Botany: An Introduction to Plant Biology - Mauseth, James D. 2017

Glossary

Numbers after definitions are the chapters where the principal discussions occur. Italicized terms are defined elsewhere in the Glossary.

A

A channel The groove in the ribosome small subunit in which the free amino acid-carrying tRNA occurs. Alternative: P channel. 15

A horizon The uppermost soil layer, the zone of leaching. 25

abiotic Refers to things that are not and never have been alive. Compare: biotic. 25

abscisic acid A hormone involved in resistance to stress conditions, stomatal closure, and other processes. 14

abscission zone The region at the base of an organ, such as a leaf or fruit, in which cells die and tear, permitting the organ to fall cleanly away from the stem with a minimum of damage. 6

absorption spectrum A graph of the relative ability of a pigment to absorb different wavelengths of light. Compare: action spectrum. 10

accessory fruit A fruit that contains nonovarian tissue. Synonym: false fruit. Alternative: true fruit. 9

accessory pigment A pigment that has an absorption spectrum different from that of chlorophyll a and that transfers its absorbed energy to chlorophyll a. 10

acid-free paper Paper produced by the kraft method of separating and delignifying fibers; acid-free paper is durable and long lasting. 24

acid rain Rain that has become acidic due to air pollution; it can damage plant cuticle as well as speed the leaching of minerals from soil. 13

actinomorphic Synonym for regular flower; radially symmetrical. 9

action spectrum A graph of the relative rates of reaction of a process as influenced by different wavelengths of light. Compare: absorption spectrum. 10

active transport The forced pumping of molecules from one side of a membrane to the other by means of molecular pumps located in the membrane. 3, 12

adaptive radiation Divergent evolution in which a species rapidly diverges into many new species. 17

adenosine triphosphate (ATP) A cofactor that contributes either energy or a phosphate group or both to a reaction; as it does so, it loses either one or two phosphate groups, becoming either ADP or AMP. 10, 11

adult plant A plant that is mature enough to flower. Alternative: juvenile plant. 14

adventitious Refers to an organ that forms in an unusual place; refers primarily to roots that form on leaves, nodes, or cuttings rather than on another root. 7

agamospermy A set of methods of asexual reproduction that involve cells of the ovule and result in seeds and fruit. 9

aggregate fruit A fruit that develops from the crowding together of several separate carpels of one flower. Alternatives: simple fruit and multiple fruit. 9

albuminous cell In gymnosperm phloem, a nurse cell connected to and controlling an enucleate sieve cell. Compare: companion cell. 5

albuminous seed A seed that contains large amounts of endosperm. Alternative: exalbuminous seed. 9

all-or-none response A situation in which an organism either responds to a stimulus or does not respond; the level of response is not correlated with the level of stimulus. Alternative: dosage-dependent response. 14

alleles Versions of a gene that differ from each other in their nucleotide sequences. 16

allelochemic See allelopathy. 25

allelopathy The inhibition of germination or growth of one species by chemicals (allelochemics) given off by another species. 25

allopatric speciation Speciation that occurs when two or more populations of one species are physically separated such that they cannot interbreed. Alternative: sympatric speciation. 17

alternation of generations A type of plant life cycle in which a diploid spore-forming plant gives rise to haploid gamete-forming plants, which in turn give rise to more diploid spore-forming plants. The generations may be similar morphologically (isomorphic) or dissimilar (heteromorphic). 9, 19—22

amino acid A small molecule containing an amino group and a carboxyl group; the monomers of proteins. 2, 15

amino acid attachment site In transfer RNA, the 3′ end where the amino acid is carried. 15

amylase An enzyme that digests amylose (starch). 10

amylopectin A simple, branched polysaccharide containing only glucose residues. Much of starch is amylopectin. 10

amyloplast See plastid. 10

amylose A simple unbranched polysaccharide containing only glucose residues. Much of starch is amylose. 10

anabolism Metabolism in which large molecules are constructed from small ones. Alternative: catabolism. 10

analogous features Features that resemble each other but are not based on homologous genes, those related by descent from common ancestral genes. Alternative: homologous features. 18

anaphase The third phase of mitosis; at the metaphaseanaphase transition, centromeres divide and the two chromatids of a chromosome become independent chromosomes. During anaphase, the two are pulled to opposite poles of the spindle by spindle microtubules. 4

anaphase I The third phase of meiosis I, similar to anaphase of mitosis except that at the metaphase I-anaphase I transition, no division of centromeres occurs. Instead, one homolog is pulled away from the other in each pair, thus reducing the number of sets of chromosomes in each daughter nucleus to the haploid condition from the diploid. 4

anaphase II A phase of meiosis II, similar to anaphase of mitosis. 4

ancestral group The group of organisms that were the ancestors of another group. This can refer to the ancestral group that gave rise to just one species or to a set of species (such as the ancestral group of a genus or family). 18

androecium (pl.: androecia) A collective term referring to all the stamens of one flower. 9

angiosperm Informal term for flowering plants, members of division Magnoliophyta; their seeds develop within a fruit. Also called anthophytes. 2, 5, 22, 23

angiospermous sporophyll The sporophyll of a flowering plant, the carpel that encloses the ovule. 23

anion An ion carrying a negative charge. 10

anisogamy A type of sexual reproduction in which the two gametes are only slightly different; usually one is larger and both are motile. Alternatives: isogamy and oogamy. 19

annual plant A plant that completes its life cycle in 1 year or less. Compare: biennial and perennial. 5, 9

annual ring In secondary xylem, the set of wood, usually early wood and late wood, produced in 1 year. 8

annular thickening A pattern of secondary wall deposition in tracheids and vessel elements; the wall occurs as separate rings. 5

anomalous secondary growth Any form of secondary growth that does not conform to that typically occurring in gymnosperms and dicots. 8

anoxygenic photosynthesis Bacterial photosynthesis that does not use water for an electron donor and does not release oxygen as a waste product. 10

anther The portion of a stamen that contains sporogenous tissue which produces microspores (pollen). 9, 23

antheridiophore In liverworts, an umbrella-shaped outgrowth of the gametophyte, bearing antheridia. 20

antheridium (pl.: antheridia) A small structure that produces sperm cells, or the equivalent of sperm cells in ascomycete fungi. 20—23

anthropomorphism Attributing to plants certain capacities that only humans have, such as decision-making. 1

anticlinal wall A wall perpendicular to a nearby surface, especially the outer surface of the plant. Alternative: periclinal wall. 8

anticodon In transfer RNA, the nucleotide triplet complementary to the codon of mRNA. 15

antioxidant A chemical that neutralizes certain types of destructive oxygen compounds within an organism’s body. 24

antipodal cell One of several (usually three) cells in the angiosperm megagametophyte, located opposite the egg cell and the synergids. 9

apical dominance The suppression of axillary buds by the growing, active apical bud of a shoot. 14

apomorphy A feature present in one (autapomorphy) or several (synapomorphy) derived members of a group, but which is not present in the ancestral members. 18

apoplast The intercellular spaces and cell walls of a plant; all the volume of a plant that is not occupied by protoplasm (the symplast). 3, 5, 7, 12

apparent competition In ecology, one predator may prey on several species; if one of the prey species increases in abundance for any reason, that may lead to an increase in the predator population, resulting in more predation on all prey species. Thus the increase of one prey species may cause the decrease in other prey species, which appears to be the result of competition but is not. 26

aquaporin A membrane protein that permits water to cross the membrane rapidly. 3, 12

archegoniophore In liverworts, an outgrowth of the gametophyte, bearing archegonia and having a stalk with radiating fingers of tissue. 20

archegonium (pl.: archegonia) Any structure in true plants (not algae) that produces an egg; the megagametangium of true plants. 20, 21

aril A thick fleshy envelope around some seeds. 22

artificial selection The process in which humans purposefully alter the gene pool of a species by selective breeding. 17

artificial system of classification A classification not based on evolutionary, phylogenetic relationships but on other characters. Alternative: natural system of classification. 18

artisan wood A wood used for beauty rather than strength or low cost. 24

assisted dispersal The artificial transport of organisms by people with the objective of introducing those organisms into new areas, thus increasing their range and reducing the risk of extinction. 26

atactostele The vascular system of monocots, a set of bundles not restricted to forming one ring. Compare: eustele and protostele. 5

autotroph An organism that synthesizes its own organic compounds, using only carbon dioxide and mineral nutrients. Compare: heterotroph. 10

auxiliary cell In red algae, a cell that receives the diploid nucleus from the fertilized carpogonium. 19

auxins Hormones involved in cell elongation, apical dominance, and rooting, among other processes. 14

axillary bud A bud located in a leaf axil, just above the attachment point of a leaf. May be either a leaf bud or a floral bud. Alternative: terminal bud. 5

axial tissue In a woody stem or root, the tissue derived from fusiform cambium cells. Alternative: ray. 8

B

B horizon In soil, the zone of deposition, which receives leached minerals from the A horizon above it. 25

bacteriochlorophyll Light-harvesting pigment involved in bacterial photosynthesis. 10

bacteriophage A virus that attacks bacteria. 15

bar A measure of pressure and of water potential; equals 0.987 atmospheres or 1.02 kg/cm². 12

basal angiosperms The several clades of angiosperms that arose before the rest of the angiosperms diverged into the monocots and eudicots. 2, 5, 18, 23

basal body See centrioles. 3

bast fiber A fiber extracted from the phloem of a plant, usually from bark. 24

betalains Water-soluble pigments characteristic of the flowering plant class Caryophyllales. 23

biennial plant A plant that requires 2 years to complete its life cycle, with cold winter temperature in the first year being necessary for reproduction. 5, 14, 23

biliprotein A protein in cyanobacteria and red algae which associates with phycobilin, forming a phycobilisome. 19

binomial classification A system of providing scientific names to organisms, each name consisting of the genus name and the species epithet. 18

biome An extensive grouping of ecosystems, characterized by the distinctive aspects of dominant plants. 27

biosphere All portions of the Earth’s surface—including land, water and air—occupied by living organisms. The organisms themselves are a component of the biosphere. 2

biotic Refers to living things. Compare: abiotic. 25

biotic potential The intrinsic rate of natural increase, the number of offspring produced by an individual which live long enough to reproduce. Symbol: r. 25

biparental inheritance Inheritance of genes from two parents, the most common case for nuclear genes. Alternative: uniparental inheritance. 16

bivalent chromosome During meiosis, homologous chromosomes pair with each other; the pairs are bivalents. 4

blind pit See pit. 5

bloom (algal) A sudden increase in the numbers of algae when environmental conditions become particularly favorable for growth. 13

blue-light responses Plant developmental responses triggered by blue-light; the photoreceptor is a small protein called phototropin. 14

bordered pit In a xylem-conducting cell, a pit in the secondary wall having a thickened rim (border). Alternative: simple pit. 5

bract A small, often thickened and protective leaflike structure; bracts usually protect developing inflorescences. 9

bran In cereal grains such as wheat and rice, bran consists of all parts of the fruit or seed that are not embryo (the embryo is referred to a the germ of the seed). 24

broadleaf plant Informal term for any member of the flowering plant class Magnoliopsida: a dicot. Alternative: monocot. 5, 23

browser An herbivore that eats twigs and leaves of shrubs. Compare: grazer. 25

bryophyte A term without uniform definition; used by some to refer only to mosses, by others to refer to mosses, liverworts, and hornworts. 20

bud scale A small, specialized leaf, usually waxy or corky, that protects an unopened bud. 5, 6

bulb A short, subterranean, vertical stem that has fleshy, scalelike leaves. Example: onion. 5

bulbil A small bulblike axillary plantlet that serves as a means of vegetative reproduction. 9

bundle sheath A set of cells, which may be parenchyma, collenchyma, or sclerenchyma, that encases some or all of the vascular bundles of a leaf. 6, 10

bundle sheath extension A set of cells, usually fibers, that extends from the bundle sheath to the upper or lower (or both) epidermis of a leaf. 6

buttress root A root that grows asymmetrically such that it becomes very tall and thin, extending up the trunk as much as a meter or more and giving the trunk lateral stability. 7

C

C₃ cycle Synonym for Calvin/Benson cycle, one type of stroma reaction. 10

C₄ metabolism (C₄ photosynthesis) A set of metabolic reactions in which carbon dioxide is fixed temporarily into organic acids that are transported to bundle sheaths, where they release the carbon dioxide and C₃ photosynthesis occurs. 10

C horizon The deepest soil layer, composed of parental rocks and rock fragments. 25

callose A long-chain carbohydrate polymer that seals certain regions, e.g., damaged sieve elements (12) or growing pollen tubes (9).

