BIO 102 – General Biology II: Exhaustive Study Notes on the Classification and Diversity of Living Organisms

Introduction to Biology and the Science of Classification

  • Nature of the Living World: The world of living things is characterized by being vast in number, ancient in history, and complex in diversity.

  • Role of Biology: Biology encompasses many disciplines that aim to provide a true picture of the nature of living things through observation and study.

  • Observation of Diversity: Casual observation reveals a wide variety of plants and animals that differ in size, shape, color, and speed of locomotion, while also exhibiting core similarities in features and behaviors.

  • Unit Objective: This study guide focuses on the various methods of classification for living organisms and identifies the characteristics of each group.

The History and Hierarchy of Classification

  • Numerical Scope of Diversity: More than 1.8×1061.8 \times 10^{6} kinds of living organisms have been examined and described, with many more yet to be discovered.

  • Foundational Figures in Taxonomy:

    • Aristotle (384−322384-322 BC): A Greek philosopher who made the first recorded attempt to classify living organisms.

    • Linnaeus (1707−17781707-1778): A Swedish naturalist whose work forms the basis of the modern method of identifying and naming organisms.

  • Taxonomy versus Systematics: These terms refer to the study of the general principles and systems of classification.

  • Hierarchical Structure (Highest to Lowest):

    1. Kingdom (Largest group; contains the greatest variety with shared important features but many differences).

    2. Phylum or Division (Division is the term typically used for Plants).

    3. Class.

    4. Order.

    5. Class (Note: The transcript lists Class twice in its hierarchy sequence).

    6. Genus.

    7. Species (Smallest unit of classification; identical in general appearance, capable of mating to produce fertile offspring, and closely related).

Binomial Nomenclature

  • Definition: A standard system for naming living organisms using two names, replacing common names such as Goat, Mango, or Lion.

  • Naming Structure:

    • First Name: The Genus to which the organism belongs (begins with a capital letter).

    • Second Name: The Species to which the organism belongs (begins with a lowercase letter).

  • Stylistic Rules: Names must be written in italics or underlined separately.

  • Verbatim Examples:

    • Pawpaw: Carica papaya

    • Lizard: Agama agama

The Evolution of Kingdom Classification

  • The Two-Kingdom System: Originally proposed by Linnaeus, this system categorized all life as either Plants or Animals. It failed because many single-celled organisms did not fit, it lacked a clear distinction between plants and animals, and it did not indicate correct relationships between organisms.

  • The Five-Kingdom System: Proposed by Whittaker in 19691969, this is the current standard. It distinguishes organisms based on cellular complexity:

    • Prokaryotes: Simple organisms without true nuclei (Kingdom Monera).

    • Eukaryotes: Highly organized cells with true nuclei (Kingdoms Protista, Fungi, Plantae, and Animalia).

Characteristics of the Five Kingdoms

  • Kingdom Monera (Prokaryotes):

    • Single-celled, microscopic structure with no definite nucleus.

    • Can be motile or non-motile.

    • Examples: Bacteria, Blue-green algae, Actinomycetes.

  • Kingdom Protista (Eukaryotes):

    • Single-celled, larger than monerans.

    • Complex cell structure with a definite nucleus.

    • Can be motile or non-motile.

    • Examples: Chlamydomonas, Amoeba.

  • Kingdom Fungi (Eukaryotes):

    • Non-motile organisms usually composed of thread-like structures called hyphae.

    • Plant-like in appearance but lack chlorophyll and cannot perform photosynthesis.

    • Nutrition: Obtain food through absorption from living or non-living organic sources.

    • Reproduction: Via asexual or sexual spores.

    • Examples: Moulds, Mushrooms, Shine moulds, Yeasts.

  • Kingdom Plantae (Eukaryotes):

    • Many-celled and non-motile.

    • Contain chlorophyll for autotrophic nutrition (Photosynthesis).

    • Growth is indeterminate.

    • Examples: Mosses, Ferns, Pines, Seed plants (Yam, Bean).

  • Kingdom Animalia (Eukaryotes):

    • Multicellular heterotrophs that obtain nutrients by ingesting other organisms.

    • Cells lack a cell wall and photosynthetic pigments.

    • Advanced tissue differentiation and complex organ systems.

    • Generally motile and responsive to stimuli via specialized nervous tissue.

    • Growth is determinate, resulting in a definite size and shape.

Deep Dive: Kingdom Plantae

  • Autotrophic Strategy: Plants anchor firmly in place to maximize surface area for capturing sunlight, transforming light energy into chemical energy.

  • Resource Management: They utilize water and carbohydrates to generate size and mass.

  • Environmental Sensitivity: Being immobile, plants have life cycles synchronized with seasons and are highly responsive to environmental cues.

  • Developmental Mode: Growth occurs via meristems at the tips. They possess a remarkable power of regeneration, where a single cell can regenerate an entire plant.

  • Phyla of the Plant Kingdom:

    1. Thallophyta (Algae): Simple green plants, mostly aquatic. They have thread-like or thallus (flat) bodies without roots or stems. They produce metabolic products exploited in biotechnology and serve as food and oxygen sources for marine life. Examples include nitrogen-fixing algae used as bio-fertilizers.

    2. Bryophyta: Colonized land but depend on water for reproduction (amphibious). They require a thin film of water for motile male gametes to reach non-motile female gametes. The sporophyte is dependent on the gametophyte.

    3. Tracheophytes: Known as vascular plants because they possess vessels/tissues to conduct water and food. This group includes Pteridophytes (ferns), Gymnosperms, and Angiosperms (flowering plants).

Deep Dive: Kingdom Animalia and Invertebrates

  • Primary Divisions: Classified into Invertebrata (animals without backbones) and Vertebrata (animals with backbones).

