Diversity in the living World

Chapter 1: The Living World

1.1 Diversity in the Living World

• Biology is the science of life forms and living processes.
• Early humans easily distinguished between inanimate matter and living organisms and sometimes deified them due to awe or fear.
• Anthropocentric views limited early biological knowledge.
• Systematic description of life forms led to identification, nomenclature, and classification systems.
• A key revelation was the sharing of similarities among living organisms, indicating that all present-day organisms are related to each other and to all organisms that ever lived, which fostered conservation movements.
• The living world exhibits an amazing diversity of living types, found in extraordinary habitats from cold mountains to hot springs. The beauty and interactions of life evoke wonder and reflection on “what indeed is life?”.
• The question “what is life?” has two implicit parts:
  • Technical: What is living as opposed to non-living?
  • Philosophical: What is the purpose of life? (Scientists focus on the technical question).
• Diversity: A large variety of living organisms are visible (potted plants, insects, birds, pets) and invisible (microbes). Increasing the area of observation increases the range and variety of organisms.
• Each different kind of plant, animal, or organism represents a species.
• The number of known and described species ranges between 1.7-1.8 million, which refers to biodiversity (number and types of organisms). New organisms are continuously being identified in new and old areas.

1.2 Taxonomic Categories

• Nomenclature: The process of standardising the naming of living organisms so a particular organism is known by the same name worldwide.
  • Naming is only possible when the organism is correctly described and identified. This process is identification.
• Scientific names are based on agreed principles and criteria established by scientists and are acceptable to biologists globally.
  • For plants: International Code for Botanical Nomenclature (ICBN).
  • For animals: International Code of Zoological Nomenclature (ICZN).
  • Scientific names ensure each organism has only one name and that this name has not been used for any other known organism.
• Binomial Nomenclature: A system of providing a name with two components.
  • Given by Carolus Linnaeus.
  • Components: Generic name and specific epithet.
  • Example: For mango, Mangifera indica. Mangifera is the genus, and indica is the specific epithet.
• Universal Rules of Nomenclature:
  1. Biological names are generally in Latin and written in italics, or Latinised/derived from Latin.
  2. The first word represents the genus, and the second component denotes the specific epithet.
  3. Both words, when handwritten, are separately underlined, or printed in italics, to indicate their Latin origin.
  4. The genus starts with a capital letter; the specific epithet starts with a small letter (e.g., Mangifera indica).
  5. The author’s name appears after the specific epithet in abbreviated form (e.g., Mangifera indica Linn. indicating Linnaeus described it).
• Classification: The process of grouping anything into convenient categories based on easily observable characters.
  • Example: Recognising groups like plants, animals, dogs, cats, or insects.
  • Taxa (singular: taxon): The scientific term for these convenient categories used to study organisms. Taxa can indicate categories at very different levels (e.g., ‘Plants’ is a taxon, ‘Wheat’ is a taxon; ‘animals’, ‘mammals’, ‘dogs’ are all taxa at different levels).
• Taxonomy: The process of classifying living organisms based on characteristics.
  • Basis of modern taxonomic studies: External and internal structure, cell structure, development process, and ecological information.
  • Basic processes of taxonomy: Characterisation, identification, classification, and nomenclature.
  • Not new: Early classifications were based on the ‘uses’ of various organisms (food, clothing, shelter).
• Systematics: The branch of study interested in knowing different kinds of organisms, their diversities, and their relationships.
  • Derived from the Latin word ‘systema’ meaning systematic arrangement of organisms.
  • Linnaeus used Systema Naturae as the title of his publication.
  • The scope of systematics was later enlarged to include identification, nomenclature, and classification, and it now takes into account evolutionary relationships between organisms.

1.3 Taxonomic Hierarchy

• Classification is a hierarchy of steps, where each step represents a rank or category.
• A taxonomic category is part of the overall taxonomic arrangement.
• All categories together constitute the taxonomic hierarchy.
• Each category is a unit of classification, commonly termed a taxon (plural: taxa).
• Common Taxonomic Categories (in descending order):
  • Kingdom
  • Phylum (for animals) or Division (for plants)
  • Class
  • Order
  • Family
  • Genus
  • Species
• Basis of arrangement: As one moves from species to kingdom (ascending order), the number of common characteristics decreases.
  • Lower the taxa: More characteristics are shared among members within that taxon.
  • Higher the category: Greater difficulty in determining relationships to other taxa at the same level, making classification more complex.

1.2.1 Species

• A group of individual organisms with fundamental similarities.
• Distinguishable from closely related species based on distinct morphological differences.
• Examples:
  • Mangifera indica (mango): indica is the specific epithet.
  • Solanum tuberosum (potato): tuberosum is the specific epithet.
  • Panthera leo (lion): leo is the specific epithet.
  • Human beings: Homo sapiens (sapiens is the specific epithet).

1.2.2 Genus

• Comprises a group of related species that have more characters in common compared to species of other genera.
• Aggregates of closely related species.
• Examples:
  • Potato (Solanum tuberosum) and brinjal (Solanum melongena) both belong to genus Solanum.
  • Lion (Panthera leo), leopard (Panthera pardus), and tiger (Panthera tigris) are species of the genus Panthera.
  • Genus Panthera differs from genus Felis (which includes cats).

1.2.3 Family

• The next category, grouping related genera.
• Has fewer similarities compared to genus and species.
• Characterised by both vegetative and reproductive features.
• Examples:
  • Plant genera Solanum, Petunia, and Datura are placed in the family Solanaceae.
  • Animal genera Panthera (lion, tiger, leopard) and Felis (cats) are placed in the family Felidae.
  • Cats (Felidae) and dogs (Canidae) are separated into two different families due to similarities and differences.

1.2.4 Order

• Identified based on aggregates of characters.
• A higher category, it is an assemblage of families which exhibit a few similar characters. The similar characters are less in number compared to different genera within a family.
• Examples:
  • Plant families like Convolvulaceae and Solanaceae are included in the order Polymoniales, mainly based on floral characters.
  • The animal order Carnivora includes families like Felidae and Canidae.

1.2.5 Class

• This category includes related orders.
• Example: Order Primata (monkey, gorilla, gibbon) is placed in class Mammalia along with order Carnivora (tiger, cat, dog).

1.2.6 Phylum / Division

• Phylum: For animals, classes with common features like the presence of notochord and dorsal hollow neural system are grouped into a higher category called Phylum.
  • Example: Fishes, amphibians, reptiles, birds, and mammals are included in phylum Chordata.
• Division: For plants, classes with a few similar characters are assigned to a higher category called Division.

1.2.7 Kingdom

• The highest category.
• Kingdom Animalia: All animals belonging to various phyla.
• Kingdom Plantae: Comprises all plants from various divisions.