Calvin/Benson cycle Synonym for C₃ cycle, one type of stroma reaction. 10

calyptra (pl.: calyptras) In nonvascular plants, a small sheath of cells, derived from the archegonium, which covers the top of the capsule. 20

calyx (pl.: calyces) A collective term for all the sepals of one flower. 9

capsaicin The compound in Capsicum peppers that causes them to be pungent (hot). 24

capsule In mosses and liverworts, the sporophyte generation. 20

carbohydrates Organic compounds composed of carbon backbones with hydrogens and oxygens attached in a ratio of about 2:1; sugars, starch, and cellulose are examples. 2, 3, 10

carbon fixation Photosynthetic conversion of carbon dioxide into an organic molecule, with carbon being reduced in the process. 10

carotenoid A class of lipid-soluble accessory pigments in chloroplasts and chromoplasts. 10

carpel Organ of a flower that contains ovules and is involved in the production of megaspores, seeds, and fruits. See gynoecium. 9, 23

carpogonium (pl.: carpogonia) In red algae, an egglike cell that fuses with a spermatium. 19

carpospores In red algae, diploid spores produced by the carposporophyte that grow into tetrasporophytes. 19

carposporophyte In red algae, the mass of diploid cells that arise after the auxiliary cell receives the diploid nucleus. 19

carrying capacity The number of individuals of a population that can live in a particular ecosystem. 25

caryopsis (pl.: caryopses) A single-seeded dry fruit that is fused to the enclosed seed; found in grasses and often mistaken for a seed rather than a fruit and a seed. 23

Casparian strip (band) A layer of impermeable lignin and suberin in the walls of endodermal cells, preventing diffusion of material through that portion of the wall. 7

cassia Usually sold as “cinnamon,” cassia is the bark of any of several trees related to the one that provides true cinnamon, Cinnamomum verum. 24

catabolism Metabolism in which large molecules are broken down into smaller ones. Alternative: anabolism. 10

cation A positively charged ion. 13

cation exchange In soil, the release of an essential element cation from a soil particle and its replacement by a proton. 13

cavitation In xylem, the breaking of a water column when tension overcomes the cohesive nature of water; an embolism forms. 12

cDNA Complementary DNA. 15

cell cycle arrest When cells stop dividing, they undergo cell cycle arrest. The cells may become dormant temporarily (dormant buds, seeds) or they may differentiate and mature. 4

cell plate During cell division, the new cell wall forms inside a large vesicle surrounded by phragmoplast microtubules. The wall, vesicle, and phragmoplast together constitute the cell plate. 4

cellulose A polysaccharide composed only of glucose residues linked by beta-1, 4-glycosidic bonds; it is the major strengthening component of plant cell walls. 3, 4

centimorgan (cM) Synonym for map unit. 16

central cell In the megagametophyte in a flower’s ovule, the cell that contains two nuclei (usually) and develops into endosperm after fertilization. 9

centrifugal growth Growth outward from a common point. 4, 19

centrioles In animals and some fungi and algae, organelles that act as basal bodies for organizing the microtubules of flagella. 3

centromere Region of a chromosome that holds the two chromatids together prior to anaphase of mitosis or anaphase II of meiosis. Spindle microtubules attach to centromeres and move the chromosomes during division. 4

CF₀ -CF₁ complex Part of ATP synthase. CF₀ is a proton channel; CF₁ is a set of enzymes that phosphorylates ADP to ATP. 10

cereal grain The edible fruit (but often called a seed) of any of several true grasses cultivated for use as food for either people or animals. 24

charophytes This clade of green algae is the sister group to the true plants (embryophytes). 19

checklist In studies of ecology and biodiversity, a checklist is simple list of all the species known to exist in a particular area. Checklists are often prepared for parks and nature preserves. 26

chemical messenger A chemical that, by its presence, carries information from one area to another. 14

chemiosmotic phosphorylation The synthesis of ATP from ADP and phosphate using the energy of an osmotic gradient and a gradient of electrical charge; occurs in chloroplasts and mitochondria. 10

chemoautotroph A bacterium that has the ability to obtain energy from chemical reactions (without photosynthesis) and obtains its carbon from carbon dioxide. Compare: photoautotroph. 11

chemosynthetic origin of life Theory that life began through a series of chemical reactions on primitive Earth when conditions were quite different than they are today. 17

chiasma (pl.: chiasmata) During diplotene of prophase I of meiosis, as homologous chromosomes begin to move away from each other, they are held together by chiasmata, thought to be tangles in the chromosomes. During diakinesis, the chiasmata slide to the ends of the chromosomes and disappear. 4

chlorophyll Pigment involved in capturing the light energy that drives photosynthesis; found in plants, algae, and cyanobacteria. See bacteriochlorophyll. 3, 10

chloroplast See plastids. 3

chlorosis A common symptom of mineral deficiency, a yellowing of leaves due to lack of chlorophyll. 13

chromatid A portion of a chromosome consisting of one DNA double helix and its histones. Before S phase, each chromosome consists of just one chromatid, but after DNA replication in S phase, each chromosome consists of two chromatids. 4

chromatin The complex formed when histone proteins bind to DNA. 3, 15, 16

chromoplast See plastids. 3

chromosome Each nuclear DNA double helix is complexed with histone into a chromosome, which consists structurally of one (pre-S phase) or two (post-S phase) chromatids plus a centromere (4). The circles of DNA found in prokaryotes, plastids, and mitochondria are occasionally called chromosomes.

cilium (pl.: cilia) Similar to a flagellum, only shorter. 3, 19

circadian rhythm An endogenous rhythm whose period is approximately 24 hours long. 14

circinate vernation Refers to the development of a fern leaf in which it must uncoil as it expands. 21

circular bordered pit A pit that is circular in cross-section and has a thickened rim (border) that slightly overarches the pit chamber. See pit. 5

cis-acting factor Portions of a strand of DNA that affect the activity of a gene on the same DNA strand. Alternative: trans-acting factor. 15

cis-unsaturated fatty acid An unsaturated fatty acid (it has one or more carbon—carbon double bonds), and the two hydrogens at the double bond are on the same side of the molecule. Compare: trans-unsaturated fatty acid. 24

citric acid cycle Metabolic pathway in which acetyl-CoA is oxidized to carbon dioxide as reduced electron carriers are generated. Synonyms: Krebs cycle and tricarboxylic acid cycle. 11

clade In studies of evolution and systematics, a clade consists of all the descendants of a particular common ancestor; the common ancestor is also a member of the clade. 2

cladogram A branching diagram showing the phylogenetic relationships of several or many taxa. 18

cladophyll A flattened stem that resembles a leaf. 5

cleavage furrow In the cell division of some algae, the inward furrowing of the cell membrane. 19

climacteric fruits Fruits that undergo a sudden burst of metabolism and ripening (the climacteric) as the last step of maturation. Alternative: nonclimacteric fruits. 14

climax community A community in which the variety and relative abundance of organisms remain the same for many years. Climax communities are typically the result of succession. 26

clumped distribution A distribution of plants in space such that they occur in groups. Alternatives: uniform and random distribution. 25

codon In mRNA, a set of three nucleotides that specifies an amino acid to be incorporated into a protein. 15

coenocyte A cell, usually large, that has many nuclei, up to several thousand. 4, 19

coenzyme Synonym for cofactor.

coenzyme A A carrier molecule, able to pick up an acetyl group, becoming acetyl-CoA. 11

coevolution A type of evolution in which two species become increasingly adapted to each other, resulting in a highly specific interaction. 9

cohesion-tension hypothesis Hypothesis that as water is pulled upward by transpiration, its molecules cohere sufficiently to withstand the tension. 12

coleoptile The outermost sheathing leaf of a grass seedling, providing protection for the shoot within. 14

collateral vascular bundle A vascular bundle that consists of both xylem and phloem. 5

collenchyma Collenchyma cells have only primary walls, but these are thickened at the corners of the cell and thin elsewhere. The walls are plastically deformable; if stretched to a new shape, they retain that shape. Alternatives: parenchyma and sclerenchyma. 5

colony A group of cells all derived from one recent mother cell and held together by an extracellular matrix, but not closely adhering to each other and not integrated as a single individual. 14, 19

commensal relationship An interaction of two species in which one benefits and the other is unaffected. 25

common ancestor During divergent evolution, a common ancestor gives rise to two or more groups. In a cladogram, it is the node that gives rise to the various taxa being considered. 2, 18

community All the populations of a region. 25, 26

community restoration Work and projects that are carried out with the objective of altering a group of organisms back to a more natural state. For example, by reintroducing wolves into various areas or by removing dams from rivers. 26

companion cell In the phloem of angiosperms, a nurse cell that is connected to, and is a sister cell to, an enucleate sieve tube member. Alternative: albuminous cell. 5

compartmentalization The formation of numerous compartments, usually surrounded by semipermeable membranes, such that each compartment has a distinct metabolism. 3

compatibility barrier Chemical interactions that prevent the fertilization of a gamete by an inappropriate gamete. 9

competition An interaction of two species which is disadvantageous to one or both. Compare: mutualism. 25

competitive exclusion The inability of a species to grow in part of its range due to competition from another species more adapted to that part of the range. 25

complementary DNA DNA synthesized with reverse transcription; the DNA is complementary to the RNA substrate and similar to the gene that coded for the RNA. 15

complementary proteins In foods, two proteins can complement each other if each contains amino acids that the other is missing. 24

complete dominance A situation in which the presence of one allele completely masks the presence of the homologous allele. Alternative: incomplete dominance. 16

complete flower A flower having sepals, petals, stamens, and carpels. Alternative: incomplete flower. 9

complete protein In food, a protein that contains all the amino acids in adequate amounts for the animal’s metabolism. 24

compound cone A cone with several lateral axes attached to a main axis; conifer seed cones are compound. Compare: simple cone. 22

compound leaf A leaf in which the blade consists of several separate parts (leaflets), all attached to a common petiole. palmately compound All leaflets are attached to the same point. pinnately compound Leaflets are attached to the rachis, an extension of the petiole. Alternative: simple leaf. 6

compression wood See reaction wood. 8

conceptacle In the brown alga Fucus, a small cavity in which sperms and eggs are produced. 19

cone A compact collection of reproductive structures on a short axis. Synonym: strobilus. 21, 22

cone scale In conifer seed cones, a scale that bears seeds; it is a flattened shoot with fused sporophylls. Synonym: ovuliferous scale. 22

conjugation A method of genetic exchange occurring in bacteria and certain green algae; DNA is passed through a tube that joins two adjacent cells. 14, 19

conjunctive tissue In monocots, the pithlike region in which vascular bundles are located in stems and roots. 5

continental climate A climate characterized by dry air and great changes of temperature from summer to winter. 27

convergent evolution Evolution of two phenotypically distinct species, organs, or metabolisms such that they strongly resemble each other, usually because they are responding to similar selection pressures. Compare: parallel evolution and divergent speciation. 17

cork cambium (pl.: cambia) A layer of cells that produces the cork cells of bark. Also called phellogen. 8

cork cell A cell in bark that has walls encrusted with suberin; cork prevents loss of water through the bark and prevents entry of pathogens. 8

corm A subterranean, vertical stem that is thick and fleshy and has only thin papery leaves. Example: gladiolus. 5

cormophyte Other than a few exceptions (hornworts and thalloid liverworts) all plants on Earth are cormophytes. Cormophytes are plants with bodies composed of an axis which usually bears leaves and roots (the earliest cormophytes lacked leaves and roots). Compare: thallophytes. 2

corolla A collective term for all the petals of a single flower. 9

cortex In stems and roots, the primary tissue located between the epidermis and the phloem. 5

cotyledon In embryos of seed plants, the rather leaflike structures involved in either nutrient storage (most dicots and gymnosperms) or nutrient transfer from the endosperm (most monocots). 9, 22

covalent bond A chemical bond in which electrons are shared between two atoms. 15, 16

cpDNA Plastid DNA; it is in the form of closed circles, without histones. Usually there are many circles per plastid. See mtDNA. 3, 19

Crassulacean acid metabolism (CAM) A metabolism in which carbon dioxide is absorbed at night and fixed temporarily into organic acids. During daytime, the acids break down, carbon dioxide is released, and C₃ photosynthesis occurs. 10

crista (pl.: cristae) One of the tubular or vesicular folds of the mitochondrial inner membranes. 3, 11

critical night length The length of darkness that must be exceeded by short-day plants, or not exceeded by long-day plants, for flowering to be initiated. 14

cross-fertilization The fertilization of a gamete by a genetically distinct gamete derived from a different parent: Alternative: self-fertilization; see cross-pollination. 16

cross-field pitting In secondary xylem, pit-pairs formed between ray cells and axial tracheids or vessels. 8

crossing-over During prophase I of meiosis, after homologous chromosomes have paired and a synaptonemal complex has formed, the DNA of the homologs breaks and the end of each homolog is attached to the other homolog, resulting in two new chromosomes. 4, 16

cross-pollination The pollination of a flower by pollen from a completely different plant. Alternative: self-pollination. 9

cryptogam Any member of the several groups of plants that never produce seeds; examples are mosses, lycopodiums, horsetails, and ferns. Compare: spermatophyte. 2

cuticle A layer of cutin on epidermal cells; the cuticle reduces water loss but also unavoidably restricts the entry of carbon dioxide. 5

cutin A polymer of fatty acids that is water impermeable; it forms a layer (cuticle) on the epidermis. 5

cyanide-resistant respiration Synonym for thermogenic respiration. 11

cyclic electron transport The flow of electrons from P700 back to plastoquinone in photosynthesis, such that there is proton pumping but no synthesis of NADPH. Alternative: noncyclic electron transport. 10

cytochromes Small electron carriers that contain iron. 10, 11

cytokinesis Division of the protoplasm of a cell, as opposed to nuclear division, karyokinesis. 4

cytokinins A class of hormones involved in cell division, apical dominance, and embryo development among other things. 14

cytoplasm Protoplasm consists of nucleus, vacuoles, and cytoplasm. 3

cytosol Synonym for hyaloplasm.

