General Biology: Major Themes and Animal Diversity Study Guide

Section 1: Major Themes in Biology

Structure to Function

In biology, the structure of an organism or cell is closely related to its function. This principle helps explain why biological forms are adapted to their roles.

• Structure determines function: For example, the surface area of lungs or red blood cells is optimized for gas exchange.

• Examples: Protein shape determines its activity; plant bodies are structured for photosynthesis.

Information Flow

Living systems rely on the flow of information to regulate processes and maintain life.

• Genetic information: DNA encodes instructions for building proteins.

• Central dogma of biology:

$\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$

Pathways That Transform Energy & Matter

Organisms require energy and matter to grow, reproduce, and maintain homeostasis. These pathways are fundamental to ecosystem dynamics.

• Energy flow: Movement, growth, reproduction; energy flows through ecosystems.

• Matter recycling: Decomposition returns nutrients to the environment.

• Chemical reactions: Metabolic processes transform molecules.

Interactions Within Biological Systems

Biological systems are complex and involve interactions among many parts, leading to emergent properties.

• Emergent properties: New characteristics arise from the interaction of system components.

• Example: The complexity of the nervous system arises from the interaction of neurons.

Evolution

Evolution explains the diversity and unity of life through change over time, primarily via natural selection.

• Diversity and unity: All life shares common features but has evolved differences.

• Natural selection: The process by which advantageous traits become more common in a population.

What Are Animals?

Animals are multicellular, eukaryotic organisms that are typically motile and heterotrophic.

• Monophyletic group: All animals descended from a common ancestor.

• Three traits all animals share:

  • Multicellularity

  • Heterotrophy (ingest food)

  • Motility (move under their own power at some point)

• MOST animals have:

  • Nerve cells (neurons)

  • Muscle cells

• Shared with other organisms:

  • Eukaryotic (nucleus, membrane-bound organelles)

  • Sexual reproduction

Phylogeny & Classification

Phylogeny is the evolutionary history of a group. Animals are classified based on shared characteristics and evolutionary relationships.

• Phylogenetic tree: Shows ancestor-descendant relationships among species/groups.

• Monophyletic group: Includes ancestor and all descendants.

• Paraphyletic group: Includes ancestor but not all descendants.

• Synapomorphy: Shared derived trait unique to a group.

Section 2: Porifera, Cnidaria, Platyhelminthes

Phylum Porifera: Sponges

Sponges are the simplest animals, lacking true tissues and organs. They are mostly marine, with some freshwater species.

• Asymmetrical

• No true tissues or organs

• Synapomorphies:

  • Choanocytes: Flagellated cells that circulate water through channels lined by flagellated cells.

  • Aquiferous system: System with external pores for water flow.

  • Mineral spicules: Provide structural support.

Phylum Cnidaria: Anemones, Jellyfish

Cnidarians are radially symmetric, mostly marine animals with specialized stinging cells.

• Radial symmetry

• Body plans:

  • Polyp: Sessile body form, stationary lifestyle for catching prey.

  • Medusa: Mobile, wider distribution but more vulnerable.

• Diploblastic: Two cell layers in the embryo (endoderm and ectoderm) with non-cellular mesoglea in between.

• Synapomorphy: Cnidocytes (stinging cells)

• Colonial polyps:

  • Hard corals: Precipitate CaCO3 from seawater to produce skeleton; contain zooxanthellae (photosynthetic dinoflagellates).

  • Soft corals: Less calcium carbonate, more flexible, no zooxanthellae.

Phylum Platyhelminthes: Flatworms

Flatworms are bilaterally symmetric, mostly parasitic or free-living in marine, freshwater, and terrestrial environments.

• Parasites: Flukes, tapeworms

• Tissues and organs for excretion and reproduction

• Bilateral symmetry: Unidirectional movement

• Symplesiomorphy: Cephalization (formation of the head region)

• Feeds on other animals

Section 3: Annelida, Mollusca, Arthropoda

Phylum Annelida: Segmented Worms

Annelids are segmented worms found in marine and terrestrial environments.

• Examples: Earthworms, leeches, polychaetes

• Segmentation: Repeated body units

• Coelom: Body cavity within mesoderm, allows independent movement and storage of gametes/embryos

Class Polychaeta

• Marine, includes Parapodia

• Feeding: Raptorial, filter, and deposit

• Synapomorphies: Setae (hooks, bristles, parachutes, defensive spines)

Class Clitellata

• Earthworms, aquatic oligochaetes, leeches

Phylum Mollusca: Clams, Snails, Squid

Mollusks are a diverse group with over 100,000 species, characterized by a soft body and, in many, a shell.

