MODERN BOTANY - P. RAVEN - 1990

GLOSSARY OF TERMS

A

Å — see angstrom.

A- (Greek *a-* — not, without) — a prefix denoting the negation of the meaning of the subsequent word ROOT; before vowels, it is replaced by an-.

ABSORPTION SPECTRUM — THE SPECTRUM OF light waves absorbed by a specific pigment.

Abscisic acid (Latin *abscissus* — to cut off) — a plant hormone that induces dormancy in buds and maintains it in seeds. It is involved in root geotropism, stomatal closure, and A number of other processes.

AUTO- (Greek *autos* — self) — a combining form meaning "self" or "own", "properly one's own".

AUTOTROPH (Greek *autos* — self + *trophos* — feeder) — an Organism capable of synthesizing the nutrients it requires from inorganic substances in the environment. Cf. heterotroph.

Agar — a gelatinous substance obtained from certain species of red Algae. Used as a solidifying agent in the preparation of culture media for growing microorganisms.

AD- (Latin *ad* — to) — a prefix meaning "toward", "to".

ADAPTATION (Latin *adaptare* — to fit) — a structural, physiological, or behavioral feature of an organism that AIDS in its survival within its environment.

ADAPTIVE RADIATION — the evolutionary diversification of a single ancestral organism into several divergent forms, each adapted to specific ecological niches.

ADENINE — a purine base that is a component of DNA, RNA, and NUCLEOTIDES such as ADP and ATP.

ADENOSINE TRIPHOSPHATE (ATP) — a nucleotide consisting of adenine, the sugar ribose, and three phosphate groups. The primary source of chemical energy in cellular METABOLISM. Upon Hydrolysis, ATP loses one phosphate group and is converted into adenosine diphosphate (ADP), releasing energy in a usable form.

ADHESION (Latin *adhaerere* — to stick to) — the binding together of dissimilar objects or substances.

ADSORPTION (Latin *ad* + *sorbere* — to suck in) — the adhesion of liquid, gaseous, or dissolved substances to a solid surface, resulting in an increased concentration of these substances.

ADP — adenosine diphosphate, see adenosine triphosphate.

NITROGENOUS BASE — a nitrogen-containing molecule with basic properties, meaning it is capable of accepting a hydrogen atom. Nitrogenous bases include Purines and Pyrimidines, which are constituents of Nucleic Acids.

Nitrogen Fixation — the incorporation of atmospheric nitrogen into chemical compounds. Carried out by specific free-living and symbiotic Bacteria.

NITROGEN-FIXING BACTERIA — soil bacteria that convert atmospheric nitrogen into nitrogen compounds.

AKINETE — a vegetative cyanobacterial Cell that transforms into a thick-walled spore resistant to unfavorable environmental conditions.

ACCLIMATION — The process of physical and physiological adjustments that prepare a plant for winter.

Active Transport — the energy-dependent transport of a dissolved substance across a cell membrane toward an area of higher concentration (against a concentration gradient).

ACTINOMORPHIC (FLOWER) (Greek *aktis* — ray of light + *morphe* — form) — a flower that can be divided into two symmetrical halves by more than one longitudinal plane. Synonym: radially symmetrical flower. Cf. zygomorphic (flower).

ALEURONE (Greek aleuron, flour) — a protein material that typically occurs as small granules within the peripheral cell layer of the endosperm in wheat and other cereals.

Alkaloids — nitrogen-containing cyclic compounds produced by plants that exert a physiological effect on vertebrates. Many alkaloids have a bitter taste, and some are toxic. Examples include nicotine, caffeine, and strychnine.

ALLELOPATHY (Greek allelon, of one another + pathos, suffering) — the suppression of one plant species by chemical substances released by another plant species.

ALLELE (Greek allelon) — one of two or more alternative states of a Gene.

ALLOSTERIC INTERACTION (Greek allos, other + steros, form) — A change in the spatial conformation of a protein molecule resulting from the binding of a non-substrate molecule to it. As a rule, this confers new properties upon the protein.

ALBUMINOUS Cells — ray and axial parenchymal cells in the phloem of gymnosperms that are structurally and functionally closely associated with sieve cells.

AMEBOID (Greek amoibe, change) — moving or feeding by means of pseudopodia (temporary cytoplasmic extensions of The Cell).

AMYLASE — an enzyme that breaks down starch into smaller fragments.

AMYLOPLAST — a leucoplast (colorless plastid) that synthesizes and stores starch grains.

Amino Acids (Greek Ammon, the Egyptian Sun god, near whose temple ammonium salts were first obtained from camel dung) — nitrogen-containing organic acids and the monomers from which protein molecules are constructed.

AMMONIFICATION — The breakdown of Amino Acids and other nitrogen-containing Organic compounds, resulting in The formation of ammonia (NH₃) and ammonium ions (NH₄₊).

AMPHI- (Greek amphi, on both sides) — a prefix meaning "on both sides," "both," or "of both kinds."

AN- (Greek an-, not, without) — a prefix equivalent to "a-", meaning "not" or "without-", used before vowels.

ANABOLISM (Greek ana-, up, upward + -bolism, as in metabolism) — the constructive phase of metabolism; the collective Chemical Reactions of Biosynthesis.

TEST CROSS — crossing a phenotypically dominant organism with a homozygous recessive one; used to determine whether the dominant individual is homozygous or heterozygous.

ANALOGOUS (Greek analogos, proportionate, similar) — similar in function but different in evolutionary origin; for example, the phyllodes of Australian acacias and oak leaves.

ANATOMY — the science of the Internal Structure of organisms. Morphology studies external structure.

ANAPHASE (Greek ana, away + phasis, phase) — the stage of mitosis in which the chromatids of each chromosome separate and move toward opposite poles; also, the stage of chromatid or homologous chromosome Separation during Meiosis.

ANAEROBIC (Greek an-, without + aer, air + bios, life) — capable of occurring or living without oxygen; obligate anaerobes are killed in the presence of oxygen.

ANGSTROM (named after A. Ångström, Swedish physicist, 1814–1874) — a unit of length equal to 10^-10 m, abbreviated as Å.

ANDRO- (Greek andros, male) — a combining form meaning "male."

ANDROECIUM (Greek andros, male + oikos, house) — in flowering plants, the collective term for the stamens; in leafy liverworts, the tubular envelope surrounding the antheridia.

ANISOGAMY (Greek aniso, unequal + gamos, marriage) — a sexual process involving the fusion of dissimilar motile Gametes.

ANION (Greek anienai, to ascend) — a negatively charged ion.

ANNULUS (Latin anus, ring) — in ferns, a row of specialized cells in the sporangium; in agarics, the remnant of the inner partial veil that forms a ring around the stipe.

ANTHERIDIUM — a unicellular or multicellular organ in which sperm cells are produced.

ANTHERIDIOPHORE (from Greek anthos, flower + phoros, bearing) — a stalk bearing antheridia in certain liverworts.

ANTIBIOTIC (from Greek anti, against + biotikos, pertaining to life) — a natural organic substance that inhibits or suppresses the growth of organisms. Typically, this term refers to substances synthesized by microorganisms that inhibit the growth of other microorganisms.

ANTICLINAL — perpendicular to the surface.

ANTIPODALS — three (or sometimes more) Cells of the embryo sac located at the end opposite to the micropyle.

ANTHOCYANIN (from Greek anthos, flower + kyanos, dark blue) — a Water-soluble blue or red pigment found in cell sap.

APICAL MERISTEM — a meristem located at the tip of a root or the apex of a SHOOT in a vascular plant.

APICAL DOMINANCE — the suppression of lateral bud growth by the apical bud.

APOMIXIS (from Greek apo, away, without + mixis, mixing) — reproduction occurring without meiosis or syngamy; vegetative propagation.

APOPLAST (from Greek apo, away, without + plastos, formed) — the continuous system formed by the cell walls of a plant or plant organ. The movement of substances through cell walls is known as apoplastic transport.

APOTHECIUM (from Greek apotheke, storehouse) — a cup-shaped or saucer-shaped open ascocarp.

ARILLUS (from Latin arillus, grape, seed) — an accessory seed covering, often formed by the outgrowth of the ovule base. It is typically brightly colored, which helps attract animals that consume it and thereby disperse the seeds of the parent plants.

ARTIFACT (from Latin ars, art + facere, to make) — an object or phenomenon that does not exist in nature, but arises As a result of human intervention.

ARCH-, ARCHAEO- (from Greek arche, archos, beginning, principal) — a combining form denoting "first", "principal", or "earliest".

ARCHEGONIUM — a multicellular organ in which a single egg cell is produced. Found in bryophytes and certain vascular plants.

ARCHEGONIOPHORE (from Greek archegonos, progenitor + phoros, bearing) — a stalk bearing archegonia in certain liverworts.

ASEPTATE (from Greek a-, without + Latin septum, partition) — not divided by septa, lacking transverse cross-walls.

ASCUS — a specialized cell characteristic of ascomycetes, in which two haploid nuclei fuse to form a zygote. The zygote immediately undergoes meiotic division. A mature ascus contains ascospores.

ASCOGENOUS HYPHAE (from Greek askos, sac + genous, producing) — hyphae containing paired haploid male and female nuclei; they develop from the ascogonium and give rise to asci.

ASCOGONIUM — an oogonium, or female gametangium, in ascomycetes.

ASCOCARP (from Greek askos, sac + karpos, fruit) — a multicellular structure in ascomycetes that bears specialized cells—asci—in which nuclear fusion and meiosis take place. An ascocarp may be open or closed.

ASCOSPORE — a spore formed inside an ascus (in ascomycetes).

ATOM (from Greek atomos, indivisible) — the smallest particle of a chemical element that retains its fundamental properties.

ATOMIC MASS — the mass of an element's atom expressed in units equal to 1/12 of the mass of a ¹²C atom.

ATOMIC NUMBER — the number of protons in The Nucleus of an atom.

ATP — see adenosine triphosphate.

ATP SYNTHASE — an enzyme complex that synthesizes ATP from ADP and phosphate during Oxidative Phosphorylation on The inner mitochondrial membrane.

AUXIN (Greek auxein — to increase) — a plant growth-regulating substance; among other Functions, it controls cell elongation.

OUTCROSSING — mating between organisms that are not closely related. In plants, this corresponds to cross-pollination.

AEROBIC Respiration — see respiration.

AEROBIC (Greek aer — air + bios — life) — requiring free oxygen.

B

BASAL BODY — a self-replicating, cylindrical organelle located at the base of a cilium or flagellum. It is structurally identical to the centriole, which participates in Mitosis and Meiosis in most animals and protists.

BASIDIOCARP (Latin basidium — a small pedestal + carpus — fruit) — a multicellular structure characteristic of Basidiomycetes, within which basidiospores are formed.

BASIDIOSPORE — a spore of basidiomycetes formed inside a basidium following nuclear fusion and meiosis, and subsequently pinched off from its outer surface.

BASIDIUM — a specialized reproductive cell of basidiomycetes, often club-shaped, in which nuclear fusion and meiotic division take place.

BACTERIOPHAGE (Greek bakterion — a small staff + phagein — to eat) — a virus that parasitizes bacterial cells.

BACTERIUM — a prokaryotic organism.

BACILLUS (Latin baculum — a rod) — a rod-shaped bacterium.

BACKCROSS — the mating of a hybrid with one of its parents or with an organism of equivalent genotype. A cross performed to determine the genetic constitution of an individual by mating it with an individual homozygous for the recessive genes under study.

PROTEIN — a complex organic compound consisting of numerous (up to 100 or more) amino acid residues linked by peptide bonds.

ASEXUAL REPRODUCTION — any form of reproduction that does not involve the fusion of gametes, such as fission or budding.

BI- (Latin bis — double, two) — a prefix denoting "two" or "twice"/"double".

BIVALENT (Latin bis — twice + valere — to be strong) — a pair of synapsed homologous Chromosomes.

BILATERALLY SYMMETRICAL — see zygomorphic flower.

BIOLOGICAL CLOCK (Greek bios — life + logos — discourse) — an internal mechanism that regulates an organism's innate biological rhythms.

BIOME — the largest biological unit, representing a very extensive assemblage of terrestrial communities under specific soil and climatic conditions.

BIOMASS — the total dry mass of all organisms in a given population, sample, or area.

BIOSPHERE — the zone of the atmosphere, land, and water inhabited by living organisms.

BIOTECHNOLOGY — the Practical Application of advances in endocrinology and DNA biochemistry to manage plant heredity.

BIOTIC — relating to living organisms.

PLAQUE — a clearing in a cell monolayer resulting from the lysis of virus-infected cells.

LEGUME — a dry fruit developing from a single carpel and dehiscing along two sutures.

LATERAL ROOT — a root originating from another, older root. If the latter is a primary root, the lateral root is referred to as secondary.

BRACT — a modified, usually reduced leaf-like structure (typically a floral bract or an inflorescence-subtending leaf).

BRYOPHYTES — representatives of non-vascular plants: mosses, liverworts, and hornworts.

Fermentation — the extraction of energy from organic compounds without the involvement of oxygen.

VENTER — the expanded basal portion of an archegonium containing the egg cell.

V

FROND — the leaf of a fern or palm.

VACUOLE (Lat. vacus — empty) — a membrane-bound space in the Cytoplasm filled with an aqueous solution, the cell sap; part of the cell's lysosomal compartment.

Vegetative Reproduction — (1) propagation of seed plants without the aid of seeds; apomixis; (2) in other groups of organisms — reproduction via vegetative spores or through body division. In the absence of Mutations, each daughter cell or organism produced by vegetative reproduction is genetically identical to the parent.

VEGETATIVE — relating to asexual reproduction or non-reproductive parts of a plant.

VECTOR (Lat. vehere — to carry) — a virus or plasmid into which a gene is inserted for transfer into a cell.

VELAMEN (Lat. velumen — fleece) — a multiseriate epidermis covering the aerial roots of certain orchids and arums. It is occasionally also found on subterranean roots.

COROLLA — the whorl of petals of a flower.

FUSIFORM INITIAL — a vertically elongated cambial cell that gives rise to the axial system cells in the secondary xylem and phloem.

SUPERIOR Ovary — an ovary attached to the receptacle above the attachment point of other floral whorls, not fused to the calyx.

SPECIES — the fundamental taxonomic unit uniting similar organisms capable of interbreeding with one another. Species names are conventionally italicized in text.

LEAF SHEATH — the base of a leaf that wraps around the stem, characteristic of grasses, for example.

PERMANENT WILTING PERCENTAGE — the percentage of water remaining in the soil when plants permanently wilt and fail to recover even when placed in a humid chamber.

EXOCARP — see exocarp.

INNER BARK — the living tissue of the bark in mature trees; the portion of the bark located inside the innermost layers of the periderm.

ENDOCARP — see endocarp.

WATER POTENTIAL — the algebraic sum of solute potential and pressure potential; a measure of the potential energy of water.

WATER VESSEL — an enlarged epidermal cell that stores water; a type of trichome.

Hydrogen bond — a weak bond between a hydrogen atom covalently bonded to an oxygen or nitrogen atom and another atom of either of the latter two elements.

HYDROGEN ION EXPONENT (pH) — a measure of the relative concentration of protons in a solution. The pH value ranges from 0 to 14. The lower the pH, the higher the proton concentration and the acidity of the solution. A neutral solution has a pH of 7, an acidic solution has a pH of less than 7, and an alkaline solution has a pH of greater than 7.

ALGAE — a traditional term for several unrelated groups of photosynthetic eukaryotes that lack multicellular reproductive Organs (with the exception of Charophytes). "Blue-green algae," or cyanobacteria, are a group of photosynthetic bacteria.

BACKCROSS — see backcross.

GRAIN — the directional arrangement of elements in wood.

FIBER — an elongated, tapering, typically thick-walled sclerenchyma cell of vascular plants. The Cell wall of a fiber may be lignified, and its protoplast may die after maturation.

VOLVA (Lat. volva — wrapper) — a cup-like structure at the Base of the stalk in certain mushrooms.

REDUCTION (originally the reduction of a metal from its oxide) — the gain of an electron by an atom. Reduction occurs simultaneously with oxidation: one atom loses an electron while another captures it.

ACCESSORY PIGMENT — a pigment that captures light energy and transfers it to chlorophyll a.

SECONDARY WALL — the inner layer of the cell wall that forms in certain cells after their elongation is complete. The secondary wall has a highly ordered microfibrillar structure.

SECONDARY PLANT BODY — the part of a plant formed by the cambium and phellogen. It consists of secondary xylem and phloem, as well as periderm.

SECONDARY Tissues — tissues formed by the cambium and phellogen.

SECONDARY ROOT — see lateral root.