D

dark reactions Synonym for stroma reactions.

day-neutral plant A plant that is induced to flower by factors other than night length. 14

degenerate code In the genetic code, many amino acids are coded by several codons, not just one each. 15

deletion mutation A mutation involving loss of DNA. 16

demography The study of the age distribution of the individuals of a population. 25

denitrification The conversion, by microbes, of nitrate to nitrogen gas, thus making nitrogen no longer available to plants. 12

deoxyribonucleic acid (DNA) The information molecule in nuclei, plastids, mitochondria, and prokaryotes. 2, 14, 15, 16

deoxyribose A five-carbon sugar occurring in DNA. 15

derived features Features present in modern organisms but not in their ancestors. Alternative: relictual features. 1, 18

determinate growth Growth that stops at a genetically predetermined size. Typical of leaves and flowers but not of whole shoots and roots. Alternative: indeterminate growth. 5

diakinesis see prophase I.

diatom Common name for algae of the class Bacillariophyceae; they have two silica shells that fit together like the parts of a Petri dish. 19

diatomaceous earth Oceanic sediments formed by accumulation of the silica shells of diatoms. 19

diatoxanthin A xanthophyll pigment found in brown algae. 19

dibiontic A life cycle with an alternation of generations. Alternative: monobiontic. 19

dichotomous branching A forking that results in two nearly equal branches (or leaf veins or secretory ducts). Alternatives: monopodial and sympodial branching. 20—23

dicot Informal term for any member of the flowering plant class Magnoliopsida, a broadleaf plant. Alternative: monocot. 2, 5

dicotyledon Synonym for dicot.

dictyosome A stack of thin vesicles held together in a flat or cup-shaped array; dictyosomes receive vesicles from endoplasmic reticulum along their forming face, then modify the material in the vesicle lumen or synthesize new material. Vesicles swell and are released from the maturing face. See Golgi apparatus. 3

differentially (selectively) permeable membrane A membrane that permits the passage of certain types of particles and inhibits the passage of others. 12

diffuse porous wood Wood in which the vessels of late wood are about as numerous and as wide as those of early wood. Alternative: ring porous wood. 8

diffusion The random motion of particles from regions of higher concentration to regions of lower concentration. 12

dihybrid cross A cross in which two characters are considered simultaneously. 16

dimorphic Having two distinct morphologies, such as in plants with a juvenile and an adult form. 5, 9

dinoflagellate Common name for algae of division Pyrrhophyta. Most have two flagella, each of which lies in a groove. 19

dioecy The condition in which a species has two types of sporophyte—one with stamens and one with carpels. See monoecy. 9

diploid Refers to two full sets of chromosomes in each nucleus, as typically found in sporophytes and zygotes. See haploid. 4, 16

diplotene See prophase I.

disaccharide A small carbohydrate composed of just two simple sugar residues. 10

distal Refers to the position of a structure distant from a point of reference; relative to a stem, a leaf blade is distal to the petiole. Alternative: proximal. 5

diurnal Daytime; a diurnal plant opens its flowers at sunrise. Alternative: nocturnal. 14

divergent speciation The evolution of part of a species into a new species, with the remainder of the species continuing as the original species or evolving into a third, new species. Alternative: phyletic speciation. 17

DNA cloning Producing large numbers of identical copies of DNA, usually by inserting it into bacteria and allowing the bacteria to multiply. 15

DNA denaturation Synonym for DNA melting. 15

DNA hybridization The slow cooling of a mixture of short DNA molecules such that complementary strands encounter each other and hydrogen bond into double helices. 15

DNA ligase An enzyme that can attach two strands of DNA to each other, repairing nicks and linking Okazaki fragments into complete molecules of DNA. 15

DNA melting Heating a DNA double helix gently until the hydrogen bonds are broken and one molecule separates from the complementary molecule. Synonym: DNA denaturation. 15

DNA microarray A microscope slide containing numerous dots, each dot being a fragment of DNA from a genome being studied. 15

DNases (DNAases) Enzymes that digest DNA. 15

domain All living organisms are now classified as belonging to one of three large clades called domains. Two domains (Bacteria and Archaea) contain prokaryotes; the third domain (Eukarya) contains eukaryotes. 1, 18,

dominant trait A trait whose phenotype completely masks that of the alternative (recessive) allele in the heterozygous condition. 16

dosage-dependent response A situation in which the amount of response is correlated with the amount of stimulus. Alternative: all-or-none response. 14

double fertilization The process unique to angiosperms in which one sperm fertilizes the egg (forming a zygote) and the other sperm fertilizes the polar nuclei (forming the primary endosperm nucleus). 9, 23

duplication division Synonym for mitosis.

drying oil A highly unsaturated (contains many double bonds) plant oil that polymerizes into a hard film when exposed to oxygen; many are used to protect wood and make it shine. 24

E

early wood Synonym for spring wood. 8

ecosystem The set of physical nonliving environmental factors of a region, plus the communities of organisms of that region. 25

ecotypes Races of a species that are each adapted to particular environmental factors in certain parts of the species range. 25

edaphic Refers to the soil: Soil factors are edaphic factors. 27

egg apparatus A name for the egg cell and the one or two adjacent synergids in an angiosperm megagametophyte. 9

elater In the sporangia of liverworts and horsetails, small twisted cells that push the spores out of the sporangium. 20—21

elasticity A property of sclerenchyma walls; if stretched to a new size or shape, they return to their original size and shape once the deforming force is removed. Alternative: plasticity. 5

electron carrier A cofactor that carries electrons between reactions. Examples: nicotinamide adenine dinucleotide (phosphate), flavin adenine dinucleotide. 11

electron transport chain A series of electron carriers that transfer electrons from a donor, which becomes oxidized, to a receptor, which becomes reduced. 10, 11, 13

electronegativity A measure of an atom’s or a molecule’s tendency to give off or take on electrons. 10

Embden-Meyerhoff pathway Synonym for glycolysis. 11

embolism A packet of water vapor formed in xylem when the water column cavitates (breaks). Often called an air bubble. 12

embryo sac The megagametophyte of flowering plants; it is initially multinucleate. 9

embryophyte A rarely used term for all plants that are not algae—that is, all that have multicellular reproductive structures with sterile tissue. 2, 19

enation A small, projecting flap of tissue, thought to have been the ancestor of leaves in the lycophytes. 21, 23

endergonic reaction A reaction that absorbs energy. 10, 11

endocarp The innermost layer of the fruit wall, the pericarp. See exocarp and mesocarp. 9

endocytosis A process of absorbing material into a cell by forming an invagination in the plasma membrane, then pinching it shut and forming a vesicle. See exocytosis. 3

endodermis A sheath of cells surrounding the vascular tissue of roots (and occasionally horizontal stems); their Casparian strips prevent uncontrolled diffusion between root cortex and root vascular tissue by means of walls and intercellular spaces. 6, 7

endogenous rhythm A rhythm generated entirely within an organism whose periodicity is not maintained by an external rhythm. 14

endomembrane system The membranous organelles of a cell. 3

endophyte The portion of a parasitic plant that grows entirely within the body of the host plant. 11

endoplasmic reticulum (ER) A system of narrow tubes and sheets of membrane that form a network throughout the cytoplasm. If ribosomes are attached, it is rough ER (RER) and is involved in protein synthesis. If no ribosomes are attached, it is smooth ER (SER) and is involved in lipid synthesis. 3

endoreduplication The repeated synthesis of all nuclear DNA without its partitioning into separate nuclei by division. See gene amplification. 4

endosperm The tissue, usually polyploid, which is formed during double fertilization only in angiosperms and which nourishes the developing embryo and seedling. 9

endosymbiont theory The theory that postulates that plastids and mitochondria arose as prokaryotes that were living symbiotically within an early eukaryotic cell. 2, 19

endosymbiosis (primary and secondary) In the endosymbiont theory, a single primary act of endosymbiosis occurred when a cyanobacterium was engulfed by an early eukaryote, initiating chloroplasts. Several acts of secondary endosymbiosis have occurred as other eukaryotes engulfed entire cells of green or red algae, establishing new groups of photosynthetic organisms, such as brown algae, dinoflagellates, and euglenoids. 19

energy flow web In community ecology, various organisms eat or decompose others, and these in turn are consumed. Because some organisms consume the same prey, and in turn each is consumed by various other organisms, energy flows through the community in a weblike pattern. 26

enhancer elements Regions of DNA upstream from the structural region of a gene, which increase the ability of RNA polymerases to transcribe the gene. 15

engineered wood An artificial wood product made by gluing smaller wood pieces or fibers into a large shape. Particle board and plywood are examples. 24

entrainment The resetting of an endogenous rhythm by an exogenous stimulus. 14

entropy A measure of disorder in a system. 10

epicotyl In the embryo of a seed, the embryonic shoot, located above the cotyledons. Synonym: plumule. 9

epidermis The outermost layer of the plant primary body, covering leaves, flower parts, young stems, and roots. 5

epigynous See inferior ovary. 9

epiphyte A plant that grows on another plant, either attached to it or climbing over it, but not parasitizing it. 5, 25

epistasis The control of the expression of one gene by another, distinct gene, often involving the genes for the various enzymes catalyzing a single metabolic pathway. 16

essential element An element required for normal growth and reproduction. Major (macro) essential elements are needed in relatively large concentration; minor (micro, trace) essential elements are needed only in low concentrations. 13

essential organs In flowers, the spore-producing organs—stamens and carpels. Alternative: nonessential organs. 9

ethnobotany The study of the relationships between plants and people; very often emphasis is placed on the ways that people use certain plants. 24

ethylene A hormone involved in fruit ripening, the initiation of aerenchyma in submerged roots and stems, and other aspects of development. 14

eudicot This is the clade of angiosperms that contains most species formerly known as dicots. They have broad leaves and pollen with more than one germination pore. 2, 5, 18, 23

eukaryotes Organisms that have true nuclei and membrane-bounded organelles. Eukaryotes are plants, animals, fungi, and protists, but not bacteria. Alternative: prokaryotes. 3

euphyllophytes Plants that have megaphylls (synonym: euphyll), the horsetails, ferns, and seed plants. 21

eustele The vascular system of the stems of seed plants, composed of bundles around a pith. Compare: protostele, siphonostele, and atactostele. 21, 22

eutrophication The process that occurs as rivers and lakes receive too many mineral nutrients (usually as pollution from fertilized fields); they develop an overabundance of algae, much of which dies and decays, depleting the oxygen in the water and harming fish. 12, 13

evolution The change of nucleotide sequences in a species’ DNA through natural selection, genetic drift, or accident. 17

exalbuminous seed A seed with little or no endosperm at maturity. Alternative: albuminous seed. 9

excited state electron An electron that has absorbed a quantum and moved to a higher orbital; it has more energy than when it is in its ground state. 10

exergonic reaction A reaction that releases energy. 10, 11

exocarp Outermost layer of the fruit wall; in fleshy fruits, the rind or peel. See mesocarp and endocarp. 9

exocytosis The transfer of vesicle or vacuole-carried material to the outside of a cell by fusion of the plasma membrane with the membrane of the vesicle or vacuole. See endocytosis. 3

exons Those portions of the structural region of a gene whose information is actually translated into protein. Alternative: intron. 15

exploitation competition Multiple species compete with each other for a resource; if they actually consume the resource and reduce it, it is exploitation competition. Compare: interference competition. 26

extrinsic protein Synonym for peripheral protein. Alternative: intrinsic protein. 3

eyespot Synomym for stigma in phototactic algae. 19

F

facilitated diffusion The diffusion of hydrophilic (polar or charged) molecules through a membrane by means of channels composed of hydrophilic, membrane-spanning proteins. 3

facilitation In community ecology, facilitation is the situation in which the presence of one species provides benefit to another although the first species is neither helped nor harmed by the situation. For example, trees provide sites where birds can nest, which helps the birds but does not affect the tree. 26

facultative aerobe (facultative anaerobe) An organism that can use oxygen if present or survive without it. 11

false fruit See accessory fruit. 9

fascicular cambium The portion of the vascular cambium that develops within a vascular bundle. Alternative: interfascicular cambium. 8

fatty acid Long chains of carbon with only hydrogens as side groups and a carboxyl group at one end. If all carbon-carbon bonds are single, the fatty acid is saturated; if it contains any double bonds, it is unsaturated. 3, 11

feedback inhibition Synonym for end-product inhibition.

fermentation Synonym for anaerobic respiration. See respiration. 11

fern A member of the monilophyte clade; ferns have vascular tissues, megaphyllous leaves (euphylls, evolved from branches) but do not produce seeds; living ferns never produce wood. 2

ferredoxin An iron-containing proteinaceous electron carrier in photosynthesis. 10

fertilization Fusion of two gametes (or their equivalents in some fungi and algae). Synonym: syngamy. 9, 19—20

Fertile Crescent The portion of the Near East that includes Iran and Iraq, and which was the site where the first cities and agriculture were established. 24

fiber A sclerenchyma cell that is long and tapered and has pointed ends; provides a tissue with strength and flexibility. Compare: sclereid. 5, 8

field capacity The amount of water held by a soil after drainage due to gravity has been completed. 13

filament The stalk of a stamen, it elevates the anther. 9, 23

first filial generation (F₁) The progeny of an experimental cross. 16

fixed effort harvesting A technique that attempts to limit damage to a species by automatically decreasing harvests whenever a resource is in short supply or is endangered. For example, effort may be fixed by allowing hunting for only a particular number of days or by limiting the number of fishing boats. Compare: fixed quota harvesting. 26

fixed quota harvesting A technique that attempts to limit damage to a species by setting limits on the amount of the species can be harvested. For example, individual hunters are typically allowed to kill only one deer each; also, the number of whales that can be killed is set at a specific number worldwide (now, the number is usually zero). Compare: fixed effort harvesting. 26

flagellum (pl.: flagella) Like a cilium but longer, an organelle of locomotion. Both flagella and cilia have a 9 + 2 arrangement of microtubules. 3, 20

floridean starch A storage polysaccharide found in red algae. 19

fluid mosaic Biological membranes are two-dimensional fluids in which various types of lipids and intrinsic proteins can diffuse laterally. 3

fluorescence The spontaneous emission of a quantum by an excited electron, which allows the electron to return to its ground state. 10

food chain A set of organisms in which some are primary producers, others are primary consumers (which consume the primary producers) and still others are secondary consumers. 26

food desert A modern term used to describe areas of a city in which fresh, high quality foods (without extensive processing and artificial additives) are scarce or unavailable. 24

food web In community ecology, various organisms eat or decompose others, and these in turn are consumed. Because some organisms consume the same prey, and in turn each is consumed by various other organisms, food flows through the community in a weblike pattern. 26

form genus A genus based on a character that is not a reliable indicator of evolutionary relationships. Unrelated species are grouped together. 18

founder The first individual(s) that establishes a population in a new habitat; especially important in adaptive radiation. 17

frameshift error During the translation of mRNA, a misalignment of the ribosome such that the triplets it reads are not true codons. 15

freely permeable membrane A membrane that allows everything to pass through. See impermeable and semipermeable membrane. 3, 12

fret A set of thylakoid membranes that connect grana in chloroplasts. 10

frond Nontechnical term for the leaf of a fern. 21

frugivore A fruit-eating animal, important in the dissemination of seeds. 9

fruit In angiosperms, the structure that forms from carpels and associated tissues after fertilization. 9

fucoxanthin Xanthophyll pigment found in brown algae. 19

fugitive species A species that survives by colonizing new patches, flourishing temporarily, and then colonizing more patches before it dies out in old ones. Weeds are familiar examples. 26

functional response In predator-prey relationships, functional response refers to the predator’s feeding rate and it’s handling time. 26

funiculus (pl.: funiculi) The stalk of an ovule. 9, 23

fusiform initials In a vascular cambium, the long cells with tapered ends that give rise to axial cells of the secondary xylem and secondary phloem. Alternative: ray initials. 8

