Set 1: Fungi/History of the Earth

Phanerozoic eras in chronological order

1. Paleozoic Era ('Ancient life')

2. Mesozoic Era ('Middle life')

3. Cenozoic Era ('Recent life')

Paleozoic Era

The geological era of 'ancient life' ($542\text{--}252\,\text{mya}$) initiated by the Cambrian explosion of animal phyla and characterized by the initial terrestrial radiation of plants and fungi.

Mesozoic Era

The geological era of 'middle life' ($252\text{--}66\,\text{mya}$), characterized by the ecological dominance of dinosaurs and gymnosperms, ending with the End-Cretaceous mass extinction.

Cenozoic Era

The geological era of 'recent life' ($66\,\text{mya}$ to the present), characterized by the ecological dominance and adaptive radiation of mammals and angiosperms (flowering plants).

Fungal growth forms

The two primary morphological states exhibited by fungi: single-celled yeasts and multicellular mycelial networks.

Yeast

A unicellular fungus that grows without forming extensive multicellular filaments.

Mycelium

The dynamic, multicellular vegetative network of branching filaments that forms the body of a fungus.

Hyphae

Long, slender branching filaments that serve as the basic structural units of a fungal mycelium.

Septa

Porous internal cross-walls that partition fungal hyphae into distinct individual cellular compartments.

Hyphal pores

Openings located within septa that allow cytoplasm, organelles, and nuclei to flow between adjacent cells.

Monokaryotic

A hyphal condition where each cellular compartment houses exactly one nucleus.

Dikaryotic

A hyphal condition where two genetically distinct, compatible haploid nuclei coexist within the same cell without fusing.

Coenocytic

A continuous fungal filament that lacks septa entirely, resulting in hundreds of nuclei scattered through a common cytoplasm.

Surface area-to-volume ratio in fungal mycelium

An anatomical feature resulting from thin, branching filaments that maximizes nutrient absorption efficiency but increases vulnerability to dehydration.

Fungal spore

A resilient, dormant reproductive unit that can withstand dry or nutrient-poor conditions and germinates via mitosis into new hyphae.

Chitin

A tough structural polysaccharide that reinforces fungal cell walls, also found in arthropod exoskeletons.

Glycogen

The primary energy-storage carbohydrate synthesized by both fungi and animals.

Extracellular digestion

A heterotrophic feeding mechanism where digestive enzymes are secreted outside the organism to break down macromolecules before absorption.

Saprophyte

An organism that acquires organic nutrients directly by digesting dead or decaying plant tissue.

Role of fungi in the carbon cycle

Decomposing dead lignin-rich wood and plant tissues to return sequestered carbon to the atmosphere as carbon dioxide.

Lignin peroxidase

A fungal enzyme that catalyzes the degradation of complex lignin compounds in wood to expose embedded cellulose.

Cellulase

A fungal enzyme that catalyzes the breakdown of cellulose into simple sugars for metabolic consumption.

Parasitism

A symbiotic relationship in which one organism derives nutrients at the expense and physiological detriment of a host organism.

Mutualism

A symbiotic partnership in which both participating organisms obtain reciprocal biological or nutritional benefits.

Commensalism

A symbiotic association where one organism benefits while the other partner experiences neither benefit nor harm.

Ectomycorrhizal fungi

Symbiotic fungi whose hyphae form a dense mantle over outer root surfaces and weave between root cells without penetrating their walls.

Arbuscular mycorrhizal fungi

Symbiotic fungi whose hyphae penetrate directly through plant root cell walls to deliver phosphorus and amino acids in exchange for photosynthetic sugars.

Lichen

A mutualistic association composed of a fungal partner living in close structural contact with a green alga, a cyanobacterium, or both.

Ecological roles of lichens

Primary colonizers that dissolve rock via secreted acid, monitor atmospheric air quality, fix soil nitrogen, and serve as winter forage for grazers.

Fungal asexual reproduction

The generation of clonal offspring through hyphal fragmentation, pinching off of buds, or mitotic spore production.

Plasmogamy

The event in sexual reproduction where the cell membranes and cytoplasm of two compatible hyphae fuse without the immediate fusion of their nuclei.

Karyogamy

The stage in sexual reproduction where two haploid nuclei within a shared cell fuse to form a single diploid zygote nucleus.

Generalized fungal sexual life cycle

A haploid-dominant life cycle in which the diploid state is confined exclusively to the single-celled zygote before undergoing meiosis.

Law of Superposition

The relative dating principle stating that within an undisturbed sequence of sedimentary strata, younger layers are deposited above older layers.

Principle of Faunal Succession

The relative dating concept stating that distinct fossilized life forms appear, evolve, and disappear through geological layers in a definite, determinable order.

Biostratigraphy

A relative dating technique that uses the known temporal ranges of overlapping index fossils to constrain the age of sedimentary rock strata.

Radiometric dating

An absolute dating method that calculates numerical ages by measuring the ratio of unstable parent isotopes to stable daughter products.