Secondary Growth — plant growth resulting from secondary, or lateral, Meristems, i.e., the cambium and phellogen. As a result of secondary growth, a plant increases in girth, whereas primary growth increases its length.

LEACHING — the downward movement of inorganic ions through the soil profile by percolating water.

G

HABITUS (Lat. habitus — condition, character) — the characteristic form and external appearance of an organism.

GAMETE (Gr. gamete — wife) — a haploid reproductive cell. Gametes fuse in pairs to form a diploid zygote.

GAMETANGIUM (Gr. gamein — to marry + Lat. tangere — to Touch) — a cell or organ in which gametes are formed.

GAMETOPHYTE — the haploid (n) gamete-producing phase in organisms that exhibit ALTERNATION OF GENERATIONS.

GAMETOPHORE (Gr. gamein + phoros — bearing) — in bryophytes, a specialized stalk bearing gametangia.

HAPLOID (Gr. haploos — single) — an organism having a single set of chromosomes (n) as opposed to a diploid (2 n) organism.

HAUSTORIUM (Lat. haustus from haurire — to drink) — a specialized branch of a fungal hypha that penetrates into host cells and functions as an absorbing organ.

HELIOTROPISM (Gr. helios — sun) — the ability of leaves and flowers of many plants to move during the day so as to remain either perpendicular or parallel to incident sunlight.

GEL — a solid or semi-solid mixture of substances.

GEMMA (Lat. gemma — bud) — a small cluster of vegetative tissue or a growth on a thallus (for example, in liverworts or certain Fungi) from which an entirely new plant can develop.

HEMICELLULOSE — a polysaccharide found mainly in cell walls; structurally similar to Cellulose, but more soluble and less structurally ordered.

GENE — the basic unit of heredity. A nucleotide sequence of DNA that encodes the Introduction/19.html">Primary Structure of a protein, tRNA, or rRNA, or regulates the Transcription of such sequences.

GENERATIVE CELL — (1) in many conifers, a cell of the male gametophyte that divides to form a sterile cell and a spermatogenous cell; (2) in angiosperms, a cell of the male gametophyte that divides to produce two sperm cells.

GENETIC RECOMBINATION — the appearance in offspring of gene combinations different from those of the parents.

Genetic Code — The system of nucleotide triplets (codons) in DNA and RNA that determines the Amino Acid Sequence of a protein. Each codon, with the exception of three stop signals, corresponds to one of the 20 amino acids.

GENE FREQUENCY — the relative proportion of a particular allele in a population.

GENOTYPE — the hidden or expressed genetic makeup of an organism; the totality of all its genes.

GEOTROPISM — the growth movement of a plant stem or root in response to the force of gravity.

HERBARIUM — a collection of dried and pressed plant specimens.

HERMAPHRODITE (from Greek Hermes and Aphrodite) — an organism possessing both female and Male reproductive organs.

HETERO- (Greek heteros — other) — a combining form meaning "other" or "different".

HETEROGAMY (Greek heteros + gamos — union or reproduction) — a sexual process involving the fusion of gametes that differ in appearance or behavior.

HETEROZYGOTE — an individual (or cell) having two different alleles at the same locus on homologous chromosomes.

HETEROSIS (Greek heterosis — change) — hybrid vigor; the superiority of a hybrid over both parents in terms of one or more Quantitative Traits.

HETEROKARYON (Greek heteros + karyon — kernel, nucleus) — a fungal mycelium containing two or more genetically distinct types of nuclei.

HETEROMORPHISM (Greek heteros + morphe — form) — morphological differences between the diploid and haploid generations.

HETEROSPORY — The production of Two Types of spores: microspores and megaspores.

HETEROSTALLISM (Greek heteros + thallus — sprout) — a condition of self-sterility in haploid organisms. Reproduction in heterothallic species requires the fusion of gametes from two compatible mating types or individuals.

HETEROTROPH (Greek heteros + trophos — feeder) — an organism that cannot synthesize organic compounds from inorganic substances and therefore must consume organic matter produced by other plants and animals. Cf. autotroph.

HETEROCYST (Greek heteros + kystis — bladder, sac) — a large, transparent, thick-walled nitrogen-fixing cell found in the filaments of certain cyanobacteria.

HYALOPLASM — see cytoplasmic ground substance.

Gibberellins (from Gibberella, a genus of fungi) — a group of Plant HORMONES best known for stimulating stem elongation.

HYBRID — the offspring of two parents that differ by at least one hereditary trait; the offspring of two different varieties or species.

Hybridization — the production of offspring from dissimilar parents.

HYBRID VIGOR — see heterosis.

HYDROXYL GROUP — an OH- ion formed, in particular, during the dissociation of a water molecule.

HYDROLYSIS (Greek hydro — water + lysis — loosening) — the Cleavage of a molecule through The addition of water (H⁺ and OH^- ions).

HYDROPHYTE (Greek hydro + phyton — plant) — a plant requiring high humidity for development or growing fully or partially submerged in water.

HILUM (Latin hilum — a trifle) — (1) the scar left on a seed after its detachment from the funiculus; (2) the region in a starch grain around which starch is deposited in more or less concentric layers.

HYMENIAL LAMELLA — a gill on the underside of the cap in basidiomycetes.

HYMENIUM (Greek hymen — membrane) — the layer of asci in an ascocarp or basidia in a basidiocarp, together with the surrounding sterile hyphae.

GYNOECIUM (Greek gyne — woman + oikos — house) — the collective FEMALE REPRODUCTIVE ORGANS (carpels) in a flower.

HYPER- (Greek hyper — above, over) — a prefix meaning "over", "more", or "above".

HYPERTONIC (SOLUTION) — a solution whose concentration is high enough to draw water from another solution separated by a semipermeable membrane.

HYPO- (Greek hypo — below, less) — a prefix meaning "under" or "less".

HYPOGYNY (Greek hypo + gyne — woman) — a floral arrangement in which the sepals, petals, and stamens are attached to the receptacle below the ovary. The opposite of epigyny.

HYPODERMIS (Greek hypo + derma — Skin) — one or more layers of cells situated beneath the epidermis and distinct from the deeper cortical or mesophyll cells.

HYPOCOTYL — the part of a plant embryo or seedling located between the cotyledons and the radicle.

HYPOCOTYL-ROOT AXIS — the embryonic axis located below the cotyledon(s), comprising the hypocotyl and the apical meristem of the root or radicle.

HYPOTHESIS (Greek hypo + tithenai — to put) — a tentative working explanation or supposition of a general cause-and-effect principle, based on available facts. It requires experimental testing and must be discarded if unsupported by the results.

HYPOTONIC (SOLUTION) — a solution of sufficiently low concentration that releases water to another solution separated by a semipermeable membrane.

Histones — a group of five basic Proteins that form part of the chromosomes in all Eukaryotic cells.

HYPHA (Greek hyphe — web) — a single tubular filament of fungi, oomycetes, and chytrids. A mass of hyphae constitutes the mycelium.

EYESPOT — a small pigmented structure in unicellular flagellates that is sensitive to light.

Glycogen (Greek glykys — sweet + gen — produced) — a carbohydrate similar to starch; a reserve nutrient in bacteria, fungi, and most other organisms, with the exception of plants.

Glycolysis — the anaerobic breakdown of glucose yielding two molecules of pyruvic acid and two molecules of ATP.

Glyoxylate cycle — a variant of the Krebs cycle found in bacteria and certain plants. In The glyoxylate cycle, acetate is converted into succinate and ultimately into new CARBOHYDRATES.

GLYOXYSOME — a microbody containing Enzymes necessary for The conversion of fats into carbohydrates. Glyoxysomes play a crucial role in seed germination.

GLYCEROL — a three-carbon molecule with three hydroxyl groups. By combining with Fatty acids, it forms fats or oils.

GLUCOSE — a six-carbon sugar C6Н₁₂О6; the most common monosaccharide in most organisms.

CAVITY — a chamber within a sporangium or ovary (where ovules are located).

ANNUAL RING — a layer of wood growth produced in a single year.

GYMNOSPERMS — seed plants in which the seeds are not enclosed within an ovary. Their most common group is the conifers.

GOLGI BODY — see dictyosome.

HOMEO-, HOMO- (from Greek homos — the same, similar) — a combining form meaning "the same" or "similar".

Homeostasis (from Greek homos + stasis — standing) — the maintenance of a relatively constant internal environment within an organism, or a stable equilibrium within a population or ecosystem. It is usually regulated by feedback mechanisms.

HOMOZYGOUS — having identical alleles at corresponding loci on homologous chromosomes.

HOMOKARYON — a fungal mycelium containing nuclei of identical genetic structure.

HOMOLOGOUS CHROMOSOMES — chromosomes that pair up During the first stage of meiosis. Homologous chromosomes in a pair originate from different parents.

Homology (from Greek homología — agreement) — shared evolutionary origin (phylogeny), despite potential differences in current Structure and function.

HOMOSPORY — the production of only one type of spores.

HOMOTHALLISM (from Greek homos + thallus — shoot) — the ability of organisms of a given species to undergo self-Fertilization.

HORMOGONIUM — a detached segment of a cyanobacterial filament that grows into a new filament.

HORMONE (from Greek hormaein — to excite) — a chemical substance synthesized, typically in small amounts, in one part of an organism and transported to another part, where it exerts a specific physiological effect.

GRANA — structures within the chloroplast, visible under a Light Microscope as green granules and under an Electron microscope as a stack of thylakoids. Grana contain chlorophyll and carotenoids and are the site of the light-dependent reactions of Photosynthesis.

GUANINE (from Spanish < kerya huanu — dung) — a purine base that is a constituent of DNA and RNA. The name originates from the fact that it is found in large quantities as white crystals in guano and other animal excrement.

SPONGY PARENCHYMA — leaf tissue composed of chloroplast-containing cells separated by large intercellular air spaces.

HUMUS — the decomposing organic matter of soil.

GUTTATION (from Latin gutta — drop) — the exudation of liquid water from leaves driven by root pressure.

GERL — the Golgi-Endoplasmic reticulum-lysosome complex, involved in the formation of vacuoles and Lysosomes in certain cells.

D

WALL PRESSURE — the pressure exerted by the cell wall, equal in magnitude and opposite in direction to the turgor pressure of the protoplast.

DOUBLE FERTILIZATION — the fusion of an egg cell and a sperm cell to form a zygote (2n), accompanied by the simultaneous fusion of another male gamete with the polar nuclei to form the primary endosperm nucleus (3n); a defining feature of all angiosperms.

DICOTS (DICOTYLEDONS) — one of the two classes of angiosperms. Dicots are characterized by the presence of two cotyledons, reticulate leaf venation, and typically four- or five-parted flowers.

DIOECIOUS — unisexual plants in which male and female gametes develop on separate individuals.

BIENNIAL — a plant that requires two growing seasons to complete its life

cycle, with flowering and fruiting taking place In the second year.

BISEXUAL FLOWER — a flower having at least one functional stamen and one functional carpel.

DE- (Lat. de — away, off) — a prefix denoting the removal of something; for example, dehydration means the removal of water.

DEOXYRIBOSE (Lat. deoxy — loss of oxygen + ribose — a type of sugar) — a five-carbon sugar containing one less oxygen atom than ribose. It is a fundamental component of deoxyribonucleic acid.

DEOXYRIBONUCLEIC ACID (DNA) — the carrier of Genetic information within the cell. It consists of chains containing a phosphate group, the sugar deoxyribose, purines, and pyrimidines. It is capable of self-Replication and directing RNA Synthesis.

DEUTERIUM — heavy hydrogen. A hydrogen atom whose nucleus contains a proton and a neutron (in most hydrogen atoms, the nucleus consists solely of a proton).

DENITRIFICATION — the conversion of nitrates into gaseous nitrogen; carried out by several genera of free-living soil bacteria.

TREE — a perennial plant with a woody stem and root, typically possessing a single main stem known as a trunk.

DESMOTUBULE (Gr. desmos — to bind, connect) — a tubule passing through the plasmodesma channel that connects The endoplasmic reticulum of two adjacent cells.

DECOMPOSERS — organisms in an ecosystem that break down organic matter into smaller molecules that are then recycled back into the biosphere. Decomposers include bacteria, fungi, and heterotrophic protists.

DETERMINATE GROWTH — growth of limited duration, characteristic of the floral meristem and leaves.

DICARYON (Gr. di — two + karyon — nut, nucleus) — a fungal mycelium containing paired nuclei, typically originating in pairs from different organisms.

DICARYOTIC — in fungi, having pairs of nuclei within the cells or compartments of the mycelium.

WILD TYPE — the phenotype or genotype characteristic of the majority of individuals of a given species in natural conditions.

DICTYOSOME — in eukaryotes, a complex of flat, disk-shaped cisternae within cells, often with tubular ramifications at the edges. Dictyosomes are involved in secretory activity and serve as centers for the accumulation and packaging of secretions. Also referred to as Golgi bodies. The term "Golgi apparatus" is used to denote the entire set of dictyosomes within a given cell.

DIMORPHISM (Gr. di — two + morphe — form) — the occurrence of two distinct forms of the same organ, such as sterile and fertile fronds in ferns, or sterile and fertile shoots in horsetails.

DIPLOID — possessing a double set of chromosomes (2n), characteristic of the sporophyte generation.

DISACCHARIDE — a carbohydrate consisting of two monosaccharide molecules joined by a covalent bond. A common example is sucrose.

DISTAL — situated away from the point of reference, typically located near the main body axis. The opposite of proximal.

DIFFERENTIATION — a developmental process during which a relatively unspecialized cell becomes specialized. The adaptation of Cells and Tissues during ontogeny to perform specific functions.

DIFFUSION (Lat. diffundere — to pour out) — the net movement of suspended or dissolved particles from a region of higher concentration to a region of lower concentration driven by the random thermal motion of individual particles. As a result of diffusion, particles become evenly distributed throughout the medium.

DICHOTOMY — the division of a single axis into two branches.

LONG-DAY PLANTS — plants that require a photoperiod exceeding a certain critical value to flower. They typically bloom in spring or summer.

DNA — see deoxyribonucleic acid.

DORMACY (SEED) — metabolic changes that must occur in certain seeds during their dormant period to enable germination.

DOMINANT ALLELE — an allele related to another allele at the same locus such that an individual homozygous for the first allele is phenotypically indistinguishable from a heterozygote, while the other allele is considered recessive.

WOOD — secondary xylem.

DRUSE — a complex, more or less spherical crystal of calcium oxalate with numerous constituent crystals protruding from its surface.

RESPIRATION — the intracellular process of oxidizing molecules (primarily Pyruvate in The Citric Acid Cycle) to release energy. The complete breakdown of sugars and other organic molecules into carbon dioxide and water is referred to as aerobic respiration, although the Initial Stages of this process are anaerobic.

E

NATURAL Selection — the differential reproduction of various genotypes.

F

FLAGELLUM — a long, thread-like organelle protruding from the cell surface. In bacteria, each flagellum consists of a single protein filament and is capable of rotational movement. The eukaryotic flagellum, involved in locomotion and feeding, consists of a (9+2) array of specifically arranged microtubules surrounded by a common membrane; it undergoes bending rather than rotational movements. A cilium is simply a shortened eukaryotic flagellum.

FLUID-MOSAIC MODEL — a model of Membrane Structure proposing that the membrane consists of a lipid bilayer with embedded protein globules.

LIFE CYCLE — the complete sequence of growth and developmental phases of an organism, from zygote to the formation of gametes.

VEIN — a vascular bundle, part of the structural framework of supportive and conducting tissues in leaves and other flattened organs.

VENATION — the arrangement or pattern of Veins in a leaf blade.

FATS — substances composed of glycerol and three fatty acid molecules. The oxygen-to-carbon ratio in fats is significantly lower than in carbohydrates. Liquid fats are commonly referred to as oils.

G

SAPWOOD — the outer, living layers of the woody stem, usually lighter in color than the heartwood, through which water is actively transported.

OVARY — the lower, expanded portion of a carpel or of a syncarpous gynoecium formed by fused carpels. A mature ovary, sometimes along with other fused floral parts, develops into a fruit.

PHLOEM LOADING — the process of active secretion of certain substances (primarily sugars) into the sieve tubes.

CLOSED BUNDLE — a vascular bundle that lacks cambium and does not undergo secondary growth.

GUARD CELLS — a pair of specialized epidermal cells surrounding a stomatal pore. Changes in the turgor pressure of guard cells cause the pore to open or close.

EMBRYO — a young sporophyte prior to the onset of rapid growth (or germination, in seed plants).

