BI 131 Exam 2 Definitive Study Guide: Prokaryotes, Evolution, Fungi, Plants, and Animal Diversity

Prokaryotic Biology: Bacteria and Archaea

• Fundamental Definition of Prokaryotes:

  • A prokaryote is a unicellular organism that lacks a membrane-bound nucleus and membrane-bound organelles.

  • Genetic material is concentrated in a non-membrane-enclosed region designated as the nucleoid.

  • Cellular organization is structurally simpler than that of eukaryotes, comprising the two taxonomic domains: Bacteria and Archaea.

• Cellular Division via Binary Fission:

  • Binary fission is an asexual reproductive process utilized by prokaryotic cells to divide into two progeny cells.

  • Process of Binary Fission:

  • The single, circular prokaryotic chromosome replicates at the origin of replication.

  • The cell elongates as the two resulting chromosomes move toward opposite poles of the cell.

  • The plasma membrane pinches inward at the cell midline, accompanied by the synthesis of a new cell wall (septum formation).

  • The cell completely divides into two daughter cells.

  • Genetic Outcome:

  • Binary fission results in two genetically identical daughter cells (clones of the parent cell), barring spontaneous DNA mutations occurring during replication.

• Morphology and Bacterial Shapes:

  • Cocci (singular: Coccus): Spherical or round-shaped bacterial cells (e.g., Streptococcus, Staphylococcus).

  • Bacilli (singular: Bacillus): Rod-shaped bacterial cells (e.g., Escherichia coli, Bacillus anthracis).

  • Spirilla (singular: Spirillum): Spiral-, corkscrew-, or helical-shaped bacterial cells with rigid cell walls.

• Metabolic Diversity:

  • Prokaryotes exhibit extraordinary metabolic diversity, enabling them to inhabit virtually every ecological niche on Earth:

  • Energy Sources: Phototrophs (capture light energy) and Chemotrophs (extract energy from chemical compounds, organic or inorganic).

  • Carbon Sources: Autotrophs (utilize inorganic carbon, primarily carbon dioxide $\text{CO}_2$, to synthesize organic compounds) and Heterotrophs (require pre-formed organic compounds for carbon and energy).

  • This versatility allows prokaryotes to drive biogeochemical cycling, decompose complex organic debris, and maintain life across diverse ecosystems.

• Helpful vs. Pathogenic Bacteria:

  • Helpful Bacteria:

  • Provide mutualistic benefits within organisms (e.g., the human intestinal microbiome, synthesizing vital vitamins such as vitamin K and assisting in nutrient breakdown).

  • Facilitate industrial applications such as food fermentation (yogurt, cheese), bioremediation (cleaning environmental pollutants and oil spills), and biotechnology (insulin synthesis).

  • Mediate nitrogen fixation in agricultural and natural environments, converting unusable atmospheric nitrogen gas into plant-absorbable ammonium.

  • Pathogenic Bacteria:

  • Pathogenic bacteria cause disease in host organisms by producing virulent structures, exotoxins (secreted toxins), or endotoxins (toxic lipopolysaccharide components released upon bacterial death).

  • Examples of bacterial diseases include strep throat, tuberculosis, cholera, and Lyme disease.

• Extremophilic Archaea:

  • Extremophiles are prokaryotes adapted to thrive in extreme physical or geochemical conditions that are lethal to most other life forms:

  • Halophiles:

    • Organisms adapted to survive and proliferate in hypersaline (extremely salty) environments.

    • Maintain osmotic balance by accumulating specialized internal solutes to resist cellular desiccation and plasmolysis.

    • Typical environments include the Dead Sea, the Great Salt Lake, and commercial solar evaporation salt ponds.

  • Thermophiles:

    • Organisms adapted to survive and thrive in excessively high temperatures (typically exceeding $45^{\circ}\text{C}$ to over $100^{\circ}\text{C}$).

    • Possess heat-stable enzymes and specialized structural lipids in their cell membranes to avoid thermal denaturation.

    • Typical environments include hydrothermal deep-sea vents, hot springs (such as those in Yellowstone National Park), and volcanic fissures.

Cellular Evolution and the Endosymbiotic Theory

• Prokaryotic vs. Eukaryotic Cells:

  • Prokaryotes: Lack a membrane-bound nucleus; lack membrane-bound organelles; have circular chromosomes; are universally microscopic and predominantly unicellular; possess $70\text{S}$ ribosomes.

