Fungi, Bacteria, and Microbial Genetics: Key Concepts and Structures

Hyphae

Thread-like, microscopic filaments that form the basic structural units of a multicellular fungus.

Septa

Internal cross-walls that divide fungal hyphae into distinct, individual cellular compartments.

Chitin

A tough, nitrogen-containing polysaccharide that forms the rigid structural component of fungal cell walls.

Mycelium

A dense, interwoven mass or network composed of multiple branching hyphae.

Heterotrophs (Absorptive heterotrophs)

Organisms that cannot manufacture their own food; instead, they absorb nutrients directly from their surrounding environment.

Extracellular digestion

The process where fungi secrete powerful digestive enzymes outside their bodies to break down complex organic matter before absorption.

Saprophytes

Fungi that feed on dead, decaying, or non-living organic matter to recycle nutrients back into the ecosystem.

Parasites

Fungi that live on or inside a living host organism, obtaining nutrients at the host's direct expense.

Spore (Sporangia)

A microscopic reproductive cell capable of developing into a new organism; sporangia are the specialized sac-like structures where asexual spores are produced and stored.

Conidiophores

Specialized, upright fungal hyphae that produce asexual spores called conidia in chains or clusters, exposed completely to the air.

Monokaryotic

A fungal cell or hypha that contains only one single nucleus per cell compartment.

Plasmogamy

The fusion of the cytoplasm from two compatible parent mycelia, bringing two distinct nuclei together into a single cell.

Dikaryotic

A unique fungal state where a single cell compartment contains two genetically distinct, compatible nuclei (n + n) that have not yet fused.

Karyogamy

The fusion of two separate haploid nuclei within a dikaryotic cell to form a single, diploid nucleus.

Mitosis

A type of cell division that results in two genetically identical daughter cells, used by fungi for growth and asexual spore production.

Meiosis

A specialized type of cell division that reduces the chromosome number by half, creating four genetically diverse haploid spores.

Gamete

A mature haploid male or female germ cell that is able to unite with another of the opposite sex in sexual reproduction.

Zygote

The temporary, diploid cell that results directly from the successful fusion of two haploid nuclei (karyogamy).

Diploid

A cell or nucleus containing two complete sets of chromosomes, one set inherited from each parent (2n).

Chytridiomycota

An ancient, primitive phylum of fungi primarily found in aquatic or moist soil environments.

Flaggelated spores

Also known as zoospores; these are unique reproductive cells equipped with a whip-like tail (flagellum) that allows them to swim through water.

Zygomycota

A phylum of terrestrial fungi that typically includes fast-growing molds, such as Rhizopus (black bread mold).

Zygosporangia / zygospores

The thick-walled, highly resilient sexual structure (zygosporangium) formed when two compatible hyphae fuse; it houses the dormant sexual zygote (zygospore).

Aseptae (Aseptate)

Hyphae that lack cross-walls (septa), resulting in a continuous, multi-nucleated cytoplasmic tube (coenocytic).

Rhizoids

Root-like, specialized hyphae that anchor the fungus to its substrate, release digestive enzymes, and absorb nutrients.

Gametangia

The specialized structures produced at the tips of mating hyphae during sexual reproduction that contain the gametes.

Ascomycota

The largest phylum of fungi, characterized by producing sexual spores inside microscopic sac-like structures.

Ascus / Asci

The microscopic, sac-like cell structure where karyogamy and meiosis occur, typically yielding eight sexual spores.

Ascocarp

The macroscopic, visible fruiting body or reproductive structure of an ascomycete fungus.

Ascospores

The haploid sexual spores formed inside the mature ascus.

Conidia

Asexual, non-motile spores produced externally at the tips or sides of specialized hyphae.

Basidiomycota

A major phylum of fungi characterized by club-shaped reproductive structures; includes traditional mushrooms and puffballs.

Basidium / Bacilia (Basidia)

The specialized microscopic, club-shaped structure on which sexual spores are produced externally.

Basidiocarp

The large, conspicuous, macroscopic fruiting body or mushroom structure of a club fungus.

Basidiospores

The sexual spores produced externally on the tips of a basidium following meiosis.

Glomeromycota

A phylum of ecologically critical fungi that form obligate, symbiotic relationships exclusively with the roots of land plants.

Symbiosis

A close, prolonged ecological interaction between two or more different biological species.

Mycorrhizae

A mutualistic symbiotic association between a fungus and the root system of a plant, where the fungus supplies soil minerals and the plant provides sugars.

Arbuscular mycorrhizae

A specific type of endomycorrhizae where the fungal hyphae physically penetrate the plant root cell walls to form highly branched, tree-like structures (arbuscules) for efficient nutrient exchange.

Lychen (Lichen)

A complex, composite organism formed by a stable, mutualistic symbiotic relationship between a fungus and a photosynthetic partner.

Symbiotic ascomycetes (algae or cyanobacteria)

The ecological pairing that creates a lichen; the ascomycete fungus forms the structural body, while green algae/cyanobacteria produce food via photosynthesis.

Crutose (Crustose)

A specific morphotype of lichen that grows flat, tightly appressed, and scale-like, forming a hard crust directly over rocks or tree bark.

Gene

A unit of heredity which is transferred from a parent to offspring and is held to determine some characteristic of the offspring.

Allele

One of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.

Dominant Allele

An allele that expresses its phenotypic effect even when heterozygous with a recessive allele; masks the other allele.

Recessive Allele

An allele that produces its characteristic phenotype only when its paired allele is identical (homozygous).

Homozygous

Having two identical alleles of a particular gene or genes.

Heterozygous

Having two different alleles of a particular gene or genes.