G

G₁ Part of interphase of the cell cycle, G₁ (gap 1) is the interval between cell division and the synthesis of DNA in the nucleus. G₁ is often the longest phase, during which the nucleus actively directs cytoplasmic metabolism. 4

G₂ Part of interphase of the cell cycle between the synthesis of DNA and the beginning of nuclear division. 4

gametangium (pl.: gametangia) Any structure that produces gametes. 19—23

gamete A haploid sex cell, such as an egg or sperm. megagamete A large, immobile gamete; an egg. microgamete A small, often mobile gamete; a sperm. 4, 9, 19—23

gametophore The leafy stem of a moss gametophyte. 20

gametophyte A haploid plant that produces gametes. Alternative: sporophyte. megagametophyte A gametophyte that produces megagametes (eggs) only. microgametophyte A gametophyte that produces microgametes (sperms) only. 9, 19—23

gene In DNA, a sequence of nucleotides which contains information necessary for the metabolism and structure of an organism. 15

gene amplification The repeated synthesis of the DNA of just one or a few genes, not the entire genome. See endoreduplication. 4, 15

gene family A set of several copies of an ancestral gene, all located within a single haploid genome. The various copies arise through gene duplication and then may evolve independently. 16

gene flow The movement of alleles within a population by the movement of pollen or seeds. 17

gene pool The total population of all the alleles in all the sex cells of the individuals of a population. 17

generative cell In the pollen grains of seed plants, the cell that gives rise directly to the sperm cells. Alternative: vegetative cell. 9, 22

genetic code The set of nucleotide triplets in DNA that code for amino acids to be inserted during protein synthesis. 15

genetic drift In a small gene pool, the alteration in allele frequencies mostly by accidents rather than by natural selection. 17

genetically modified (GM) plant A plant whose genotype and phenotype have been altered using recombinant DNA techniques. This term is not used for hybrids that have been produced in crosses using selective breeding. 15, 24

genome All the alleles of an organism. 4

geotextiles Nets and coarse fabrics used to cover and stabilize bare ground after construction damage or a fire; the geotextiles should decompose as plants become re-established. 24

germ (of a seed) The embryo of a seed. Compare: bran. 24

genotype The set of alleles present in an organism’s genome. Alternative: phenotype. 16

genus (pl.: genera) A group of species closely related by descent from a common ancestor. 18

gibberellic acid A natural gibberellin. 14

gibberellins A class of hormones involved in stem elongation, seed germination, and other processes. 14

gluconeogenesis Formation of glucose from 3-phosphoglyceraldehyde. 10, 11

glucose One of the most abundant simple sugars, a six-carbon monosaccharide. Component of starch, cellulose, and many metabolic pathways. 10, 11

gluten A protein found in the flour of wheat and several other cereals; it gives bread its elasticity and allows it to rise. 24

glycemic index A measurement of the rate at which carbohydrates are digested and how quickly they cause an increase in blood sugar levels. Foods with a high glycemic index cause blood sugar levels to rise more quickly than those with a low index. 24

glycolipid Lipid molecules with sugars attached. See glycoprotein. 3

glycolysis The metabolic pathway by which glucose is broken down to pyruvic acid. Synonym: Embden-Meyerhoff pathway. 11

glycoprotein A protein with sugars attached; often the sugars occur in short chains less than ten sugars long. See glycolipid. 3

glyoxysome See microbody. 3

GMO (Genetically modified organism) An organism whose DNA has been artificially modified by means of recombinant DNA technology. Organisms produced by cross-breeding and artificial selection are not considered to be GMOs. 24

Golgi apparatus A collection of interconnected dictyosomes, as many as several thousand, the entire set forming a cup-shaped apparatus. Often treated as a synonym for dictyosome; Golgi apparatuses are rare in plants, common in animals. Synonym: Golgi body. 3

Golgi body See Golgi apparatus.

Gondwanaland Southern portion of the ancient continent of Pangaea. Compare: Laurasia. 2, 27

grade In some studies of evolution and systematics, a grade is a “level of evolution.” Common grades are vascular plants, cryptogams, and seed plants. Compare: clade. 2

granum (pl.: grana) A set of flat vesicles in chloroplasts, involved in chemiosmotic phosphorylation. 3, 10, 11

grazer An herbivore that eats low herbs such as grasses. Compare: browser. 26

ground meristem A term refering to any expanse of meristematic tissue that produces a somewhat uniform mature tissue. 5

ground state electron An electron in its most stable orbital, when it contains the least amount of energy. Alternative: excited state electron. 10

growth ring Synonym for annual ring in wood. “Growth ring” is preferred because rings are occasionally not strictly annual (sometimes two are produced in 1 year, and none might be produced in adverse years). 8

guard cells A pair of epidermal cells capable of adjusting their size and shape, causing the stomatal pore to open when they swell and close when they shrink. 5

gymnosperm Common name for plants with naked seeds; all seed plants that are not angiosperms. Examples: conifers and cycads. 2, 22

gynoecium (pl.: gynoecia) A collective term referring to all the carpels of a flower. 9

H

habit The characteristic shape or appearance of the individuals of a species. 5

habitat The set of conditions in which an organism completes its life cycle. 25

habitat fragmentation The conversion of a large habitat into several smaller ones as various regions of it become uninhabitable for the organism being considered. Building canals or logging strips of forest are examples of activities that fragment habitats. 26

habitat loss The result of any of several processes that cause a habitat to be unable to support the species diversity it had when in a natural state. Clearing land for agriculture, cities, and mining all contribute to habitat loss, as does climate change. 26

hairpin loop A small kink in the end of a messenger RNA molecule that is being transcribed; the kink appears involved in signaling that transcription should stop. 15

half-inferior ovary An ovary that is partly inferior, such that the sepals, petals, and stamens appear attached to its side; those appendages are perigynous. Alternatives: superior and inferior ovary. 9

haploid Refers to one full set of chromosomes per nucleus. Gametes, spores, and gametophytes typically have haploid nuclei. See diploid. 4, 16, 19

hardwood A term applied to both dicot trees and shrubs and to their wood, because in general dicot wood contains fibers. Alternative: softwood. 8

hard fiber A term used in the textile industry for fibers derived from leaves rather than bark or wood. 24

haustorium (pl.: haustoria) The structure by which a parasite enters and draws nutrients from a plant; in fungi, it is a hypha; in mistletoes and similar parasites, it is a modified root. 7

heartwood The colored, aromatic wood in the center of a trunk or branch; all the wood parenchyma cells have died and no water conduction is occurring. Alternative: sapwood. 8

helical thickening A pattern of secondary wall deposition in tracheids and vessel elements; the wall occurs as one or two helical bands. 5

hemicelluloses A set of cell wall polysaccharides that cross-link cellulose molecules in plant cell walls. 3

hemiparasite A parasite that draws water, minerals, and perhaps some organic material from its host but also carries out photosynthesis. Compare: holoparasite. 2

herb A plant that consists only of primary tissues; lacking wood. 2, 5, 24

herbivore An animal that eats plants. Compare browser and grazer. 25

heteroblasty The phenomenon in which an individual plant produces several different types of leaves. 6

heterokont A clade of organisms with the synapomorphy of having two different types of flagella: one whiplash, one tinsel. 19

heteromorphic generations A dibiontic life cycle in which sporophyte and gametophyte are easily distinguishable morphologically. Alternative: isomorphic generations. 19

heterospory A condition in which the life cycle of a plant contains two types of spores, microspores and megaspores. Alternative: homospory. 9, 19—23

heterotroph An organism that obtains its carbon from organic molecules, not from carbon dioxide. Compare: autotroph. 10

heterozygote A diploid organism with two different alleles for a particular gene. Alternative: homozygote. 16

hexose monophosphate shunt Synonym for pentose phosphate pathway.

hilum (pl.: hila) Scar produced when a seed breaks from the funiculus. 9

histones A set of basic nuclear proteins that complex together and with DNA, first forming nucleosomes and then complexing further into chromosomes. 3, 4, 16

hnRNA Heterogeneous nuclear RNA. 15

holdfast The portion of a nonmotile, attached alga that holds the alga to its substrate. 19

holoparasite A parasite that draws all its water, minerals, and organic material from its host and is unable to carry out photosynthesis. Compare: hemiparasite. 2

homeotic mutation A mutation that causes organs to be produced in unusual places on a body or in altered numbers. Flowers that have excess numbers of petals are the result of homeotic mutations. 14

homologous chromosomes In a diploid nucleus, each type of chromosome is present as a pair, one inherited paternally, the other maternally. 4

homologous features Features that are the phenotypic expression of homologous genes, those related by descent from common ancestral genes. Alternative: analogous features. 18

homospory A condition in which the life cycle of a plant contains only one type of spore. Alternative: heterospory. 9, 19—23

homozygote A diploid organism with two identical alleles for a particular gene. Alternative: heterozygote. 16

hormone A chemical that is produced by one part of a plant, often in response to a stimulus, and then is transported to other parts and induces responses in appropriate sites. 14, 15

hyaloplasm The liquid substance of protoplasm, excluding all the organelles such as nuclei, plastids, ribosomes: Synonym: cytosol. 3

hybrid sterility A postzygotic isolation mechanism in which a hybrid zygote can grow into an adult but cannot form fertile gametes. 17

hydrogen bonding The weak attraction between polar molecules. 12

hydroids In the stems of some mosses, cells that resemble tracheids and are involved in water conduction. 20

hydrolysis The breaking of a chemical bond by adding water to it, a proton being added to one product and a hydroxyl to the other. 12

hydrophilic “Water loving”—refers to compounds that are relatively soluble in water and other polar solvents and insoluble in lipids and other nonpolar solvents. Opposite: hydrophobic. 3

hydrophobic “Water fearing”—refers to compounds that are relatively insoluble in water and other polar solvents and soluble in lipids and other nonpolar solvents. Opposite: hydrophilic. 3

hydroponics The growing of plants in a water solution, without the use of soil. 13

hyphae (sing.: hypha) The long, narrow filaments, either coenocytic or cellular, that constitute the body of a fungus. 7

hypocotyl The portion of an embryo axis located between the cotyledons and the radicle. 9

hypogynous See superior ovary. 9

hypothesis (pl.: hypotheses) A model of a phenomenon constructed from observations of the phenomenon. It must make testable predictions about the outcome of future observations or experiments. 1

I

immobile essential element An element that cannot be removed from mature tissues; if a plant becomes deficient in an immobile element, young tissues show symptoms even though older tissues may have extra. Alternative: mobile essential element. 13

imperfect flower A flower lacking either stamens or carpels or both. Alternative: perfect flower. 9

impermeable A barrier that allows nothing to pass through. See freely permeable and semipermeable membrane. 3

incipient plasmolysis As a plant cell is losing water and shrinking, the point at which the protoplast just begins no longer to exert pressure against the wall. 12

included phloem In certain types of anomalous secondary growth, patches of secondary phloem may be located within the secondary xylem. 8

incomplete dominance A situation in which the phenotypes of both alleles of a heterozygote are expressed. Alternative: complete dominance. 16

incomplete flower A flower that is missing one or more of the four basic appendages (sepals, petals, stamens, carpels, or any combination). Alternative: complete flower. 9

incomplete protein In nutrition, an incomplete protein lacks some of the essential amino acids, or has some of them in very low, inadequate amounts. Consequently a person cannot rely on an incomplete protein as a sole source of amino acids. Compare: complete proteins and complementary proteins. 24

indehiscent Remaining closed at maturity, not opening; true of many fruits and the megasporangia of seed plants. 9, 22, 23

independent assortment In a double heterozygote, the distribution of one allele of one gene during meiosis is not linked to the distribution of either allele of the homologous gene. Alternative: linked genes. 16

indeterminate growth Growth not limited by a plant’s own genetic development program: Most trees have indeterminate growth. Alternative: determinate growth. 5

indole acetic acid (IAA) An auxin. 14

infection thread During the invasion of roots by nitrogen-fixing bacteria, the bacteria are encased in an invagination of the plant cell wall, the infection thread. 7

inferior ovary An ovary located below the sepals, petals, and stamens; those appendages are epigynous. Alternatives: superior and half-inferior ovary. 9

inflorescence A discrete group of flowers. 9

infusion A drink such as tea in which plant material is steeped in water, then the plant material is discarded and only the water extract is used. 24

inner bark The innermost, living layer of bark, located between the vascular cambium and the innermost cork cambium. Alternative: outer bark. 8

insertion mutation A mutation involving insertion of the new DNA into a sequence of pre-existing DNA. 16

insertion sequence A small transposable element that contains only the genes coding for the enzymes necessary for the element’s excision and insertion. See transposon. 16

integument In flowers, the covering layer over the nucellus of an ovule. Usually two integuments (inner and outer) are present. 9, 22, 23

intercalary meristem See meristem. 5

interfascicular cambium The portion of the vascular cambium that develops from parenchyma cells located between vascular bundles. Alternative: fascicular cambium. 8

interference competition In community ecology, an interaction of two species in which one organism restricts another organism’s access to resources even though the first might not be using it. Compare: exploitation competition. 26

interkinesis (pl.: interkineses) The portion of meiosis that occurs between telophase I and prophase II. There is no duplication of DNA. 4

internode Portion of a stem where there are no leaves; portion between nodes. 5

interphase The portion of the cell cycle that is not cell division; interphase consists of G₁, S, and G₂. 4

interpolation theory The theory that vascular plants arose from monobiontic algae and a sporophyte generation was gradually interpolated into the life cycle. Compare: transformation theory. 21

intrinsic protein A protein that is an integral part of a membrane, deeply embedded in it; it cannot be washed out of the membrane easily. Alternative: peripheral protein. 3

intron A portion of the structural region of a gene whose information is not translated into protein; instead, the intron-transcribed portions of the hnRNA are removed and digested. Alternative: exon. 15

invasive species In community ecology, a species is invasive if it can increase from very low population density even if one or several competitors are present. 26

inversion mutation A mutation in which a portion of the DNA double helix is excised, turned end for end, and ligated into place with reverse order. 16

ionic bond Chemical bond between two molecules, one of which is negatively charged, the other positively charged. 10

isogamy Sexual reproduction in which all gametes are structurally identical; there are no sperms and eggs. Alternatives: anisogamy and oogamy. 9, 19—21

isolation mechanism A structure or metabolism that inhibits the movement of substances from one region to another. 12

isomorphic generations A dibiontic life cycle in which sporophytes and gametophytes are almost indistinguishable. Alternative: heteromorphic generations. 19

isopentenyl adenosine A natural cytokinin. 14

isotype specimen A specimen obtained from the same plant or clone as the type specimen. 18