EMBRYO SAC — the female gametophyte of angiosperms, typically consisting of eight or seven cells: an egg cell, two synergids, three antipodals, and one or two central cells. If There is a single central cell, it contains two nuclei, whereas the other cells are uninucleate.

PROTHALLUS — see prothallium.

ENTRAINMENT — a process whereby a periodic alternation of light and darkness, or some other external cycle, causes a circadian rhythm to synchronize with a modifying cycle that acts as the entraining agent.

ZEATIN — a plant hormone; a naturally occurring cytokinin isolated from corn.

CARYOPSIS — a simple, dry, one-seeded, indehiscent fruit in which the pericarp is fused along its entire surface with the seed coat. Typical of grasses (family Poaceae).

ZYGOMORPHIC (FLOWER) (from Greek zygos, yoke + morphe, form) — a flower that can be divided into two symmetrical halves by only one plane passing through its axis. Synonym: bilaterally symmetrical flower.

ZYGOSPORE — a thick-walled, highly resilient spore that develops from a zygote formed by the fusion of isogametes.

ZYGOTE (from Greek zygotos, joined together) — a diploid (2n) cell formed by the fusion of male and female gametes.

TRANSITION ZONE — the part of a primary plant body with a structure intermediate between those of the stem and the root.

UMBEL — an inflorescence in which all flower pedicels arise from a single point at the apex of the flowering shoot.

ZOORANGIUM — a sporangium containing zoospores.

ZOOSPORE — a motile spore found in algae, oomycetes, and chytridiomycetes.

I

NEEDLE — a hard, slender, sharply pointed structure, typically a modified leaf or part of a leaf.

SELECTIVE PERMEABILITY OF A MEMBRANE — the capacity of a membrane to permit the diffusion of different substances at different rates.

VARIATION — differences among individuals of the same species.

ISO- (from Greek isos, equal) — a combining form meaning "equal"; functionally similar to "homo-" and "homeo-".

ISOGAMY — a type of Sexual reproduction in which the gametes or gametangia are similar in size. Found in certain algae and fungi.

ISOMERS (from Greek isos + meros, part) — chemical compounds that have the same atomic composition but differ in molecular structure, such as glucose and fructose.

ISOMORPHIC (from Greek isos + morphe, form) — identical in form.

ISOTONIC — having the same osmotic concentration.

ISOTOPES — variants of a chemical element that differ from one another in the number of neutrons in the atomic nucleus, while sharing the same chemical properties.

IMBIBITION — the absorption of water and subsequent Swelling of Materials due to the adsorption of water molecules onto their internal surfaces.

Inbreeding — the mating of closely related plants or animals. In plants, inbreeding is commonly the result of repeated self-pollination.

INVERTASE — see sucrose.

FEEDBACK INHIBITION — a regulatory mechanism in biological systems whereby an increase in the concentration of a substance suppresses its further synthesis.

INDOLEACETIC ACID — a naturally occurring auxin and plant hormone.

INDUSIUM (Lat. indusium — woman's undergarment) — an outgrowth of the leaf epidermis in ferns forming a membranous cover over the sorus.

INITIAL — (1) a cell that remains permanently within the meristem and produces new plant body cells through division; (2) a meristematic cell that ultimately differentiates into a mature, highly specialized cell.

INTEGUMENT — the outer layer or layers of cells protecting the ovule nucellus; develops into the seed coat.

INTER- (Lat. inter — between) — a prefix used in compound words meaning "between" or "in the middle of".

INTERCALARY (Lat. intercalare — to insert) — a term describing meristematic tissue or growth that is not restricted to the apex of an organ, such as growth occurring in the nodal region.

INTERPHASE — the period between two meiotic or mitotic cycles. Cell growth and DNA replication occur during interphase.

EXINE — the inner wall layer of a spore or pollen grain.

INTRA- (Lat. intra — within) — a prefix in compound words meaning "within" or "inside".

INTRON — a segment of DNA transcribed into the precursor mRNA and subsequently removed by enzymatic splicing in eukaryotes prior to Translation. Cf. exon.

ION — an atom or molecule that has gained or lost one or more electrons, thereby acquiring a positive or negative electrical charge.

FOSSIL FUEL — transformed remains of ancient organisms burned to release energy. Examples include petroleum, natural gas, and coal.

FOSSILS — the preserved remains, impressions, or traces of organisms found in the Earth's crust.

ARTIFICIAL SELECTION — the breeding of selected organisms to develop strains with desired traits.

IAA — see indole-3-acetic acid.

K

CALYPTRA (Gk. kalyptra — HEAD covering) — a cap that wholly or partially covers the sporangium in certain moss species, formed from the enlarged archegonial wall.

CALLOSE — a branched polysaccharide found in the cell walls of sieve areas within sieve elements; it can also form in response to injury in sieve elements and parenchyma cells.

CALLUS (Lat. callus — thick skin) — unspecialized or undifferentiated plant tissue. The term is used in tissue culture, grafting, and wound healing.

CALORIE (Lat. calor — heat) — The amount of thermal energy required to raise the Temperature of 1 g of water by 1°C. In metabolic measurements, the kilocalorie (kcal) is commonly used, representing the heat required to raise 1 kg of water by 1°C.

CALVIN CYCLE — a series of photosynthetic enzymatic reactions in which Carbon dioxide is reduced to 3-phosphoglyceraldehyde while regenerating the CO2 acceptor, ribulose-1,5-bisphosphate. For every 6 molecules of CO₂ entering the cycle, two molecules of glyceraldehyde-3-phosphate are produced.

CAMBIAL ZONE — a region of thin-walled, undifferentiated meristematic cells situated between the secondary xylem and phloem; it consists of cambial initials and their immediate derivatives.

CAMBIUM (Lat. cambiare — to exchange) — a cylindrical meristem that produces secondary xylem and phloem.

CAPSID — the protein shell of a virion or virus particle.

CAPSULE — a gelatinous or mucous layer surrounding the cells of certain bacteria.

KARYOGAMY (Gk. karyon — nut nucleus + gamos — marriage) — the fusion of cell nuclei following plasmogamy.

CAROTENE (from Lat. carota — carrot) is a red, yellow, or orange pigment belonging to the carotenoid group.

CAROTENOIDS are a Class of fat-soluble pigments that include yellow, red, or orange carotenes and yellow xanthophylls; found in plant Chloroplasts and chromoplasts, where they function as accessory pigments in photosynthesis.

CARPEL (from Gr. karpos — fruit) is one of the elements of the gynoecium, or the inner floral whorl. It contains one or more ovules. One or more carpels form a pistil.

CARPOGONIUM (from Gr. karpos + gonos — offspring) is the female gametangium in red algae.

CARPOSPORE is a single diploid protoplast located within the carposporangium of red algae.

CARPOSPORANGIUM (from Gr. karpos + spora — seed + angeion — vessel) is a cell in red algae that contains a carpospore.

Catabolism (from Gr. katabole — casting down) is the set of metabolic pathways that break down complex molecules into simpler units, releasing energy.

CATALYST (from Gr. katalysis — dissolution) is a substance that increases The rate of a chemical reaction without being consumed in the process. Enzymes act as catalysts.

CATION (from Gr. katienai — to go down) is a positively charged ion.

QUANTA (QUANTUM) is the elementary unit of light energy.

QUANTOSOMES (from Lat. quantus — how much + Gr. soma — body) are granular structures on the inner surface of chloroplast lamellae; they are believed to participate in the light-dependent reactions of photosynthesis.

KINETIN (from Gr. kinetikos — putting in motion) is a purine that presumably does not occur naturally in plants; it acts similarly to plant Cytokinins.

KINETOCHORE — see centromere.

ACID is a substance that dissociates in water to yield protons (H⁺), thereby increasing their concentration; the pH of an acid solution is below 7. An acid functions as a proton donor and is chemically opposed to a base.

RACEME (OR GRAPE) is an indeterminate inflorescence with an elongated main axis and flowers borne on pedicels of approximately equal length.

CLADISTICS is an approach to biological systematics based on the analysis of primitive and evolutionarily advanced (derived) traits, effectively reflecting the Phylogenetic relationships among organisms.

CLADODE (from Gr. klados — branch) is a flattened stem that resembles and functions as a leaf.

CLASS is a taxonomic rank situated between division (or phylum) and order. It comprises one or more orders and belongs to a specific division.

CLEISTOTHECIUM (from Gr. kleistos — closed + thekion — small receptacle) is a closed, spherical ascocarp.

CELL is the Structural and functional unit of an organism. In plants, it consists of a cell wall and a protoplast.

FOOT CELL — see sterile cell.

COMPANION CELL is a specialized phloem parenchyma cell in angiosperms, intimately associated with a sieve-tube element and originating from the same mother cell.

BODY CELL — see spermatogenous cell.

TUBE CELL is a cell of the pollen grain that develops into the pollen tube.

CELL MEMBRANE — see Plasma Membrane.

CELL WALL — a rigid outer covering of plant cells, certain protists, and most bacteria.

CELL PLATE — a structure that forms at the equator of the spindle in dividing cells of plants and certain green algae during early telophase. As it matures, it develops into the middle lamella.

Cell Division — the division of a cell and its components into two approximately equal parts.

CELL SAP — the fluid contents of vacuoles.

CLIMAX COMMUNITY — The final stage of ecological succession; its characteristics are primarily determined by the climate and soil of a given area.

CLINE — a series of gradual changes in certain traits of a species, often associated with gradual shifts in climate and other environmental factors.

CLONE (from Greek klon meaning twig or slip) — a population of cells or individuals produced asexually from a single cell or organism.

CLONING — the derivation of cell lines or cultures in which all members share a specific DNA sequence. A key Procedure in Genetic Engineering.

TUBER — an enlarged, short, fleshy underground stem, such as in the potato.

ROOT NODULES — swellings on the roots of legumes and certain other plants, inhabited by symbiotic nitrogen-fixing bacteria.

CORM — a thickened, vertically oriented underground stem that serves as a storage organ for reserve nutrients, mainly starch.

COVALENT BOND — a chemical bond between atoms formed by the sharing of a pair of electrons.

COHESION (from Latin cohaerere — to cleave together) — the mutual attraction between molecules of the same substance.

CODON — a sequence of three adjacent nucleotides in a DNA or mRNA molecule that codes for a specific amino acid or the termination of a polypeptide chain.

COCCUS (from Greek kokkos — berry) — a spherical bacterium.

COLEOPTILE (from Greek koleos — sheath + ptilon — feather) — a protective sheath covering the apical meristem and leaf primordia in grass embryos; often considered the first leaf.

COLEORHIZA (from Greek koleos + rhiza — root) — a protective sheath enclosing the embryonic root of grasses.

COLLENCHYMA (from Greek kolla — glue) — a supportive plant tissue composed of collenchymatous cells, typically located in zones of primary growth in stems and certain leaves.

COLLENCHYMA CELL — an elongated living cell with unevenly thickened primary walls.

COLLOID — a stable suspension of fine particles.

SPIKE — an indeterminate inflorescence with an elongated main axis and sessile flowers.

SPIKELET — the basic unit of inflorescence in grasses; a small group of flowers resembling a miniature spike.

RINGING (GIRDLING) — the removal of a ring of bark down to the cambium around a tree trunk.

RING-POROUS WOOD — wood in which the vessels formed early in the growing season are significantly larger than those formed later, resulting in clearly distinguishable annual rings on a transverse section.

THORN — a hard, woody, pointed modified stem or branch.

CONVERGENT EVOLUTION (from Lat. convergeré — to converge) — the independent development of similar structures in unrelated organisms; typically occurs in similar habitats.

CONIDIOPHORE — a hypha that bears one or more conidia.

CONIDIUM (from Gk. konis — dust) — an asexual fungal spore produced outside a sporangium. Conidia may be solitary or form chains. Most conidia are multinucleate.

COMPETITION — an interaction between individuals of the same or different populations for the acquisition of essential resources that are in limited supply.

CONSUMER — an organism in an ecosystem that obtains its food from other organisms.

CONCENTRATION GRADIENT — The change in the concentration of a substance per unit of distance.

CONJUGATION TUBE — a tube formed during conjugation to facilitate The transfer of genetic material.

CONJUGATION — a temporary pairwise fusion of certain bacteria, Protozoans, algae, or fungi, during which genetic material is transferred from one individual to another.

CHROMOSOME CONJUGATION — the close temporary pairing of homologous chromosomes preceding the first meiotic division; Crossing Over occurs at this stage.

BARK — an informal term for all tissues outside the vascular cambium in a woody stem; see also inner bark and outer bark.

ROOT — typically, the descending axial organ of a plant, usually located underground. It serves to anchor the plant and to absorb and conduct water and mineral nutrients.

RIND — see outer bark.

RHIZOME — a more or menos horizontal underground stem.

ROOT PRESSURE — pressure developed in roots through osmosis, which causes guttation of water on leaves and its exudation on cut stumps.

ROOT CAP — a thimble-like mass of cells that covers and protects the root tip.

ROOT HAIRS — tubular outgrowths of root epidermal cells in the zone of maturation.

CAPSULE — (1) in angiosperms, a dry, dehiscent fruit developing from two or more carpels; (2) in bryophytes, a sporangium.

SHORT-DAY PLANTS — plants that require a light period shorter than a certain critical threshold in order to flower. Usually flower in autumn.

DRUPE — a simple, fleshy, usually single-seeded fruit developing from a single carpel, with a hardened endocarp that may adhere to the seed.

COTRANSPORT — membrane transport in which the movement of one substance depends on the simultaneous or subsequent transport of another.

COFACTOR — one or more non-protein components required for an enzymatic reaction to proceed; many Cofactors are Metal Ions, while others are called Coenzymes.

COENZYME — a non-protein organic molecule that performs an auxiliary function in enzymatic processes, often acting as an electron donor or acceptor. Examples include NAD⁺ and FAD.

KRANZ ANATOMY (from Ger. Kranz — wreath) — the wreath-like arrangement of mesophyll cells around a layer of large bundle-sheath cells, resulting in the vascular bundle being surrounded by two concentric cell layers. Characteristic of Plants with C₄ metabolism.

STARCH — an insoluble polysaccharide; the primary energy-storage compound in plants, consisting of more than a thousand glucose monomers.

KREBS CYCLE — a series of reactions in which pyruvic acid is oxidized to produce hydrogen atoms, electrons, and carbon dioxide. The electrons are then passed through a system of electron-transport molecules, the oxidative phosphorylation chain, and finally through the terminal stages of oxidation.

CRISTAE — infoldings of the inner mitochondrial membrane that house the Electron Transport Chain involved in ATP production.

Crossing-over — the exchange of homologous segments of genetic material between chromatids of homologous chromosomes during meiosis.

CYPSELA — a simple dry one- or two-seeded indehiscent fruit with wing-like outgrowths of the pericarp.

XANTHOPHYLL (from Greek xanthos — yellowish-brown + phyllon — leaf) — a yellow chloroplast pigment belonging to the carotenoid group.

XEROPHYTE (from Greek xeros — dry + phyton — plant) — a plant adapted to arid habitats.

XYLEM (from Greek xylon — wood) — the vascular tissue responsible for the primary transport of water and mineral nutrients in plants; characterized by the presence of tracheary elements.

TISSUE CULTURE — a technique for growing living plant or animal tissues in a specialized medium after extracting them from an organism.

SHRUB — a perennial woody plant of relatively small height. It produces multiple stems originating directly from or very close to the soil surface.

CUTICLE — a waxy or fatty layer on the outer wall of epidermal cells, composed of cutin or wax.

CUTIN (from Latin cutis — skin) — a fatty substance deposited on the walls of many PLANT CELLS AND on the outer wall of epidermal cells, forming a layer called the cuticle.

CAM (Crassulacean Acid Metabolism) — see Crassulacean acid metabolism.

L

LAMELLA (from Latin lamella — thin metal plate) — a layer of cell membranes, typically containing chlorophyll and involved in photosynthesis.

LAMINARIN — a glucose polymer and one of the main reserve nutrients in brown algae.

LATERAL MERISTEMS — meristems from which secondary tissues develop; namely, the cambium and phellogen.

LEUKOPLAST (from Greek leukos — white + plassein — to form) — a colorless plastid that typically serves as a center for starch formation.

PETAL — an element of the corolla, often brightly colored.

LIANA (from French liane, from lier — to bind) — a plant with a long woody stem that climbs or twines around other plants.

Lignin — one of the most important components of secondary cell walls in vascular plants (though not all of them contain it). It is the second most abundant plant polymer after cellulose.

LIGULE (from Latin ligula — little Tongue) — a small outgrowth at the base of the leaves in grasses and certain lycophytes.

LYSIS (from Greek lysis — loosening or dissolution) — the process of cell breakdown or destruction.

