Biology
The word biology first appeared in the title of Volume 3 of Michael Christoph Hanow's Philosophiae naturalis sive physicae dogmaticae, published in 1766. This volume included Geologia, biologia, phytologia generalis et dendrologia. The term gained modern usage independently through several figures in the late eighteenth and early nineteenth centuries. Thomas Beddoes used it in 1799, while Karl Friedrich Burdach introduced it in 1800. Gottfried Reinhold Treviranus published Biologie oder Philosophie der lebenden Natur in 1802, and Jean-Baptiste Lamarck followed with Hydrogéologie that same year. Ancient roots trace back to Greek βίος (bíos) meaning life and λογία (logia) meaning study of. Early scientific inquiry into living things began in ancient Egypt and Mesopotamia around 3000 to 1200 BCE. Aristotle contributed extensively to biological knowledge between 384 and 322 BCE, exploring causation and diversity. His successor Theophrastus started the scientific study of plants. Medieval Islamic scholars like al-Jahiz, Al-Dīnawarī, and Rhazes wrote on botany, anatomy, and physiology. Anton van Leeuwenhoek dramatically improved the microscope, revealing spermatozoa, bacteria, and infusoria. In 1838, Schleiden and Schwann promoted cell theory, though they initially opposed the idea that all cells come from division of other cells. Robert Remak and Rudolf Virchow later confirmed this third tenet by the 1860s.
Life arose from Earth's first ocean approximately 3.8 billion years ago. Water remains the most abundant molecule in every organism today. It acts as an effective solvent capable of dissolving solutes like sodium and chloride ions. A water molecule consists of two hydrogen atoms bonded to one oxygen atom via polar covalent bonds. This structure creates a slight negative charge on oxygen and positive charges on hydrogens. Hydrogen bonds make water cohesive and give it surface tension. Ice floats above liquid water because it is less dense than its liquid form. This property insulates ponds, lakes, and oceans from cold air above. Carbon forms the backbone of nearly all organic molecules except water. It can bond with up to four other atoms to create diverse structures. The Miller-Urey experiment in 1953 showed organic compounds could be synthesized abiotically within a closed system mimicking early Earth conditions. Macromolecules include carbohydrates, lipids, proteins, and nucleic acids. Carbohydrates consist of sugar monomers or polymers. Lipids are nonpolar substances including steroids and phospholipids. Proteins contain twenty different amino acid monomers. Nucleic acids store and transmit hereditary information through nucleotide polymers.
Most cells range from 1 to 100 micrometers in diameter, visible only under microscopes. Cell theory states that all living things compose one or more cells arising from preexisting cells. Eukaryotic cells contain a nucleus while prokaryotic cells do not. A cell membrane separates cytoplasm from extracellular space using a lipid bilayer. Cholesterol sits between phospholipids to maintain fluidity at various temperatures. Membrane proteins act as transporters or enzymes shaping the cell. Organelles like mitochondria generate adenosine triphosphate to power cellular processes. The endoplasmic reticulum synthesizes proteins while the Golgi apparatus packages them. Lysosomes engulf biomolecules for breakdown. Plant cells possess additional organelles including chloroplasts that harvest sunlight energy. Microtubules made of tubulin provide structural support inside eukaryotic cells. Metabolism converts food into energy to run cellular processes. Catabolic reactions break down compounds releasing energy while anabolic reactions build up compounds consuming energy. Enzymes catalyze these reactions by reducing activation energy needed. Cellular respiration converts chemical energy from nutrients into ATP through glycolysis and the citric acid cycle. Fermentation occurs when oxygen is absent converting pyruvate into waste products like lactic acid or ethanol.
Gregor Mendel outlined principles of biological inheritance in 1865 though significance remained unrealized until the early twentieth century. Alfred Hershey and Martha Chase conducted experiments in the 1940s pointing to DNA as trait-carrying units within chromosomes. James Watson and Francis Crick discovered the double-helical structure of DNA in 1953 marking the transition to molecular genetics. Har Gobind Khorana, Robert W. Holley, and Marshall Warren Nirenberg cracked the genetic code after understanding codons. The Human Genome Project launched in 1990 aimed to map the human genome. A gene corresponds to a region of deoxyribonucleic acid controlling form or function. DNA exists as linear chromosomes in eukaryotes and circular chromosomes in prokaryotes. Mutations arise spontaneously from replication errors or induced by environmental mutagens like radiation. Beneficial mutations provide variation for evolution while harmful ones may result in loss of function. Gene expression flows from DNA to RNA to protein according to Francis Crick's central dogma formulated in 1958. Transcription converts DNA into RNA while translation turns RNA into proteins. Regulatory proteins called transcription factors bind near promoters to control gene activity. Operons cluster genes sharing the same promoter mainly found in prokaryotes. Hox genes determine where repeating body parts grow during development.
