Origin of the Universe, Organic Evolution, and Prokaryotes

Vocabulary flashcards covering the origin of the universe and life, mechanisms and evidences of organic evolution, prokaryotic domains and extremophiles, and the structural features of DNA.

The Big Bang Theory

The leading scientific model explaining that approximately $13.8\text{ billion}$ years ago, the universe began expanding rapidly from an extremely hot, infinitely dense point known as a singularity, creating space, time, and matter.

The Chemosynthetic Theory

The theory proposing that life on Earth originated gradually from non-living organic molecules through chemical reactions in primordial waters, driven by energy sources such as U.V. radiation or lightning.

Early Earth Conditions

The environmental conditions of Earth $4.6\text{ billion}$ years ago, characterized by a warm, molten environment, no free oxygen (filled primarily with nitrogen, carbon dioxide, and water vapour), high energy from lightning and U.V. radiation, intense volcanic activities, and meteorite bombardments.

Abiotic Synthesis of Organic Monomers

The first stage in the origin of life where energy sources (U.V. radiation, lightning, intense heat) drove chemical reactions among inorganic molecules (water vapor, ammonia, methane, hydrogen) to form simple organic compounds, including amino acids.

Organic Evolution

The gradual, cumulative, heritable changes that occur in populations of organisms from simple ancestral forms to more complex and diverse species over time, driven by natural selection, genetic drift, mutation, and gene flow.

Homologous Structures

Anatomical structures in different species that share a similar underlying structure but perform different functions, indicating divergent evolution from a common ancestor (e.g., forelimbs of humans, bats, whales, and cats).

Analogous Structures

Structures that possess different underlying structural origins but perform similar functions, indicating convergent evolution (e.g., the wings of birds and insects).

Embryological Evidences

Evidence supporting evolution through shared, conserved developmental pathways in the early embryonic stages of diverse species, such as pharyngeal slits and tails found in early vertebrate embryos (humans, birds, and fish).

Palaeontological Evidences

The study of fossils—preserved remains or traces of ancient organisms found in rocks—that provides a chronological timeline of life, revealing transitional forms and the extinction or emergence of species.

Molecular Evidences

Evolutionary evidence demonstrating that all life shares a universal genetic code and fundamental biochemical pathways; for example, humans and chimpanzees share $98\%\text{--}99\%$ of their DNA.

Prokaryotes

Unicellular organisms that lack a membrane-bound nucleus and membrane-bound organelles, possessing genetic material localized in an irregular, unenclosed region called the nucleoid.

Photoautotrophy

A prokaryotic nutritional mode in which organisms harvest energy from sunlight and use inorganic carbon dioxide to synthesize organic compounds via photosynthesis (e.g., cyanobacteria, green and purple sulfur bacteria).

Chemoautotrophy

A nutritional mode in which prokaryotes obtain energy by oxidizing inorganic chemical substances (such as hydrogen sulfide or ammonia) and use that energy to fix carbon dioxide into organic molecules.

Photoheterotrophy

A mode of nutrition where prokaryotes obtain energy from sunlight but must acquire their carbon from pre-formed organic molecules rather than carbon dioxide (e.g., certain purple non-sulfur bacteria).

Chemoheterotrophy

The most common prokaryotic nutritional mode, wherein organisms consume pre-formed organic compounds to satisfy both their energy and carbon requirements (e.g., decomposers and pathogenic bacteria).

Domain Bacteria

A domain of prokaryotic, typically unicellular organisms characterized by a single circular DNA molecule located in the nucleoid and a cell wall composed primarily of peptidoglycan.

Domain Archaea

A domain of prokaryotic organisms with circular chromosomes whose cell walls lack peptidoglycan, many of which are adapted to live in extreme environments.

Extremophiles

Organisms adapted to survive and reproduce under extreme environmental conditions, such as high temperature, high salinity, or extreme pH.

Thermophiles

Extremophilic organisms (such as Thermococcus, Pyrococcus, and Sulfolobus) that grow and reproduce at very high temperatures, typically inhabiting hot springs, hydrothermal vents, and geothermal areas.

Halophiles

Extremophilic organisms (such as Halobacterium, Haloferax, and Halococcus) that grow and reproduce in environments with very high salt concentrations, such as salt lakes and salt evaporation ponds.

Acidophiles

Extremophiles that grow and reproduce in highly acidic environments with very low pH, such as acidic hot springs, volcanic areas, and acid mine drainage (e.g., Sulfolobus, Thermoplasma, Ferroplasma).

Alkaliphiles

Extremophiles that grow and reproduce in highly alkaline environments where the pH is very high, such as soda lakes and alkaline soils (e.g., Natronomonas, Alkaliphilus, Bacillus alcalophilus).

Methanogens

Archaea that produce methane gas ($\text{CH}_4$) as a metabolic by-product in oxygen-free (anaerobic) environments, such as wetlands, sewage digesters, and the digestive systems of ruminants.

Natural Selection

The process by which organisms with advantageous inherited characteristics are more likely to survive and reproduce, gradually increasing the prevalence of those beneficial traits in subsequent generations.

Neo-Darwinism (The Modern Synthetic Theory)

The evolutionary theory stating that evolution occurs through changes in allele frequencies within populations across successive generations, driven by variation from mutation and recombination and influenced by natural selection, genetic drift, and gene flow.

Gene Flow

The movement of alleles from one population to another via the migration and subsequent reproduction of individuals, resulting in changes in allele frequencies.

Genetic Drift

Random fluctuations in allele frequencies within a population due to chance events, especially significant in small populations, which can lead to the loss or fixation of alleles.

Antiparallel Strands

The arrangement of the two polynucleotide chains in a DNA molecule running in opposite directions, where one strand is oriented in the $5' \rightarrow 3'$ direction and the complementary strand runs in the $3' \rightarrow 5'$ direction.

Complementary Base Pairing

The specific hydrogen bonding between nitrogenous bases in DNA: adenine (A) pairs with thymine (T) via two hydrogen bonds, and guanine (G) pairs with cytosine (C) via three hydrogen bonds.

DNA Double Helix Structure

The double-stranded molecular structure consisting of two antiparallel polynucleotide chains featuring a sugar-phosphate backbone and complementary nitrogenous base pairs.