LYSOGENIC BACTERIA — bacteria containing Viruses (phages) in a non-infectious form (prophages). Prophages can excise from the bacterial chromosome and enter an active lytic cycle, causing the destruction of the host bacteria.

LYSOSOME (from Greek lysis + soma — body) — a single-membrane-bounded organelle containing hydrolytic enzymes. These enzymes are released upon its rupture and participate in the Hydrolysis of Proteins and other macromolecules.

Lipids (from Greek lipos — fat) — a diverse class of non-polar organic compounds that are insoluble in water but readily soluble in non-polar organic Solvents. This group includes fats, oils, Steroids, Phospholipids, and carotenoids.

LEAF BLADE — the expanded, flattened part of a leaf.

PULVINUS — a joint-like thickening at the base of a leaf or leaflet petiole that plays a role in their movement.

FOLICLE — a dry fruit developing from a single carpel and dehiscing along one side.

LEAF PRIMORDIUM MOUND — a lateral outgrowth below the apical meristem, representing the initial stage of leaf primordium development.

LEAF PRIMORDIUM (lat. primordium — beginning) — a lateral outgrowth of the apical meristem that develops into a leaf.

LEAF GAP — a parenchymatous region in the primary vascular cylinder located just above the departure point of a leaf trace.

LEAF SCAR — a scar left on the stem after a leaf falls.

LEAF TRACE — the portion of a vascular bundle extending from the leaf base to its connection with the stem vascular bundle.

LEAFLET — a component of a compound leaf or frond. It may be further divided into secondary leaflets and so on.

LOCUS — the specific physical Location of a gene on a chromosome.

BULB — a shortened underground stem covered with broadened, fleshy leaf bases containing nutrient reserves.

RAY INITIAL — a cambial meristematic cell that gives rise to the ray cells of secondary xylem and phloem.

M

MACROMOLECULE (Greek makros — large) — a molecule with a very high molecular weight, such as a protein, nucleic acid, or polysaccharide.

MACROFIBRIL — a structure formed by microfibrils and visible under a light microscope.

MACROCYST — an irregular, flattened structure bounded by a thin membrane, inside which zygotes are formed during The life cycle of cellular slime Molds.

MACROELEMENTS — inorganic chemical elements required in large quantities for plant growth, such as nitrogen, potassium, calcium, phosphorus, magnesium, and sulfur.

MALTASE — an enzyme that hydrolyzes maltose into glucose.

MANNITOL — a sugar alcohol and one of the reserve nutrients in brown algae.

MARGINAL MERISTEM — a meristem located along the edge of a leaf primordium that forms the leaf blade.

MEGASPORE MOTHER CELL — see megasporocyte.

MICROSPORE MOTHER CELL — see microsporocyte.

POLLEN MOTHER CELL — a microsporocyte in flowering plants.

SPORE MOTHER CELL — a diploid (2n) cell that undergoes meiosis to produce (typically) four haploid cells (spores) or four haploid nuclei.

TEMPLATE — a pattern or model according to which a complementary "reverse" copy is synthesized. The term is commonly used in describing DNA replication or transcription.

Messenger RNA — a class of RNA molecules that carry genetic information from DNA to the Ribosomes, where it is translated into protein.

MEGA- (Greek megas — large) — a combining form meaning "large" or "great".

MEGAGAMETOPHYTE (Greek megas + gamos — marriage + phyton — plant) — the female gametophyte in heterosporous plants; in angiosperms, it is located within the ovule.

MEGASPORE — in heterosporous plants, a haploid (n) spore that gives rise to the female gametophyte. In most groups, it is larger than the microspore.

MEGASPORANGIUM — a sporangium in which megaspores are produced; see nucellus.

MEGASPOROPHYLL — a leaf or leaf-like organ that bears a megasporangium.

MEGASPOROCYTE — a diploid cell whose meiotic division results in the formation of four megaspores.

MEGAPHYLL (Greek megas + phyllon — leaf) — typically a large leaf with several to many veins, whose leaf trace is associated with a leaf gap. Antonym: microphyll.

INTERNODE — the region of a stem between two successive nodes.

MESOCARP — see mesocarp.

INTERFASCICULAR CAMBIUM — cambium that develops within the interfascicular parenchyma between vascular bundles.

MESO- (Greek mesos — middle) — a combining form meaning "middle" or "intermediate".

MESOCARP (Greek mesos + karpos — fruit) — the Middle layer of the pericarp, situated between the exocarp and the endocarp.

MESOPHYLL — the ground tissue (parenchyma) of a leaf located between the epidermal layers; its cells typically contain chloroplasts.

MESOPHYTE (Greek mesos + phyton — plant) — a plant that requires adequate soil moisture and a relatively humid atmosphere for normal development.

MEIOSIS (Greek meioun — to diminish) — two successive nuclear divisions in which the chromosome number is reduced from diploid (2n) to haploid (n), resulting in the formation of gametes or spores (in organisms with alternation of generations).

MENDEL'S FIRST LAW: for each alternative trait, there is a separate factor that determines it and is carried by a single gamete.

MENDEL'S SECOND LAW: the inheritance of one pair of traits is independent of the inheritance of other traits, allowing for various combinations of them (this law was later revised following the discovery of genetic linkage).

MERISTEM (Greek merizein — to divide) — undifferentiated plant tissue from which new cells develop.

PRIMARY THICKENING MERISTEM — in many monocots, the meristem responsible for the thickening of the shoot axis.

HABITAT — the natural environment in which an organism lives; the place where it is normally found.

METABOLISM (Greek metabole — change) — the sum of all chemical processes occurring within a living cell or organism.

CRASSULACEAN ACID METABOLISM (CAM) — a variant of C₄ metabolism in which phosphoenolpyruvate fixes CO₂ at night to form C₄ compounds, and then, during the day, the bound CO₂ is released and transferred to ribulose bisphosphate in The Calvin Cycle. Typical of most succulents, particularly cacti.

METAXYLEM (Greek meta — after) — the part of the primary xylem that differentiates after the protoxylem, reaching maturity after the plant organ in which it is located ceases to elongate.

METAPHASE — the stage of mitosis or meiosis during which chromosomes align along the equatorial plane of the spindle.

PANICLE — an inflorescence with a branched main axis, upon the branches of which loose clusters of flowers are borne.

MYCO- (from Greek mykes, fungus) — a combining form meaning "fungal" or "pertaining to fungi".

MYCOLOGY — the scientific study of fungi.

MYCORRHIZA — a symbiotic association between certain fungi and plant roots, characteristic of most vascular plant species.

MICRO- (from Greek mikros, small) — a combining form meaning "small".

MICROGAMETOPHYTE (from Greek mikros + gamos, marriage + phyton, plant) — the male gametophyte in heterosporous plants.

MICROMETER — a unit of length used for measuring cellular structures; 1/1000 mm; abbreviated as µm.

MICROPYLE — an opening formed by the incomplete closure of the ovule integuments in seed plants, through which the pollen tube typically enters.

MICROSPORE — in heterosporous plants, a spore that develops into a male gametophyte.

MICROSPORANGIUM — a sporangium in which microspores are formed.

MICROSPOROPHYLL — a leaf-like organ bearing one or more microsporangiums.

MICROSPOROCYTE — a cell that undergoes meiosis to produce four microspores.

MICROBODIFY — a single-membrane-bounded organelle containing various enzymes, evolutionarily related to the endoplasmic reticulum. Examples of Microbodies include Peroxisomes and glyoxysomes.

MICTRABECULAR LATTICE — a three-dimensional network of ultra-fine filaments pervading the ground substance of the cell.

MICROTUBULES — narrow (approximately 25 nm in diameter), elongated, non-membranous tubules of indefinite length found in eukaryotic cells. They direct chromosome movement during cell division and form the internal structure of Cilia and flagella.

MICROFIBRILS — thread-like components of cell walls composed of cellulose molecules, visible only under an electron microscope.

MICROFILAMENTS (from Greek mikros + filum, thread) — long filaments, 5–7 nm in thickness, composed of Actin. They are believed to be involved in cytoplasmic streaming.

MICROPHYLL (from Greek mikros + phyllon, leaf) — a small leaf possessing a single unbranched vein and a leaf trace not associated with a leaf gap.

MICRONUTRIENTS — inorganic chemical elements required by plants in very small or trace quantities: iron, chlorine, copper, manganese, zinc, molybdenum, and boron.

MIMICRY (from Greek mimos, mimic) — superficial resemblance in color, shape, or behavior of one organism to another, typically stronger or better protected, which provides the mimic with defense, concealment, or other advantages.

MITOSIS (from Greek mitos, thread) — the process in which replicated chromosomes separate longitudinally and the resulting daughter chromosomes segregate to form two genetically identical nuclei, typically followed by cytokinesis.

MITOCHONDRION (from Greek mitos + chondrion, little grain) — a double-membrane-bounded organelle of eukaryotic cells that contains the Enzymes of the Krebs cycle and The electron transport chain. It serves as the primary source of ATP in non-photosynthetic cells.

MYCELIUM (from Greek mykes, fungus) — the mass of hyphae forming the vegetative body of a fungus, oomycete, or chytridiomycete.

PERENNIAL — a plant that lives and produces reproductive structures for several or many years.

MULTIPLE EPIDERMIS — a tissue composed of multiple layers of cells derived from the protoderm, with only its outermost layer exhibiting typical epidermal structure.

MOLECULE — the smallest particle of a chemical compound consisting of two or more atoms.

CARRIER MOLECULES — see permeases.

MOLECULAR WEIGHT — the relative mass of a molecule expressed in units equal to 1/1₂ of the mass of the most abundant carbon isotope. The sum of the relative atomic masses of the atoms making up the molecule.

MONO- (Greek monos — single) — a prefix meaning "one" or "single".

MONOKARYOTIC (Greek monos + karyon — kernel, nut) — in fungi, having a single haploid nucleus per cell or hyphal compartment.

MONOSACCHARIDE (Greek monos + sakcharon — sugar) — a simple sugar, such as a pentose or hexose, that cannot be hydrolyzed into simpler sugars.

MORPH- (Greek morphe — form) — a combining form meaning "form".

MORPHOGENESIS — The Development of form.

MORPHOLOGY (Greek morphe — form + logos — discourse) — The Study of form and its development.

MOSSES — see bryophytes. mRNA — see messenger RNA.

MULTIGENE FAMILY — a set of genes in a chromosome that are similar in origin and function. Most eukaryotic genes belong to such families.

MUTAGEN (Latin imitare — to change + Greek genaio — to produce) — an agent that increases the mutation rate.

MUTANT — an organism carrying a mutant gene.

MUTATION — a heritable change of one allelic form of a gene into another.

WHORL — a ring of leaves or floral parts.

MUTUALISM — an association between multiple organisms that is beneficial to each of them.

SOFTWOOD — a common term for the wood of conifers.

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NANOPLANKTON (Greek nanos — dwarf + planktos — wandering) — plankton ranging from less than 20 to 75 µm in size.

OUTER BARK — in mature trees, the dead portion of the bark; the innermost layer of the periderm and all tissues external to it.

HEREDITY — the TRANSMISSION OF TRAITS from parents to offspring via gametes.

Nastic Movements — Plant Movements in response to specific stimuli, where the direction of movement is independent of the direction of the stimulus.

INDEHISCENT (FRUIT) — remaining closed at maturity (e.g., a samara).

INDEPENDENT ASSORTMENT — see Mendel's second law.

DAY-NEUTRAL PLANTS — plants that flower regardless of day length.

NEUTRON (Latin neuter — neither) — an uncharged particle slightly heavier than a proton. Present in the nuclei of all chemical elements except hydrogen, whose nucleus consists of a single proton.

NECTARIES (Greek nektar — drink of the gods) — glands in angiosperms that secrete nectar, a sugary fluid serving to attract animals to plants.

IMPERFECT FLOWER — a flower in which one or more of the four whorls (calyx, corolla, stamens, carpels) are absent.

CONTINUOUS VARIATION — variation of traits determined by several different genes. As a rule, the quantitative values of these traits in a population are distributed according to a normal (bell-shaped) curve.

FUNGI IMPERFECTI (DEUTEROMYCETES) — fungi in which the sexual cycle is unknown. It is generally believed that most Fungi Imperfecti are insufficiently studied ascomycetes.

NON-CYCLIC ELECTRON FLOW — a light-induced flow of electrons from water to NADP during photosynthetic oxygen evolution; associated with Photosystems I and II.

INFERIOR OVARY — an ovary completely or partially fused with the calyx, so that all other floral parts appear to arise from the top of the ovary.

NICOTINAMIDE ADENINE DINUCLEOTIDE (NAD) — a coenzyme that serves as an electron acceptor in many oxidative reactions of respiration.

NICOTINAMIDE ADENINE DINUCLEOTIDE PHOSPHATE (NADP) — a coenzyme that serves as an electron acceptor in many biosynthetic reduction reactions. Structurally, it differs from NAD only in the presence of an additional phosphate group.

SPINDLE FIBERS — microtubules extending from the centromeres of chromosomes to the spindle poles and between the poles of a dividing cell spindle.

NITRIFICATION — The oxidation of ammonium ions or ammonia to nitrates. It is carried out by specific free-living soil bacteria.

NICHE — the role played by a species in an ecosystem.

NUCLEIC ACID — an organic acid composed of linked nucleotide residues. Two Types of Nucleic acids are known: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

NUCLEOPLASM — the ground substance of the nucleus.

NUCLEOTIDE — the basic structural unit of a nucleic acid, consisting of a phosphate group, a five-carbon sugar (ribose or deoxyribose), and a purine or pyrimidine base.

NUCELLUS (Latin nucella — little nut) — the tissue that forms the main body of the young ovule, within which the embryo sac develops; equivalent to a megasporangium.

NAD — see nicotinamide adenine dinucleotide.

NADP — see nicotinamide adenine dinucleotide phosphate.

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BUNDLE SHEATH — a layer or layers of cells surrounding a vascular bundle in the leaf mesophyll. It may consist of parenchyma cells, sclerenchyma cells, or both. The bundle sheath has a specialized structure in plants with C₄ metabolism.

Facilitated Diffusion — the diffusion of a dissolved substance down its concentration gradient with the assistance of a carrier molecule.

OBLIGATE ANAEROBE — an organism that exhibits metabolic activity only in the absence of oxygen.

PERFECT FLOWER — a flower possessing both stamens and pistils.

BULK FLOW — the movement of a mass of water or other fluid driven by gravity and/or pressure.

MONOCOTS — one of the two Major Classes of angiosperms, characterized by the presence of a single cotyledon in the embryo.

MONOECIOUS — plants in which stamens and pistils develop in separate flowers on the same individual organism.

ANNUAL — a plant whose life cycle is completed entirely within a single growing season.

UNISEXUAL FLOWER — a flower that lacks either stamens or carpels.

MONOXENOUS (PARASITE) — an organism whose life cycle takes place entirely on a single host plant (for example, some rust fungi).

-OID (Greek oid — resembling) — a combining form meaning "similar to" or "like"ებელი.

BORDERED PIT — a pit in which the secondary cell wall arches over the pit membrane.

FOSSIL — see fossil remains.

OXIDATION — the loss of an electron by an atom or molecule. Oxidation and reduction (the gain of an electron) occur simultaneously, as the electron lost by one atom is captured by another. Redox reactions are vital mechanisms for energy transfer in living systems.

OXIDATIVE PHOSPHORYLATION — the formation of ATP from ADP and inorganic phosphate. It takes place in the Mitochondrial Electron Transport chain.

PERICARP — see pericarp.

PERIANTH — the collective term for the sepals and petals.

ONTOGENY (Greek on, being + genesis, origin) — the life cycle, or individual development, of an organism or its parts.

OO- (Greek oion, egg) — a combining form meaning egg.

OOGAMY — a type of sexual reproduction in which one gamete (the egg) is large and non-motile, while the other (the sperm) is smaller and motile.

OOGONIUM — a unicellular female reproductive organ containing one or more egg cells.

OOSPORE — a thick-walled zygote characteristic of oomycetes.

OPERATOR — a nucleotide sequence recognized by a repressor protein, involved in the Regulation of Gene Expression.

OPERCULUM (Lat. operculum — lid) — the lid of the sporangium in mosses.

Operon (Lat. operis — work) — a cluster of adjacent genes transcribed together as a single mRNA molecule. Operons are common in bacteria, but rare in eukaryotes.

FERTILIZATION — the fusion of the nuclei of two gametes resulting in the formation of a diploid zygote.

PROP ROOTS — adventitious roots that arise from the stem above the soil level and help anchor the plant. Common in many monocots, such as maize.