All life on Earth descended from a last universal common ancestor living about 3.5 billion years ago. Geologists divide Earth history into four eons starting with Hadean followed by Archean, Proterozoic, and Phanerozoic. The Phanerozoic eon began 539 million years ago subdivided into Paleozoic, Mesozoic, and Cenozoic eras. Microbial mats dominated early Archean environments where major evolutionary steps likely occurred. Earliest evidence of eukaryotes dates from 1.85 billion years ago. Multicellular organisms appeared around 1.7 billion years ago with differentiated cells performing specialized functions. Algae-like land plants date back approximately one billion years though microorganisms formed earliest terrestrial ecosystems at least 2.7 billion years ago. Vertebrates originated about 525 million years ago during the Cambrian explosion. Synapsids including mammal ancestors dominated land during the Permian period before most went extinct in the Permian-Triassic extinction event 252 million years ago. Dinosaurs dominated Jurassic and Cretaceous periods until non-avian dinosaurs died off 66 million years ago following the Cretaceous-Paleogene extinction event. Mammals increased rapidly in size and diversity after this catastrophe. Speciation occurs when lineages split due to reproductive isolation caused by genetic incompatibilities or physical barriers.
Bacteria constitute a large domain of prokaryotic microorganisms typically a few micrometers long existing as spheres rods or spirals. They inhabit soil water acidic hot springs radioactive waste and deep biosphere crusts. Only about 27 percent of bacterial phyla have species cultivable in laboratories. Archaea form another prokaryotic domain initially classified as bacteria receiving name archaebacteria now fallen out of use. Some archaea display unique shapes like flat square cells of Haloquadratum walsbyi. Their cell membranes rely on ether lipids called archaeols distinct from other domains. Salt-tolerant haloarchaea use sunlight as energy source while others fix carbon but no known species performs both functions. Archaea reproduce asexually via binary fission fragmentation or budding without forming endospores. Eukaryotes hypothesized to have split from archaea followed by endosymbioses giving rise to mitochondria and chloroplasts. Five major eukaryotic clades collectively known as protists are mostly microscopic organisms not plants fungi or animals. Plants derive from cyanobacterial endosymbiosis into early eukaryotes about one billion years ago creating chloroplasts. Fungi digest foods outside bodies secreting enzymes breaking down molecules before absorption. Over 1.5 million animal species described though estimates suggest over 7 million total exist. Viruses replicate inside host cells infecting all life forms including bacteria and archaea. More than 6000 virus species described making them most numerous biological entities found almost everywhere.
An ecosystem combines living biotic organisms with nonliving abiotic components like water light temperature humidity atmosphere acidity soil. Energy enters systems through photosynthesis incorporated into plant tissue then moves matter and energy through food webs. Decomposers release carbon back to atmosphere converting nutrients stored in dead biomass usable again by plants. Carrying capacity represents maximum population size sustainable given available resources such as food habitat water. New technologies like Green revolution increased Earth's carrying capacity for humans stymying predictions of decline made famous by Thomas Malthus in eighteenth century. Communities consist groups populations same geographical area simultaneously interacting intraspecifically or interspecifically. Symbioses range mutualism beneficial both partners competition harmful both partners. Trophic levels structure food webs starting primary producers converting energy into organic compounds used rest community. Heterotrophs obtain energy breaking apart organic compounds from other organisms. Primary consumers eat plants secondary consumers eat herbivores tertiary consumers eat secondary consumers omnivorous heterotrophs consume multiple levels. Total energy incorporated biomass trophic level per unit time about one-tenth energy consumed next trophic level waste heat lost make remaining ninety percent. Up to 50% species planet disappear within next 50 years according estimates contributing poverty starvation resetting course evolution globally.
Common questions
When did the word biology first appear in a published title?
The word biology first appeared in the title of Volume 3 of Michael Christoph Hanow's Philosophiae naturalis sive physicae dogmaticae, published on the 1st of January 1766. This volume included Geologia, biologia, phytologia generalis et dendrologia.
Who discovered the double-helical structure of DNA and when?
James Watson and Francis Crick discovered the double-helical structure of DNA in 1953 marking the transition to molecular genetics. Their discovery built upon earlier work by Alfred Hershey and Martha Chase who conducted experiments in the 1940s pointing to DNA as trait-carrying units within chromosomes.
How old is the last universal common ancestor of all life on Earth?
All life on Earth descended from a last universal common ancestor living about 3.5 billion years ago. Geologists divide Earth history into four eons starting with Hadean followed by Archean, Proterozoic, and Phanerozoic.
What are the main differences between bacteria and archaea cell membranes?
Bacteria constitute a large domain of prokaryotic microorganisms while Archaea form another prokaryotic domain initially classified as bacteria receiving name archaebacteria now fallen out of use. Their cell membranes rely on ether lipids called archaeols distinct from other domains.
When did non-avian dinosaurs die off following the Cretaceous-Paleogene extinction event?
Non-avian dinosaurs died off 66 million years ago following the Cretaceous-Paleogene extinction event. Dinosaurs dominated Jurassic and Cretaceous periods until this catastrophe occurred after which mammals increased rapidly in size and diversity.