Table 1.1: Organisms with their Taxonomic Categories

Chapter 2: Biological Classification

Historical Context and Whittaker’s System

• Early attempts to classify organisms were instinctive and based on utility (food, shelter, clothing).
• Aristotle: Earliest to attempt a more scientific basis, using simple morphological characters.
  • Classified plants into trees, shrubs, and herbs.
  • Divided animals into two groups: those with red blood and those without.
• Linnaeus’ Two Kingdom System: Developed with Plantae and Animalia kingdoms, including all plants and animals respectively.
  • Limitations:
    • Did not distinguish between eukaryotes and prokaryotes.
    • Did not distinguish between unicellular and multicellular organisms.
    • Did not distinguish between photosynthetic (e.g., green algae) and non-photosynthetic (e.g., fungi) organisms.
  • Found inadequate because many organisms did not fit neatly into either category.
• Evolution of Classification Systems: A need arose to include characteristics beyond gross morphology, such as cell structure, nature of cell wall, mode of nutrition, habitat, methods of reproduction, and evolutionary relationships.
• Plant and animal kingdoms have been constant under all systems, but the understanding of which groups belong to them has changed. The number and nature of other kingdoms have also varied.

2.1 R.H. Whittaker’s Five Kingdom Classification (1969)

• Kingdoms proposed: Monera, Protista, Fungi, Plantae, and Animalia.
• Main criteria for classification:
  • Cell structure
  • Body organisation
  • Mode of nutrition
  • Reproduction
  • Phylogenetic relationships (evolutionary relationships).
• Three-domain system: A more recent proposal that divides Kingdom Monera into two domains, leaving the eukaryotic kingdoms in a third domain, resulting in a six-kingdom classification (details for higher classes).
• Improvements over earlier systems:
  • Earlier systems placed diverse groups like bacteria, blue-green algae, fungi, mosses, ferns, gymnosperms, and angiosperms all under ‘Plants’ simply because they had a cell wall. This grouped prokaryotic bacteria with eukaryotic groups, and unicellular organisms with multicellular ones.
  • Fungi were grouped with green plants, despite their characteristic differences (fungi had chitin cell walls, green plants had cellulosic cell walls) and heterotrophic mode of nutrition.
  • Whittaker’s system placed fungi in a separate Kingdom Fungi.
  • All prokaryotic organisms were grouped under Kingdom Monera.
  • All unicellular eukaryotic organisms were placed in Kingdom Protista, bringing together organisms that were previously in different kingdoms (e.g., Chlamydomonas and Chlorella from ‘Plants’ with Paramoecium and Amoeba from ‘Animal kingdom’).
• These changes reflect improved understanding of characteristics and evolutionary relationships, a trend expected to continue.

Table 2.1: Characteristics of the Five Kingdoms

2.2 Kingdom Monera

• Bacteria are the sole members of Kingdom Monera.
• Most abundant micro-organisms, found almost everywhere, including extreme habitats like hot springs, deserts, snow, and deep oceans. Many are parasites.
• Grouped by shape:
  • Coccus (pl.: cocci): Spherical
  • Bacillus (pl.: bacilli): Rod-shaped
  • Vibrium (pl.: vibrio): Comma-shaped
  • Spirillum (pl.: spirilla): Spiral
• Show extensive metabolic diversity despite simple structure.
  • Autotrophic: Synthesize own food from inorganic substrates.
    • Photosynthetic autotrophic
    • Chemosynthetic autotrophic
  • Heterotrophic: Depend on other organisms or dead organic matter for food (vast majority).

2.1.1 Archaebacteria

• Special bacteria found in harsh habitats:
  • Extreme salty areas (halophiles)
  • Hot springs (thermoacidophiles)
  • Marshy areas (methanogens)
• Differ from other bacteria by a different cell wall structure, which aids survival in extreme conditions.
• Methanogens are present in the gut of ruminant animals (cows, buffaloes) and produce methane (biogas) from dung.

2.1.2 Eubacteria (True Bacteria)

• Characterised by a rigid cell wall. If motile, they have a flagellum.
• Cyanobacteria (blue-green algae):
  • Have chlorophyll a (similar to green plants) and are photosynthetic autotrophs.
  • Unicellular, colonial, or filamentous; found in freshwater, marine, or terrestrial environments.
  • Colonies often surrounded by a gelatinous sheath.
  • Can form blooms in polluted water bodies.
  • Some fix atmospheric nitrogen in specialised cells called heterocysts (e.g., Nostoc, Anabaena).
• Chemosynthetic autotrophic bacteria:
  • Oxidise inorganic substances (nitrates, nitrites, ammonia) to produce ATP.
  • Play a great role in recycling nutrients like nitrogen, phosphorus, iron, and sulphur.
• Heterotrophic bacteria:
  • Most abundant in nature, majority are important decomposers.
  • Useful roles: Making curd from milk, antibiotic production, fixing nitrogen in legume roots.
  • Pathogens: Cause diseases in humans, crops, farm animals, and pets (e.g., cholera, typhoid, tetanus, citrus canker).
• Reproduction in bacteria:
  • Mainly by fission.
  • Under unfavourable conditions, they produce spores.
  • Also reproduce by a primitive type of DNA transfer (sexual reproduction).
• Mycoplasma:
  • Completely lack a cell wall.
  • Smallest living cells known.
  • Can survive without oxygen.
  • Many are pathogenic in animals and plants.

2.3 Kingdom Protista

• Includes all single-celled eukaryotes.
• Boundaries are not well-defined, leading to varied classifications among biologists.
• Members are primarily aquatic.
• Forms a link with plants, animals, and fungi kingdoms.
• Eukaryotic cell body: Well-defined nucleus and other membrane-bound organelles.
• Some have flagella or cilia.
• Reproduction: Asexually and sexually (involving cell fusion and zygote formation).
• Groups included: Chrysophytes, Dinoflagellates, Euglenoids, Slime moulds, and Protozoans.

2.2.1 Chrysophytes

• Includes diatoms and golden algae (desmids).
• Found in fresh water and marine environments.
• Microscopic and float passively in water currents (plankton).
• Most are photosynthetic.
• Diatoms:
  • Cell walls form two thin overlapping shells that fit like a soapbox.
  • Walls embedded with silica, making them indestructible.
  • Leave behind large cell wall deposits forming ‘diatomaceous earth’ (used in polishing, filtration of oils and syrups).
  • Are the chief ‘producers’ in the oceans.

2.2.2 Dinoflagellates

• Mostly marine and photosynthetic.
• Appear yellow, green, brown, blue, or red depending on main pigments.
• Cell wall has stiff cellulose plates on the outer surface.
• Most have two flagella: one longitudinal, one transverse in a furrow.
• Red dinoflagellates (e.g., Gonyaulax) can multiply rapidly, causing red tides, and release toxins that kill other marine animals.

2.2.3 Euglenoids

• Majority are freshwater organisms found in stagnant water.
• Instead of a cell wall, they have a protein-rich layer called pellicle, which makes their body flexible.
• Have two flagella (one short, one long).
• Mixotrophic: Photosynthetic in sunlight, but behave as heterotrophs (predating on smaller organisms) when deprived of sunlight.
• Pigments are identical to those in higher plants.
• Example: Euglena.

2.2.4 Slime Moulds

• Saprophytic protists.
• Body moves along decaying twigs and leaves, engulfing organic material.
• Under suitable conditions, form an aggregation called plasmodium, which can grow and spread.
• During unfavourable conditions, plasmodium differentiates into fruiting bodies bearing spores at their tips.
• Spores possess true walls, are extremely resistant, and survive for years; dispersed by air currents.