ORGAN — a structure composed of different tissues, such as a root, stem, leaf, or parts of a flower.

ORGANELLE (Greek organella — small instrument) — a specialized subunit within a cell.

ORGANISM — a unicellular or multicellular living entity.

ORGANIC — relating to living organisms in general, the substances they produce, and the chemistry of carbon-containing compounds.

NUT — a dry, indehiscent, single-seeded fruit with a hard pericarp, typically developing from several fused carpels.

AXIAL SYSTEM — secondary xylem and phloem cells formed from fusiform cambial initials. The long axis of these cells is oriented parallel to the main axis of the root or stem. Sometimes also referred to as the longitudinal or vertical system.

OSMOSIS (Greek osmos — push) — the Diffusion of Water or another solvent through a semipermeable membrane. In the absence of other factors, water movement during osmosis proceeds from a region of higher water potential to one of lower potential.

OSMOTIC POTENTIAL — the change in Free energy, or chemical potential, of water caused by a dissolved substance. It carries a negative sign.

OSMOTIC PRESSURE — the potential pressure that a solution can develop when separated from pure water by a semipermeable membrane. An indicator of solution concentration.

BASE — a substance that dissociates in water, thereby lowering the concentration of protons (H+) often through the release of hydroxyl ions (OH^-): the pH of basic solutions is greater than 7. Its chemical properties are opposite to those of an acid.

GROUND MERISTEM (Greek meristos — divisible) — the primary meristem from which ground tissues develop.

GROUND TISSUE — any tissue except the epidermis (or periderm) and the vascular tissue.

CYTOPLASMIC MATRIX — the least differentiated part of the cytoplasm, as observed under an electron microscope, surrounding the nucleus and Organelles.

DIVISION — one of the highest taxonomic ranks used in plant Classification, equivalent to a phylum in animals and heterotrophic protists. Divisions (phyla) are grouped into kingdoms.

ABSCISSION ZONE — a region at the base of a leaf, flower, fruit, or other plant part containing tissues involved in the shedding of that part from the plant body.

OPEN VASCULAR BUNDLE — a bundle in which cambium forms after the differentiation of primary vascular elements is complete.

ROOT SUCKER — a shoot arising from the roots of certain plants that eventually develops into a new plant; sometimes also originates at the base of the stem.

ALTERNATE — buds (or leaves) arranged singly at each node.

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AXIL — the upper angle between a shoot or leaf and the stem from which it grows.

AXILLARY — a term used to describe branches or buds located within a leaf axil.

PALEOBOTANY (Greek palaios — ancient) — the branch of science concerned with fossil plants.

PALISADE PARENCHYMA — leaf tissue consisting of cylindrical parenchymal cells containing chloroplasts and oriented with their long axes perpendicular to the leaf surface.

PARA- (Greek para — beside, near) — a combining form meaning "beside" or "near".

PARADERMAL SECTION (Greek para + derma — skin) — a section parallel to The surface of a flat structure, such as a leaf.

PARASITE — an organism that lives on or within the body of an organism of another species and obtains nutrients from it.

PARALLEL EVOLUTION — the independent development of similar structures performing similar functions in different evolutionary lineages as a result of similar selection pressures.

PARALLEL VENATION — an arrangement of the main leaf veins approximately parallel to one another, characteristic of monocots.

PARAMYLON — a carbohydrate storage reserve found in euglenoids.

PIT PAIR — two opposing pits with a pit membrane between them.

PARASEXUAL CYCLE — the fusion and division of heterokaryotic haploid nuclei in certain fungi, resulting in the formation of recombinant nuclei.

PARAPHYSES (Greek para + physis — growth) — sterile filaments interspersed among reproductive cells in a fruit body, found, for example, in certain fungi and brown algae.

PARENCHYMA (Greek para + en — in + chein — to pour) — tissue composed of parenchymatous cells.

PARENCHYMA CELLS — living, typically thin-walled cells that vary in size and shape. The most common type of plant cell.

PARTHENOCARPY (Greek parthenos — virgin + karpos — fruit) — the development of fruit without fertilization. Such fruits are typically seedless.

PASSIVE TRANSPORT — the movement of dissolved substances across a membrane down a concentration or electrochemical gradient via simple or facilitated diffusion, requiring no metabolic energy.

PATHOGEN (Greek pathos — suffering + genesis — producing) — an organism that causes disease.

PATHOGENIC — disease-causing.

PATHOLOGY — the study of diseases in animals and plants, their effects on the organism, and Methods of Treatment.

PECTIN — a complex organic compound that is a component of the intercellular substance and primary cell walls; The basis of fruit jellies.

Pentose Phosphate Pathway — a pathway of glucose-6-phosphate oxidation resulting in the formation of pentose phosphates.

PEPTIDE — two or more amino acids linked by peptide bonds.

PEPTIDE BOND — a bond formed between the carboxyl (-COOH) group of one Amino Acid and the amino (-NH₂) group of another, with the release of a water molecule.

CORTEX (PRIMARY CORTEX) — the region of ground tissue in a stem or root, bounded externally by the epidermis and internally by The Vascular System. Formed from primary tissue.

PRIMARY MERISTEM — protoderm, procambium, and ground meristem, which originate from the apical meristem.

PRIMARY WALL — the cell wall layer formed during the period of cell growth.

PRIMARY PIT FIELD — a thin region of the primary cell wall through which plasmodesmata pass (although plasmodesmata may also traverse other Regions of the wall).

PRIMARY PLANT BODY — the plant part developing from the apical meristem and its derivatives. It consists entirely of primary tissues.

PRIMARY ENDOSPERM NUCLEUS — the result of the fusion of a sperm nucleus with two polar nuclei.

PRIMARY TISSUES — tissues developing from the apical and primary meristems of the stem and root. In contrast, secondary tissues develop from the cambium. Primary growth results in an increase in plant length.

PRIMARY ROOT — the first root of a plant, developing from the embryonic radicle. In gymnosperms and dicotyledons, it becomes the taproot.

PRIMARY GROWTH — plant growth resulting from The activity of the apical meristems of the shoot and root.

TRANSFER CELL — a specialized parenchyma cell with wall ingrowths that increase the surface area of The Plasma Membrane. It is believed to be involved in the short-distance transport of solutes.

CROSS-FERTILIZATION — the fusion of gametes produced by different individuals. The opposite of self-fertilization.

CROSS-POLLINATION — the transfer of pollen from the anther of one plant to the stigma of the pistil of another.

PERI- (Greek peri — around) — a prefix meaning "around" or "about".

PERIANTH (Greek peri + anthos — flower) — a tubular structure surrounding the archegonium, and subsequently the developing sporophyte, in leafy liverworts.

PERIGYNY (Greek peri + gyne — woman) — a floral arrangement in which the petals, sepals, and stamens are attached to the margins of a cup-like, expanded concave receptacle. Externally, this gives the appearance that all the aforementioned structures are attached to the ovary.

PERIDERM (Greek peri + derma — skin) — an outer protective tissue composed of cork, cork cambium (phellogen), and phelloderm, which replaces the epidermis as it breaks down during secondary growth.

PERICARP (Greek peri + karpos — fruit) — the fruit wall, developing from the matured ovary wall.

PERICLINAL — parallel to the surface.

DOUBLING TIME — the time period required for a population to double in size.

PERISPERM (Greek peri + sperma — seed) — a nutritive tissue in the seeds of certain flowering plants, derived from the nucellus.

PERISTOME (Greek peri + stoma — Mouth) — in mosses, a ring of Teeth surrounding the opening of the sporangium.

PERITHECIUM — a spherical or flask-shaped ascocarp.

PERICYCLE (Greek peri + kyklos — circle) — a plant tissue bounded on the outside by the endodermis and on the inside by the phloem. Characteristic of roots.

PERMEASE — a transport protein involved in the translocation of substances across The cell membrane without undergoing irreversible changes in the process.

PEROXISOME — a microbody that plays a crucial role in glycolate metabolism linked to photosynthesis. Photorespiration takes place within peroxisomes.

PERFORATION PLATE — a perforated area of the cell wall of a vessel member.

PISTIL — the central organ of a flower, typically consisting of an ovary, style, and stigma. It may comprise one or more fused carpels.

PISTILLATE (FLOWER) — a flower containing one or more carpels but lacking functional stamens.

PIGMENT — a substance that absorbs light (usually selectively).

PINOCYTOSIS — see endocytosis.

PYRAMID OF ENERGY — the energetic relationships between various trophic levels in a given food chain. Autotrophs (at the base of the pyramid) possess the greatest amount of available energy, followed by herbivores, primary carnivores, secondary carnivores, and so on. Similar pyramids of mass, size, and numbers can be observed in natural communities.

PYRENOID (Greek pyren — fruit stone + eidos — like) — a specialized region of the chloroplast in green algae and hornworts that serves as a center for starch formation.

PYRIMIDINES — the smaller of the two types of nitrogenous bases found in DNA and RNA. They possess a single-ring structure. Cytosine, thymine, uracil.

Digestion — the enzymatic breakdown of complex, typically insoluble food substances into simpler, usually soluble forms.

FOOD CHAIN (WEB) — a sequence of organisms in an ecological community, each member of which serves as food for the next. Rarely comprising more than six links, it begins with autotrophs and ends with large carnivores.

-PLASMA, PLASMO-, -PLAST (Greek plasma — form, mold) — combining forms meaning "formed" or "molded"; for example, protoplasm — "first formed" (living matter), chloroplast — "formed green body".

Plasmalemma — see plasma membrane.

PLASMA MEMBRANE — the outer boundary of the protoplast, adjacent to the cell wall; formed by a single unit membrane. Also referred to as the cell membrane or ectoplast.

PLASMID — a relatively small DNA fragment that can exist freely in the bacterial cytoplasm, integrate into the chromosome, and replicate along with it. Plasmids constitute about 5% of the DNA in many bacteria; they are rare in eukaryotes.

PLASMOGAMY (Greek plasma + gamos, marriage) — the fusion of gamete protoplasts not accompanied by the fusion of their nuclei.

PLASMODESMATA (Greek plasma + desma, bond) — microscopic cytoplasmic strands passing through pores in cell walls and connecting the living protoplasts of adjacent cells.

PLASMODIUM — a stage in the Life Cycle of myxomycetes; a membrane-bound mass of protoplasm containing numerous nuclei.

PLASMOLYSIS (Greek plasma + lysis, loosening) — the detachment of the protoplast from the cell wall due to water loss by osmosis.

PLANKTON (Greek planktos, wandering) — freely floating, predominantly microscopic aquatic organisms.

PLASTID — a cellular organelle found in certain eukaryotes that synthesizes and stores organic compounds; bounded by a double membrane.

Placenta (Latin placenta, flat cake) — the site of attachment of an ovule or seed within the ovary.

PLACENTATION — the arrangement and manner of attachment of ovules within an ovary.

PLEIOTROPY (Greek pleios, more + tropos, turn) — the ability of a single gene to influence multiple phenotypic traits.

FRUIT — in angiosperms, a mature ovary or group of Ovaries containing seeds. It may also include floral parts that fuse with it as it matures. The term is sometimes used informally, as in "fruiting body," to denote the reproductive structures of various organisms.

CARPEL — see carpel.

CARNIVOROUS — feeding on animals.

PNEUMATOPHORES (Greek pneuma, breath + phoros, bearing) — specialized root outgrowths of certain trees growing in waterlogged habitats, exhibiting negative geotropism. They project vertically above the water surface and are believed to facilitate normal aeration.

SHOOT — the aerial part of a vascular plant, comprising the stem, leaves, and buds.

SUBSIDIARY CELL — an epidermal cell morphologically distinct from other epidermal cells and associated with a pair of guard cells.

SUSPENZOR — see suspensor.

ABSORPTION SPECTRUM — see absorption spectrum.

SUBSPECIES — the largest taxonomic rank below the species level. May comprise several varieties.

LATE WOOD — wood produced toward the end of the growing season. It differs from early wood in having smaller cells and greater density.

QUIESCENT CENTER — a relatively inactive internal region of the root apical meristem.

DERMAL TISSUE — the epidermis or periderm.

ANGIOSPERMS — a group of plants producing seeds enclosed within an ovary (fruit).

FIELD CAPACITY — the percentage of water retained in the soil against the force of gravity.

POLY- (Greek polys — many) — a combining form meaning "many" in compound words.

POLYGENIC INHERITANCE — the inheritance of quantitative traits determined by the joint action of multiple genes.

POLYMER — a large molecule composed of many identical or similar molecular subunits (monomers).

POLYMERIZATION — the chemical bonding of monomers (such as glucose or nucleotides) to form polymers (starch or nucleic acid, respectively).

POLYNUCLEOTIDE — a single-stranded DNA or RNA molecule.

POLYPEPTIDE — a molecule less complex than a protein, also consisting of amino acids linked by peptide bonds.

POLYPLOID — an organism, tissue, or cell having more than two complete sets of chromosomes.

POLYRIBOSOME — see polysome.

POLYSACCHARIDE — a polymer consisting of A large number of monosaccharide molecules linked into long chains; examples include glycogen, starch, and cellulose.

POLYSOME — a group of ribosomes simultaneously translating the same mRNA molecule.

POLYEMBRYONY — the formation of multiple embryos within a single seed.

COMPLETE FLOWER — a flower having all four whorls of floral organs: sepals, petals, stamens, and carpels.

SEXUAL REPRODUCTION — the fusion of gametes followed by meiosis and recombination at a specific point in the life cycle.

CELL CAVITY — the space enclosed by the cell wall.

SEMIRESPERMEABLE MEMBRANE — a membrane permeable to water and certain solutes, but impermeable to other solutes.

POLAR MOLECULE — a molecule carrying positive and negative charges at opposite ends.

POLAR NUCLEI — two nuclei that form at opposite poles of the embryo sac and migrate to its center, fusing with a sperm nucleus to form the primary endosperm nucleus (3n).

CROSS-SECTION — a section perpendicular to the longitudinal axis of an organ.

POPULATION — a group of individuals of the same species living in a given area at the same time.

PIT — a depression in a cell wall where the secondary wall fails to form.

PIT MEMBRANE — the partition between two pits, consisting of the primary cell walls of adjacent cells and the middle lamella.

ORDER — a taxonomic category between class and family; a class contains one or more orders, and an order contains one or more families.

PLUMULE — the first bud of an embryo; the portion of a young shoot above the cotyledons.

BUD — (1) an embryonic shoot, usually protected by young leaves or bud scales; (2) a vegetative outgrowth in Yeasts and certain bacteria specialized for asexual reproduction.

CASPARIAN STRIP (named after Robert Casparri, a German botanist) — a band-like region of the primary cell wall containing suberin and lignin, extending along the radial and transverse (anticlinal) walls of endodermal cells in roots.

REGULAR FLOWER — see actinomorphic flower.

PROEMBRYO — an embryo at the earliest Stages of development before the proper embryo and suspensor become differentiated.

PREPROPHASE BAND — a circumferential band of microtubules located just beneath the plasma membrane, encircling the equatorial plane of the future mitotic spindle in a cell preparing for division.

PUNCTUATED EQUILIBRIUM — an evolutionary model proposing that long periods of little or no morphological change are punctuated by brief periods of rapid change.

ADVENTITIOUS BUD — a bud located typically above or to the side of the main axillary bud.

ADVENTITIOUS STRUCTURE — a structure arising in an atypical location, such as a bud outside a shoot apex or leaf axil, or a root on a leaf or stem.

GRAFTING — the joining of two plant organisms in which a part of one (the scion) is inserted into the stem or root of the other (the rootstock).

STIPULES — appendages on both sides of the leaf base, often leaf-like; sometimes encircling the stem. Found in many flowering plants.

PRIMORDIUM (Lat. primus, first + ordiri, to begin to weave) — a cell or organ at the earliest stage of differentiation.

BRACT — see bracteat.

PRO- (Gr. pro, before) — a prefix in compound words meaning "before" or "prior to".

CORK — a secondary tissue produced by the cork cambium. It consists of polygonal cells that die at maturity, with walls impregnated with suberin, a wax- or fat-like substance that renders them impermeable to gases and water vapor. It forms the outer part of the periderm.

CORK CAMBIUM — a lateral meristem that forms the periderm, producing cork to the outside and phelloderm to the inside. Characteristic of the stems and roots of gymnosperms and dicots.

VASCULAR SYSTEM — the aggregate of conducting tissues in a plant or organ.

VASCULAR BUNDLE — a strand of conducting tissues containing primary xylem, primary phloem, and procambium (if still retained). Often surrounded by a sheath of parenchyma and/or fibers.