  • Eukaryotes: Possess a membrane-enclosed nucleus containing linear DNA; contain compartmentalized, membrane-bound organelles (mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus); exhibit larger cell dimensions ($10\text{--}100\,\mu\text{m}$); possess $80\text{S}$ cytosolic ribosomes.

• The Endosymbiotic Theory:

  • Proposes that eukaryotic organelles, specifically mitochondria and chloroplasts, originated as small, free-living prokaryotic cells that were engulfed by ancestral host cells.

  • Rather than being digested, the engulfed prokaryotic cells developed an intimate, mutually beneficial endosymbiotic relationship with the host.

  • Evidence for Endosymbiosis:

  • Mitochondria and chloroplasts contain their own circular, double-stranded DNA molecules distinct from the nuclear genome.

  • They replicate independently within the cell through a process resembling binary fission.

  • They are bounded by two (or more) concentric membranes, consistent with an engulfment mechanism.

  • They contain internal $70\text{S}$ ribosomes structurally and functionally homologous to prokaryotic ribosomes.

• Origin and Advantage of Chloroplasts:

  • Chloroplasts evolved through the endosymbiosis of an ancestral photosynthetic prokaryote (related to cyanobacteria) by a non-photosynthetic, eukaryotic host cell.

  • Evolutionary Advantage: Retaining an intact photosynthetic bacterium allowed the host cell to synthesize its own organic sugars directly from abundant solar light energy and carbon dioxide ($\text{CO}_2$). This freed the host organism from total reliance on consuming external organic food sources, granting exceptional metabolic independence.

• Origin of the Endomembrane System:

  • The endomembrane system—comprising the nuclear envelope, endoplasmic reticulum (rough and smooth), Golgi apparatus, lysosomes, and vesicles—arose independently of endosymbiosis.

  • Formed via the progressive infolding and invagination of the prokaryotic plasma membrane in ancestral cells.

  • These internal membrane folds pinched inward to form isolated, internal compartments, allowing the physical segregation of cellular processes such as transcription, translation, lipid synthesis, and protein modification.

Fungi: Structure, Nutrition, and Ecological Functions

• Eukaryotic and Heterotrophic Nature:

  • Fungi are eukaryotic organisms that belong to their own distinct kingdom, possessing membrane-bound organelles, linear chromosomes, and cell walls composed predominantly of chitin.

  • Absorptive Heterotrophs: Fungi do not ingest food like animals or photosynthesize like plants. Instead, they secrete hydrolytic digestive enzymes externally into their immediate substrate to break down complex polymers into simpler monomers, which are then absorbed directly across the fungal cell wall and plasma membrane.

• Fungal Anatomy:

  • Hyphae:

  • Slender, threadlike, tubular filamentous structures that form the structural basis of fungi.

  • Contain cytoplasm and nuclei, bounded by a rigid chitinous cell wall.

  • Mycelium:

  • A densely branched, interconnected network or mass composed of bundled hyphae.

  • Maximizes surface-area-to-volume ratio to optimize external nutrient absorption from soil, wood, or living host tissue.

  • Fruiting Body:

  • The complex, above-ground reproductive structure that develops from the underlying mycelial network.

  • The visible and edible portion of a typical mushroom represents this above-ground fruiting body.

  • Specialized for the production and aerial dissemination of reproductive spores.

• Ecological Role:

  • Fungi function as major decomposers (saprotrophs) in terrestrial ecosystems.

  • They break down recalcitrant dead organic matter, such as cellulose and lignin in plant wood, which few other organisms can digest.

  • Through decomposition, fungi liberate essential chemical elements—particularly carbon, nitrogen, and phosphorus—recycling them back into the soil and atmosphere to maintain ecosystem sustainability.

  • Fungal Examples: Edible portobello mushrooms, baker's yeast (Saccharomyces cerevisiae), penicillium mold, shelf/bracket fungi.

Plant Evolution, Anatomy, and Reproduction

• Chronological Sequence of Major Plant Adaptations:

  • The evolutionary transition of plants from aquatic green algal ancestors to land followed three major structural milestones in chronological order:

  • $\text{Vascular Tissue} \rightarrow \text{Seeds} \rightarrow \text{Flowers}$

  • Vascular Tissue: Evolved first, allowing internal transport of fluid and upright structural growth away from water.

  • Seeds: Evolved next, providing protective, nutritive packages for embryos to survive desiccation and disperse across land.

  • Flowers: Evolved most recently in angiosperms, facilitating highly targeted sexual reproduction via animal pollinators and fruit production.