  • Classification Criteria: Based on body symmetry, body design, and body cavity (coelom).

  • Sub-Phylum Invertebrata Phyla:

    • Protozoa: No tissues, no coelom.

    • Coelenterates (Cnidaria): Aquatic, radial symmetry, possess tissues but no coelom. Divided into Hydrozoa (e.g., Hydra), Scyphozoa, Cubozoa, and Anthozoa.

    • Platyhelminthes (Flatworms): Triploblastic (three germ layers: ectoderm, endoderm, mesoderm). Bilaterally symmetrical and dorsiventrally flattened. They are acoelomates (lack a body cavity). Only have a mouth (no anus). Examples: Tapeworms.

    • Nematoda: Bilateral symmetry with a radial tendency. Circular cross-section with no segmentation. Possess a complex cuticle and a pseudocoel (body cavity at high pressure). Gut extends from mouth to anus. Growth involves cell size increase rather than cell number increase.

    • Annelida: The first Coelomate phylum (cavity lined by mesoderm epithelium). Metamerically segmented (rings). Possess nephridia (excretion), a closed blood vascular system, and chitinous setae for locomotion (except leeches). Examples: Earthworms, Leeches.

    • Mollusca: Soft-bodied animals with a distinct head, muscular foot, and a mantle that often secretes a hard calcareous shell. Generally unsegmented. Respiration via gills or lungs. Examples: Snails, Clams.

    • Arthropoda: Largest phylum (>700,000 species). Body segmented into head, thorax, and abdomen with jointed appendages. Chitinous exoskeleton that is periodically moulted. Open circulatory system with a dorsal heart and haemocoels. Nervous system is of the annelidan type.

    • Echinodermata: Exclusively marine (6,0006,000 species). Pentamerous radial symmetry in adults. No brain. Locomotion via tube feet or spines. Internal skeleton (endoskeleton) made of calcium carbonate plates. Examples: Starfishes, Sea urchins.

Sub-Phylum Vertebrata (Sub-phylum of Chordata)

  • Chordate Characteristics: Notochord (flexible rod), tubular dorsal nerve cord, and gill slits at some life stage.

  • General Vertebrate Features:

    • Skeletal structure: Backbone (vertebral column) replaces the notochord; internal skeleton of bone and cartilage.

    • Body Plan: Bilaterally symmetrical; divided into head, trunk, and tail (with a neck in most).

    • Nervous System: Well-developed brain (in a brain case) and dorsal spinal cord.

    • Circulation: Closed system with a ventral muscular heart.

    • Excretion: Kidneys for waste elimination.

    • Limbs: Two pairs (tetrapods).

Classes of Vertebrates

  • Pisces (Fishes):

    • Aquatic poikilotherms (cold-blooded).

    • Respiratory organs: Gills. Bony fish have gill covers; cartilaginous fish do not.

    • Structural units: Skeletons of cartilage (sharks, rays) or bone (Tilapia, carp). Bony fish have swim bladders for buoyancy.

    • Sensory: Two-chambered heart, inner ears, and lateral line system for detecting pressure changes.

    • Environments: Moving through dense water requires a streamlined body; osmoregulation differs between freshwater and marine bony fish.

  • Amphibia:

    • First transition to terrestrial life; poikilothermic with naked, moist skin used for cutaneous respiration.

    • Heart Structure: Three-chambered.

    • Life Cycle: Aquatic larval stage (tadpoles with gills and streamlined tails); adults often breathe via lungs and live on land.

    • Adaptations: Sticky tongues for insect catching, webbed feet for swimming, powerful hind legs for jumping.

  • Reptilia:

    • Lowest truly terrestrial vertebrates; move via crawling (L. repere).

    • Skin: Dry with scales developed from outer layers; devoid of glands.

    • Reproduction: Independent of water due to amniotic eggs (containing amnion and allantois).

    • Heart Structure: Imperfectly four-chambered.

    • Special Feature: Autotomy (power to break off the tail automatically) found in some lizards to escape enemies.

  • Aves (Birds):

    • Warm-blooded (homoiothermic) vertebrates adapted for flight.

    • Flight Adaptations: Feathers (hold a blanket of warm air for buoyancy), streamlined body, wings as propellers, light/welded skull, and a reduced rectum to minimize fecal weight.

    • Skeletal: Tail vertebrae fused into a pygostyle; jawbones modified into a beak without teeth.

    • Heart Structure: Four-chambered.

  • Mammalia:

    • Top of the evolution of living animals due to superior nervous systems and high intelligence.

    • Main Characteristics: Warm-blooded, skin with sweat/sebaceous glands and hair, external ears (pinnae), and a diaphragm separating thoracic and abdominal cavities.

    • Reproduction: Internal fertilization; most are viviparous with a placenta; young fed by mammary glands.

    • Rabbit Case Study: Survival hinges on high fertility, burrowing habits, crepuscular nature, and acute senses (smell, hearing, and wide field of vision from protuberant eyes). Rabbits possess 1313 pairs of ribs for better breathing during high-speed runs.

Anatomical and Embryological Classifications

  • Coelom Classification:

    • Coelom: Body cavity lined by mesoderm.

    • Coelomates: Annelids, Molluscs, Arthropods, Echinoderms, Chordates.

    • Pseudocoelomates: Mesoderm present in scattered pouches; cavity not fully lined (e.g., Aschelminthes/Nematoda).

    • Acoelomates: Body cavity absent (e.g., Platyhelminthes).

  • Tissue Layer Organization:

    • Diploblastic: Cells arranged in two layers: external ectoderm and internal endoderm (e.g., Coelenterates).

    • Triploblastic: Cells arranged in three layers: ectoderm, endoderm, and mesoderm.

    • Mesoglea: An undifferentiated layer found between the ectoderm and endoderm in diploblastic animals.