BUNDLE SHEATH EXTENSION — a plate of parenchyma, sclerenchyma, or collenchyma cells extending from the vascular bundle sheath to the upper or lower epidermis, or both, within the leaf mesophyll.

PROCAMBIUM (Gr. pro + Lat. cambiare, to exchange) — a primary meristem from which primary Vascular Tissues develop.

PROKARYOTES (Gr. pro + karyon, nut kernel) — bacteria. Cells lacking membrane-bound nuclei and organelles.

PROXIMAL (Lat. proximus, nearest) — situated closer to a point of reference, usually the main body or point of attachment. Antonym: distal.

PROLAMELLAR BODY — a semi-crystalline structure in Plastids whose development has been arrested due to the absence of light.

PROMOTER — a specific nucleotide sequence on a chromosome to which RNA polymerase must bind for gene transcription and mRNA formation to begin.

PROPLASTID — a small, self-replicating body within the protoplasm from which a plastid develops.

PASSAGE CELLS — endodermal cells of the root that retain thin walls and Casparian strips while other endodermal cells develop thick secondary walls.

GERMINATION — the beginning or resumption of GROWTH AND DEVELOPMENT of a spore, seed, bud, or other structure.

SEEDLING — a young sporophyte developing from a germinating seed.

SIMPLE PIT — a pit that lacks the arched border of secondary wall material found in bordered pits.

PROSTHETIC GROUP — a metal ion or inorganic group tightly bound to an enzyme, functioning as its Active Site.

BINARY FISSION — a form of asexual reproduction in unicellular organisms where an individual divides into two daughter cells of equal size.

SIMPLE LEAF — a leaf with an undivided blade. Antonym — compound leaf.

SIMPLE FRUIT — a fruit developing from a single carpel or several fused carpels.

PROTHALLIAL CELL (Greek pro + thallos, sprout) — a sterile cell within the male gametophytes (microgametophytes) of vascular plants, excluding angiosperms. It is believed to represent a remnant of the vegetative tissue of the male gametophyte.

PROTHALLUS — a more or less independent, photosynthetic gametophyte of homosporous vascular plants, particularly ferns.

PROTEASE — an enzyme that breaks down proteins by hydrolyzing peptide bonds.

PROTO- (Greek protos, first) — a combining form meaning "first"; for example, Protozoa means "first animals."

PROTODERM (Greek protos + derma, skin) — the primary meristem that gives rise to the epidermis.

PROTOXYLEM — the early primary xylem that differentiates while the plant organ containing it is still elongating.

PROTON — an elementary particle that is a fundamental component of all atomic nuclei, having a positive charge equal in magnitude to that of an electron and a mass of approximately 1.

PROTONEMA (Greek protos + nema, thread) — a thread-like or thalloid structure representing the initial developmental stage of the gametophyte in mosses and some liverworts.

PROTOPLASM — cytoplasm excluding organelles.

PROTOPLAST — a plant cell stripped of its cell wall.

PROTOSTELE (Greek protos + stele, pillar) — the simplest type of stele, consisting of a solid core or cylinder of vascular tissue.

PROPHAGE — a non-infectious phage genome integrated into a bacterial chromosome, which replicates along with the host bacterium without causing lysis; a stage in the life cycle of a temperate phage.

PROPHASE (Greek pro + phasis, appearance) — the early stage of nuclear division during which chromosomes condense, shorten, thicken, and begin moving toward the metaphase plate.

PROEMBRYO — see pre-embryo.

CLAMP CONNECTION — in basidiomycetous fungi, a hook-like structure formed between adjacent cells of dikaryotic hyphae, ensuring that each daughter cell receives two genetically different nuclei during division.

PSEUDO- (Greek pseudes, false) — a combining form meaning "false."

PSEUDOPLASMODIUM — a multicellular mass formed by the aggregation of individual amoeboid cells; a characteristic stage in the life cycle of cellular slime molds.

BULLIFORM CELLS — large epidermal cells forming longitudinal rows on the leaves of grasses, also known as motor cells, believed to be involved in leaf rolling and unrolling.

PURINES — the larger of the two types of nitrogenous bases found in DNA and RNA, characterized by a double-ring structure; adenine and guanine.

FASCICULAR CAMBIUM — cambium that originates within a vascular bundle.

BUNDLE SCAR — a mark within a leaf scar left by the broken vascular bundles when a leaf falls.

ANTHER — the pollen-bearing part of a stamen.

POLLEN — the aggregate of pollen grains.

POLLEN TUBE — a tube through which male gametes reach the ovule; it develops following the germination of a pollen grain.

POLLEN GRAIN — a seed plant microspore containing a mature or immature male gametophyte (microgametophyte).

POLLEN SAC — a cavity within an anther that contains pollen grains.

R

HOMOSPOROUS — see homospory.

RADIAL SYSTEM — ray cells formed within the secondary xylem and phloem from ray initials.

RADIALLY SYMMETRICAL — see actinomorphic.

RADIAL SECTION — a longitudinal section parallel to the radius of a cylindrical organ, such as a root or stem. In secondary xylem and phloem, it runs parallel to the medullary rays.

AUTORADIOGRAPH — an image produced on a sensitive photographic film by a radioactive substance.

RADIOISOTOPE — an unstable isotope of an element that spontaneously decays with the emission of radioactivity.

VARIETY — a taxonomic rank below that of a subspecies.

HETEROSPORY — see heterospory.

HETEROECIOUS (PARASITE) — an organism that requires two different host species to complete its life cycle. Heteroecious parasites are commonly found among rust fungi.

EARLYWOOD — wood formed at the beginning of the growing season. It features larger cells and lower density compared to latewood.

SOLUTION — typically a liquid in which the molecules of a solute (e.g., sugar) are dispersed among the molecules of a solvent (e.g., water).

DIFFUSE-POROUS WOOD — wood in which the vessels are distributed fairly evenly throughout the annual ring, or in which there is little variation in vessel size between earlywood and latewood.

RAPHIDES (Greek rhaphis, a needle) — sharp, slender, needle-like crystals of calcium oxalate formed in the vacuoles of many plant cells.

RACHIS (Greek rhachis, spine) — the main axis of an inflorescence spike; the axis of a frond from which leaflets arise; in compound leaves, the continuation of the petiole corresponding to the midrib of a simple leaf.

REACTION WOOD — abnormal wood that develops in leaning trunks and branches.

REACTION CENTER — a chlorophyll molecule in a photosystem capable of utilizing energy to drive a photochemical reaction.

REGULATOR — a gene that suppresses the activity of a structural gene within an operon.

REDUCER — see decomposer.

RECOMBINANT DNA — DNA fragments from two different species, such as a mammal and a bacterium, joined together into a single molecule under laboratory conditions.

RECOMBINATION — the formation of a new combination of genes.

REPLICATION — the production of an exact copy. This term typically refers to the duplication of a DNA molecule or the formation of a sister chromatid.

REPRESSOR — a protein that regulates DNA Transcription by blocking the binding of RNA polymerase to the promoter, thereby preventing transcription. See operator.

CILIA — short flagella, usually numerous and arranged in rows.

RESTRICTION ENZYMES — enzymes that "cut" DNA molecules at sites characterized by strictly specific nucleotide sequences.

RECESSIVE — an allele whose phenotypic expression in a heterozygote is masked by a dominant allele. Consequently, the heterozygote is phenotypically indistinguishable from the dominant homozygote.

RIBOSE — a five-carbon sugar, a component of RNA.

RIBONUCLEIC ACID — a nucleic acid synthesized on a chromosomal DNA template and involved in Protein Synthesis. It is a polymer chain consisting of phosphate, a five-carbon sugar (ribose), purines, and pyrimidines. In many viruses, it serves as the genetic material.

RIBOSOME — a small particle composed of Protein and RNA; the site of protein synthesis.

RHIZOIDS (Greek rhiza — root) — (1) branching, root-like outgrowths of fungi and algae that serve for the absorption of water and nutrients; (2) root-like Hair-like structures of the free-living gametophyte in liverworts, mosses, and certain vascular plants.

RHYTIDOME — see outer bark.

RNA — see ribonucleic acid.

GENUS — a taxonomic rank intermediate between family and species. It includes one or more species.

HILUM — see hilum (1).

STIGMA — the part of a carpel specialized for receiving pollen grains, where they germinate.

C

SAVANNA — a grassland community with scattered trees¹

¹ In Soviet literature, this term is applied exclusively to tropical communities. — Editor's note.

SAPROBIONT (Greek sapros — rotten + bios — life) — an organism that feeds on non-living organic matter.

SATELLITE DNA — a sequence consisting of many thousands of tandemly repeated short nucleotide sequences. It differs in base composition from other regions of the chromosome and is not transcribed.

SUCRASE — an enzyme that hydrolyzes sucrose into glucose and fructose.

SUCROSE — a disaccharide composed of glucose and fructose residues; the primary transport form of carbohydrates produced during photosynthesis.

AGGREGATE FRUIT — a fruit developing from several separate carpels of a single flower.

LIGHT REACTIONS — reactions of photosynthesis that require light to proceed and cannot take place in the dark.

CIRCINATE VERNATION — the cochleate or coiled arrangement of leaves and leaflets within a bud. This spiral gradually uncoils as the leaves develop. It is characteristic of ferns.

FREE ENERGY — energy that is available to do work.

CROP ROTATION — the practice of growing a series of Different types of crops in the same area across a sequenced schedule to mitigate pest and disease flare-ups, enhance soil fertility, and reduce erosion.

FAMILY — a taxonomic rank situated between order and genus. The scientific Latin name of a family in animals and heterotrophic protists ends in -idae, and in other organisms in -aceae. A family is a subdivision of an order and comprises one or more genera.

SEED COAT (TESTA) — the outer protective covering of a seed, developing from the integuments of the ovule.

OVULIFEROUS SCALE — in certain conifers, an outgrowth or scale-like shoot to which the ovules are attached.

SEED — a reproductive structure formed from a ripened ovule following fertilization.

COTYLEDON — an embryonic leaf. In monocotyledons, it typically functions in nutrient absorption, whereas in dicotyledons, it serves as a nutrient storage organ.

OVULE — a structure in seed plants comprising the female gametophyte with an egg cell, surrounded by the nucellus and one or two integuments. Upon maturation, it develops into a seed.

ACHENE — a simple, dry, indehiscent, single-seeded fruit in which the seed coat is not fused to the pericarp.

FUNICULUS — see funicle.

OVULE — see ovule.

SEPTATE (from Lat. septum — partition) — divided into cells or compartments by transverse walls.

PITH (MEDULLA) — the central ground tissue of a stem or root, enclosed by the vascular cylinder. It typically consists of parenchyma cells.

MEDULLARY RAYS (PITH RAYS) — radial sheets of tissue within a stem, situated between the vascular bundles.

CATKIN (AMENT) — a spike-like inflorescence of unisexual flowers, found exclusively in woody plants.

RETICULATE VENATION — a network-like arrangement of veins within a leaf blade. It is characteristic of dicotyledons.

SESSILE — attached directly by the base without an intervening stalk. The term applies to leaves lacking a petiole, flowers without a pedicel, and fruit lacking a stalk.

SYM-, SYN- (from Gr. syn — together with) — a prefix meaning "together" or "with".

Symbiosis (from Gr. syn + bios — life) — the close and prolonged functional association of two or more organisms of different species. It manifests either as parasitism, where the interaction is detrimental to one organism, or as mutualism, where the interaction is beneficial to all participants.

SYMPLAST (from Gr. syn + plastos — formed, molded) — the interconnected network of plant cell protoplasts linked by plasmodesmata. The movement of substances through this pathway is known as symplastic transport.

SYMPODIUM — a stem vascular bundle together with its associated leaf traces.

SYNGAMY (from Gr. syn + gamos — marriage) — the fusion of two haploid cells to form a diploid zygote; synonymous with fertilization.

SYNERGIDS — two short-lived cells adjacent to the egg cell within the mature embryo sac of flowering plants.

SYNTHESIS — the formation of more complex chemical compounds from simpler ones.

SYNCYTIUM — see coenocytic.

SYSTEMATICS — the science of organismal diversity, taxonomic groups, and their evolutionary relationships.

TISSUE SYSTEM — a tissue or group of tissues forming a structural and functional unit of a plant or its organ. There are 3 tissue systems: dermal, vascular, and ground.

SIEVE CELL — an elongated, slender sieve element with relatively unspecialized sieve areas and slanted end walls that lack sieve plates. Characteristic of the phloem of gymnosperms and lower vascular plants.

SIEVE PLATE — a portion of the wall of a sieve-tube member bearing one or more highly differentiated sieve areas.

SIEVE TUBE — a series of end-to-end connected sieve-tube members with sieve plates between them.

SIEVE AREA — a region of the cell wall of sieve elements bearing clusters of pores through which the protoplasts of adjacent sieve elements communicate.

SIEVE ELEMENTS — phloem cells involved in long-distance transport of nutrients. They are subdivided into sieve cells and sieve-tube members.

SIPHONOUS STRUCTURE (Greek siphon — tube) — an algal structure characterized by the presence of multinucleate cells lacking cross walls. See coenocytic.

SIPHONOSTELE (Greek siphon + stele — pillar) — a stele in the form of a hollow cylinder of vascular tissue surrounding the pith.

SCARIFICATION — the scratching or softening of the seed coat to accelerate germination.

SCLEREIDS (Greek skleros — hard) — sclerenchymatous cells with thick, lignified secondary walls pierced by numerous pits. They vary in shape and are usually not very long. They may die or remain alive at maturity.

SCLERENCHYMA (Greek skleros + Latin enhima — filling) — a mechanical tissue composed of sclerenchymatous cells — sclereids and fibers.

SCLERENCHYMOUS CELLS — cells of various SHAPES AND SIZES with more or less thick, often lignified secondary walls. They may die or remain alive at maturity. Sclerenchymatous cells include sclereids and fibers.

THALLUS — a plant body not differentiated into root, stem, and leaves. The term thallus was traditionally used when fungi and algae were classified as plants, to distinguish their simple structure, as well as that of certain gametophytes, from the differentiated body of plant sporophytes and the gametophytes of some bryophytes.

COMPOSITE LEAF — a leaf whose blade is divided into several separate leaflets.

RESIN DUCTS — tubular intercellular spaces lined by epithelial cells that secrete resin and filled with it.

PERFECT FLOWER — see bisexual flower.

SAP — (1) the fluid content of xylem or phloem sieve elements; (2) cell sap — the fluid content of vacuoles.

CONTRACTILE VACUOLE — a clear vacuole found in certain groups of protists; by expanding, it absorbs water from the intracellular environment, and then, by contracting, expels it outside the cell.

SOMATIC CELLS (Greek soma — body) — all body cells except gametes and the cells from which gametes develop.

COMMUNITY — an assemblage of organisms living in the same area and interacting with one another.

MULTIPLE FRUIT — a cluster of fused fruits developing from multiple flowers, as in the pineapple.

COUPLED REACTIONS — linked reactions, one of which proceeds with the release of energy and the other with its consumption.

SOREDIUM (Greek soros — heap) — a specialized structure for vegetative reproduction in Lichens, consisting of several cyanobacterial or green algal cells surrounded by fungal hyphae.

WEED — a wild, typically herbaceous plant that has no practical or ornamental value, competing for space or otherwise inhibiting the growth of cultivated plants.

CULTIVAR — a plant variety that exists only in cultivation.

SORUS (Greek soros) — a cluster of spores or sporangia.

DORMANT STATE (DORMANCY) — the cessation of growth in an entire plant, its buds, or seeds until a specific environmental stimulus is received, such as cold exposure or a specific photoperiod. This requirement for a stimulus prevents development during unreliably transient favorable conditions.

VASCULAR CAMBIUM — see cambium.

VESSELS — tubular xylem elements consisting of elongated cells (vessel elements) joined end-to-end and interconnected by perforations. The function of vessels is to transport water and minerals throughout the plant body. They are found in almost all angiosperms and certain other vascular plants, such as the Gnetales.

INFLORESCENCE — a cluster of flowers on a specialized shoot.

ACTION SPECTRUM — the spectrum of light wavelengths that triggers a specific physiological response.

SPERMATANGIUM (Greek sperma — seed + Latin tangere — to touch) — a cell in red algae in which spermatia are produced.

SPERMATOGENOUS CELL — a cell of the male gametophyte (pollen grain) in gymnosperms that divides mitotically to produce two sperms.

SPERMATOPHYTE (Greek sperma + phyton — plant) — a seed plant.

SPERMATIUM — a non-motile male gamete of red algae and certain fungi.

SPERM — a mature male gamete, typically motile and smaller in size than the female gamete.

SPERGONIUM (Greek sperma + gonos — offspring) — a structure in rust fungi that produces spermatia.