J

juvenile plant A plant that is too immature to flower, even if otherwise appropriate stimuli are present. Alternative: adult plant. 14

K

K Symbol for carrying capacity. 25

karyogamy Fusion of the nuclei of two gametes after protoplasmic fusion (plasmogamy). See syngamy. 9

karyokinesis (pl.: karyokineses) Division of a nucleus, as opposed to cell division, cytokinesis. The two types of karyokinesis are mitosis and meiosis. 4, 16

keystone species In community ecology, a species that dramatically affects the structure of its community, having an impact out of proportion to its size or the number of individuals present. 26

kinetin An artificial cytokinin. 14

kinetochore In a chromosome, the kinetochore is the point at which spindle microtubules attach to the centromere. 4

Krebs cycle Synonym for citric acid cycle and tricarboxylic acid cycle. 11

L

labyrinthine wall Synonym for transfer wall. 12

lamina (pl.: laminae or laminas) The broad, expanded part of a leaf; not the petiole. 6

laminarin A reserve polysaccharide found in brown algae. 19

late wood Synonym for summer wood. 8

lateral meristem A name describing the position of the vascular cambium and cork cambium. 8

lateral veins The major, large vascular bundles of a leaf, which are attached to the midrib or the petiole. Larger than minor veins. 6

Laurasia Northern portion of the ancient continent of Pangaea. Compare: Gondwanaland. 2, 27

leaf axil Portion of a node immediately above the attachment point of a leaf. 5

leaf gap In fern vascular tissue, an area above a leaf trace where there is no conducting tissue. 21

leaf primordium (pl.: primordia) An extremely early stage in leaf development, when the leaf exists only as a pronounced bulging of the shoot apical meristem. 6

leaf scar The region on a stem where a leaf was attached prior to abscission. 6

leaf sheath Almost exclusively in monocots, the basal portion of a leaf, wrapped around the stem above a node. 6

leaf trace A vascular bundle that extends from the stem vascular bundles through the cortex and enters a leaf. 6, 21

legume Any member of the family Fabaceae, such as peas, beans, and lentils. Legumes are typically an excellent source of protein. 24

lenticel In bark, a region of cork cells with intercellular spaces, permitting diffusion of oxygen into inner tissues. 8

leptoids In the stems of some mosses, elongate cells that resemble sieve cells and are involved in carbohydrate conduction. 20

leptotene See prophase I. 4

lethal allele An allele whose expression results in death. 16

leucoplast See plastid. 3

life forms A classification of the ways plants are adapted morphologically for surviving stressful seasons. 25

light compensation point The level of illumination at which photosynthetic fixation of carbon dioxide just matches respiratory loss. 10

light-dependent reactions In photosynthesis, the set of reactions directly driven by light. Alternative: stroma reactions. 10

lignin A complex compound that impregnates most secondary cell walls, making them stronger, more waterproof, and resistant to attack by fungi, bacteria, and animals. 3, 8, 11

lignophyte Synonym for a plant that develops wood. This is used as an informal name for the clade that contains the woody plants. 21, 22

ligule In selaginellas, a small flap of tissue on the upper surface of a leaf. 21

limiting factor The growth of any organism depends on the availability of many factors such as water, light, and various nutrients; the rate of the organism’s growth is limited by whichever factor is in short supply. 13, 25

linkage group A set of genes that do not undergo independent assortment, being part of one chromosome. 16

linked genes Genes located close to each other on a chromosome undergo crossing over only rarely, so they are linked. Alternative: independent assortment. 16

lipid body A spherical droplet of oil or other lipid, common in the cells of many seeds. 3

lipids A class of compounds that are hydrophobic and water insoluble. Examples: fats, oils, and waxes. 10

lithotroph An organism (all are prokaryotes) that obtains energy by oxidizing inorganic mineral elements. 11

littoral zone On a sea coast, the region between low tide and high tide; a common habitat for brown algae. 19

locule The cavity within a structure such as a sporangium, gametangium, or carpel. 23

long-day plant A plant that is induced to flower by nights shorter than the critical night length. 14

lumen The interior of any structure such as a vesicle, vacuole, oil chamber, or resin duct. 3

lycophyte clade The group of plants that have microphyll leaves. Living members are Lycopodium, Selaginella, and Isoetes, and extinct members were the zosterophyllophytes. 2

lysis The bursting of an animal cell or a plant protoplast due to excessive absorption of water. Do not confuse with plasmolysis. 12

lysosome An organelle that contains digestive enzymes and is involved in recycling the components of worn-out organelles; in plants, the central vacuole acts as the lysosome. 3

M

macronutrient Synonym for major essential element. 13

mannitol A reserve polysaccharide in brown algae. 19

manoxylic wood Wood that contains significant amounts of axial parenchyma, such as that of cycads. Compare: pycnoxylic wood. 22

map unit A measure of the separation of genes on a chromosome; one map unit equals a 1% probability that crossing over will occur between them. Synonym: centimorgan (cM). 16

maternal inheritance Uniparental inheritance for genes contributed by the megagamete but not by the microgamete. 16

matric potential A component of water potential; a measure of the effect of a matrix on a substance’s ability to absorb or release water. 12

matrix The liquid within a mitochondrion. 3, 11

maximum sustained yield The amount of an organism’s population that can be harvested without causing the population to decrease. Because many organisms have a sigmoidal growth curve (they increase more slowly as populations become overcrowded), harvesting the proper amount from an overcrowded population should maintain the population at its most productive level. 26

megagametangium (pl.: megagametangia) A structure that produces megagametes (eggs). 19

megagamete In an oogamous species, the larger, immobile gamete. Synonym: egg. 9, 19—23

megagametophyte See gametophyte. 9

megapascal (MPa) A unit for quantifying pressure; 1 MPa is about 10 bars or 10 atmospheres of pressure. 12

megaphyll A leaf that has evolved from a branch system. Present in ferns and all seed plants. Alternative: microphyll. 21—23

megasporangium (pl.: megasporangia) A structure that produces megaspores. 9, 19—23

megaspore A large spore that grows into a megagametophyte that produces egg cells. Alternative: microspore. 9, 19—23

megaspore mother cell Synonym for megasporocyte. 9

megasporocyte In a heterosporous species, a cell that undergoes meiosis, resulting in the production of a megaspore. Synonym: megaspore mother cell. 9, 21, 22

meiosis Reduction division, a process in which nuclear chromosomes are duplicated once but divided twice, such that the resulting nuclei each have only one half as many chromosomes as the mother cell. 4, 16

meiosis I The first division of meiosis, during which the chromosome number per nucleus is reduced. Synapsis and crossing over occur during meiosis I. 4

meiosis II The second division of meiosis, during which centromeres divide and the two chromatids of one chromosome become independent chromosomes. 4

meristem A group of cells specialized for the production of new cells.apical meristem Located at the farthest point of the tissue or organ produced. basal meristem Located at the base. intercalary meristem Located between the apex and the base. lateral meristem Located along the side. 5

meristoderm In brown algae, the outer layer of the body, which is both meristematic and photosynthetic. 19

mesocarp The middle layer of the fruit wall. See exocarp and endocarp. 9

mesokaryotes A term proposed for dinoflagellate algae, because their nuclear and cytoplasmic organization appears to be intermediate between those of prokaryotes and eukaryotes. 19

mesophyll All tissues of a leaf except the epidermis. 6

metaphase The second phase of mitosis during which chromosomes move to the center of the spindle, the metaphase plate. 4

metaphase I The second phase of meiosis I, similar to metaphase of mitosis except that homologous pairs of chromosomes are involved. 4

metaphase II A phase of meiosis II, similar to metaphase of mitosis. 4

metaphase plate The region in the center of the spindle where chromosomes become aligned during nuclear division. 4

metaphloem The part of the primary phloem that differentiates late, after adjacent cells have completed their elongation. Alternative: protophloem. 5

metapopulation A population that consists of several local populations interconnected by migration and gene flow between the patches. 26

metaxylem The part of the primary xylem that differentiates late, after adjacent cells have completed their elongation. Alternative: protoxylem. 5

MPa Megapascal, a unit of pressure measurement equivalent to about 70 pounds per square inch. 12

microbody A class of two types of small, vesicle-like organelles. Peroxisomes are involved in photorespiration, the detoxification of harmful products of photosynthesis. Glyoxysomes are involved in respiring stored fatty acids. 3, 10, 11

microfibril As adjacent molecules of cellulose are synthesized, they crystalize into a microfibril, which may be 10 to 25 nm wide. 3

microfilaments A structural element composed of actin and believed to be involved in the movement of organelles other than flagella, cilia, or chromosomes. 3

microgametangium (pl.: microgametangia) A structure that produces microgametes (sperm cells). 19

microgametophyte See gametophyte. 9

micronutrient Synonym for minor essential element. 13

microphyll The type of leaf that evolved from an enation; present in lycophytes. Alternative: megaphyll. 21, 22

micropyle In an ovule, the small apical opening created where the integuments do not meet; the pollen tube enters through the micropyle. 22, 23

microRNA general term for any of several types of RNA that are extremely short (a few dozen nucleotides or less) and appear to be involved in controlling gene expression. 15

microsporangium (pl.: microsporangia) A structure that produces microspores. 9, 19—23

microspore A small spore that grows into a microgametophyte that produces sperm cells. Alternative: megaspore. 9, 23

microspore mother cell Synonym for microsporocyte.

microsporocyte In a heterosporous species, a cell that undergoes meiosis, resulting in the production of four microspores. Synonym: microspore mother cells. 9

microtubules A skeletal element in eukaryotic cells, composed of alpha and beta tubulin. Microtubules constitute the mitotic spindle, phragmoplast, and axial component of flagella. 3

middle lamella (pl.: lamellae or lamellas) The layer of adhesive pectin substances that acts as the glue that holds the cells of a multicellular plant together. 3

midrib The large, central vascular bundle of a leaf. Alternative: lateral and minor veins. 6

minor (micro) essential element See essential element. 13

minor veins The smallest veins of a leaf, branching off lateral veins. There is no criterion that strictly distinguishes between minor veins and lateral veins. 6

mitochondrion (pl.: mitochondria) The eukaryotic organelle involved in aerobic respiration, particularly the citric acid cycle and respiratory electron transport. 3, 11

mitosis (pl. mitoses) Duplication division—a type of nuclear division (karyokinesis) in which nuclear chromosomes are first duplicated, then divided in half, one daughter nucleus receiving one set, the other daughter nucleus receiving the other set. Alternative: meiosis. 4, 16, 19

mobile essential element An element that can be removed from mature tissues and transported to young or newly formed tissues. Alternative: immobile essential element. 13

molecular pump An integral membrane protein that forces molecules from one side of a membrane to the other, using energy in the process called active transport. 3, 12

monilophytes The clade containing ferns in a broad sense (Psilotum, Equisetum, Leptosporangiatae, Marattiales, and Ophioglossales). 21

monobiontic A life cycle with only one free-living generation; there is no alternation of generations. Alternative: dibiontic. 19

monocot Informal term for any member of the flowering plant class Liliopsida. Examples, lily, iris, palm, agave. Alternative: dicot. 2, 5, 23

monocotyledon Synonym for monocot. 5

monoecy The condition in which a species has imperfect flowers (some staminate, others carpellate), but both are located on the same sporophyte. See dioecy. 9

monohybrid cross A cross in which only a single trait is analyzed, disregarding all other traits. 16

monomer The subunit of a polymer. 3, 11

monopodial branching Branching in which one shoot is dominant and forms a distinct trunk, all other shoots being significantly different from the trunk. Alternatives: sympodial and dichotomous branching. 21—23

monosaccharide Synonym for simple sugar; the monomer of polysaccharides. 3, 10, 12

morphogenic (morphogenetic) response A response in which the quality of the plant changes, such as conversion from a vegetative state to a floral state. 14

motor cells Cells that swell and shrink in plant organs capable of repeated, reversible movement, such as insect traps and petioles of leaves that undergo sleep movements. 12

mtDNA Mitochondrial DNA: it is in the form of closed circles, without histones. See cpDNA. 3

mucigel The mucilaginous, slimy material secreted by root caps and root hairs. 7

multiple fruit A fruit formed by the crowding together of the individual fruits of an entire inflorescence. Alternatives: simple fruit and aggregate fruit. 9

mutagen Any chemical or physical force that causes a change in the sequence of nucleotides in DNA. 16

mutation Any change in the sequence of DNA. 16

mutualism An interaction of two species in which both species benefit. Compare: competition. 13, 25, 26

mycelium (pl.: mycelia) The diffuse mass of hyphae which constitutes the vegetative body of a fungus. 7

mycorrhizae (sing.: mycorrhiza) Fungi that form a symbiotic relationship with roots, usually of benefit to plants because they provide phosphorus. ectomycorrhizae A type in which the fungi invade only the outermost cells of the root. endomycorrhizae A type in which the fungi invade all cells of the root cortex. 7, 13

