whose body temperature fluctuates with the environment (e.g., frogs).

Classes of Vertebrates

1. Cyclostomata

  • Characteristics: Ectoparasites on certain fish. Body is elongated and eel-like, lacking scales and paired fins. Mouth is sucking and circular without jaws. Closed circulation; gill slits for respiration.

  • Examples: Lamprey, Hagfish.

2. Pisces (Fish)

  • Characteristics: Streamlined body with fins and tail. Aquatic (marine/freshwater). Skin covered with scales. Skeleton can be bone or cartilage. Gills for respiration.

  • Metabolism: Cold-blooded; Two-chambered heart (one auricle and one ventricle).

  • Reproduction: Mostly oviparous; some are viviparous. Some have electric organs or poison stings.

  • Examples: Sea horse, Rohu, Katla, Torpedo.

3. Amphibia

  • Characteristics: Found in water and on land. Body divided into head and trunk. A tympanum represents the ear. Mucus glands in skin. Respiration via gills or lungs.

  • Systems: Three-chambered heart (two auricles, one ventricle). Alimentary, urinary, and reproductive tracts open into a common cloaca.

  • Metabolism: Cold-blooded; oviparous.

  • Examples: Toad, Frog, Salamanders.

4. Reptilia

  • Characteristics: Creeping and crawling locomotion. Body covered by scales or scutes. Respiration via lungs. Fertilization is internal; oviparous with tough coverings on eggs.

  • Metabolism: Cold-blooded; Three-chambered heart (exception: Crocodiles have a four-chambered heart).

  • Examples: Lizards, Turtles, Snakes, Crocodiles.

5. Aves (Birds)

  • Characteristics: Warm-blooded; four-chambered heart. Respiration via lungs. Body covered with feathers; forelimbs modified into wings. Digestive system includes specialized parts: Crop and Gizzard.

  • Reproduction: Internal fertilization; oviparous.

  • Examples: Crow, Pigeon, Ostrich, Peacock, Penguin, Vulture.

6. Mammalia

  • Characteristics: Warm-blooded; four-chambered heart. Presence of Mammary glands, skin with hair, sweat glands, and oil glands. External ears (pinnae) are present. Respiration via lungs.

  • Reproduction: Mostly viviparous, with few oviparous exceptions like the platypus. Internal fertilization.

  • Examples: Monkey, rat, blue whale, bat, dolphin, human beings.

Universal Rules of Nomenclature

Nomenclature is the standardized system of naming organisms to ensure a specific life form is recognized by the same name globally. The system of Binomial Nomenclature was introduced by Carolus Linnaeus.

Scientific Naming Rules:

  1. Names are generally in Latin.

  2. Scientific names are written or printed in italics.

  3. The first word represents the Genus (always capitalized).

  4. The second word represents the Specific Epithet/Species (always lowercase).

  5. When handwritten, the Genus and Species names must be underlined separately.

Example: Homo sapiens (Printed) or Homo sapiens (Handwritten).