SPECIALIZED CELL — a cell adapted to perform a specific function.

SPECIALIZED ORGANISM — an organism possessing specific adaptations for a particular habitat or way of life.

Specificity — uniqueness; restriction to a strictly defined organism or process.

SPIRILLUM (Latin spira — coil) — a long, spirally twisted bacterium.

SPORANGIOPHORE — see sporangiophore.

SPORANGIUM (Greek spora — seed + angeion — vessel) — a single-celled or multicellular hollow structure in which spores are formed.

SPORANGIOPHORE (Greek spora + angeion + pherein — to bear) — an outgrowth bearing one or more sporangia.

SPOROPOLLENIN — a highly durable substance that makes up the outer wall of spores and pollen grains.

SPOROPHYLL — a modified leaf or leaf-like organ bearing a sporangium. Sporophylls include the stamens and carpels of angiosperms, the fertile fronds of ferns, and similar structures.

SPOROPHYTE — the diploid (2n) spore-producing phase in the life cycle of organisms exhibiting alternation of generations.

SPOROPHYTE — in bryophytes, the stalk bearing a capsule. A portion of the sporophyte (sometimes absent).

SPORES — reproductive, typically single-celled structures from which an adult organism can develop without fusing with other cells.

MIDDLE LAMELLA — a layer of intercellular substance rich in pectic compounds that binds together the primary walls of adjacent cells.

STATOLITHS (from Greek statos, standing, + lithos, stone) — gravity receptors; starch grains and other inclusions within the cytoplasm.

STEM — the axial organ of vascular plants situated above the soil level, as well as anatomically similar underground parts such as the rhizome and corm.

STEM BUNDLE — a vascular bundle of the stem.

STELE (from Greek stele, pillar) — the central cylinder; the complex of vascular and mechanical Tissues of the stem and root of vascular plants, surrounded by the cortex.

TAPROOT — the primary root of a plant that develops as a direct continuation of the embryonic root; it appears as a massive, cone-shaped main root from which smaller lateral roots branch off.

STERIGMATA (singular sterigma, from Greek sterigma, prop) — small, slender outgrowths of basidia upon which basidiospores are borne.

STERILE CELL — one of the two cells formed during the division of the generative cell in a developing gymnosperm pollen grain; it is not a gamete and eventually degenerates.

STIGMA — the light-sensitive eyespot found in certain algae.

COLUMNAR ROOTS — a specialized type of prop roots.

STOLON (from Latin stolo, shoot) — a horizontal stem growing parallel to the soil surface that occasionally gives rise to adventitious roots; exemplified by strawberry runners.

STRATIFICATION — the process of exposing seeds to low temperatures for an extended period prior to germination at higher temperatures.

STROBILUS (from Greek strobilos, pine cone) — a reproductive structure consisting of numerous modified leaves (sporophylls) or scales bearing sporangia, densely clustered at the apex of a shoot; characteristic of many gymnosperms, lycophytes, and horsetails.

STROMA (from Greek stroma, mattress or bed) — the colorless fluid matrix of a plastid.

SILIQUE — a dry fruit characteristic of the mustard family (Brassicaceae). It develops from two carpels and dehisces by two Valves from the base to the apex, with seeds attached to a false partition (replum) between the valves. A short, flattened silique is called a silicle.

SUB- (from Latin sub, under, below) — a prefix meaning "under"; for example, subepidermal means situated beneath the epidermis.

SUBERIN (from Latin súber, cork oak) — a fat-like substance deposited in the cell walls of cork tissue and in the Casparian strips of the endodermis.

SUBSTRATE (from Latin substratus, strewn underneath) — (1) the surface or base upon which an organism attaches or lives; (2) the substance upon which an enzyme acts.

SUBSTRATE-LEVEL PHOSPHORYLATION — the formation of ATP from ADP and inorganic phosphate during the process of glycolysis.

SUCCULENT — a plant with fleshy, water-storing stems or leaves.

SUCCESSION — in ecology, the orderly, directional replacement of plant communities from the initial colonization of a barren area to the establishment of a climax community typical of that geographic zone.

OPPOSITE — buds or leaves arranged in pairs at a node.

SUSPENSION — a heterogeneous system consisting of relatively large solid particles dispersed throughout a fluid phase from which they do not readily settle out under The Influence of gravity.

SUSPENSOR — a structure at the base of the embryo in many vascular plants that pushes the developing embryo deep into the endosperm.

SPHEROSOMES — single spherical structures in the cytoplasm of plant cells, consisting mainly of lipids and bounded by a membrane. They are thought to serve as centers for lipid synthesis and accumulation.

SCHIZO- (Greek schizein — to split) — a combining form meaning "splitting" or "cleaved".

SCHIZOCARP — a dry fruit composed of two or more fused carpels that separate as the fruit matures.

LINKAGE — the tendency of certain genes to be inherited together due to their location on the same chromosome.

T

TAIGA — the northern coniferous forest.

CRYPTOGAMS — an outdated term designating All living organisms except for flowering plants (phanerogams), animals, and heterotrophic protists.

TAXON — a general term for any taxonomic category, such as species, order, class, division, etc.

Taxonomy (Greek taxis — arrangement + nomos — law) — the science of organism classification.

THALLUS (Greek thallos — sprout) — see thallome.

THALLOPHYTES — an outdated term formerly used to designate fungi and algae.

TANGENTIAL SECTION — a longitudinal section passing perpendicular to the radius of a cylindrical structure, such as a root or stem; in secondary xylem and phloem, it passes at right angles to the medullary rays.

TANDEM CLUSTERS — multiple copies of a single gene arranged in rows one after another.

TAPETUM (Greek tapes — carpet) — a tissue within the sporangium, particularly the anther, that provides Nutrition for developing spores (pollen).

HARDWOOD — a common term for the wood of dicotyledonous plants.

TEXTURE (OF WOOD) — the size-dependent distribution of elements within an annual ring.

TELIOSORUS — a structure in rust fungi where teliospores are formed.

TELIOSPORE — a thick-walled spore of rust fungi in which karyogamy and meiosis take place and from which basidia develop.

TELOPHASE — the final phase of mitosis and meiosis during which two new nuclei are formed from the chromosomes.

DARK REACTIONS — light-independent enzymatic reactions in photosynthetic cells associated with the formation of glucose from СO₂ involving ATP and NADPH.

THEORY (Greek theorein — to look at) — a well-tested hypothesis that is unlikely to be disproved by future observations.

Thermodynamics (Greek therme — heat + dynamis — power) — the science of energy exchange, treating heat as the most convenient form of energy measurement. The First Law of thermodynamics states that in any process, the total energy of the universe remains constant. According to the second law of thermodynamics, Entropy—i.e., a measure of disorder—tends to increase.

TETRAD — a group of four haploid spores formed from a mother spore cell as a result of meiosis.

TETRAPLOID (Greek tetra — four + ploos — fold) — a cell or organism with a chromosome number of 4n, which is twice the normal diploid Complement (2n).

TETRASPORANGIUM (Greek tetra + spora — seed + angeion — vessel) — a sporangium of certain red algae in which meiosis occurs to form tetraspores.

TETRASPOROPHYTE (Greek tetra + spora + phyton — plant) — the diploid phase in the life cycle of certain red algae that produces tetrasporangia.

TETRASPORES — four spores formed through meiotic division of the parent spore cell within the tetrasporangium of certain red algae.

THIGMOTROPISM (Greek thigma — touch) — an organism's directional growth response to contact with a solid object.

THYLAKOID (Greek thylakos — sac + oidēs — like) — a membrane-bound compartment inside cyanobacteria and chloroplasts of eukaryotic organisms, pouch-like in appearance. Contains chlorophyll. In chloroplasts, stacks of thylakoids form grana.

TYLOSES (Greek tylos — swelling) — bladder-like outgrowths of axial or ray parenchyma cells that penetrate through pitting in vessel walls into the lumens of the vessels.

THYMINE — a pyrimidine base found in DNA but absent in RNA.

PHYLUM — a taxonomic rank used in the classification of animals and heterotrophic protists; equivalent to division in botany.

MATING TYPE — a particular genetic strain of organisms of the same species whose members cannot mate with each other, but can mate only with members of other mating types of the same species.

TISSUE — a group of similar cells that perform a shared structural and functional role.

TONOPLAST (Greek tonos — tension + plastos — formed) — the cytoplasmic membrane surrounding the vacuole of a plant cell.

TORUS — the central thickened portion of the pit membrane in conifers and certain other gymnosperms.

TOTIPOTENCY — the ability of tissues or cells to differentiate into any cell type of a mature organism.

POINT MUTATION — an alteration of a single nucleotide within a chromosomal DNA molecule.

HERBS — non-woody seed plants with relatively short-lived aerial parts.

Transduction — the transfer of genetic material from one organism to another by a viral vector.

TRANSCRIPTION — the enzymatic synthesis of an RNA molecule complementary to one of the DNA strands.

TRANSLOCATION — (1) the long-distance transport of water, mineral ions, and nutrients within plants; (2) the interchange of chromosomal segments between nonhomologous chromosomes.

TRANSLATION — the synthesis of proteins from amino acids on ribosomes guided by The Genetic Code carried by mRNA.

Transpiration (French transpirer — to perspire) — the evaporation of water from plants, occurring primarily through the Stomata.

TRANSPOSITION — the relocation of a genetic element within a chromosome.

TRANSPOSON (Latin transponere — to transpose) — a DNA sequence containing one or more genes flanked by specific terminal sequences that grant the element The ability to move from one DNA molecule to another; a transposable element.

Transfer RNA — a small RNA molecule that binds a specific amino acid and delivers it to the ribosome at the correct position during protein synthesis. At least one type of tRNA exists for each amino acid.

TRANSPORT PROTEINS — specialized Membrane Proteins that facilitate the movement of solutes across Biological Membranes.

TRANSFORMATION — the uptake and incorporation of foreign DNA by a cell from its environment. In laboratory settings, Transposons are often used as vectors for transformation.

TRACHEARY ELEMENTS — a collective term for the water-conducting cells of vascular plants, namely vessel members and tracheids.

TRACHEID — an elongated, tapering, thick-walled xylem conducting and supporting cell with pitted walls. The walls of T. are pitted, but unlike vessel elements, they lack perforations. T. are present in almost all vascular plants.

Tricarboxylic Acid Cycle — see Krebs cycle.

TRIOSE (Greek tries — three + ose — suffix denoting a carbohydrate) — a sugar containing three carbon atoms.

TRIPLOID (Greek triploos — triple) — an organism or cell having a chromosome set of 3n.

TRITIUM — a radioactive hydrogen isotope ³H with a nucleus containing one proton and two neutrons (the Nucleus of the most abundant hydrogen isotope consists of a proton only).

TRICHOGYNE (Greek trichos — hair + gyne — woman) — an outgrowth of the female gametangium that receives and conducts spermatia. Found in red algae, certain ascomycetes, and basidiomycetes.

TRICHOME (Greek trichos — hair) — an epidermal outgrowth (hair, scale, bristle, water vesicle, etc.).

tRNA — see transfer RNA.

TRIPLE FUSION — in angiosperms, the fusion of the second male gamete (sperm) with the polar nuclei, resulting in the Formation of the primary endosperm nucleus, which is triploid (3n) in most groups.

TROPISM (Greek trope — turning) — a directional motor response to an external stimulus, where the direction of movement is typically determined by the direction of the stimulus.

-TROPH, TROPHO- (Greek trophos — feeder) — a combining form meaning "feeding" or "nourishing", for example, autotroph — "self-feeding".

TROPHIC LEVEL — a specific stage in the flow of energy through an ecosystem, represented by a group of organisms with a similar feeding mode.

TUBULAR FLOWERS — actinomorphic flowers of composites, typically located in the center of the inflorescence and surrounded by flattened zygomorphic ligulate flowers.

TUBULAR COROLLA — a tube-like structure formed by the fusion of petal margins.

TUNDRA — a treeless circumpolar biome best developed in the Northern Hemisphere, north of the Arctic Circle.

TUNICA-CORPUS THEORY — a theory of the Organization OF THE shoot apical meristem in most angiosperms and some gymnosperms, according to which the meristem consists of one or more peripheral cell layers (the tunica) and an internal core (the corpus). The tunica provides surface growth of the meristem (via anticlinal divisions), while the corpus drives volume increase (via cell divisions in various planes).

TURGOR PRESSURE (Latin turgor — swelling) — the pressure inside a cell resulting from the inward flow of water.

STAMEN — the pollen-producing part of a flower, typically consisting of an anther and a filament. Collectively, stamens form the androecium.

FILAMENT — the stalk of a stamen that Supports the anther.

STAMINATE (FLOWER) — a flower bearing stamens but lacking functional carpels.

U

Hydrocarbons — organic compounds consisting entirely of carbon and hydrogen atoms.

CARBOHYDRATES — organic compounds composed of carbon chains attached to hydrogen and oxygen atoms in a 2:1 ratio. Examples include sucrose, starch, glycogen, and cellulose.

CARBON CYCLE — the global Circulation and utilization of carbon atoms throughout the biosphere.

NODE — the region of a stem where one or more leaves are attached.

TEMPERATE PHAGE — a bacterial virus that can exist in a latent state (as a prophage) within a host bacterial cell. The prophage is integrated into the bacterial chromosome and replicates along with it.

URACIL — a pyrimidine found in RNA but absent in DNA.

UREDINEUM (from Lat. ureredo — plant disease) — a structure that produces urediniospores in rust fungi.

UREDINIOSPORES (from Lat. uredo + Gk. spora — seed) — binucleate reddish spores produced by rust fungi during the summer.

TENDRIL — a leaf, part of a leaf, or stem modified into a slender, spiraling structure that serves to anchor the stem. Found only in certain angiosperms.

STOMA — a microscopic pore in the epidermis of leaves and stems, bordered by guard cells and designed for gas exchange. The stomatal apparatus refers to the stoma together with its guard cells.

F

PHAGE — see bacteriophage.

PHAGOCYTOSIS — see endocytosis.

P-PROTEIN — phloem protein; a proteinaceous substance found in the phloem cells of angiosperms, most frequently in sieve-tube elements.

PHELLEM — see cork.

PHELLOGEN — see cork cambium.

PHELLODERM (from Gk. phellos — cork + derma — skin) — the inner layer of the periderm. It is produced by the cork cambium inward, i.e., in the direction opposite to the cork.

PHENOTYPE — the observable physical expression of an organism, resulting from the interaction between its genotype and the environment.

ENZYME — a protein capable of accelerating a specific chemical reaction by lowering its activation energy. A biological catalyst that remains unchanged by the reaction.

FERREDOXINS — iron-rich proteins that participate in electron transport, including photosynthetic processes.

PHYSIOLOGY — the branch of science dealing with the processes occurring in living organisms.

PHycobilins — a group of water-soluble accessory pigments found in red algae and cyanobacteria; includes phycocyanins and phycoerythrins.

PHYCOLOGY (from Gk. phykos — seaweed) — the study of algae.

PHycoplast — a system of microtubules that forms between two daughter nuclei parallel to the plane of cell division. Found exclusively in green algae of the class Chlorophyceae.

CARBON FIXATION — the conversion of CO₂ into organic compounds during photosynthesis.

-PHYLL, PHYLLO- (from Gk. phyllon — leaf) — a combining form meaning "leaf".

PHYLLODE — a flattened and expanded petiole or stem that serves as a photosynthetic substitute for the leaf blade in certain vascular plants.

PHYLOGENY (from Gk. phylon — tribe, race) — the evolutionary relationships among organisms; the evolutionary history of a taxonomic group.

-PHYTE, PHYTO- (from Gk. phyton — plant) — a combining form meaning "plant" or "botanical".

PHYTOPLANKTON — autotrophic plankton.

PHYTOPHAGE — a herbivorous organism.

Phytochrome — a phycobilin-like pigment found in the cytoplasm of plants and certain green algae. A red and far-red light photoreceptor; involved in the photoperiodic regulation of flowering, dormancy, leaf formation, and seed germination.

FLAVOPROTEIN — a dehydrogenase containing flavin and often a metal; plays a crucial role in oxidation.

FLORIGEN (Lat. flor — flower + Gk. genes — producing) — a plant hormone that stimulates flowering.

PHLOEM (Gk. phloos — bark) — the organic-nutrient-conducting tissue of vascular plants, consisting of sieve elements, various parenchymatous cells, fibers, and sclereids.

PHOSPHATES — compounds formed from phosphoric acid by the replacement of one or more hydrogen atoms.

PHOSPHOLIPIDS — phosphorylated lipids; structurally similar to fats, but differing in that one of the three fatty acids linked to glycerol is replaced by a phosphorus-containing molecule; an essential component of cell membranes.