2.2.5 Protozoans

• All are heterotrophs, living as predators or parasites.
• Believed to be primitive relatives of animals.
• Four major groups:
  1. Amoeboid protozoans:
     • Live in fresh water, sea water, or moist soil.
     • Move and capture prey using pseudopodia (false feet) (e.g., Amoeba).
     • Marine forms have silica shells on their surface.
     • Some are parasites (e.g., Entamoeba).
  2. Flagellated protozoans:
     • Either free-living or parasitic; have flagella.
     • Parasitic forms cause diseases (e.g., sleeping sickness by Trypanosoma).
  3. Ciliated protozoans:
     • Aquatic, actively moving due to thousands of cilia.
     • Have a cavity (gullet) that opens to the outside; coordinated ciliary movement steers food-laden water into gullet.
     • Example: Paramoecium.
  4. Sporozoans:
     • Diverse organisms with an infectious spore-like stage in their life cycle.
     • Example: Plasmodium (malarial parasite), which causes malaria.

2.4 Kingdom Fungi

• A unique kingdom of heterotrophic organisms.
• Great diversity in morphology and habitat.
• Examples: Mushrooms, toadstools, white spots on mustard leaves (parasitic), yeast (unicellular, used in bread/beer), Puccinia (wheat rust), Penicillium (source of antibiotics).
• Cosmopolitan: Occur in air, water, soil, animals, and plants. Prefer warm and humid places (food kept in refrigerators to prevent fungal/bacterial infections).
• Structure:
  • Mostly filamentous (except unicellular yeasts).
  • Bodies consist of long, slender thread-like structures called hyphae.
  • Network of hyphae is called mycelium.
  • Some hyphae are continuous tubes filled with multinucleated cytoplasm (coenocytic hyphae); others have cross walls (septae).
  • Cell walls are composed of chitin and polysaccharides.
• Nutrition:
  • Most are saprophytes: Absorb soluble organic matter from dead substrates.
  • Some are parasites: Depend on living plants and animals.
  • Can live as symbionts:
    • Lichens: Association with algae.
    • Mycorrhiza: Association with roots of higher plants.
• Reproduction:
  • Vegetative means: Fragmentation, fission, budding.
  • Asexual reproduction: By spores called conidia, sporangiospores, or zoospores. These spores are produced in distinct structures called fruiting bodies.
  • Sexual reproduction: By oospores, ascospores, and basidiospores.
    • Involves three steps:
      1. Plasmogamy: Fusion of protoplasms between two motile or non-motile gametes.
      2. Karyogamy: Fusion of two nuclei.
      3. Meiosis in zygote: Results in haploid spores.
    • In some fungi, fusion of haploid cells immediately results in diploid cells (2n).
    • In other fungi (ascomycetes and basidiomycetes), an intervening dikaryotic stage (n + n, two nuclei per cell) occurs, called dikaryophase. Later, parental nuclei fuse to become diploid.
    • Fungi form fruiting bodies where reduction division occurs, leading to haploid spores.
• Classification Basis: Morphology of mycelium, mode of spore formation, and fruiting bodies.

2.3.1 Phycomycetes

• Found in aquatic habitats, on decaying wood in moist places, or as obligate parasites on plants.
• Mycelium is aseptate and coenocytic.
• Asexual reproduction: By zoospores (motile) or aplanospores (non-motile); these spores are endogenously produced in sporangium.
• Sexual reproduction: A zygospore is formed by fusion of two gametes, which can be similar (isogamous) or dissimilar (anisogamous or oogamous) in morphology.
• Examples: Mucor, Rhizopus (bread mould), Albugo (parasitic fungi on mustard).

2.3.2 Ascomycetes (Sac-Fungi)

• Mostly multicellular (e.g., Penicillium), rarely unicellular (e.g., yeast, Saccharomyces).
• Saprophytic, decomposers, parasitic, or coprophilous (growing on dung).
• Mycelium is branched and septate.
• Asexual spores: Conidia, produced exogenously on special mycelium called conidiophores. Conidia germinate to produce mycelium.
• Sexual spores: Ascospores, produced endogenously in sac-like asci (singular: ascus). Asci are arranged in different types of fruiting bodies called ascocarps.
• Examples: Aspergillus, Claviceps, Neurospora (used extensively in biochemical and genetic work).
• Many members like morels and truffles are edible delicacies.

2.3.3 Basidiomycetes

• Commonly known forms: Mushrooms, bracket fungi, puffballs.
• Grow in soil, on logs, tree stumps, and in living plant bodies as parasites (e.g., rusts and smuts).
• Mycelium is branched and septate.
• Asexual spores: Generally not found.
• Vegetative reproduction: Common by fragmentation.
• Sex organs: Absent. Plasmogamy brought about by fusion of two vegetative or somatic cells of different strains/genotypes.
• Resultant structure is dikaryotic, which ultimately gives rise to basidium. Karyogamy and meiosis occur in the basidium, producing four basidiospores.
• Basidiospores: Exogenously produced on the basidium (pl.: basidia).
• Basidia are arranged in fruiting bodies called basidiocarps.
• Examples: Agaricus (mushroom), Ustilago (smut), Puccinia (rust fungus).

2.3.4 Deuteromycetes (Imperfect Fungi)

• Commonly called imperfect fungi because only the asexual or vegetative phases are known.
• If sexual forms are discovered, they are moved into their rightful classes (often ascomycetes and basidiomycetes).
• Reproduce only by asexual spores known as conidia.
• Mycelium is septate and branched.
• Some members are saprophytes or parasites, while a large number are decomposers of litter and help in mineral cycling.
• Examples: Alternaria, Colletotrichum, and Trichoderma.

2.5 Kingdom Plantae

• Includes all eukaryotic chlorophyll-containing organisms commonly called plants.
• A few members are partially heterotrophic:
  • Insectivorous plants: Bladderwort, Venus fly trap.
  • Parasites: Cuscuta.
• Plant cells: Eukaryotic structure with prominent chloroplasts and cell wall mainly made of cellulose.
• Includes algae, bryophytes, pteridophytes, gymnosperms, and angiosperms.
• Life cycle: Has two distinct phases that alternate with each other (alternation of generations):
  • Diploid sporophytic phase
  • Haploid gametophytic phase
• The length and independence of these phases vary among different plant groups.

2.6 Kingdom Animalia

• Characterised by heterotrophic eukaryotic organisms.
• Are multicellular and their cells lack cell walls.
• Directly or indirectly depend on plants for food.
• Digest food in an internal cavity and store food reserves as glycogen or fat.
• Mode of nutrition is holozoic (by ingestion of food).
• Follow a definite growth pattern and grow into adults with a definite shape and size.
• Higher forms show elaborate sensory and neuromotor mechanisms.
• Most are capable of locomotion.
• Sexual reproduction: By copulation of male and female, followed by embryological development.

2.7 Viruses, Viroids, Prions, and Lichens

• These are not mentioned in Whittaker’s five kingdom classification.