• Plant Tissue Definition:

  • A plant tissue is defined as a coordinated group of specialized cells with a shared structural organization that work together to perform a specific physiological function.

• Non-Vascular Plants (Bryophytes / Mosses):

  • Mosses lack specialized vascular tissues (xylem and phloem) and structural lignin.

  • Limitations on Stature: Because they lack vascular transport vessels, water and nutrients must move strictly by slow cell-to-cell osmosis and diffusion. Furthermore, the absence of rigid, lignin-reinforced vascular cell walls prevents them from supporting significant mechanical weight against gravity. Consequently, mosses cannot grow tall and remain restricted to small, low-lying sizes in damp environments.

• Vegetative Plant Adaptations for Terrestrial Life:

  • Cuticle:

  • A waxy, hydrophobic layer secreted on the outer epidermal surface of aerial plant organs (leaves and stems).

  • Serves as a vital terrestrial adaptation by establishing a waterproof seal that dramatically reduces evaporative water loss (desiccation) to the dry surrounding atmosphere.

  • Roots:

  • Below-ground organ systems that anchor the plant securely into the terrestrial substrate.

  • Specialize in absorbing dissolved water and mineral ions from soil pore spaces.

  • Shoots:

  • Above-ground organ systems consisting of photosynthetic leaves, stems, and reproductive structures.

  • Function to elevate leaves to capture sunlight energy and exchange atmospheric carbon dioxide ($\text{CO}_2$) and oxygen ($\text{O}_2$) for photosynthesis.

• Angiosperm Reproductive Structures:

  • Flowers: Specialized reproductive shoots of angiosperms whose primary biological function is to facilitate sexual reproduction, primarily by attracting animal pollinators (e.g., insects, birds) using color, nectar, and scent to ensure targeted pollen transfer.

  • Stamen: The male reproductive organ of a flower, consisting of the pollen-bearing anther supported by a slender filament.

  • Carpel (Pistil): The female reproductive organ of a flower, typically composed of the sticky receptive stigma, the elongated neck-like style, and the swollen basal ovary.

  • Ovule: A protective structure located within the ovary containing the female gametophyte (egg cell); following successful fertilization, the ovule develops into a seed.

  • Pollen Tube: An elongated tubular conduit that germinates from a pollen grain deposited on the stigma; it elongates down through the tissues of the style directly to the ovule to deliver non-flagellated sperm nuclei to the egg.

  • Endosperm: A nutrient-dense, triploid ($3n$) nutritive storage tissue produced during angiosperm double fertilization inside the seed, providing vital metabolic nourishment to the growing embryonic plant until seed germination.

  • Seeds: Highly specialized dispersal packages containing a dormant embryonic plant, a concentrated food reserve (endosperm), and a tough outer protective seed coat.

• Monocots vs. Dicots:

  • Monocots (Monocotyledons):

  • Characterized by parallel leaf venation and fibrous, diffuse root systems (lacking a dominant taproot).

  • Possess a single embryonic cotyledon in the seed.

  • Examples: Corn, wheat, grasses, lilies, orchids.

  • Dicots (Eudicotyledons):

  • Characterized by branched, net-like (reticulate) leaf venation and a central, deep-penetrating taproot system.

  • Possess two embryonic cotyledons in the seed.

  • Examples: Oak trees, roses, sunflowers, garden beans.

• Plant Symbioses:

  • Mycorrhizae: A mutualistic symbiosis between fungal hyphae and plant roots. The extensive fungal mycelium acts as an extension of the root system, dramatically increasing the surface area for absorbing soil water and mineral nutrients (particularly phosphorus), while the host plant provides the heterotrophic fungus with organic photosynthetic sugars.

  • Nitrogen-Fixing Bacteria: Mutualistic associations (such as Rhizobium residing inside the root nodules of legume plants) where bacteria convert atmospheric dinitrogen gas ($\text{N}_2$) into bioavailable ammonium ($\text{NH}_4^+$), while the host plant supplies carbohydrate energy and an oxygen-regulated microenvironment.

• Cellular Energetics:

  • Photosynthesis:

  • Biological process by which autotrophs convert light energy into stable chemical energy stored within the chemical bonds of organic sugar molecules:

  • $\text{Light Energy} + 6\text{CO}_2 + 6\text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$

  • Cellular Respiration:

  • Aerobic metabolic pathway by which eukaryotic organisms break down the chemical bonds of sugars to harvest metabolic energy, storing it in high-energy adenosine triphosphate ($\text{ATP}$) molecules to power cellular work:

  • $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP}$

Invertebrate Diversity and Body Symmetry

• Symmetry Classifications:

  • Radial Symmetry:

  • Body design characterized by circular organization around a central longitudinal axis.