N

nastic response A nongrowth response that is stereotyped and not oriented with regard to the stimulus. 14

natural selection The preferential survival, in natural conditions, of those individuals whose alleles cause them to be more adapted than other individuals with different alleles. 17

natural system of classification A classification based on evolutionary, phylogenetic relationships. Alternative: artificial system of classification. 18

nectary A gland that secretes a sugary solution that typically attracts pollinators. 9, 23

negative feedback system An enzyme system in which the product inhibits the action of one or several of the enzymes that produce it. 14

netted venation Synonym for reticulate venation, typically found in leaves of dicots. 6

niche The set of conditions exploited best by one species. 25

nitrogen assimilation The incorporation of ammonium into organic compounds within an organism. 13

nitrogen fixation The conversion of atmospheric nitrogen into any compound that can be used by plants, typically either nitrate or ammonium. 13

nitrogenase The enzyme responsible for nitrogen fixation. 13

nocturnal Nighttime; a nocturnal plant opens its flowers at dusk. Alternative: diurnal. 14

node Point on a stem where a leaf is attached. 5, 18

nodule In roots of plants that form symbiotic associations with nitrogen-fixing bacteria, regions of the root swell, forming nodules whose cells contain the bacteria. 7

nonclimacteric fruits Fruits that ripen slowly and steadily, without a sudden burst of metabolism (the climacteric) at the end. Alternative: climacteric fruits. 14

noncyclic electron transport The flow of electrons from water to NADPH during the light-dependent reactions of photosynthesis. Alternative: cyclic electron transport. 10

nondisjunction During meiosis II, the nonseparation of the two chromatids of a chromosome, such that one daughter cell receives both while the other daughter cell receives none. 16

nonessential organs In flowers, the sepals and petals. Alternative: essential organs. 9

nonstoried cambium A cambium in which the fusiform initials are not aligned horizontally. Alternative: storied cambium. 8

nonvascular plant A plant that lacks vascular tissue: mosses, liverworts, and hornworts. 2, 20

nucellus (pl.: nucelli) The megasporangium of an ovule. 9, 23

nuclear envelope A set of two membranes, the inner and the outer nuclear envelopes, that surround the nucleus. 3

nuclear pores Structures in the nuclear envelope that are involved in transport of material between nucleus and cytoplasm. 3

nucleic acid A polymer of nucleotides. 15, 16

nucleolus (pl.: nucleoli) Organelles located within the nucleus, nucleoli are areas where ribosomal RNAs are synthesized and assembled into ribosomal subunits. 3, 15

nucleoplasm The substance located in the nucleus-DNA, histones, RNA, enzymes, nucleic acids, water. 3

nucleosome A nuclear particle composed of histones with DNA wrapped around them; a basic aspect of chromosome structure. 15

nucleotide The monomer of nucleic acids; each nucleotide consists of a nitrogenous base, a sugar, and a phosphate group. 15, 16

nucleus (pl.: nuclei) In eukaryotic cells, the organelle that contains DNA and is involved in inheritance, metabolism control, and ribosome synthesis. 3

nurse plant In ecology, the presence of some plants creates conditions that allow other plants to become established. The nurse plant may provide shade, camouflage, or protection to the seedlings of the second plant. 26

O

obligate aerobe An organism that must have oxygen to survive. Synonym: strict aerobe. Alternative: obligate anaerobe. 11

obligate anaerobe An organism that is killed by exposure to oxygen. Synonym: strict anaerobe. Alternative: obligate aerobe. 11

Okazaki fragments During DNA replication, the set of short fragments that grow discontinuously along one strand of DNA and must be ligated into one continuous DNA molecule. 16

old growth forest A forest that has existed without major disturbance for a long time (usually defined as more than 120 years). Many old growth forests have been destroyed by people who log them for lumber, firewood or other resources. 24

oligosaccharide A compound made up of a few simple sugars (monosaccharides). 3

ontogeny Synonym for development, morphogenesis. 14, 15

oogamy A type of sexual reproduction in which the two gametes are distinctly different structurally; one is a microgamete (sperm), and the other is a megagamete (egg). Alternatives: anisogamy and isogamy. 9, 19—23

oogonium Synonym for megagametangium in certain organisms. 19

open reading frame (ORF) A sequence of DNA that has many components of a gene (promotor, transcription start and end sites, exon/intron boundaries) but which is not actually known to act as a gene. 15

operational habitat Those aspects of a habitat that definitely affect the organism being considered. 25

operculum (pl.: opercula) In mosses, the lidlike top of a sporangium. 20

organ A structure composed of a variety of tissues; seed plants are considered to have only three organs: roots, stems, and leaves. 5

organelles The “little organs” of a cell, such as nuclei, plastids, mitochondria, and ribosomes. Many are membrane-bounded compartments, others are nonmembrane structures composed of protein or protein and RNA. 3

osmosis Diffusion through a membrane. 12

osmotic potential A component of water potential; a measure of the effect of solute particles on a substance’s ability to absorb or release water. 12

outcrossing Synonym for cross fertilization. 16

outer bark The outermost dead layers of bark, from the surface to the innermost cork cambium. Alternative: inner bark. 8

ovary In a flower, the base of the carpel; the region that contains ovules and will develop into a fruit. 9, 23

overtopping In the evolution of unequal branching, the ability of one shoot to grow for a longer time than the other shoot that resulted from the branching. 21, 22

ovule The structure in a carpel that contains the megasporangium and will develop into a seed. 9, 23

ovuliferous scale The scale that bears the ovule in gymnosperm seed cones. Synonym: cone scale. 22

oxidation state A measure of the number of electrons added to or removed from a molecule during an oxidation-reduction reaction. 10, 11

oxidative phosphorylation The formation of ATP from ADP and phosphate, powered by energy released through respiration. 10, 11

oxidize To raise the oxidation state of a molecule by removing an electron from it. 10, 11

oxidizing agent An electron carrier that is not carrying electrons. Alternative: reducing agent. 10, 11

P

P680 The reaction center of photosystem II. 10

P700 The reaction center of photosystem I. 10

P_fr See phytocrome. 14

P_r See phytochrome. 14

P channel The groove in the ribosome small subunit in which the nascent protein-carrying tRNA occurs. Alternative: A channel. 15

pachytene See prophase I. 4

palisade parenchyma Any part of leaf mesophyll in which the cells are elongate and aligned parallel to each other. 6

palmately compound See compound leaf. 6

Pangaea The ancient supercontinent composed of all the world’s land, it existed in the late Paleozoic Era and consisted of Laurasia (north) and Gondwana (south). 2, 27

paradox of enrichment In community ecology, the reduction or loss of a population from a habitat as a result of that habitat being altered to benefit the population. The mechanism often includes a temporary increase in the population, followed by either a harmful increase in the predators of the population or a harmful overconsumption of a limited resource. 26

parallel evolution The evolution of similar homologous features in two or more groups due to similar selective pressures, the features being derived from a common ancestral feature. Compare: convergent evolution. 17

parallel venation Almost exclusively in monocot leaves, a pattern in which all veins run approximately parallel to each other, either from the base of the leaf to its tip or from the midrib to the margin. Alternative: reticulate venation. 6

paralog Genes within single species that evolved from the same ancestral gene. 16

paramylon A storage polysaccharide in euglenoid algae. 19

paraphyletic group A clade that contains an ancestral taxon and several but not all its descendants. 18

parenchyma Cells with only thin primary walls; all other features are highly variable from type to type. Alternatives: collenchyma and sclerenchyma. 5

parental type chromosome A chromosome that, after meiosis, has not undergone crossing over. Alternative: recombinant chromosome. 16

parsimony The concept of minimum complexity; the simplest hypothesis that explains several observations is the most parsimonious. In cladistics, a cladogram with the least number of steps is the most parsimonious. 18

passage cell A cell in the endodermis that has only Casparian strips whereas all surrounding endodermis cells have thickened waterproof walls. 7

pectic substances A set of polysaccharides that constitute the middle lamella and act as the glue that holds together the cells of multicellular plants. 3

pedicel The stalk of an individual flower. Compare: peduncle. 9

peduncle The stalk of an inflorescense, a group of flowers. Compare: pedicel. 9

pellicle In euglenoid algae, a layer of elastic proteins on the cell surface. 19

pentose phosphate pathway A type of respiration in which glucose is converted either to ribose or erythrose. Synonyms: hexose monophosphate shunt and phosphogluconate pathway. 11

peptide bond The chemical bond that holds the amino acid residues together in a protein. 15

perennial plant A plant that lives for more than 2 years. Compare: annual and biennial plant. 5

perfect flower A flower that has both stamens and carpels. Alternative: imperfect flower. 9

perforation In a vessel element, the hole(s) where both primary and secondary walls are missing. Alternative: pit. 5

pericarp Technical term for the fruit wall, composed of one or more of the following: exocarp, mesocarp, endocarp. 9

periclinal wall A wall that is parallel to a nearby surface, especially the outer surface of the plant. Alternative: anticlinal wall. 8

pericycle An irregular band of cells in the root, located between the endodermis and the vascular tissue. 7

periderm Technical term for bark; it consists of cork, cork cambium, and any enclosed tissues such as secondary phloem. 8

perigynous See half-inferior ovary. 9

peripheral protein A membrane protein that is only weakly associated with the surface of the membrane. Alternative: intrinsic protein. 3

perisperm A nutritive tissue in seeds of the dicot order Caryophyllales, formed as nucellus cells proliferate. 9, 23

peristome teeth In a moss capsule, the one or two sets of teeth-like structures around the mouth of the sporangium. 20

permeable membrane A membrane through which materials can pass. Alternative: impermeable membrane. Compare: differentially permeable membrane. 12

peroxisome See microbody. 3

petals The appendages, usually colored, on a flower, most often involved in attracting pollinators. See also corolla. 9, 23

petiole The stalk of a leaf. 6

petiolule The stalk that attaches a leaflet to the rachis of a compound leaf. 6

phage Synonym for bacteriophage. 15

phellem Technical term for cork. 8

phelloderm Parenchyma cells produced to the inside by the cork cambium; usually only a layer or two are formed, and phelloderm is not present in all species. 8

phellogen Synonym for cork cambium. 8

phenotype The physical, observable characteristics of an organism. Alternative: genotype. 16, 17

phloem The portion of vascular tissues involved in conducting sugars and other organic compounds, along with some water and minerals. Alternative: xylem. 2, 5, 8

phosphogluconate pathway Synonym for pentose phosphate pathway.

phospholipid A type of lipid containing two fatty acids and a phosphate group bound to glycerol. 3, 11

phosphorylation The attaching of a phosphate group to a substrate. See chemiosmotic phosphorylation, photophosphorylation, and substrate-level phosphorylation. 10, 11

photoautotroph An organism that obtains its energy through photosynthesis and its carbon from dioxide. Compare: chemoautotroph. 10, 11

photoperiod In reference to cycles of light and darkness, the length of time that uninterrupted light is present. 14

photophosphorylation The formation of ATP from ADP and phosphate by means of light energy; a part of photosynthesis. 10

photorespiration The oxidation of phosphoglycolate produced when RuBP carboxylase adds oxygen, not carbon dioxide, to RuBP. 10

photosynthetic unit A cluster of photosynthetic pigments and electron carriers embedded in the chloroplast membrane. 10

photosynthesis In plants, photosynthesis refers exclusively to the reduction of carbon dioxide to carbohydrate by means of energy captured by several pigments (which always include chlorophylls a and b among others) accompanied by the release of oxygen. In other organisms such as algae, cyanobacteria, and photosynthetic bacteria, photosynthesis may involve other pigments and other products. 2

photosystem I The pigments and electron carriers that transfer electrons from P700 to NADPH. 10

photosystem II The pigments and electron carriers that transfer electrons from water to P700 in photosystem I. 10

phragmoplast During cell division, the phragmoplast is a set of short microtubules oriented parallel to the spindle microtubules; it catches dictyosome vesicles and guides them to the site where the new cell wall (cell plate) is forming. See phycoplast. 4, 19

phragmosome In cell division, a set of microtubules, actin filaments, and cytoplasm that is involved in dividing a large vacuole and creating a cytoplasmic bridge through which the phragmoplast and cell plate can grow. 4

phycobilins The accessory pigments of cyanobacteria and red algae. Phycocyanin absorbs blue light, and phycoerythrin absorbs red light. 19

phycobilisome In cyanobacteria and red algae, a particle involved in photosynthesis and composed of phycobilins and biliproteins. 19

phycocyanin See phycobilins. 19

phycoerythrin See phycobilins. 19

phycoplast In the cell division of some algae, a set of microtubules oriented parallel to the plane of the new cell wall and involved in wall formation. Compare: phragmoplast. 4, 19

phyletic speciation The evolution of one species into a new species, such that the original species no longer exists. Alternative: divergent speciation. 17

phyllode Synonym for cladophyll. 5

phyllotaxy The arrangement of leaves and axillary buds on a stem. 5

phylogenetic relationships The evolutionary relationships that result as one taxon evolves into others that then evolve into still more. 18

phytochrome A pigment involved in many aspects of morphogenesis in which the stimulus is red light or the length of a dark period. P_fr absorbs far-red light, P_r absorbs red light. 14

phytoferritin A protein molecule that binds and stores iron; mostly found in plastids. 3

pinna (pl.: pinnas or pinnae) Technical name for a leaflet of a fern. 21

pinnately compound See compound leaf. 6

pioneers The first plants to inhabit an area that previously had no life. 25

pit In a sclerenchyma cell, an area where there is no secondary wall over the primary wall and material can pass into or out of the cell.

blind pit A pit that does not meet another pit in the adjacent cell.