Viruses

• Not considered truly ‘living’ if ‘living’ is defined by cellular structure.
• Are non-cellular organisms with an inert crystalline structure outside the living cell.
• Obligate parasites: Once they infect a cell, they take over the host cell’s machinery to replicate, killing the host.
• History:
  • Dmitri Ivanowsky (1892): Recognised microbes causing mosaic disease of tobacco; found them smaller than bacteria (passed through filters).
  • M.W. Beijerinck (1898): Called the infectious fluid “Contagium vivum fluidum” (infectious living fluid).
  • W.M. Stanley (1935): Showed viruses could be crystallised, and crystals largely consist of proteins.
• Composition:
  • A nucleoprotein.
  • Contain genetic material (either RNA or DNA, never both).
  • The genetic material is infectious.
  • Plant viruses generally have single-stranded RNA.
  • Animal viruses have either single or double-stranded RNA or double-stranded DNA.
  • Bacterial viruses (bacteriophages) are usually double-stranded DNA viruses.
  • Capsid: A protein coat made of small subunits called capsomeres, which protects the nucleic acid. Capsomeres are arranged in helical or polyhedral geometric forms.
• Diseases:
  • Humans: Mumps, smallpox, herpes, influenza, AIDS.
  • Plants: Mosaic formation, leaf rolling and curling, yellowing, vein clearing, dwarfing, stunted growth.

Viroids

• T.O. Diener (1971): Discovered a new infectious agent smaller than viruses that caused potato spindle tuber disease.
• Found to be a free RNA.
• Lacked the protein coat found in viruses.
• RNA of low molecular weight.

Prions

• Infectious agents consisting of abnormally folded protein.
• Similar in size to viruses.
• Cause certain infectious neurological diseases.
• Examples: Bovine spongiform encephalopathy (BSE, ‘mad cow disease’ in cattle) and its analogous variant Creutzfeldt-Jacob disease (CJD) in humans.

Lichens

• Symbiotic associations (mutually useful) between algae and fungi.
  • Algal component (phycobiont): Autotrophic, prepares food for fungi.
  • Fungal component (mycobiont): Heterotrophic, provides shelter and absorbs mineral nutrients and water for the alga.
• Their association is so close that they appear as a single organism in nature.
• Very good pollution indicators – they do not grow in polluted areas.

Chapter 3: Plant Kingdom

3.1 Overview and Classification Systems

• Kingdom Plantae in Whittaker’s system now excludes Fungi, Monera, and Protista (even those with cell walls), unlike earlier classifications. Cyanobacteria are no longer considered ‘algae’ in this context.
• The Plant Kingdom includes Algae, Bryophytes, Pteridophytes, Gymnosperms, and Angiosperms.
• Classification Systems within Angiosperms:
  • Earlier Artificial Systems:
    • Used only gross superficial morphological characters (habit, colour, number/shape of leaves).
    • Mainly based on vegetative characters or androecium structure (e.g., Linnaeus’ system).
    • Separated closely related species because they were based on few characteristics.
    • Gave equal weightage to vegetative and sexual characteristics, which is not ideal as vegetative characters are more easily affected by the environment.
  • Natural Classification Systems:
    • Based on natural affinities among organisms.
    • Considered external features as well as internal features (ultrastructure, anatomy, embryology, phytochemistry).
    • Example for flowering plants: Given by George Bentham and Joseph Dalton Hooker.
  • Phylogenetic Classification Systems:
    • Currently acceptable, based on evolutionary relationships between organisms.
    • Assumes organisms in the same taxa have a common ancestor.
    • Use information from many sources, especially when fossil evidence is lacking.
  • Numerical Taxonomy:
    • Easily carried out using computers.
    • Based on all observable characteristics.
    • Numbers and codes assigned to characters, data processed.
    • Each character given equal importance, and hundreds of characters can be considered.
  • Cytotaxonomy: Based on cytological information (chromosome number, structure, behaviour).
  • Chemotaxonomy: Uses the chemical constituents of the plant to resolve classification confusions.

3.2 Algae

• Characteristics: Chlorophyll-bearing, simple, thalloid (undifferentiated body), autotrophic, and largely aquatic (fresh water and marine).
• Habitats: Moist stones, soils, wood. Some associate with fungi (lichen) or animals (sloth bear).
• Form and Size: Highly variable.
  • Colonial forms: Volvox.
  • Filamentous forms: Ulothrix, Spirogyra.
  • Massive marine forms: Kelps (can be 100 meters tall).
• Reproduction:
  • Vegetative: By fragmentation; each fragment develops into a thallus.
  • Asexual: By different types of spores, most common being zoospores (flagellated, motile), which germinate into new plants.
  • Sexual: Fusion of two gametes.
    • Isogamous: Gametes are flagellated and similar in size (e.g., Ulothrix) or non-flagellated but similar in size (e.g., Spirogyra).
    • Anisogamous: Gametes are dissimilar in size (e.g., Eudorina).
    • Oogamous: Fusion between a large, non-motile (static) female gamete and a smaller, motile male gamete (e.g., Volvox, Fucus).
• Economic Importance:
  • Perform at least half of the total CO2 fixation on Earth through photosynthesis, increasing dissolved oxygen.
  • Paramount as primary producers in aquatic food cycles.
  • Food: Many species of marine algae (e.g., Porphyra, Laminaria, Sargassum) are consumed.
  • Hydrocolloids (water-holding substances) produced by some brown and red algae:
    • Algin (from brown algae).
    • Carrageen (from red algae).
  • Agar: Commercial product from Gelidium and Gracilaria, used to grow microbes and in preparations of ice-creams and jellies.
  • Chlorella: A unicellular alga rich in proteins, used as a food supplement, even by space travellers.
• Classes: Divided into three main classes: Chlorophyceae, Phaeophyceae, and Rhodophyceae.

3.1.1 Chlorophyceae (Green Algae)

• Commonly called green algae due to dominance of chlorophyll a and b pigments.
• Plant body: Unicellular, colonial, or filamentous.
• Pigments localised in definite chloroplasts, which can be discoid, plate-like, reticulate, cup-shaped, spiral, or ribbon-shaped.
• Pyrenoids: One or more storage bodies located in chloroplasts; contain protein besides starch. Some store food as oil droplets.
• Cell wall: Rigid, made of an inner layer of cellulose and an outer layer of pectose.
• Reproduction:
  • Vegetative: Usually by fragmentation.
  • Asexual: By flagellated zoospores produced in zoosporangia.
  • Sexual: Shows considerable variation, can be isogamous, anisogamous, or oogamous.
• Examples: Chlamydomonas, Volvox, Ulothrix, Spirogyra, Chara.

3.1.2 Phaeophyceae (Brown Algae)

• Primarily found in marine habitats.
• Show great variation in size and form: from simple branched filamentous forms (Ectocarpus) to profusely branched forms like kelps (can reach 100 metres).
• Pigments: Chlorophyll a, c, carotenoids, and xanthophylls (e.g., fucoxanthin, which gives olive green to various shades of brown colour).
• Food stored as complex carbohydrates (laminarin or mannitol).
• Cell wall: Cellulosic, usually covered outside by a gelatinous coating of algin.
• Protoplast contains plastids, a centrally located vacuole, and a nucleus.
• Plant body structure: Usually attached to substratum by a holdfast, has a stalk called stipe, and a leaf-like photosynthetic organ called frond.
• Reproduction:
  • Vegetative: By fragmentation.
  • Asexual: By biflagellate zoospores (pear-shaped with two unequal laterally attached flagella).
  • Sexual: May be isogamous, anisogamous, or oogamous. Gamete union can be in water or within the oogonium (for oogamous species). Gametes are pyriform (pear-shaped) and bear two laterally attached flagella.
• Examples: Ectocarpus, Dictyota, Laminaria, Sargassum, Fucus.

