Lecture 10: The Tree of Life and Overview of Animals

Comprehensive vocabulary flashcards covering the origin of life, early Earth conditions, eukaryotic evolution, and key innovations in animal phylogeny and body architecture.

Big Bang Theory

The model proposing that a massive explosion approximately $14\text{ billion}$ years ago produced the matter and energy of the universe.

Oparin-Haldane Hypothesis

A hypothesis proposed in the 1920s stating that early Earth had a strongly reducing atmosphere of $H_2$, $CH_4$, $NH_3$, and water, which enabled the abiotic formation of organic molecules in the absence of oxygen.

Reducing atmosphere

An early atmospheric condition characterized by an abundance of electrons and hydrogen for reduction reactions and an absence of oxygen, preventing the oxidative destruction of newly formed organic compounds.

Protocells

Primitive, membrane-bound aggregations of molecules formed by chance assembly in the prebiotic soup, representing an essential intermediate step toward true cellular life.

RNA World Model

The hypothesis proposing that RNA was the first genetic material because of its ability to both store genetic information and catalyze biochemical reactions via ribozyme activity.

Endosymbiosis

The evolutionary mechanism by which eukaryotic organelles originated, specifically mitochondria from purple nonsulfur bacteria and chloroplasts from cyanobacteria.

Compartmentalization

A key eukaryotic adaptation involving an extensive endomembrane system that divides the cell into functional units, allowing increased subcellular specialization and regulated transcription and translation.

Parazoa

The branch of multicellular animals (sponges) that lack true tissues and symmetry.

Eumetazoa

A major animal group consisting of all animals other than sponges that possess true tissues and well-defined body symmetry.

Diploblasts

Animals whose embryos produce only two primary germ layers: ectoderm and endoderm.

Triploblasts

Animals whose embryos produce three primary germ layers: ectoderm, endoderm, and mesoderm.

Ectoderm

The outermost primary embryonic germ layer that gives rise to the external body covering and the nervous system.

Endoderm

The innermost primary embryonic germ layer that develops into the lining of the digestive gut and, in some animals, respiratory organs.

Mesoderm

The middle primary embryonic germ layer that forms the body wall muscles and most internal structures between the gut and external covering.

Radial symmetry

A body organization where parts are arranged around a central axis like spokes on a wheel, allowing the organism to be bisected into equal halves along any two-dimensional plane.

Bilateral symmetry

A body organization characterized by distinct right and left halves that are mirror images, allowing bisection into equal halves only along the sagittal plane.

Cephalization

An evolutionary trend in bilaterally symmetrical animals characterized by the localization of a definite brain area and a centralized nervous system at the anterior end.

Acoelomates

Animals that lack a body cavity between the gut and the outer body wall.

Pseudocoelomates

Animals possessing a pseudocoelom, which is a body cavity located between the mesoderm and endoderm.

Coelomates

Animals possessing a coelom, which is a true body cavity located entirely within the mesoderm and lined by the peritoneum.

Peritoneum

A membrane derived from the mesoderm that lines the true body cavity (coelom).

Blastula

A hollow ball of cells produced by mitotic cell divisions of the fertilized egg during early bilaterian animal development.

Blastopore

The initial opening to the outside formed when the blastula indents during embryonic gastrulation.

Archenteron

The primitive, pouch-like body cavity that forms the primitive gut when the blastula indents.

Protostomes

A bilaterian animal lineage in which the mouth develops first from or near the blastopore, featuring spiral cleavage and determinate development.

Deuterostomes

A bilaterian animal lineage in which the anus develops first from the blastopore and the mouth forms secondarily, featuring radial cleavage and indeterminate development.

Spiral cleavage

The characteristic pattern of embryonic cell division seen in protostomes.

Radial cleavage

The characteristic pattern of embryonic cell division seen in deuterostomes.

Determinate development

A developmental pattern found in protostomes where cell fates are established early in embryonic life and the coelom arises directly from the mesoderm.

Indeterminate development

A developmental pattern found in deuterostomes where early embryonic cells retain potential to develop into complete organisms and the coelom forms indirectly from the archenteron.

Segmentation

The morphological division of the body into repeated segments, providing redundant organ systems and enabling more flexible, efficient movement.

Amnion

A fluid-filled sac surrounding the embryo during development that protects terrestrial vertebrate embryos from desiccation.