  • Any imaginary longitudinal plane slicing through the central axis divides the organism into roughly mirror-image halves.

  • Lacks distinct left and right sides, or head and tail regions; typical of sessile or slow-moving organisms.

  • Bilateral Symmetry:

  • Body design divided along a single vertical median plane to produce distinct left and right mirror-image halves.

  • Characterized by anatomical polarity: anterior (head) vs. posterior (tail) ends, and dorsal (back) vs. ventral (belly) surfaces.

  • Correlated with cephalization (concentration of sensory and neural organs at the anterior end), supporting directional movement.

• Sponges (Phylum Porifera):

  • Morphologically asymmetrical animals lacking any defined plane of symmetry.

  • Structurally unique among animals for lacking true tissues or organs; cellular processes operate at the loose cellular grade of organization.

  • Sessile, aquatic filter feeders utilizing specialized flagellated collar cells.

• Cnidarians (Phylum Cnidaria):

  • Display radial symmetry throughout their life cycles.

  • Possess true, organized tissues derived from two embryonic germ layers (diploblastic: ectoderm and endoderm).

  • Possess specialized stinging cells called cnidocytes (containing stinging organelles known as nematocysts) used for prey capture and defense.

  • Examples: Jellyfish, sea anemones, hydras, corals.

• Mollusks (Phylum Mollusca):

  • Display bilateral symmetry.

  • Characterized by a soft, unsegmented body typically divided into a muscular foot, a visceral mass containing internal organs, and a tissue mantle that frequently secretes a hard calcium carbonate shell.

  • Examples: Snails, clams, octopuses, squids, oysters.

• Arthropods (Phylum Arthropoda):

  • Exhibit bilateral symmetry with segmented bodies, a hard chitinous exoskeleton, and paired jointed appendages.

  • Represent the most diverse and abundant animal phylum.

  • Spiders are classified specifically as arachnids (possessing eight walking legs, chelicerae, and two main body divisions: cephalothorax and abdomen).

  • Examples: Spiders, scorpions, crabs, lobsters, butterflies, beetles.

• Echinoderms (Phylum Echinodermata):

  • Exhibit secondary radial symmetry as adults (typically five-part pentaradial symmetry), although their free-swimming larvae exhibit bilateral symmetry.

  • Possess an internal calcium-rich endoskeleton situated beneath an outer epidermal layer.

  • Possess a unique internal hydraulic system (water vascular system) operating rows of tube feet for locomotion, feeding, and gas exchange.

  • Examples: Sea stars (starfish), sea urchins, sand dollars, sea cucumbers.

Chordates and Vertebrate Evolution

• The Four Hallmarks of Chordates:

  • All members of the phylum Chordata exhibit four diagnostic anatomical characteristics at some stage of their development:

  • Notochord: A flexible, longitudinal rod of supportive tissue located dorsal to the digestive tract and ventral to the nerve cord, providing skeletal axis support.

  • Dorsal Hollow Nerve Cord: A longitudinal, fluid-filled hollow nerve tube located dorsal to the notochord, which develops into the central nervous system (brain and spinal cord).

  • Pharyngeal Slits (or Clefts): Perforations or grooves along the pharynx behind the mouth, functioning as suspension-feeding structures in invertebrate chordates, gill slits in aquatic vertebrates, and contributing to parts of the inner ear, head, and neck in terrestrial tetrapods.

  • Post-Anal Tail: A muscular elongation of the body extending posterior to the anus, adapted for aquatic propulsion in many chordates (often reduced or resorbed during embryonic development in humans and apes).

  • Examples of chordates include invertebrate lancelets, tunicates, and all true vertebrates.

• Vertebrates:

  • Chordates distinguished by the evolutionary development of a backbone (vertebral column).

  • The vertebral column encloses, protects, and supports the dorsal hollow nerve cord (spinal cord) and provides an anchor for body musculature.

  • Possess a defined cranium (skull) enclosing a distinct, cephalized brain.

  • Examples: Trout, salamanders, lizards, eagles, humans.

• Fish Adaptations:

  • Bony fish (Osteichthyes) possess an internal, air-filled organ designated as the swim bladder.

  • Function: Regulates neutral buoyancy by dynamically adjusting gas volume within the bladder, allowing the fish to maintain stable depth in the water column without expending continuous muscular energy swimming up or down.

