Animal Diversity, Structure, and Digestion: Study Guide (Chapters 18–21)

Chapter 18: The Evolution of Invertebrate Diversity

Cnidarians

Cnidarians are a phylum of simple aquatic animals known for their unique body structure and specialized cells.

• Radial Symmetry: Cnidarians, such as jellyfish and sea anemones, have body parts arranged around a central axis.

• Tentacles: Used for capturing prey and defense.

• Stinging Cells (Cnidocytes): Specialized cells that release toxins to immobilize prey.

Bilateral Symmetry

Many animal phyla display bilateral symmetry, meaning their body can be divided into mirror-image halves along one plane.

• Examples: Flatworms, annelids, arthropods, mollusks, chordates.

Sponges (Phylum Porifera)

Sponges are simple, sessile animals lacking true tissues and organs.

• Body Features: Porous body, filter-feeding system, no symmetry, no true tissues.

Nematodes (Roundworms)

Nematodes are unsegmented worms with a complete digestive system.

• Body Cavity: Possess a pseudocoelom (fluid-filled body cavity).

• Digestive Tract: Complete, with both mouth and anus.

Arthropods

Arthropods are the most diverse animal phylum, including insects, arachnids, crustaceans, and more.

• Key Features: Segmented body, exoskeleton made of chitin, jointed appendages.

• Diversity: Largest number of described species among all animal phyla.

Chordates and the Notochord

Chordates are animals defined by the presence of a notochord at some stage in development.

• Notochord: Flexible, rod-shaped structure that provides support.

• Other Features: Dorsal hollow nerve cord, pharyngeal slits, post-anal tail (at least in embryonic stages).

Chapter 19: The Evolution of Vertebrate Diversity

Ectothermic vs. Endothermic Organisms

• Ectothermic: Organisms that rely on external sources for body heat (e.g., reptiles, amphibians, fish).

• Endothermic: Organisms that regulate body temperature internally (e.g., birds, mammals).

Hominins and Bipedalism

• Bipedalism: Walking upright on two legs; earliest defining trait of hominins (human lineage).

Amphibian Life Cycle

• Metamorphosis: Amphibians (e.g., frogs) undergo a transformation from aquatic larvae (tadpoles) to terrestrial adults.

Mammal Characteristics

• Hair: Provides insulation and protection.

• Milk: Mammary glands produce milk to nourish young.

Monotremes

• Key Features: Egg-laying mammals (e.g., platypus, echidna).

Marsupials

• Key Features: Give birth to underdeveloped young, which complete development in a pouch (e.g., kangaroo, koala).

Chapter 20: Unifying Concepts of Animal Structure and Function

Levels of Organization

• Tissue: Group of similar cells performing a specific function.

• Organ: Structure composed of multiple tissue types working together (e.g., heart, liver).

• Organ System: Group of organs that work together to perform a major function (e.g., digestive system).

Four Main Types of Animal Tissues

• Epithelial Tissue: Covers body surfaces and lines internal organs and cavities.

• Connective Tissue: Supports and binds other tissues; includes bone, blood, cartilage, fat.

• Muscle Tissue: Responsible for movement; includes skeletal, cardiac, and smooth muscle.

• Nervous Tissue: Senses stimuli and transmits signals; composed of neurons and supporting cells.

Blood as Connective Tissue

• Matrix: Blood's matrix is plasma, a liquid that suspends cells and proteins.

Bone as Connective Tissue

• Matrix: Hard mineral matrix (mainly calcium phosphate) and collagen fibers provide strength and flexibility.

Nervous Tissue

• Neurons: Specialized cells that transmit electrical impulses.

• Supporting Cells (Glia): Provide support, protection, and nourishment for neurons.

• Function: Communication and coordination throughout the body.

Chapter 21: Nutrition and Digestion

Definition of Digestion

• Digestion: The process of breaking down food into molecules small enough for the body to absorb.

Order of the Digestive System

• Pathway: Mouth → Pharynx → Esophagus → Stomach → Small Intestine → Large Intestine → Anus

Peristalsis

• Definition: Rhythmic contractions of smooth muscle that propel food through the digestive tract.

Roles of Digestive Organs

• Stomach: Secretes acid and enzymes to begin protein digestion.

• Intestines: Small intestine absorbs nutrients; large intestine absorbs water and forms feces.

• Pancreas: Produces digestive enzymes and bicarbonate to neutralize stomach acid.

• Liver: Produces bile to emulsify fats for digestion.

Animal Feeding Strategies

• Bulk Feeders: Most animals ingest large pieces of food (e.g., humans, lions).

• Other Strategies: Fluid feeders (e.g., mosquitoes), filter feeders (e.g., whales), substrate feeders (e.g., earthworms).