pit-pair A set of aligned pits in adjacent sclerenchyma cells. 5

pit connection In red algae, a large hole in the wall between two cells. 19

pit membrane The set of two primary walls and middle lamella that occurs between the two pits of a pit-pair. 5

pit plug In red algae, material that fills the hole (pit connection) between two cells. 19

pith The region of parenchyma located in the center of most shoots and some roots, surrounded by vascular bundles. 5

placenta (pl.: placentas or placentae) Tissue in the ovary of a carpel to which the ovules are attached. 9

planation In the telome theory of the origin of megaphylls, the concept that all branching occurred in one plane, resulting in a flat system. 21

plant Technically a plant is any individual organism that is a member of the clade that evolved from green algae and that have an alternation of heteromorphic generations. 2

plant growth substance Term used for any hormone-like compound, whether natural or artificial. 14

plasma membrane The semipermeable membrane that surrounds the protoplasm of a cell. Synonym: plasmalemma. 3

plasmalemma Synonym for plasma membrane. 3

plasmid A small circle of DNA occurring in some bacteria and acting like a bacterial chromosome. 15

plasmodesma (pl.: plasmodesmata) A narrow hole in a primary wall, containing some cytoplasm, plasma membrane, and a desmotubule; a means of communication between cells. See symplast. 3, 5

plasmogamy The fusion of the cytoplasm of two gametes during sexual reproduction. See karyogamy. 9

plasmolysis The shrinking of a cell due to loss of water. Do not confuse with lysis. 12

plasticity A property of collenchyma walls; once stretched to a new shape or size, usually by growth, the wall retains that new shape or size. Alternative: elasticity. 5

plastids A family of organelles within plant cells only. proplastids Young plastids common in meristematic cells. chloroplasts Chlorophyll-rich plastids that carry out photosynthesis. amyloplasts Plastids that store starch. chromoplasts Plastids that contain red or yellow pigments, located in flowers and fruits. leucoplasts Colorless plastids. 3

plastochron The length of time required for an apical meristem to make the cells of one node and internode. 5

plastocyanin A copper-containing electron carrier. 10

plastoglobulus (pl.: plastoglobuli) A droplet of lipid located within a plastid. 3

plastoquinone A class of lipid-soluble electron carriers. 10

plesiomorphic feature A feature that was present in a taxon’s ancestors. Plesiomorphic features are often referred to as relictual or primitive features. 18

pleiotropic effects The multiple phenotypic expressions of a single allele whose activity affects various aspects of metabolism. 16

plumule Synonym for epicotyl. 9

plurilocular gametangium (pl.: gametangia) In brown algae, a multicellular structure in which each cell produces a gamete. Alternative: unilocular sporangium. 19

pneumatocyst Synonym for air bladder, a swollen, hollow structure in brown algae; it increases buoyancy. 19

poikilohydry The ability of some simple plants and lichens to allow their bodies to become extremely dehydrated without dying, then being capable of rehydrating and becoming metabolically active quickly. 12

point mutation A mutation affecting only a single nucleotide. 16

polar nuclei (sing.: nucleus) The two nuclei of the central cell of the megagametophyte in a flowering plant; after fertilization, they become the endosperm nucleus. 9

polar transport Transport in one direction based on an organ’s structure, regardless of its spatial orientation. 14

polarity In development and morphogenesis, having two different ends, usually a shoot/root polarity, or a petiole/leaf tip polarity. 14

pollen In seed plants, the microspores and microgametophytes. 9, 21—23

pollen chamber In gymnosperms, a cavity just above the nucellus in the ovule, the site where pollen accumulates and germinates. 22

pollen tube After landing on a compatible stigma or gymnosperm megasporophyll, a pollen grain germinates with a tubelike process that carries the sperm cells to the vicinity of the egg cell. 9, 22

polymer A large compound composed of a number of subunits, monomers. 3, 5, 10

polymerase chain reaction A method of copying minute quantities of DNA using bacterial enzymes. 15

polyploid Refers to a nucleus that contains three or more sets of chromosomes. 16

polysaccharide A compound made up of many simple sugars (monosaccharides). 3, 10

polysome The complex formed when numerous ribosomes bind to the same molecule of messenger RNA. 3, 15

population All the individuals of a species that live in a particular area at the same time and can interact with each other. 17, 25

positive feedback system An enzyme system in which the product stimulates the action of one or several of the enzymes that produce it. The ripening of climacteric fruits is an example. 14

postzygotic isolation mechanisms Phenomena that prevent successful interbreeding of two populations but that act after fertilization; the two sets of chromosomes are incompatible and cannot produce a fertile adult. Alternative: prezygotic isolation mechanism. 17

P-protein Phloem-protein, or fibrillar protein that plugs sieve pores and prevents leakage if sieve elements are damaged. 12

predation A relationship in which one species benefits and the other is harmed; not often used in botany. 25

preprophase band Prior to cell division, the preprophase band is a set of microtubules that encircles the cell just interior to the cell membrane and located at the site where the new wall will attach to the pre-existing wall. 4

presentation time The length of time a stimulus must be present in order for an organism to perceive it. 14

pressure flow hypothesis The hypothesis that flow in phloem is due to active loading in sources and active unloading in sinks. 12

pressure potential A component of water potential; a measure of the effect of pressure or tension on a substance’s ability to absorb or release water. 12

prezygotic isolation mechanism Phenomena that prevent successful interbreeding of two populations but that act so early that fertilization is not possible. Alternative: postzygotic isolation mechanism. 17

primary cell wall A cell wall present on all plant cells except some sperm cells; it is formed during cell division and is usually thin, but some may be thick. See secondary cell wall and collenchyma. 3

primary consumer In ecology, a synonym for herbivore. 25

primary endosperm nucleus The nucleus formed by the fusion of one sperm nucleus and two polar nuclei. 9

primary growth The production of new cells by shoot and root apical meristems and leaf primordia. Alternative: secondary (woody) growth. 5, 8

primary phloem The phloem of the primary body; it differentiates from cells derived from apical meristems or forms in leaves, flowers, and fruits. Compare: secondary phloem. 5, 8

primary pit field An area of a primary cell wall that is especially thin and contains numerous plasmodesmata. See plasmodesma. 3, 5

primary plant body The herbaceous body produced by apical meristem (roots, stems, leaves, flowers, and fruits). Alternative: secondary (woody) plant body. 5, 8

primary producer In ecology, synonym for autotroph. 25

primary structure of a protein The order of the sequence of amino acids in the protein. 15, 16

primary tissues The tissues derived more or less directly from an apical meristem or leaf primordium; the tissues of the primary plant body. Alternative: secondary tissues. 5, 8

primary xylem The xylem of the primary body; the xylem produced from cells derived from apical meristems or formed in leaves, flowers, and fruits. Compare: secondary xylem. 5, 8

primer RNA During DNA replication, a short piece of RNA that is synthesized against open DNA and from which DNA polymerase can begin building a new molecule of DNA. 16

primary succession The establishment of plants in a habitat that has been devoid of them, for example, the establishment of the first plants on the new land that is available as a glacier retreats or on the barren land produced by a volcano. 26

primordium (pl.: primordia) A small mass of cells that grows into an organ such as a leaf or petal. 5

procambium (pl.: procambia) Tissue that matures into primary xylem and primary phloem. 5

prochlorophytes A group of prokaryotes that have both chlorophyll a and b; believed to be closely related to the ancestors of plastids in algae and plants. 19

procumbent cell In rays in secondary xylem, cells that are longer radially than they are tall; they typically have little or no cross-field pitting. Alternative: upright cell. 8

proembryo An early stage of embryo development, usually considered to encompass the stages between the zygote and the initiation of the cotyledon primordia. 9

progymnosperms A group of extinct plants believed to have been the ancesters of gymnosperms. 22

prokaryotes Organisms that have no true nucleus or membrane-bounded organelles. Prokaryotes are eubacteria, cyanobacteria, and archaebacteria. Alternative: eukaryotes. 3

promoter region That portion of a gene in which control molecules and RNA polymerases bind during gene activation and transcription. Alternative: structural region. 15

propagules Parts of a plant involved in reproduction and dissemination. Examples are seeds, bulbs, plant pieces that can form roots and grow into a new plant. 9, 25

prophase The initial phase of mitosis during which the nucleolus and nuclear membrane break down, chromosomes begin to condense, and the spindle begins to form. 4

prophase I The first phase of meiosis, similar to prophase of mitosis, with the following additional processes: leptotene Initiation of chromosome condensation. zygotene The pairing of homologous chromosomes (synapsis). pachytene Formation of the synaptonemal complex. diplotene Homolog separation and chiasmata become visible. diakinesis Complete separation of homologs and terminalization of chiasmata. 4

proplastid See plastids. 3

protoderm A term that refers to any immature epidermal cell. 5

protonema (pl.: protonemata) In nonvascular plants, the mass of alga-like cells that grow from the spore during germination. 20

protophloem The part of the primary phloem that differentiates early, while adjacent cells are still elongating. Alternative: metaphloem. 5

protoplasm All the substance of a cell, usually considered not to include the cell wall. The protoplasm of a single cell is a protoplast. See cytoplasm and hyaloplasm. 3

protostele A vascular cylinder that has no pith; common in roots and early vascular plants. Alternative: siphonostele. 21—23

protoxylem The part of the primary xylem that differentiates early, while adjacent cells are still elongating. Alternative: metaxylem. 5, 21—23

provascular tissue Cells in the primary plant body that later differentiate into xylem, phloem, or vascular cambium. Synonym: procambium. 5

proximal Refers to the position of a structure near a point of reference; relative to a stem, a petiole is proximal to a leaf blade. Alternative: distal. 5

pseudomonopodial branching A type of sympodial branching that strongly resembles monopodial branching, having what appears to be one main shoot. 21

pulvinus (pl.: pulvini) A jointlike region of a petiole where motor cells are located and flexion occurs during nastic responses. 14

pycnoxylic wood Wood with little or no axial parenchyma, such as that of gymnosperms and progymnosperms. Compare: manoxylic wood. 22

pyrenoid In many algae and hornworts, a region of the choroplast believed to be involved in polymerization of polysaccharides. 19, 20

Q

quantitative trait locus (QTL) analysis Most phenotype characters are the result of interactions of many genes (loci); QTL analysis involves numerous crosses to determine just how much various genes contribute to a particular phenotype. 16

quantum (pl.: quanta) A particle of electromagnetic energy. Synonym: photon. 10

quaternary structure The association of several proteins into a large structure such as a microtubule or synthetic complex. 10

quiescent center Portion of the root apical meristem in which cell division does not occur. 7

R

r Symbol for biotic potential. 25

rachis (pl.: rachises) The extension of the petiole in a compound leaf; all leaflets are attached to the rachis. 6

radial system (of wood) The set of rays within wood. 8

radially symmetrical Divisible into two equal halves by any median longitudinal section. Synonym: actinomorphic. 9

radicle The main root of a seed; it is the direct continuation of the embryonic stem. 7, 9

rain shadow The diminished amount of rainfall on the leeward side of a mountain compared to the side that faces an ocean. 27

random distribution In ecology, the distribution of individuals in the habitat with no obvious, identifiable pattern. Compare: clumped and uniform distribution. 25

raphe In seeds, a ridge caused by the fusion of the funiculus to the side of the ovule. In diatoms, a groove in the shell. 19

raphide A long, narrow, needle-like crystal, occurring in clusters in specialized cells. 3

ray In secondary xylem and phloem, a radial series of cells produced by ray initials. Alternative: axial tissue. 8

ray initials In a vascular cambium, the short cells that give rise to the rays of the secondary xylem and phloem. Alternative: fusiform initials. 8

ray tracheid Horizontal tracheids in the secondary xylem rays of gymnosperms. 8

reaction center A special chlorophyll a molecule actually involved in the transfer of electrons in photosynthesis. 10

reaction wood Wood formed in response to mechanical stress. tension wood The reaction wood of dicots, formed on the upper side of a branch. compression wood The reaction wood of gymnosperms, formed on the lower side of a branch. 8

reannealing Synonym for DNA hybridization by slowly cooling a mixture of single-stranded DNA molecules. 15

receptacle The stem (axis) of a flower, to which all the other parts are attached. 8 In the brown alga Fucus, the ends of the branches where conceptacles are located. 9, 19

recessive trait A trait whose phenotype is completely masked by that of the alternative (dominant) allele in the heterozygous condition. 16

recombinant chromosome A chromosome that results from crossing-over in meiosis, being composed of parts of the paternal and maternal homologs. Alternative: parental type chromosome. 16

recombinant DNA DNA constructed from pieces of DNA from several sources, either through crossing-over in meiosis or laboratory manipulation. 15

red tide A bloom of algae in which the cells become so numerous as to give the water a reddish tint. 19

redox potential The tendency of a molecule to accept or donate electrons during a chemical reaction. 10

reduce To lower the oxidation state of a molecule by adding an electron to it. 10, 11

reducing agent An electron carrier that is carrying electrons. Alternative: oxidizing agent. 10, 11

reducing power The ability of an electron carrier to force electrons onto another compound. 10, 11

reduction division Synonym for meiosis.

regular flower A radially symmetrical flower. Alternative: zygomorphic flower. 9

relictual feature A feature that occurs in a modern organism and was inherited relatively unchanged from an ancient ancestor. Alternative: derived feature. 1, 18

replication fork In DNA replication, the point at which the double helix opens and formation of new DNA occurs. 16

replicon During DNA replication, a short segment of DNA that has opened and where replication is occurring. 16

reproductive barrier Any physical or metabolic phenomenon that prevents two members of a species from interbreeding. 17

reproductive isolation The inability of some members of a species to interbreed with other members through either biotic or abiotic reproductive barriers. 17

reproductive organ An organ (a set of tissues) that are involved in either asexual or sexual reproduction. Examples are flowers, cones, antheridia, and archegonia. Compare: vegetative organ. 2

respiration The breakdown of molecules such that part of their energy is used to make ATP. If oxygen is required as an electron acceptor, the process is aerobic respiration; if not, it is anaerobic respiration (fermentation). 2, 11

respiratory quotient An indicator of the type of substrate being respired, RQ (carbon dioxide liberated)/(oxygen consumed). 11

resting phase Old synonym for interphase.