3.1.3 Rhodophyceae (Red Algae)

• Commonly called red algae due to predominance of the red pigment, r-phycoerythrin.
• Majority are marine, with higher concentrations in warmer areas.
• Found in both well-lighted surface waters and great depths where little light penetrates.
• Thalli of most are multicellular and can have complex body organisation.
• Food stored as floridean starch, which is very similar to amylopectin and glycogen in structure.
• Reproduction:
  • Vegetative: Usually by fragmentation.
  • Asexual: By non-motile spores.
  • Sexual: By non-motile gametes; it is oogamous and accompanied by complex post-fertilisation developments.
• Examples: Polysiphonia, Porphyra, Gracilaria, Gelidium.

Table 3.1: Divisions of Algae and their Main Characteristics

3.3 Bryophytes

• Includes various mosses and liverworts.
• Found commonly growing in moist shaded areas in the hills.
• Called amphibians of the plant kingdom because they can live in soil but depend on water for sexual reproduction.
• Usually occur in damp, humid, and shaded localities.
• Ecological Importance:
  • Play an important role in plant succession on bare rocks/soil by decomposing rocks and making substrate suitable for higher plants.
  • Mosses form dense mats on soil, reducing impact of rain and preventing soil erosion.
  • Some mosses provide food for herbaceous mammals, birds, and other animals.
  • Species of Sphagnum (a moss) provide peat, used as fuel and packing material for trans-shipment due to high water-holding capacity.
• Plant Body: More differentiated than algae.
  • Thallus-like, prostrate or erect, attached to substratum by unicellular or multicellular rhizoids.
  • Lack true roots, stem, or leaves, but may possess root-like, leaf-like, or stem-like structures.
• Main plant body: Haploid gametophyte, which produces gametes.
• Sex Organs: Multicellular.
  • Antheridium (male sex organ): Produces biflagellate antherozoids.
  • Archegonium (female sex organ): Flask-shaped, produces a single egg.
• Fertilisation: Antherozoids are released into water, come in contact with archegonium, and fuse with the egg to produce the zygote.
• Sporophyte: The zygote does not undergo reduction division immediately but produces a multicellular body called a sporophyte.
  • Not free-living, but attached to the photosynthetic gametophyte and derives nourishment from it.
  • Some cells undergo meiosis to produce haploid spores.
  • These spores germinate to produce a new gametophyte.
• Divisions: Bryophytes are divided into liverworts and mosses.

3.2.1 Liverworts

• Grow in moist, shady habitats like stream banks, marshy ground, damp soil, bark of trees, and deep in woods.
• Plant body: Thalloid (e.g., Marchantia), dorsiventral, and closely appressed to the substrate. Leafy members have tiny leaf-like appendages in two rows on stem-like structures.
• Asexual reproduction:
  • By fragmentation of thalli.
  • By specialised structures called gemmae (singular: gemma). Gemmae are green, multicellular, asexual buds that develop in small receptacles called gemma cups on the thalli. They detach and germinate to form new individuals.
• Sexual reproduction: Male and female sex organs produced on same or different thalli.
  • The sporophyte is differentiated into a foot, seta, and capsule.
  • Spores are produced after meiosis within the capsule.
  • These spores germinate to form free-living gametophytes.

3.2.2 Mosses

• Predominant stage: The gametophyte, which consists of two stages.
  1. Protonema stage: Develops directly from a spore; creeping, green, branched, frequently filamentous.
  2. Leafy stage: Develops from the secondary protonema as a lateral bud; consists of upright, slender axes bearing spirally arranged leaves. Attached to soil by multicellular and branched rhizoids. This stage bears the sex organs.
• Vegetative reproduction: By fragmentation and budding in the secondary protonema.
• Sexual reproduction: Antheridia and archegonia are produced at the apex of the leafy shoots.
  • After fertilisation, the zygote develops into a sporophyte (foot, seta, and capsule).
  • The sporophyte in mosses is more elaborate than in liverworts.
  • The capsule contains spores formed after meiosis.
  • Mosses have an elaborate mechanism of spore dispersal.
• Examples: Funaria, Polytrichum, and Sphagnum.

3.4 Pteridophytes

• Includes horsetails and ferns.
• Uses: Medicinal purposes, soil-binders, ornamentals.
• Evolutionary significance: They are the first terrestrial plants to possess vascular tissues (xylem and phloem).
• Habitats: Found in cool, damp, shady places; some may flourish in sandy-soil conditions.
• Main plant body: Sporophyte, which is the dominant phase.
  • Differentiated into true root, stem, and leaves.
  • These organs possess well-differentiated vascular tissues.
• Leaves:
  • Small (microphylls), as in Selaginella.
  • Large (macrophylls), as in ferns.
• Sporangia: Bear sporangia, subtended by leaf-like appendages called sporophylls.
• Strobili or Cones: In some cases, sporophylls may form distinct compact structures (e.g., Selaginella, Equisetum).
• Spores: Sporangia produce spores by meiosis in spore mother cells.
  • Spores germinate to give rise to inconspicuous, small but multicellular, free-living, mostly photosynthetic thalloid gametophytes called prothallus.
• Gametophytes: Require cool, damp, shady places to grow. This specific requirement and need for water for fertilisation limit the spread of living pteridophytes to narrow geographical regions.
• Sex Organs on Gametophytes:
  • Male sex organs: Antheridia.
  • Female sex organs: Archegonia.
• Fertilisation: Water is required for transfer of antherozoids (male gametes) from antheridia to the mouth of archegonium. Fusion of male gamete with egg forms a zygote.
• The zygote produces a multicellular, well-differentiated sporophyte.
• Homosporous: In the majority of pteridophytes, all spores are of similar kinds.
• Heterosporous: Genera like Selaginella and Salvinia produce two kinds of spores – macro (large) and micro (small) spores.
  • Megaspores and microspores germinate to give rise to female and male gametophytes, respectively.
  • Female gametophytes are retained on the parent sporophytes for variable periods.
  • The development of zygotes into young embryos within the female gametophytes is a precursor to the seed habit, considered an important step in evolution.
• Classes: Classified into four classes:
  • Psilopsida: (Psilotum)
  • Lycopsida: (Selaginella, Lycopodium)
  • Sphenopsida: (Equisetum)
  • Pteropsida: (Dryopteris, Pteris, Adiantum)

