Gen Bio II

Objectives

• Identify the different taxonomic levels of classification and understand hierarchal relationships.

• Explain how a phylogenetic tree shows the history of speciation through nodes and branches.

• Determine which groups on a phylogenetic tree are most closely related by identifying recent common ancestors.

• Describe the trade-offs of large body size and the advantages/disadvantages of multicellularity.

• Explain the inverse relationship between size and the surface area-to-volume ratio ($S/V$).

• Describe how bulk flow and gastrulation enabled the evolution of complex multicellular animals.

• List the defining characteristics of animals, specifically heterotrophy and specialized tissues.

• Discuss the evolution of body plans, including symmetry, germ layers, and body cavities.

Linnaean Classification

• Hierarchical Taxa:

  1. Domain

  2. Kingdom

  3. Phylum

  4. Class

  5. Order

  6. Family

  7. Genus

  8. Species

  • Mnemonic: Dear King Philip Came Over For Good Soup.

• Binomial Nomenclature:

  • System devised by Carolus Linnaeus.

  • Scientific names consist of the Genus (capitalized) and species (lowercase), always italicized (e.g., Canis lupus).

The Domains of Life

• Bacteria: Unicellular prokaryotes with peptidoglycan in cell walls.

• Archaea: Unicellular prokaryotes; often extremophiles with unique membrane lipids.

• Eukarya: Organisms with membrane-bound organelles and nuclei, including:

  • Kingdom Animalia: Multicellular heterotrophs.

  • Kingdom Plantae: Multicellular autotrophs.

  • Kingdom Fungi: Absorptive heterotrophs.

  • Protists: A diverse paraphyletic group of mostly unicellular eukaryotes.

Phylogenetic Trees

• Tree Interpretation:

  • Node: A branching point representing the last common ancestor of the descendant lineages.

  • Root: The most recent common ancestor of all entities in the tree.

  • Sister Taxa: Two lineages that are each other's closest relatives (sharing a node not shared by others).

  • Monophyletic Group (Clade): Includes an ancestor and all of its descendants.

• Homology vs. Analogy:

  • Homologous traits: Inherited from a common ancestor (e.g., vertebrate forelimbs).

  • Analogous traits (Homoplasy): Result from convergent evolution (e.g., wings of a bat vs. wings of a butterfly).

• Synapomorphies: Shared derived characters used to define clades.

Size and Surface Area-Volume ($S/V$) Relationship

• Mathematical Principles:

  • For a cube of side $s$: $SA = 6s^2$; $V = s^3$.

  • For a sphere of radius $r$: $SA = 4\pi r^2$; $V = \frac{4}{3}\pi r^3$.

  • $S/V$ Ratio: $S/V = \frac{Surface Area}{Volume}$.

• Scaling Effects:

  • As an organism grows, volume (mass) increases by the cube, while surface area increases only by the square.

  • Large organisms have a low $S/V$ ratio, making simple diffusion inefficient for gas exchange and nutrient absorption.

  • Adaptations: Specialized structures like lungs (alveoli), small intestines (villi), and gills increase surface area without significantly increasing volume.

Multicellularity and Complex Animals

• Simple vs. Complex Multicellularity:

  • Simple: Cells show little differentiation and remain in contact with the environment.

  • Complex: Specialized tissues and organs; cells are not all in contact with the environment.

• Bulk Flow: Mechanisms (like the circulatory system) skip the limitations of diffusion by transporting oxygen and nutrients over long distances via pressure gradients.

• Gastrulation: A crucial developmental stage where the blastula folds inward, creating germ layers (Ectoderm, Mesoderm, Endoderm) and the basic body plan.

Animal Development and Body Plans

• General Characteristics: Multicellular, eukaryotic, heterotrophic (via ingestion), no cell walls, and possess Collagen.

• Symmetry:

  • Radial: Organized around a central axis (e.g., Jellyfish).

  • Bilateral: Right/left mirror images, associated with Cephalization (concentration of sense organs at the anterior end).

• Embryonic Germ Layers:

  • Diploblastic: Ectoderm and Endoderm (e.g., Cnidarians).

  • Triploblastic: Ectoderm, Mesoderm (muscles/circulatory), and Endoderm (gut lining).

• Body Cavities (Coeloms):

  • Acoelomate: No cavity (flatworms).

  • Pseudocoelomate: Cavity partially lined with mesoderm (roundworms).

  • Coelomate: Cavity completely lined with mesoderm (earthworms, humans).

• Developmental Pathways:

  • Protostomes: Blastopore becomes the mouth.

  • Deuterostomes: Blastopore becomes the anus (e.g., Chordates, Echinoderms).