Gene locus (loci)

The specific physical location or position of a gene or significant sequence on a chromosome.

Allelic frequency

The proportion of a specific allele among all allele copies at a given locus within a population.

Genotypic frequency

The proportion of a particular genotype among all individuals within a population.

Trends under selection pressures

The predictable shift in allele frequencies favoring traits that enhance survival and reproduction in a specific environment.

Algal evolution & identification

The evolutionary history of photosynthetic eukaryotes; identified under microscopes by pigment color, cellular organization, and flagella.

Hardy-Weinberg Assumption: No natural selection

All genotypes have equal survival and reproductive success; no phenotype is favored over another.

Hardy-Weinberg Assumption: Random mating

Sexual selection does not occur; individuals choose mates completely by chance with no preference for specific genotypes.

Hardy-Weinberg Assumption: No mutations

No new alleles are introduced into the population's gene pool through spontaneous genetic updates.

Hardy-Weinberg Assumption: No gene flow

No migration occurs; individuals do not enter (immigrate) or leave (emigrate) the population.

Hardy-Weinberg Assumption: No genetic drift

The population size is infinitely large, minimizing chance fluctuations in allele frequencies.

Hypothesis

A proposed, testable, and falsifiable explanation for a narrow set of phenomena or observations.

Null Hypothesis

A statement asserting that there is no significant relationship, effect, or difference between variables being tested.

Alternative Hypothesis

The statement that proposes a significant relationship, effect, or difference exists between variables being tested.

Theory

A well-substantiated, broad explanation of an aspect of the natural world, supported by a vast body of evidence.

Observation

The act of noting and describing events or processes in a careful, orderly way using senses or tools.

Question

A clear, focused inquiry derived from observations that guides scientific investigation.

Prior knowledge

Pre-existing scientific understanding and literature used to contextualize observations and formulate hypotheses.

Experimental Design

A detailed plan outlining variables, controls, sample sizes, and methods to safely and reliably test a hypothesis.

Data Collection

The systematic gathering of qualitative or quantitative measurements and observations during an experiment.

Conclusion

An evaluation of the experimental data that states whether the results support or reject the hypothesis.

Peer Review

The evaluation of scientific work by independent experts in the same field to ensure quality, validity, and accuracy.

Unicellular

An organism consisting of only a single cell that performs all vital life functions.

No membrane-bound organelles

The structural hallmark of prokaryotes, lacking specialized internal structures like mitochondria or a true nucleus.

Plasma membrane

A microscopic membrane of lipids and proteins which forms the external boundary of the cytoplasm and regulates passage of molecules.

Cell wall

A rigid structural layer surrounding the plasma membrane, providing shape, protection, and structural support.

Pili

Hair-like appendages on the surface of many bacteria used for attachment to surfaces or bacterial conjugation.

Flagella

Whip-like cellular appendages used primarily for locomotion and movement through fluid environments.

Bacillus

A bacterium with a cylindrical or rod-shaped physical morphology.

Coccus

A bacterium with a spherical, ovoid, or round physical morphology.

Spirillum

A bacterium with a rigid, spiral, or helical physical morphology.

Colony shapes

The distinct macroscopic appearance (margin, elevation, form) of a bacterial cluster grown on a solid agar medium.

Binary fission

A form of asexual reproduction in single-celled organisms where one cell divides into two identical daughter cells.

Heterotrophic (Bacteria)

Bacteria that must consume organic matter from external sources for energy and nutrients.

Autotrophic (Bacteria)

Bacteria capable of synthesizing their own organic nutrients from inorganic substances using light or chemical energy.

Decomposers

Organisms that break down dead or decaying organic materials, recycling essential nutrients into the ecosystem.

Pathogenic

Organisms (such as specific bacteria or fungi) capable of causing disease in a host.

Commensal

A symbiotic relationship where one organism benefits while the other is neither helped nor harmed.

Mutualistic / Symbiotic

An interaction where both organisms benefit mutually, or live in close physical association.

Nitrogen fixation

The chemical process of converting atmospheric nitrogen (N2) into biological molecules like ammonia (NH3) usable by plants.

Gram Staining: Antibiotic sensitivity

A diagnostic technique correlating cell wall structure with drug vulnerability; Gram-positive and Gram-negative bacteria react differently to antibiotics.

Gram-positive (Staining)

Bacteria that retain the primary crystal violet stain, appearing purple under a microscope due to a thick peptidoglycan layer.

Gram-negative (Staining)

Bacteria that lose crystal violet and take up the pink/red counterstain (safranin) due to a thin peptidoglycan layer and outer membrane.

Peptidoglycan cell wall

A polymer of sugars and amino acids forming a mesh-like layer outside the plasma membrane; thick in Gram+, thin in Gram-.

Bacterial Outer membrane

A lipopolysaccharide layer unique to Gram-negative bacteria that acts as an additional protective barrier against toxins and drugs.

Gram Staining Procedure steps

A four-step method involving: 1) Crystal violet (primary), 2) Iodine (mordant), 3) Alcohol (decolorizer), and 4) Safranin (counterstain).

Cyanobacteria

A phylum of photosynthetic, oxygen-producing bacteria formerly known as blue-green algae.

Chlorophyll (Cyanobacteria)

The primary photosynthetic pigment utilized by cyanobacteria to capture light energy.

Mucilaginous Sheath

A protective, gelatinous outer coating surrounding cyanobacterial colonies or filaments that retains moisture.

Archaea (Extremophiles)

A domain of unicellular prokaryotes distinct from bacteria, often thriving in extreme environments like hot springs or hypersaline pools.

Bacteria / Bacterium

A vast domain of microscopic, single-celled prokaryotic organisms lacking a nucleus.