PHOSPHORYLATION (Gk. phosphoros — bringing light) — the reaction of adding a phosphate group to any compound, for example, the formation of ATP from ADP and inorganic phosphate.

PHOTO- (Gk. photos — light) — a combining form meaning "light".

PHOTORESPIRATION — light-dependent formation of glycolic acid in chloroplasts followed by its oxidation in peroxisomes.

PHOTOLYSIS (OF WATER) — the light-dependent splitting of water molecules occurring in Photosystem II during the light reactions of photosynthesis.

PHOTON — an elementary particle of light.

Photoperiodism — a response to the relative lengths of day and night that enables an organism to distinguish the seasons.

PHOTOSYNTHESIS (Gk. photos + syn — together + tithenai — to place) — the conversion of light energy into chemical energy. The synthesis of carbohydrates from carbon dioxide and water in the presence of chlorophyll using light energy.

PHOTOSYSTEM — a discrete organizational unit in chloroplast thylakoids consisting of chlorophyll and other pigment molecules involved in the light reactions of photosynthesis.

PHOTOTROPISM (Gk. photos + trope — a turning) — growth, turning, or bending in a direction determined by the location of a light source.

Photophosphorylation — the formation of ATP in chloroplasts during photosynthesis.

FP — see flavoprotein.

PHRAGMOPLAST — a spindle-shaped system of fibrils that forms between two daughter nuclei in telophase. During cytokinesis, the cell plate forms within the phragmoplast. Phragmoplast fibrils consist of microtubules. It is found in all plants and green algae except members of the class Chlorophyceae.

FUCOXANTHIN (Gk. phykos — seaweed + xanthos — yellowish-brown) — a brownish carotenoid found in brown algae and chrysophytes.

FUNICULUS (Lat. funiculus — little cord) — the stalk by which an ovule is attached to the ovary wall.

F₁ — the first generation of offspring resulting from a cross. Subsequent generations are designated F₂, F₃, etc.

X

CHALAZA (Gk. chalaza — a small tubercle) — the basal region of an ovule or seed where the funiculus attaches to the integuments and nucellus.

HARDY-WEINBERG LAW — a mathematical expression for the relative frequencies of two or more alleles in a population. According to the H.-W. law, in the absence of inbreeding, selection, and other Evolutionary Processes in a randomly mating population, allele and genotype frequencies remain constant.

Chemiosmotic Coupling — the coupling of ATP synthesis to electron transport across a membrane via an electrochemical gradient of H⁺.

CHEMOAUTOTROPHS — bacteria capable of synthesizing essential nutrients using energy released during certain inorganic reactions. See autotrophs.

CHIASMA (Greek chiasma, cross) — an X-shaped structure formed by non-sister chromatids of homologous chromosomes; the site where crossing-over occurs.

HILL REACTION — the evolution of oxygen and the photoreduction of an artificial electron acceptor by isolated chloroplasts from leaves in the absence of carbon dioxide.

CHEMICAL REACTION — the formation or breaking of chemical bonds between atoms or molecules.

CHEMICAL POTENTIAL — the Free energy of a substance, which depends on the average velocity of molecular motion and their concentration.

Chitin (Greek chiton, tunic or covering) — a tough, rigid, nitrogen-containing polysaccharide that forms the cell walls of certain fungi, the exoskeleton of Arthropods, the epidermal cuticle, and other surface structures in some protists and animals.

CARNIVOROUS — see carnivorous.

CHLOR- (Greek chloros, green) — a combining form meaning "green".

CHLORENCHYMA — parenchyma tissue containing chloroplasts.

CHLOROSIS — the complete loss or deficiency of chlorophyll.

CHLOROPLAST — a chlorophyll-containing plastid in which photosynthesis takes place. Chloroplasts are found in plants and algae.

CHLOROPHYLL (Greek chloros + phyllon, leaf) — the green pigment of plant cells; the primary receptor of light energy in photosynthesis. Also found in algae and photosynthetic bacteria.

PROP ROOTS — a specialized type of supportive roots.

HOST — an organism upon or within which a parasite lives.

COLD HARDENING — the capacity acquired by plants under the influence of cold to withstand extremely low temperatures and the desiccating effects of winter weather.

CHRYSOLAMINARIN — a storage carbohydrate found in chrysophytes.

CHROM- (Greek chroma, color) — a combining form meaning "color" or "colored".

CHROMATID (Greek chroma + Latin -id, daughter) — one of the two identical thread-like strands of a replicated chromosome joined together by a centromere.

Chromatin — a readily stainable complex of DNA and proteins that makes up eukaryotic chromosomes.

CHROMATOPHORE (Greek chroma + phorus, bearing) — in some bacteria, a single-membrane-bounded vesicle containing Photosynthetic Pigments.

CHROMOPLAST — a plastid containing pigments other than chlorophyll, typically yellow and orange carotenoids.

CHROMOSOME (Greek chroma + soma, body) — a nuclear structure containing genes. Eukaryotic chromosomes are clearly visible only during mitosis or meiosis as thread-like or rod-like chromatin bodies, remaining enclosed within the nucleus at other times. Bacterial chromosomes consist of circular DNA molecules.

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KINGDOM — the largest taxonomic category. Five kingdoms are typically distinguished: bacteria, protists, animals, fungi, and plants.

FLORAL TUBE — a cup or tube formed by the fusion of the basal parts of sepals, petals, and stamens. Commonly found in plants with an inferior ovary.

FLOWER — the reproductive structure of angiosperms. A complete flower consists of a calyx, corolla, androecium (stamens), and gynoecium (carpels). Each flower contains at least one stamen or one carpel.

RECEPTACLE — the region of the pedicel (peduncle) to which the floral parts are attached.

PEDICEL — the stalk of an individual flower within an inflorescence.

PEDUNCLE — the stalk of an inflorescence or a solitary flower.

CELLULASE — an enzyme that hydrolyzes cellulose.

CELLULOSE — an insoluble polysaccharide formed by microfibrils of linearly linked glucose residues; the primary component of the cell walls of plants and certain protists.

CENOCYTIC (from Greek koinos, common, + kytos, vessel) — an organism or tissue region containing multiple nuclei not separated by walls or membranes. See Siphonaceous structure.

CENTRAL MOTHER CELLS — relatively large, vacuolated cells located beneath the surface of the shoot apical meristem.

CENTRIOLE (from Greek kentron, center, + Latin -olus, diminutive) — a cytoplasmic organelle located near the nuclear envelope, structurally identical to a basal body. During mitosis and meiosis, it divides and participates in spindle formation. Found in most eukaryotes, with the exception of fungi, red algae, and non-flagellated plant cells.

CENTROMERE (from Greek kentron + meros, part) — the specialized region of a chromosome to which spindle fibers attach during cell division.

CYCLIC ELECTRON FLOW — a light-induced flow of electrons in chloroplasts that both begins and ends in Photosystem I.

CYCLOSIS (from Greek kyklosis, movement in a circle) — the streaming or circulation of cytoplasm within a cell.

CIRCADIAN RHYTHMS (from Latin circa, about, + dies, day) — regular rhythms of growth and activity with a period of approximately 24 hours.

CISTERNA (from Latin cisterna, reservoir) — a flattened or sac-like compartment of the endoplasmic reticulum or a dictyosome (Golgi body).

-CYTE, CYTO- (from Greek kytos, vessel) — combining form denoting a relation to a cell.

CYTOSINE — a pyrimidine base that is a constituent of DNA and RNA.

CYTOKINESIS — see Cell division.

CYTOKININS (from Greek kytos + kinesis, movement) — a class of plant hormones that stimulate cell division and induce various other physiological effects.

Cytology — the branch of biology that studies the structure and function of cells.

CYTOPLASM — the fluid content of a cell, excluding the nucleus.

Cytoskeleton — a dynamic intracellular network of microtubules and microfilaments.

CYTOCHROME (from Greek kytos + chroma, color) — a heme-containing protein that functions as an electron carrier in respiration and photosynthesis.

TCA CYCLE — see Tricarboxylic acid cycle.

C₃ metabolism — see Calvin cycle.

C₄ metabolism — a series of reactions in which carbon dioxide is fixed to phosphoenolpyruvate to form the four-carbon compound oxaloacetate.

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CALYX — the outer whorl of floral organs, consisting of individual sepals that typically protect the other flower parts in the bud stage.

CAMBIUM — see lateral meristem.

CARBOHYDRATE — an organic compound consisting of carbon, hydrogen, and oxygen, typically with a hydrogen-to-oxygen ratio of 2:1 (as in water); includes sugars, starches, and cellulose.

CARBON FIXATION — the conversion of inorganic carbon (carbon dioxide) into organic compounds by living organisms, most notably during photosynthesis.

CARPEL — the female reproductive organ of a flower, consisting of an ovary, style, and stigma; may be single or fused with others to form a pistil.

CELL — the basic structural, functional, and biological unit of all known living organisms.

CELL DIVISION — the process by which a parent cell divides into two or more daughter cells.

CELL MEMBRANE — a biological membrane that separates the interior of all cells from the outside environment, regulating The transport of materials entering and exiting the cell.

CELL WALL — a rigid layer surrounding a cell, located outside the cell membrane, providing structural support and protection.

CENTROMERE — the specialized region of a chromosome where sister chromatids are joined and spindle fibers attach during cell division.

CHLOROPLAST — an organelle found in plant cells and eukaryotic algae that conducts photosynthesis.

CHROMATIN — a complex of DNA and protein found in eukaryotic cells, The primary function of which is to package long DNA molecules into more compact, denser structures.

CHROMOSOME — a DNA molecule containing all or part of the genetic material of an organism.

COHESION — the binding together of like molecules, often by Hydrogen Bonds, which is particularly strong in water.

COLLENCHYMA — plant tissue supporting growth in young stems and leaves, characterized by unevenly thickened primary cell walls.

COMPANION CELL — a specialized cell located adjacent to a sieve tube element in angiosperm phloem, directing its cellular activities.

CORTEX — the outermost layer of the stem or root in a plant, bounded by the epidermis outside and the vascular tissue inside.

COTYLEDON — an embryonic leaf in seed-bearing plants, one or more of which are the first to appear from a germinating seed.

CROSSING OVER — the EXCHANGE OF GENETIC material between non-sister chromatids of homologous chromosomes during meiosis, resulting in new combinations of alleles.

CUTICLE — a protective, hydrophobic waxy covering produced by the epidermal cells of leaves, young shoots, and other plant organs of vascular plants.

CYTOPLASM — the gelatinous liquid that fills the inside of a cell, comprising the Cytosol and the organelles suspended within it.

CYTOSKELETON — a microscopic network of protein filaments and tubules in the cytoplasm of many living cells, giving them shape and coherence.

ECO- (Greek oikos — house) — a combining form meaning "habitat".

ECOLOGY — the scientific Study of the interactions between organisms and their physical environment, as well as with each other.

ECOSYSTEM — a large-scale system comprising interacting organisms and their physical environment.

ECOTYPE (Greek oikos + Latin typus — type) — a population or group of organisms within a given species that is adapted to local environmental conditions and genetically differentiated from other ecotypes of the same species.

ECTOPLAST — see plasma membrane.

ELATERS (Greek elater — driver) — (1) elongated, spindle-shaped sterile cells within the sporangia of liverworts that aid in spore dispersal; (2) spirally coiled, hygroscopic bands attached to the spores of horsetails.

ELECTROLYTE — a substance that dissociates into ions in aqueous solution, thereby enabling the solution to conduct an electric current.

ELECTRON — an elementary particle carrying a negative charge equal in magnitude to the positive charge of a proton, and possessing a mass 1837 times smaller than the latter. Electrons Orbit the atomic nucleus and determine The chemical properties of an atom.

ELECTRON-DENSE — impermeable to an electron beam, appearing as a dark region in the field of view of an electron microscope.

ELEMENT — a specific type of atom. Just over a hundred natural and synthetic elements, individually and in various combinations, constitute the entire diversity of substances in the Universe.

UNIT MEMBRANE — a trilaminar membrane which, when viewed under a microscope, appears as two dark layers separated by a light-colored central layer.

Embryogenesis — the development of an embryo.

ENDERGONIC — requiring an inward input of energy from an external source to proceed. Antonym: exergonic.

ENDO- (Greek endo — within) — a combining form meaning "within" or "internal".

ENDOGENOUS (Greek endo + genos — race, birth) — originating from tissues located deep within; an example is lateral roots.

ENDODERMIS (Greek endo + derma — skin) — a layer of cells enclosing the vascular cylinder in roots and certain stems. The radial and transverse walls of endodermal cells bear Casparian strips. In seed plants, the endodermis represents the innermost layer of the primary cortex.

ENDOCARP (Greek endo + karpos — fruit) — the innermost layer of the pericarp.

ENDOMEMBRANE SYSTEM — a network of cellular membranes that are continuous with one another, including the plasma membrane, tonoplast, endoplasmic reticulum, Golgi bodies, and nuclear envelope.

ENDOPLASMIC RETICULUM — a three-dimensional membranous network that divides the cytoplasm of eukaryotic cells into compartments and channels. Regions studded with numerous ribosomes are referred to as rough ER, whereas regions with few or no ribosomes are termed smooth ER.

ENDOSPERM (Greek endo + sperma — seed) — tissue that develops as a result of the fusion of a male gamete with the polar nuclei of the central cell. It contains nutrient reserves and is digested by the growing sporophyte either before or after seed maturation. Found exclusively in angiosperms.

ENDOCYTOSIS (Greek endo + kytos — vessel, cell) — a cellular uptake mechanism for external substances through the invagination of the plasma membrane. The ingestion of solid particles is termed phagocytosis, whereas the uptake of fluids is called pinocytosis.

ENTROPY — a quantitative measure of the randomness or disorder of a system.

EPI- (Greek epi — upon) — a prefix meaning "upon", "on", or "over".

EPIGYNY (Greek epi — upon + gyne — woman) — a floral arrangement in which the sepals, petals, and stamens appear to arise from the top of the ovary. The opposite of hypogyny.

EPIDERMIS — the outermost, primary cell layer covering leaves, young stems, and roots.

EPICOTYL — the upper portion of the axis of an embryo or seedling, located above the cotyledons and below the first true leaf.

EPISTASIS (Greek epistasis — halting) — The Effect of one gene on the phenotypic expression of a gene at a different locus.

EPIPHYTE — an organism that grows on another organism without being parasitic on it.

Ethylene — a simple hydrocarbon with the formula Н2С=СН₂. A plant hormone involved in fruit ripening.

ETIOLATION (French étioler — to blanch) — the set of changes observed in plants grown in darkness or under very low light intensity, characterized by stem elongation, poor leaf development, and chlorophyll loss.

ETIOPLAST — a type of plastid found in plants grown in the dark, containing a prolamellar body.

EUKARYOTES (Greek eu — good + karyon — kernel, nut) — organisms whose cells feature a true nucleus, membrane-bound organelles, and chromosomes consisting of DNA and proteins. Eukaryotes comprise four kingdoms: plants, animals, fungi, and protists.

AECIUM — a cup-shaped structure in rust fungi in which aeciospores are produced.

AECIOSPORE (Greek aikia — injury + spora — seed) — a dikaryotic spore of rust fungi produced within an aecium.

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POME — a simple fleshy fruit whose outer portion is formed by floral tissues surrounding the ovary, which enlarge as the fruit ripens. Found in a subfamily

of the rose family (Rosaceae), such as in apple, pear, quince, and others.

BERRY — a simple, fleshy, multi-seeded fruit developing from one or more fused carpels that form a fleshy pericarp, for example, in grapes, tomatoes, and bananas.

NUCLEAR ENVELOPE — the double membrane enclosing the Cell Nucleus.

NUCLEUS — (1) a specialized, double-membrane-bounded structure within eukaryotic cells that contains the chromosomes; (2) the central part of an atom containing protons and neutrons, surrounded by electrons.

HEARTWOOD — non-living, typically dark-colored wood that no longer conducts water, surrounded by sapwood.

NUCLEOLUS — a small, spherical body within the nucleus of eukaryotic cells, composed mainly of rRNA transcribed from copies of corresponding genes; the site of ribosome assembly.

NUCLEOLAR ORGANIZER — a specialized chromosomal region associated with the formation of the nucleolus.

RAY FLORETS — see disk florets.

LIGULE — see ligula.

EGG APPARATUS — the egg cell and two synergids located at the micropylar end of the female gametophyte, or embryo sac, in angiosperms.

EGG CELL — a non-motile female gamete, typically larger than the male gamete of the same species.

VERNALIZATION — the induction of flowering by exposure to cold.