3.5 Gymnosperms

• “Naked seeds”: The term gymnos (naked), sperma (seeds). Ovules are not enclosed by any ovary wall and remain exposed both before and after fertilisation. The seeds that develop post-fertilisation are not covered.
• Size: Include medium-sized trees or tall trees and shrubs. The giant redwood tree Sequoia is one of the tallest tree species.
• Roots: Generally tap roots.
  • In some genera (Pinus), roots have fungal association in the form of mycorrhiza.
  • In others (Cycas), small specialised roots called coralloid roots are associated with N2-fixing cyanobacteria.
• Stems: Unbranched (Cycas) or branched (Pinus, Cedrus).
• Leaves: May be simple or compound.
  • In Cycas, pinnate leaves persist for a few years.
  • Leaves are well-adapted to withstand extremes of temperature, humidity, and wind.
  • In conifers, needle-like leaves reduce surface area; thick cuticle and sunken stomata also reduce water loss.
• Heterosporous: They produce haploid microspores and megaspores.
• Sporangia and Strobili/Cones: The two kinds of spores are produced within sporangia borne on sporophylls, which are arranged spirally along an axis to form lax or compact strobili or cones.
  • Male strobili (microsporangiate): Bear microsporophylls and microsporangia.
    • Microspores develop into a highly reduced male gametophytic generation (a few cells) called a pollen grain.
    • Development of pollen grains takes place within the microsporangia.
  • Female strobili (macrosporangiate): Bear megasporophylls with ovules or megasporangia.
  • Male or female cones/strobili may be borne on the same tree (Pinus) or on different trees (Cycas).
• Megaspore Formation:
  • The megaspore mother cell differentiates from one of the cells of the nucellus.
  • The nucellus is protected by envelopes, forming the composite structure called an ovule.
  • Ovules are borne on megasporophylls, which may be clustered to form female cones.
  • The megaspore mother cell divides meiotically to form four megaspores.
  • One of the megaspores, enclosed within the megasporangium, develops into a multicellular female gametophyte that bears two or more archegonia (female sex organs).
  • The multicellular female gametophyte is retained within the megasporangium.
• Gametophytes: Unlike bryophytes and pteridophytes, male and female gametophytes do not have an independent free-living existence; they remain within the sporangia retained on the sporophytes.
• Pollination and Fertilisation:
  • Pollen grains are released from the microsporangium and carried by air currents.
  • They come in contact with the opening of the ovules borne on megasporophylls.
  • The pollen tube, carrying male gametes, grows towards archegonia in the ovules and discharges contents near the mouth.
  • Following fertilisation, the zygote develops into an embryo, and the ovules develop into seeds (which are uncovered).

3.6 Angiosperms

• Flowering plants.
• Unlike gymnosperms, ovules are enclosed in specialised structures called flowers.
• After fertilisation, the seeds are enclosed in fruits.
• An exceptionally large group of plants found in a wide range of habitats.
• Size varies from the smallest Wolffia to tall trees of Eucalyptus (over 100 meters).
• Provide food, fodder, fuel, medicines, and several other commercially important products.
• Classes: Divided into two classes:
  • Dicotyledons
  • Monocotyledons

Chapter 4: Animal Kingdom

4.1 Basis of Classification

• With over a million animal species described, classification is crucial for assigning systematic positions to newly described species.
• Despite differences in structure and form, fundamental features common to various animals are used as the basis for classification.

4.1.1 Levels of Organisation

• All members of Animalia are multicellular but exhibit different patterns of cell organisation.
  • Cellular Level of Organisation: Cells arranged as loose aggregates, with some division of labour (e.g., sponges).
  • Tissue Level of Organisation: Cells performing the same function are arranged into tissues (e.g., coelenterates, ctenophores).
  • Organ Level of Organisation: Tissues are grouped to form organs, each specialised for a particular function (e.g., Platyhelminthes and other higher phyla).
  • Organ System Level of Organisation: Organs associate to form functional systems, each concerned with a specific physiological function (e.g., Annelids, Arthropods, Molluscs, Echinoderms, Hemichordates, Chordates).
• Complexities in Organ Systems:
  • Digestive System:
    • Incomplete: Single opening serving as both mouth and anus (e.g., Platyhelminthes).
    • Complete: Two openings, mouth and anus.
  • Circulatory System:
    • Open type: Blood is pumped out of the heart, directly bathing cells and tissues.
    • Closed type: Blood is circulated through a series of vessels (arteries, veins, capillaries).

4.1.2 Symmetry

• Animals can be categorised based on their body symmetry.
  • Asymmetrical: Any plane passing through the centre does not divide them into equal halves (e.g., sponges).
  • Radial Symmetry: Any plane passing through the central axis divides the organism into two identical halves (e.g., Coelenterates, Ctenophores, Echinoderms).
  • Bilateral Symmetry: The body can be divided into identical left and right halves in only one plane (e.g., Annelids, Arthropods). (Note: Echinodermata larvae are bilaterally symmetrical, but adults are radial).

4.1.3 Diploblastic and Triploblastic Organisation

• Diploblastic Animals: Cells arranged in two embryonic layers:
  • External ectoderm
  • Internal endoderm
  • An undifferentiated layer, mesoglea, is present between the ectoderm and endoderm (e.g., coelenterates, ctenophores).
• Triploblastic Animals: Developing embryo has a third germinal layer, mesoderm, between the ectoderm and endoderm (e.g., Platyhelminthes to Chordates).

4.1.4 Coelom (Body Cavity)

• Coelom: Body cavity lined by mesoderm.
  • Coelomates: Animals possessing a coelom (e.g., annelids, molluscs, arthropods, echinoderms, hemichordates, and chordates).
• Pseudocoelom: Body cavity not lined by mesoderm; mesoderm is present as scattered pouches between the ectoderm and endoderm.
  • Pseudocoelomates: Animals possessing a pseudocoelom (e.g., aschelminthes).
• Acoelomates: Animals in which the body cavity is absent (e.g., platyhelminthes).

4.1.5 Segmentation

• In some animals, the body is externally and internally divided into segments with a serial repetition of at least some organs.
• This pattern is called metameric segmentation, and the phenomenon is known as metamerism (e.g., earthworm).

4.1.6 Notochord

• A mesodermally derived rod-like structure formed on the dorsal side during embryonic development in some animals.
• Chordates: Animals with a notochord.
• Non-chordates: Animals that do not form this structure (e.g., Porifera to Echinoderms).

4.2 Classification of Animals (Phyla)

4.2.1 Phylum – Porifera (Sponges)

• Commonly known as sponges.
• Generally marine and mostly asymmetrical.
• Primitive multicellular animals with cellular level of organisation.
• Have a water transport or canal system:
  • Water enters through minute pores (ostia) into a central cavity (spongocoel), then exits through the osculum.
  • This pathway aids in food gathering, respiratory exchange, and waste removal.
• Choanocytes or collar cells line the spongocoel and canals.
• Digestion is intracellular.
• Body supported by a skeleton of spicules or spongin fibres.
• Sexes are not separate (hermaphrodite); eggs and sperms produced by the same individual.
• Reproduction: Asexually by fragmentation; sexually by gamete formation.
• Fertilisation is internal; development is indirect with a larval stage morphologically distinct from the adult.
• Examples: Sycon (Scypha), Spongilla (Freshwater sponge), Euspongia (Bath sponge).

4.2.2 Phylum – Coelenterata (Cnidaria)

• Aquatic (mostly marine), sessile or free-swimming, radially symmetrical animals.
• Name “Cnidaria” derived from cnidoblasts or cnidocytes. These cells contain stinging capsules (nematocysts) on tentacles and body, used for anchorage, defense, and prey capture.
• Exhibit tissue level of organisation and are diploblastic.
• Have a central gastro-vascular cavity with a single opening (mouth on hypostome).
• Digestion is extracellular and intracellular.
• Some (e.g., corals) have a skeleton composed of calcium carbonate.
• Exhibit two basic body forms:
  • Polyp: Sessile and cylindrical form (e.g., Hydra, Adamsia).
  • Medusa: Umbrella-shaped and free-swimming (e.g., Aurelia or jellyfish).
• Those existing in both forms exhibit alternation of generations (Metagenesis): polyps produce medusae asexually, and medusae form polyps sexually (e.g., Obelia).
• Examples: Physalia (Portuguese man-of-war), Adamsia (Sea anemone), Pennatula (Sea-pen), Gorgonia (Sea-fan), Meandrina (Brain coral).