• Tetrapods:

  • Vertebrates characterized by having four distinct limbs with digits (or evolutionary lineages derived from four-limbed ancestors, such as snakes and whales).

  • Emerged from lobe-finned ancestral fishes, enabling the historic vertebrate transition from water to land.

• Amphibians:

  • Tetrapods possessing moist, permeable skin used for gas exchange, lacking epidermal scales.

  • Reproductive Constraints: Amphibian eggs completely lack an amnion and protective shell. Because these gelatinous eggs are prone to fatal desiccation, amphibians cannot reproduce away from water or exceptionally moist environments, requiring external water for laying eggs and supporting aquatic larval stages.

  • Examples: Frogs, toads, salamanders, newts.

• Reptiles and the Amniotic Egg:

  • Fully terrestrial tetrapods with water-retaining keratinized scales that prevent cutaneous desiccation.

  • The Amniotic Egg:

  • Contains four specialized extraembryonic membranes: the amnion (which encloses the embryo in a protective fluid-filled amniotic cavity resembling a private aquatic pond), the yolk sac (providing rich nutrition), the allantois (metabolic waste disposal), and the chorion (gas exchange).

  • Enclosed by a tough, leathery or calcified shell that protects against physical trauma and drying out while permitting gas diffusion.

  • Evolutionary Significance: The amniotic egg eliminated the historical evolutionary requirement for an external aquatic environment to reproduce, enabling amniotes (reptiles, birds, and mammals) to complete their full life cycles and diversify across dry terrestrial habitats.

  • Reptilian examples: Lizards, snakes, turtles, crocodilians, alligators.

• Birds:

  • Endothermic, feathered amniote reptiles specialized for powered flight.

  • Flight adaptations include aerodynamic keratin feathers, wings, lightweight hollow bones with internal honeycombed air cavities, highly efficient one-way respiratory air sacs, and a high-rate metabolic furnace.

• Mammals and Marsupials:

  • Endothermic vertebrates characterized by insulating hair and mammary glands that synthesize milk to nourish neonates.

  • Marsupials:

  • A mammalian lineage characterized by giving birth to extremely immature, altricial young after a brief gestation period.

  • The developing joey completes its embryonic growth and development anchored to a maternal nipple inside an external abdominal pouch (the marsupium).

  • Examples: Kangaroos, koalas, opossums, wallabies.

Core Conceptual Relationships and Ecological Roles

• Nutritional Strategies:

  • Autotrophs: Self-feeding primary producers that assemble organic macromolecules from inorganic molecules ($\text{CO}_2$ and $\text{H}_2\text{O}$) using outside energy (light in photoautotrophs, inorganic redox reactions in chemoautotrophs).

  • Heterotrophs: Consumers and decomposers that cannot synthesize their own fuel and must acquire carbon and energy by ingesting, absorbing, or processing other organisms or organic matter.

• Symmetry Patterns and Ecological Lifestyle:

  • Radial Symmetry: Correlated with a sessile, drifting, or slow, non-directional ecological existence. Allows an organism to sense, defend against, and capture environmental stimuli and prey equally from any $360^{\circ}$ horizontal direction.

  • Bilateral Symmetry: Correlated with active, directed locomotion. Concentrates sensory organs, nervous tissue, and mouth apparatus at the anterior leading edge (cephalization), allowing rapid detection and navigation of the environment in forward motion.

• Decomposer Dynamics in Global Ecosystems:

  • Decomposers—predominantly fungi and heterotrophic prokaryotes—act as essential recyclers in biogeochemical cycles.

  • Without continuous decomposition, dead organic matter would accumulate indefinitely, permanently locking away finite planetary pools of carbon, nitrogen, and phosphorus.

  • Decomposer activity converts complex biological waste into simple inorganic nutrients ($\text{NH}_4^+$, $\text{NO}_3^-$, $\text{PO}_4^{3-}$, $\text{CO}_2$), replenishing the abiotic reservoirs utilized by primary producers.

• The Principle of Structure-to-Function:

  • Biological structures are adapted to perform specific mechanical, physiological, and ecological tasks across all domains of life:

  • Waxy cuticles match the terrestrial requirement to prevent desiccation.

  • Filamentous fungal hyphae provide high surface area matching absorptive heterotrophy.

  • Air-filled swim bladders match the physical density requirements of aquatic buoyancy.

  • Rigid vascular xylem tubes match the hydraulic and mechanical challenges of upward fluid transport against gravity.

  • Protective amniotic shells match the arid conditions of terrestrial reproduction.