Decay constant

The constant, characteristic mathematical rate at which a specific radioactive parent isotope spontaneously transforms into a daughter isotope.

Half-life

The duration of time required for exactly $50\%$ of an unstable parent isotope in a sample to decay into daughter atoms.

Parent-to-daughter isotope ratio over time

A relationship where parent atoms decrease exponentially by half with every half-life while daughter atoms accumulate at a complementary rate.

Intact fossil

Preserved organic remains that undergo no decomposition due to environmental conditions such as freezing, desiccation, or anoxia.

Compression fossil

A fossil formed when rapid sediment burial and physical pressure leave behind a thin film of concentrated carbon.

Mold fossil

A three-dimensional hollow cavity preserved in rock after an organism's buried body dissolves away.

Cast fossil

A three-dimensional solid replica formed when mineral precipitates or sediments fill in the empty space of an internal mold.

Permineralization

A fossilization mode in which mineral-laden water precipitates inside cellular spaces, preserving partially organic structures.

Petrifaction

A fossilization process in which all original organic molecules are completely replaced by inorganic minerals.

Impression fossil

A two-dimensional negative imprint in sediment containing no remaining organic carbon material.

Trace fossil

Preserved physical evidence of an ancient organism's biological activity, such as trackways, footprints, burrows, or coprolites.

Index fossil

A distinctive, abundant, and geographically widespread fossil species that existed for a brief geological interval, used to date rock strata.

Mass extinction

The rapid global demise of at least $50\%$ to $60\%$ of species across diverse, unrelated lineages within a timeframe under $1\text{ million years}$.

The Big Five mass extinctions

The five major historical extinction pulses: End-Ordovician, Late Devonian, End-Permian, Late Triassic, and End-Cretaceous.

End-Permian mass extinction

The most severe extinction event ($252\,\text{mya}$) that eliminated approximately $90\%$ of Earth's species due to rapid environmental and climate degradation.

End-Cretaceous mass extinction

The global extinction event ($66\,\text{mya}$) triggered by an asteroid impact on the Yucatán Peninsula that wiped out non-avian dinosaurs.

Adaptive radiation

The rapid evolutionary divergence of a single ancestral species into multiple specialized descendant lineages occupying different ecological niches.

Ecological opportunity

A driver of adaptive radiation where the appearance or opening of vacant environmental niches allows rapid diversification.

Morphological innovation

A driver of adaptive radiation where the evolution of a novel structural or physiological trait unlocks previously inaccessible lifestyle niches.

Cambrian explosion

A major evolutionary radiation ($\approx 542\,\text{mya}$) characterized by the rapid diversification of complex animal phyla and body plans.

Fossil changes of the Cambrian explosion

The sudden geological appearance of mineralized shells, exoskeletons, segmented bodies, limbs, sensory eyes, heads, and swimming muscles.

Trigger: Rise in atmospheric oxygen (Cambrian explosion)

Increased oxygen levels enabled efficient aerobic respiration, supporting larger animal bodies and active motility.

Trigger: Rise of algae (Cambrian explosion)

The proliferation of multicellular algae provided a larger and richer nutritional base for expanding animal lineages.

Trigger: Evolution of predation (Cambrian explosion)

The emergence of active hunters created intense selective pressure that accelerated the coevolution of protective armors, shells, and speed.

Trigger: New niche space (Cambrian explosion)

Animals evolved to move off the seafloor into the pelagic water column, opening up previously unexploited ocean habitats.

Trigger: Hox gene diversification (Cambrian explosion)

Duplications and functional changes in master regulatory genes provided the genetic flexibility to pattern increasingly complex animal body plans.

Hox genes

Master regulatory developmental genes that specify positional identity and pattern the structural organization of animal bodies.

Precambrian

The informal supereon spanning from Earth's formation ($4.6\,\text{bya}$) to $541\,\text{mya}$, encompassing the Hadean, Archean, and Proterozoic eons.

Hadean Eon

The earliest geological eon ($4.6\text{--}4.0\,\text{bya}$), characterized by the initial accretion, formation, and surface cooling of the Earth.

Archean Eon

The geological eon ($4.0\text{--}2.5\,\text{bya}$) marked by a reducing atmosphere of methane and ammonia, during which the earliest cellular life appeared.

Proterozoic Eon

The geological eon ($2.5\,\text{bya}\text{--}542\,\text{mya}$) marked by the buildup of atmospheric oxygen from photosynthetic bacteria and the emergence of multicellularity.

Phanerozoic Eon

The current geological eon ($542\,\text{mya}$ to present), also known as the age of visible life, divided into the Paleozoic, Mesozoic, and Cenozoic eras.

Paleozoic Era

The geological era of ancient life ($542\text{--}252\,\text{mya}$) initiated by the Cambrian explosion, featuring the terrestrial radiation of plants and fungi.

Cenozoic Era

The geological era of recent life ($66\,\text{mya}$ to the present) dominated by the adaptive radiation of mammals and flowering plants.