4.2.3 Phylum – Ctenophora

• Commonly known as sea walnuts or comb jellies.
• Exclusively marine, radially symmetrical, diploblastic organisms with tissue level of organisation.
• Body bears eight external rows of ciliated comb plates, which help in locomotion.
• Digestion is both extracellular and intracellular.
• Bioluminescence (ability to emit light) is well-marked.
• Sexes are not separate.
• Reproduction takes place only by sexual means.
• Fertilisation is external with indirect development.
• Examples: Pleurobrachia and Ctenoplana.

4.2.4 Phylum – Platyhelminthes (Flatworms)

• Have a dorso-ventrally flattened body, hence called flatworms.
• Mostly endoparasites found in animals, including human beings.
• Bilaterally symmetrical, triploblastic, and acoelomate animals with organ level of organisation.
• Parasitic forms have hooks and suckers. Some absorb nutrients directly through their body surface.
• Specialised cells called flame cells help in osmoregulation and excretion.
• Sexes are not separate.
• Fertilisation is internal; development is through many larval stages.
• Some members like Planaria possess high regeneration capacity.
• Examples: Taenia (Tapeworm), Fasciola (Liver fluke).

4.2.5 Phylum – Aschelminthes (Roundworms)

• Body is circular in cross-section, hence called roundworms.
• May be free-living (aquatic and terrestrial) or parasitic in plants and animals.
• Have organ-system level of body organisation.
• Are bilaterally symmetrical, triploblastic, and pseudocoelomate animals.
• Alimentary canal is complete with a well-developed muscular pharynx.
• An excretory tube removes body wastes from the body cavity through the excretory pore.
• Sexes are separate (dioecious); females are often longer than males.
• Fertilisation is internal; development may be direct (young ones resemble adult) or indirect.
• Examples: Ascaris (Roundworm), Wuchereria (Filaria worm), Ancylostoma (Hookworm).

4.2.6 Phylum – Annelida

• May be aquatic (marine and freshwater) or terrestrial; free-living, and sometimes parasitic.
• Exhibit organ-system level of body organisation and bilateral symmetry.
• Are triploblastic, metamerically segmented (body distinctly marked into segments or metameres), and coelomate animals.
• Possess longitudinal and circular muscles which help in locomotion.
• Aquatic annelids like Nereis possess lateral appendages (parapodia), which help in swimming.
• A closed circulatory system is present.
• Nephridia help in osmoregulation and excretion.
• Neural system consists of paired ganglia connected by lateral nerves to a double ventral nerve cord.
• Sexes: Nereis is dioecious, but earthworms and leeches are monoecious.
• Reproduction is sexual.
• Examples: Nereis, Pheretima (Earthworm), and Hirudinaria (Blood sucking leech).

4.2.7 Phylum – Arthropoda

• Largest phylum of Animalia, includes insects. Over two-thirds of all named species on Earth are arthropods.
• Have organ-system level of organisation.
• Are bilaterally symmetrical, triploblastic, segmented, and coelomate animals.
• Body covered by a chitinous exoskeleton.
• Body consists of head, thorax, and abdomen.
• Have jointed appendages (arthros-joint, poda-appendages).
• Respiratory organs: Gills, book gills, book lungs, or tracheal system.
• Circulatory system is of open type.
• Sensory organs: Antennae, eyes (compound and simple), statocysts (balancing organs).
• Excretion takes place through malpighian tubules.
• Mostly dioecious.
• Fertilisation is usually internal.
• Mostly oviparous.
• Development may be direct or indirect.
• Examples:
  • Economically important insects: Apis (Honey bee), Bombyx (Silkworm), Laccifer (Lac insect).
  • Vectors: Anopheles, Culex, and Aedes (Mosquitoes).
  • Gregarious pest: Locusta (Locust).
  • Living fossil: Limulus (King crab).

4.2.8 Phylum – Mollusca

• The second largest animal phylum.
• Terrestrial or aquatic (marine or freshwater).
• Having an organ-system level of organisation.
• Are bilaterally symmetrical, triploblastic, and coelomate animals.
• Body covered by a calcareous shell and is unsegmented with a distinct head, muscular foot, and visceral hump.
• A soft and spongy layer of skin forms a mantle over the visceral hump.
• The space between the hump and the mantle is called the mantle cavity, containing feather-like gills for respiratory and excretory functions.
• The anterior head region has sensory tentacles.
• Mouth contains a file-like rasping organ for feeding, called radula.
• Usually dioecious and oviparous with indirect development.
• Examples: Pila (Apple snail), Pinctada (Pearl oyster), Sepia (Cuttlefish), Loligo (Squid), Octopus (Devil fish), Aplysia (Sea-hare), Dentalium (Tusk shell), and Chaetopleura (Chiton).

4.2.9 Phylum – Echinodermata

• Animals with an endoskeleton of calcareous ossicles, hence named Echinodermata (Spiny bodied).
• All are marine with organ-system level of organisation.
• Adult echinoderms are radially symmetrical, but larvae are bilaterally symmetrical.
• Are triploblastic and coelomate animals.
• Digestive system is complete with mouth on the lower (ventral) side and anus on the upper (dorsal) side.
• The most distinctive feature is the presence of a water vascular system, which helps in locomotion, capture and transport of food, and respiration.
• An excretory system is absent.
• Sexes are separate. Reproduction is sexual.
• Fertilisation is usually external.
• Development is indirect with free-swimming larva.
• Examples: Asterias (Star fish), Echinus (Sea urchin), Antedon (Sea lily), Cucumaria (Sea cucumber), and Ophiura (Brittle star).

4.2.10 Phylum – Hemichordata

• Formerly considered a sub-phylum under phylum Chordata, now placed as a separate phylum under non-chordata.
• Have a rudimentary structure in the collar region called stomochord, similar to notochord.
• Small group of worm-like marine animals with organ-system level of organisation.
• Are bilaterally symmetrical, triploblastic, and coelomate animals.
• Body is cylindrical and composed of an anterior proboscis, a collar, and a long trunk.
• Circulatory system is of open type.
• Respiration takes place through gills.
• Excretory organ is proboscis gland.
• Sexes are separate.
• Fertilisation is external.
• Development is indirect.
• Examples: Balanoglossus and Saccoglossus.

4.2.11 Phylum – Chordata

• Fundamentally characterised by the presence of:
  • A notochord
  • A dorsal hollow nerve cord
  • Paired pharyngeal gill slits
• Are bilaterally symmetrical, triploblastic, coelomate with organ-system level of organisation.
• Possess a post-anal tail and a closed circulatory system.

Table 4.1: Comparison of Chordates and Non-chordates

• Phylum Chordata is divided into three subphyla: Urochordata (Tunicata), Cephalochordata, and Vertebrata.

Protochordates

• Subphyla Urochordata and Cephalochordata are often referred to as protochordates.
• They are exclusively marine.
  • Urochordata: Notochord present only in the larval tail (e.g., Ascidia, Salpa, Doliolum).
  • Cephalochordata: Notochord extends from head to tail region and is persistent throughout their life (e.g., Branchiostoma (Amphioxus or Lancelet)).