• Body form: Shell (lost in some), nacreous layer

• Synapomorphies:

  • Reduced coelom

  • Radula (feeding organ)

  • Foot (muscular appendage for movement)

Class Bivalvia

• Scallops, clams, mussels, oysters, cockles

• Giant clams: zooxanthellae

• Synapomorphy: Unique 2-part shell

Class Gastropoda

• Largest class of mollusks

• Snails, slugs, sea hares, abalone, whelks, nudibranchs, pteropods (sea butterflies)

Class Cephalopoda

• Octopus, squid, cuttlefish

• Highly organized, predatory lifestyle

• Synapomorphies: Foot becomes tentacles, chromatophores (color-changing cells)

Phylum Arthropoda: Crustaceans

Arthropods are the most diverse animal phylum, with over 750,000 species. They have jointed legs and an exoskeleton.

• Exoskeleton: Molting required for growth

• Segmented body: Developed externally from Annelida

• Loss of motile cilia

Subphyla

• Hexapoda: Insects

• Myriapoda: Centipedes, millipedes

• Trilobitomorpha: Trilobites (extinct)

• Chelicerata: Spiders, scorpions, mites, ticks, horseshoe crabs

• Crustacea: Crabs, barnacles, shrimp, lobster

Section 4: Echinodermata, Chordata

Phylum Echinodermata

Echinoderms are marine animals with a hard shell and unique water vascular system.

• 7000 marine species

• Synapomorphies:

  • Tube feet (Water Vascular System): Feeding and locomotion

  • Pentaradial symmetry (five-part symmetry)

  • Calcareous internal skeleton

Classes

• Asteroidea: Sea stars/starfish (predators, crawl)

• Ophiuroidea: Brittle stars, basket stars (arms demarcated from body)

• Crinoidea: Feather stars (attach to rocks, swim)

• Echinoidea: Sea urchins, sand dollars (not star-shaped, feeding: grazers, deposit, suspension feed)

• Holothuroidea: Sea cucumbers, sea pig (soft body)

Phylum Chordata

Chordates are animals with a notochord, dorsal hollow nerve cord, pharyngeal gill slits, and post-anal tail at some stage of development.

• Synapomorphies:

  • Notochord (axial skeletal rod)

  • Pharyngeal gill slits

  • Dorsal hollow nerve cord

  • Post-anal tail

  • Endostyle or thyroid gland

Subphylum Urochordata/Tunicata

• Class Ascidiacea: Sea squirts (sessile filter feeders)

• Class Thaliacea: Salps and Pyrosomes (pelagic, transparent, solitary or colonial)

• Class Larvacea: Larvaceans (zooplankton in gelatinous matrix)

Subphylum Vertebrata

• Synapomorphies:

  • Internal skeleton of bone

  • Articulated, dorsal vertebral column

  • Bony cranium

  • Chambered heart

• Class Agnatha: Lampreys & hagfish (no jaws, scavengers, parasites)

• Class Chondrichthyes: Cartilaginous fish (sharks, skates, rays)

• Class Osteichthyes: Bony fish (swim bladder for buoyancy)

• Class Aves: Birds (wings, feathers, reduced bone, endothermy)

• Class Reptilia: Turtles, lizards, snakes, sea turtles

• Class Mammalia: Endothermic, hair, mammary glands, live birth

• Order Sirenia: Manatees & dugongs

• Order Cetacea: Whales (rear limbs disappeared, blowhole, baleen or teeth)

Summary Table: Major Animal Phyla and Key Features

Phylum	Symmetry	Key Features	Examples
Porifera	None	No tissues, choanocytes, aquiferous system	Sponges
Cnidaria	Radial	Diploblastic, cnidocytes, polyp/medusa forms	Jellyfish, corals, anemones
Platyhelminthes	Bilateral	Cephalization, tissues/organs, flat body	Flatworms, tapeworms
Annelida	Bilateral	Segmentation, coelom	Earthworms, leeches
Mollusca	Bilateral	Shell (in most), foot, radula	Clams, snails, squid
Arthropoda	Bilateral	Exoskeleton, jointed legs, segmentation	Insects, crabs, spiders
Echinodermata	Pentaradial (adult)	Water vascular system, tube feet, calcareous skeleton	Sea stars, sea urchins
Chordata	Bilateral	Notochord, dorsal nerve cord, pharyngeal slits, post-anal tail	Fish, birds, mammals

Additional info: Academic context and expanded explanations have been added to ensure completeness and clarity for exam preparation.