Origins of Life and Early Cellular Evolution

Vocabulary practice flashcards covering the origins of life, chemical evolution, early Earth conditions, endosymbiosis, and the domains of life.

Homeostasis

The ability of an organism to regulate its internal environment so that physiological conditions remain relatively constant, such as sweating to remove heat and maintain body temperature.

Cell Theory

A foundational biological principle consisting of three main tenets: all organisms are composed of one or more cells, the cell is the smallest unit possessing all properties of life, and cells arise only from the growth and division of preexisting cells.

Prokaryote

A unicellular organism that lacks internal membrane-bound compartments and a nucleus, possessing a cytoplasm surrounded by a plasma membrane and rigid cell wall.

Eukaryote

A complex single-celled or multicellular organism defined by a membrane-enclosed nucleus containing linear chromosomes and specialized endomembrane-bound organelles.

Abiotic

Non-living or physical and chemical processes occurring in the absence of life or cellular machinery, such as the primordial synthesis of organic monomers.

Biotic

Relating to or produced by living organisms and biological systems.

Oparin and Haldane Hypothesis

A 1920s proposal that early Earth possessed a reducing atmosphere rich in $H_2$, $CO_2$, $CH_4$, and $NH_3$ that promoted the formation of C-C bonds and abiotic synthesis of organic compounds when driven by UV and electrical energy.

Miller-Urey Experiment

A 1953 experiment simulating early Earth conditions ($H_2O$, $CH_4$, $H_2$, $NH_3$) with electrical spark discharges, which successfully synthesized organic precursors of life including amino acids, simple sugars, lipids, and nucleotides.

Proteinoid

An abiotically produced chain of amino acids formed spontaneously on charged surfaces like hot sand, clay, or rock without templates, genes, or ribosomes.

Liposome

A spherical, membrane-bound vesicle formed spontaneously by amphipathic phospholipids in an aqueous solution, with hydrophilic heads facing the water and hydrophobic tails tucked into the interior bilayer.

Protobiont

A pre-cell aggregate of abiotically produced organic molecules surrounded by a lipid boundary; it maintains a distinct internal environment, exhibits basic metabolism, and can replicate imperfectly.

Central Dogma of Biology

The framework governing molecular genetic information flow: genetic information stored in DNA is transcribed into RNA, which then guides the synthesis of proteins.

RNA World Hypothesis

The hypothesis proposing that RNA was the first genetic material because it can both store hereditary genetic information and catalyze biochemical reactions.

Ribozyme

An RNA molecule with catalytic enzyme-like activity capable of facilitating chemical reactions, such as self-replication or cleaving RNA messages (examples include ribosomes and spliceosomes).

Alkaline Hydrothermal Vent

A deep-sea fissure near tectonic activity that expels superheated ($100\text{--}150\,^{\circ}\text{C}$), alkaline ($\text{pH } 9\text{--}11$) water rich in reducing molecules ($H_2$, $NH_3$, $H_2S$), where metal-mineral complexes ($Fe\text{-}S$) catalyzed early metabolic reactions.

Stromatolites

Fossilized microbial mats formed by photosynthetic cyanobacteria, providing some of the earliest physical evidence for cellular life on Earth dating back to approximately $3.4\text{--}3.5\,\text{BYA}$.

Cyanobacteria

A phylum of bacteria that evolved oxygenic photosynthesis, using water as an electron donor and releasing oxygen as a byproduct, leading to the oxygenation of Earth's atmosphere.

Anoxygenic Photosynthesis

A primitive form of bacterial photosynthesis that does not generate molecular oxygen because it uses alternative electron donors, such as $H_2S$, instead of water.

Oxygenic Photosynthesis

A highly efficient form of photosynthesis developed by cyanobacteria that splits $H_2O$ as an electron source for light-dependent reactions, releasing $O_2$ as a byproduct.

Aerobic Respiration

A metabolic pathway evolved after atmospheric oxygen accumulated that utilizes $O_2$ to generate ATP, yielding significantly more energy than anaerobic pathways.

Endomembrane System

A system of internal, interconnected eukaryotic membranes—including the nuclear envelope, endoplasmic reticulum, and Golgi apparatus—believed to have formed from invaginations of the plasma membrane in ancient archaeal host cells.

Endosymbiosis

The evolutionary process wherein an ancestral host cell engulfed a smaller prokaryote that took up permanent residence inside, eventually evolving into an organelle such as the mitochondrion.

Serial Endosymbiosis

The sequential acquisition of endosymbionts, in which an ancestral host engulfed an aerobic bacterium (which became the mitochondrion), followed later by the engulfment of a photosynthetic cyanobacterium (which became the chloroplast).

Mitochondria

Energy-generating organelles in eukaryotes that arose endosymbiotically from an engulfed aerobic bacterium (closely related to the Rickettsia bacterial family) and replicate by binary fission.

Chloroplasts

Photosynthetic organelles found in plants and algae that evolved from an engulfed cyanobacterial endosymbiont, retaining circular DNA and bacterial-like translation machinery.

Eubacteria

A primary domain of prokaryotic organisms featuring circular chromosomes, 70S ribosomes, peptidoglycan in their cell walls, and ester-linked membrane lipids.

Archaea

A domain of prokaryotic microbes characterized by ether-linked membrane lipids, the absence of peptidoglycan, methionine initiator tRNA, and deep evolutionary affinities with eukaryotes.

Eukarya

A taxonomic grouping containing all single-celled and multicellular organisms whose cells contain a nucleus, 80S ribosomes, linear chromosomes, and membrane-enclosed organelles.

Tree of Life (2 Domain Model)

A phylogenetic classification based on small subunit rRNA gene sequencing proposing that life comprises two primary prokaryotic domains (Bacteria and Archaea), with Eukarya arising as an internal branch within Archaea.

LUCA (Last Universal Common Ancestor)

The most recent common ancestor from which all modern organisms on Earth descended; it had a lipid plasma membrane, a DNA genetic code, ribosomes, ATP currency, and shared metabolic pathways.