Subphylum – Vertebrata

• Members possess a notochord during the embryonic period.
• The notochord is replaced by a cartilaginous or bony vertebral column in the adult.
• Key concept: All vertebrates are chordates, but not all chordates are vertebrates.
• Besides basic chordate characters, vertebrates have:
  • A ventral muscular heart with two, three, or four chambers.
  • Kidneys for excretion and osmoregulation.
  • Paired appendages (fins or limbs).
• Vertebrata is divided into two divisions based on presence of jaws:
  • Agnatha (lacks jaw)
  • Gnathostomata (bears jaw)

4.2.11.1 Class – Cyclostomata (Agnatha)

• All living members are ectoparasites on some fishes.
• Elongated body bearing 6-15 pairs of gill slits for respiration.
• Have a sucking and circular mouth without jaws.
• Body is devoid of scales and paired fins.
• Cranium and vertebral column are cartilaginous.
• Circulation is of closed type.
• Are marine but migrate for spawning to fresh water, dying within days after. Larvae return to ocean after metamorphosis.
• Examples: Petromyzon (Lamprey) and Myxine (Hagfish).

Gnathostomata (Jawed Vertebrates)

• Divided into two super classes:
  • Pisces (bear fins)
  • Tetrapoda (bear limbs)

Super Class – Pisces (Fishes)

• Includes two classes: Chondrichthyes and Osteichthyes.

4.2.11.2 Class – Chondrichthyes (Cartilaginous Fishes)

• Marine animals with a streamlined body and cartilaginous endoskeleton.
• Mouth located ventrally.
• Notochord is persistent throughout life.
• Gill slits are separate and without operculum (gill cover).
• Skin is tough, containing minute placoid scales.
• Teeth are modified placoid scales, backwardly directed, with powerful jaws; these animals are predaceous.
• Due to the absence of an air bladder, they must swim constantly to avoid sinking.
• Heart is two-chambered (one auricle and one ventricle).
• Some have electric organs (e.g., Torpedo) and some possess a poison sting (e.g., Trygon).
• Are cold-blooded (poikilothermous) animals, lacking the capacity to regulate body temperature.
• Sexes are separate; in males, pelvic fins bear claspers.
• Have internal fertilisation and many are viviparous.
• Examples: Scoliodon (Dog fish), Pristis (Saw fish), Carcharodon (Great white shark), Trygon (Sting ray).

4.2.11.3 Class – Osteichthyes (Bony Fishes)

• Includes both marine and fresh water fishes with a bony endoskeleton.
• Body is streamlined. Mouth is mostly terminal.
• Have four pairs of gills covered by an operculum on each side.
• Skin is covered with cycloid/ctenoid scales.
• Air bladder is present, which regulates buoyancy.
• Heart is two-chambered.
• Are cold-blooded animals.
• Sexes are separate.
• Fertilisation is usually external.
• Mostly oviparous and development is direct.
• Examples:
  • Marine: Exocoetus (Flying fish), Hippocampus (Sea horse).
  • Freshwater: Labeo (Rohu), Catla (Katla), Clarias (Magur).
  • Aquarium: Betta (Fighting fish), Pterophyllum (Angel fish).

Super Class – Tetrapoda (Limbed Vertebrates)

• Includes four classes: Amphibia, Reptilia, Aves, and Mammalia.

4.2.11.4 Class – Amphibia

• Name means “dual life” (Greek: Amphi - dual, bios - life) as they can live in aquatic and terrestrial habitats.
• Most have two pairs of limbs. Body divisible into head and trunk; tail may be present.
• Skin is moist and without scales.
• Eyes have eyelids. A tympanum represents the ear.
• Alimentary canal, urinary, and reproductive tracts open into a common chamber called cloaca.
• Respiration is by gills, lungs, and through skin.
• The heart is three-chambered (two auricles and one ventricle).
• Are cold-blooded animals.
• Sexes are separate. Fertilisation is external.
• They are oviparous and development is indirect.
• Examples: Bufo (Toad), Rana (Frog), Hyla (Tree frog), Salamandra (Salamander), Ichthyophis (Limbless amphibia).

4.2.11.5 Class – Reptilia

• Class name refers to their creeping or crawling locomotion (Latin: repere or reptum).
• Mostly terrestrial animals.
• Body is covered by dry and cornified skin, epidermal scales or scutes.
• Do not have external ear openings; tympanum represents ear.
• Limbs, when present, are two pairs. (Note: Limbs are absent in snakes).
• Heart is usually three-chambered, but four-chambered in crocodiles.
• Reptiles are poikilotherms (cold-blooded).
• Snakes and lizards shed their scales as skin cast.
• Sexes are separate. Fertilisation is internal.
• They are oviparous and development is direct.
• Examples: Chelone (Turtle), Testudo (Tortoise), Chameleon (Tree lizard), Calotes (Garden lizard), Crocodilus (Crocodile), Alligator (Alligator), Hemidactylus (Wall lizard).
• Poisonous snakes: Naja (Cobra), Bangarus (Krait), Vipera (Viper).

4.2.11.6 Class – Aves (Birds)

• Characteristic features: Presence of feathers. Most can fly, except flightless birds (e.g., Ostrich). Possess a beak.
• Forelimbs are modified into wings.
• Hind limbs generally have scales and are modified for walking, swimming, or clasping tree branches.
• Skin is dry without glands, except for the oil gland at the base of the tail.
• Endoskeleton is fully ossified (bony), and long bones are hollow with air cavities (pneumatic).
• Digestive tract has additional chambers: the crop and gizzard.
• Heart is completely four-chambered.
• Are warm-blooded (homoiothermous) animals, able to maintain a constant body temperature.
• Respiration is by lungs, supplemented by air sacs connected to lungs.
• Sexes are separate. Fertilisation is internal.
• They are oviparous and development is direct.
• Examples: Corvus (Crow), Columba (Pigeon), Psittacula (Parrot), Struthio (Ostrich), Pavo (Peacock), Aptenodytes (Penguin), Neophron (Vulture).

4.2.11.7 Class – Mammalia

• Found in a variety of habitats: polar ice caps, deserts, mountains, forests, grasslands, dark caves. Some adapted to fly or live in water.
• Most unique characteristic: presence of milk-producing glands (mammary glands) by which young ones are nourished.
• Have two pairs of limbs, adapted for walking, running, climbing, burrowing, swimming, or flying.
• Skin is unique in possessing hair.
• External ears or pinnae are present.
• Different types of teeth are present in the jaw.
• Heart is four-chambered.
• Are homoiothermous (warm-blooded).
• Respiration is by lungs.
• Sexes are separate. Fertilisation is internal.
• They are viviparous with few exceptions (e.g., Platypus). Development is direct.
• Examples:
  • Oviparous: Ornithorhynchus (Platypus).
  • Viviparous: Macropus (Kangaroo), Pteropus (Flying fox), Camelus (Camel), Macaca (Monkey), Rattus (Rat), Canis (Dog), Felis (Cat), Elephas (Elephant), Equus (Horse), Delphinus (Common dolphin), Balaenoptera (Blue whale), Panthera tigris (Tiger), Panthera leo (Lion).

Table 4.2: Salient Features of Different Phyla in the Animal Kingdom