restriction endonucleases Enzymes that recognize specific sites in DNA double helices, then cut the two strands in complementary sites. 15

restriction map A map of a DNA molecule made by exposing it to restriction endonucleases, thus showing the number of cleavage sites and the number of bases between sites. 15

reticulate thickening A pattern of secondary wall deposition in tracheids and vessel elements; the wall is deposited as a series of intersecting bands that have a netlike appearance. 5

reticulate venation A netlike pattern of veins in a leaf, found primarily in leaves of dicots (broadleaf plants). Synonym: netted venation. Alternative: parallel venation. 6

retrovirus A virus whose genetic material is single-stranded RNA; the most common type of plant virus. 15

retting Extracting fibers from plant material by placing the harvested plants in a shallow pool of water and allowing the soft parts of the plants to be decomposed by fungi and bacteria. 24

reverse transcriptase An enzyme that catalyzes the synthesis of DNA, using RNA as a template. 15

rhizoids In certain fungi, algae, and nonvascular plants, cells or parts of cells that project into the substrate and anchor the organism. 19—20

rhizome A fleshy, horizontal, subterranean stem involved in allowing the plant to migrate laterally. Example: bamboo, iris. 5

rhyniophytes The common name for Rhynia and its close relatives, the earliest vascular plans. 21

ribonucleic acid (RNA) A polymer of ribose-containing nucleotides; there are three classes: messenger RNA, transfer RNA, and ribosomal RNA. 15, 16

ribophorin An integral membrane protein that binds ribosomes to the membrane, usually in rough endoplasmic reticulum. 3

ribose A five-carbon sugar occurring in ribonucleic acid, among other things. 11

ribosome An organelle responsible for protein synthesis; ribosomes consist of a large subunit and a small subunit, both made of proteins and ribosomal RNA (rRNA). 3, 15

ring porous wood Wood in which the early wood has more numerous and larger vessels than the late wood. Alternative: diffuse porous wood. 8

RNA polymerase I The enzyme that transcribes ribosomal genes into ribosomal RNA. 15

RNA polymerase II The enzyme responsible for transcribing genes into messenger RNA. 15

RNA polymerase III The enzyme responsible for transcribing the 5S RNA gene into 5S RNA. 15

root cap A layer of parenchyma cells that cover and protect the root apex. 7

root hair A short-lived trichome near a root apex. Root hairs increase the surface area and absorptive capacity of roots; being single, slender cells, they enter soil pores that are too small for whole root tips to enter. 7

root hair zone Region of a root tip, just proximal to the zone of elongation, where epidermal cells grow out as root hairs. 7

root nodule Several species of plants have symbiotic relationships with nitrogen-fixing bacteria; in some species, especially those of legumes, portions of roots become swollen and occupied by the bacteria. 7

root pressure Water in root xylem is under pressure due to the active acculumation of salts by the endodermis and the accompanying influx of water. 7, 12

rough ER (RER) See endoplasmic reticulum. 3

RUBISCO Synonym for RuBP carboxylase. 10

RuBP carboxylase The enzyme in photosynthesis that carboxylates RuBP, thus bringing carbon into the plant’s metabolism. Synonym: RUBISCO. 10

S

S phase The synthesis phase of the cell cycle, during which nuclear DNA is replicated (synthesized). 4, 16

sapwood The light-colored, light-scented outermost wood of a trunk or branch; conduction is still occurring and many wood parenchyma cells are alive. Alternative: heartwood. 8

scalariform thickening A pattern of secondary wall deposition in tracheids and vessel elements; the wall is interrupted by broad, short pits that cause the wall to have a ladder-like appearance. 5

scientific method A means of analyzing the physical universe. Observations are used as the basis for constructing a hypothesis that predicts the outcome of future observations or experiments. Anything that can never be verified cannot be accepted as part of a scientific hypothesis. 1

scientific name The binomial name of a species, consisting of the genus name and the species epithet. 18

sclereid A sclerenchyma cell that is rather cubical, not long like a fiber. Masses of sclereids provide a tissue with strength and rigidity. Alternative: fiber. 5

sclerenchyma Sclerenchyma cells have both a primary wall and an elastic secondary wall; if stretched to a new size or shape, the wall returns to its original size and shape after the deforming force is removed. Alternatives: parenchyma and collenchyma. 5

scutellum (pl.: scutella) In grass seeds, the single cotyledon, which is shield-shaped and digests and absorbs the endosperm during germination. 9

secondary cell wall A cell wall present only in certain cells (sclerenchyma) and formed only after cell division has been completed. When present, the secondary wall is located interior to the primary wall and is typically impregnated with lignin. See primary cell wall, sclerenchyma, and xylem. 3, 5

secondary consumer In ecology, a synonym for carnivores and omnivores. 25

secondary (woody) growth Growth that occurs by means of either the vascular cambium or the cork cambium. It results in wood and bark, the secondary tissues. Alternative: primary growth. 5, 8

secondary phloem Phloem derived from the vascular cambium. Compare: primary phloem. 5, 8

secondary (woody) plant body The wood and bark produced by the vascular cambium and cork cambium. Alternative: primary plant body. 5, 8

secondary tissues The tissues of the secondary plant body-those produced by the vascular cambium and the cork cambium. Alternative: primary tissues. 8

secondary xylem Xylem derived from the vascular cambium. Compare: primary xylem. 5, 8

seed coat The protective layer on a seed; the seed coat develops from one or both integuments. Synonym: testa. 9

seed plant Any plant that bears seeds as part of its reproductive cycle. Seeds may have originated twice in evolution; if so, then the concept of seed plant is a grade (a level of evolution), not a clade (a group of closely related organisms sharing a common ancestor). 2

selectively permeable membrane Synonym for differentially permeable membrane. 12

selfing Pollinating a plant’s stigma with pollen from the same plant or a plant of identical genotype. 16

self-pollination The pollination of a flower by pollen from the same flower or another flower on the same plant. Alternative: cross-pollination. 9

semiconservative replication Refers to the fact that during DNA replication, one new molecule is paired with one original molecule such that in every new chromosome, half the DNA is conserved from the pre-existing chromosome. 16

semipermeable membrane A membrane that is relatively permeable to some substances and relatively impermeable to others. Synonym: differentially permeable. See impermeable and freely permeable. 3, 12

sepal In flowers, the outermost of the fundamental appendages, most often providing protection of the flower during its development. See calyx. 9

sessile Refers to an organ that has no stalk but rather is attached directly to the stem or other underlying organ. For leaves, alternative is petiolate. 6

seta (pl.: setae) In mosses and liverworts the stalk of the capsule, located between the foot and the sporangium. 20

sexual reproduction Reproduction in which genomes of two individuals are brought together in one nucleus followed by meiosis with crossing-over. 9, 16

short-day plant A plant that is induced to flower by nights longer than the critical night length. 14

sieve area In phloem, an area on a sieve element wall in which numerous sieve pores occur. 5

sieve cell The phloem conducting cell in nonangiosperms; sieve cells are long and tapered with small sieve areas over much of their surfaces. Alternative: sieve tube member. 5

sieve element Refers to either or both types of phloem-conducting cells: sieve cells and sieve tube members. 5

sieve plate In phloem, the end walls of sieve tube members, bearing one or several large sieve areas with large sieve pores. 5

sieve pore In sieve elements, the holes (enlarged plasmodesmata) in the primary walls; sieve pores permit movement of phloem sap from one sieve element to another. 5

sieve tube In the phloem of angiosperms, a column of sieve tube members interconnected by large sieve areas and sieve pores. 5

simple cone A cone with just one axis, bearing only sporophylls. Most cones are simple cones. Alternative: compound cone. 22

simple fruit A fruit that develops from a single carpel or the fused carpels of a single flower. Alternatives: aggregate fruit and multiple fruit. 9

simple leaf A leaf in which the blade consists of just one part. Alternative: compound leaf. 6

simple pit In sclerenchyma cells, a pit with no border. Alternative: bordered pit. 6

simple sugar A sugar that is not composed of smaller sugar molecules, the monomer for polysaccharides. Synonym: monosaccharide. 10, 11

sink In phloem transport, any organ or tissue that receives material transported by the phloem. Alternative: source. 12

sink habitat In the theory of metapopulations, a sink habitat is one that is so poor that it cannot support a population of a particular species indefinitely; the species is maintained only by migration from nearby richer habitats (source habitats). Compare: source habitat. 26

siphonostele A vascular cylinder that contains pith; common in stems but absent in early vascular plants. Compare: protostele. 21—23

siphonous In algae, a synonym for coenocyte-a long, tubular cell with many nuclei and few or no cross walls. 19

skepticism The concept of systematic doubt or suspended belief; keeping an open mind so that even if numerous observations support a hypothesis, new evidence is still considered as it becomes available. 1

smooth ER (SER) See endoplasmic reticulum. 3

softwood A term applied to both gymnosperms and their wood, because few gymnosperms have any fibers in their wood. Alternative: hardwood. 8

soft fiber Among textile fibers, soft fibers are those extracted from phloem, cortex, or bark. Synonym: bast fiber. 24

somatic mutation A mutation in a cell that is not a gamete and does not give rise to gametes. 16

sorus (pl.: sori) In ferns, a cluster of sporangia on the underside of leaves. 21

source In phloem transport, any organ or tissue that supplies material to be transported. Alternative: sink. 12

source habitat In the theory of metapopulations, a source habitat is one that can support a population of a particular species indefinitely. Seeds, spores or other propagules become dispersed from source habitats to poorer sink habitats. Compare: sink habitat. 26

speciation The conversion of one species or population of a species into a new species. 17

species A set of individuals that are closely related by descent from a common ancester and can reproduce with each other but not with members of any other species. 18

species abundance distribution In community ecology, a plot of the number of species in a region into various abundance classes; a common result is that a few species are extremely common, the rest are each rather rare. 26

species-area relationship The relationship between the size of an area and the number of species present; often, a small area has fewer species than does a large area. 26

spermatium (pl.: spermatia) Generally, a synonym for sperm cell, but in botany it usually refers only to the nonmobile sperms of red algae. 19

spermatophytes Plants that produce seeds. Alternative: vascular cryptogams. 2, 21, 22

spherosome See lipid body. 3

spindle The framework of microtubules that pulls the chromosomes from the center of the cell to the poles during nuclear division. 4

split genome virus A type of virus in which the genome occurs as two or more separate double helices of DNA, each packaged in separate viral particles. 15

spongy mesophyll Any part of leaf mesophyll in which the cells are not aligned parallel to each other and are separated by large intercellular spaces. 6

sporangiophore In the arthrophytes (sphenophytes), a stalked, umbrella-like structure that bears sporangia. 21

sporangium (pl.: sporangia) A structure that produces spores. 9, 19—23

spore A single cell that is a means of asexual reproduction; it can grow into a new organism but cannot fuse like a gamete. 9, 19—23

sporophyll A leaf that bears sporangia. 21—23

sporophyte A diploid plant that produces spores. Alternative: gametophyte. 9, 19—23

spring wood In secondary xylem, the wood formed early in the season, usually with an abundance of vessels in angiosperms or with wide tracheids in gymnosperms. Also called early wood. Alternative: summer wood. 8

stamens The organs of a flower involved in producing microspores (pollen). See also androecium, anther, and filament. 9, 23

start codon In messenger RNA, a codon (set of three nucleotides) that indicates the beginning of information for protein synthesis. 15

statocytes Cells within the root cap that detect the direction of gravity. 14

statolith A type of starch grain that is so dense it sinks to the bottom of a cell’s cytoplasm, indicating the direction of gravity. 14

stele The set of vascular tissues in a root or stem (but not in a leaf). 5, 21, 22

stigma (pl.: stigmas) In the carpel of a flower, the receptive tissue to which pollen adheres. 9, 23 In algae, an eyespot, a set of pigment droplets involved in detecting light direction. 19

stipe The stalk of certain organisms-fern leaves, kelps, mushrooms. 19, 21

stipules Small flaps of tissue located at the base of a leaf, near its attachment to the stem. Stipules may range from quite leaflike to small and inconspicuous. 6

STM/CC complex In many species, sieve tube members and guard cells are believed to function together in phloem loading and conduction, making it more accurate to speak of both rather than of just the sieve tube members. 12

stolon An aerial stem with elongate internodes; it establishes plantlets periodically when it contacts soil. Example: strawberry. 5

stoma (pl.: stomata) A word sometimes used to mean “stomatal pore,” the intercellular space between guard cells through which carbon dioxide and water are exchanged, and sometimes used to mean “stomatal complex,” the stomatal pore plus guard cells plus associated cells. 5

stomatal pore The intercellular space between two guard cells; carbon dioxide is absorbed through the pore and water is lost. 5

stop codon In messenger RNA, a codon (set of three nucleotides) that indicates the end of information for protein synthesis. 15

storied cambium A vascular cambium in which fusiform initials are aligned horizontally. Alternative: nonstoried cambium. 8

streptophyte An informal name for the clade that contains charophytes, embryophytes, and their most recent common ancestor. 19

strict aerobe Synonym for obligate aerobe. 11

strict anaerobe Synonym for obligate anaerobe. 11

strobilus (pl.: strobili) Synonym for cone. 21

stroma reactions In plant photosynthesis, the set of reactions that occur in the stroma and are not directly powered by light. Synonym: dark reactions. Alternative: light-dependent reactions. 10

structural region The portion of a gene consisting of nucleotide triplets that specify which amino acids are to be incorporated into protein. Alternative: promotor region. 15

style In the carpel, the tissue that elevates the stigma above the ovary. 9, 23

subapical meristem The region of a shoot or root just proximal to the apical meristem. 5

suberin Lipid material that causes the hydrophobic properties of cork cell walls and the Casparian strip of the endodermis. 7, 8

substrate The reactant acted upon by an enzyme. 10, 11

substrate-level phosphorylation The formation of ATP from ADP by having a phosphate group transferred to it from a substrate molecule. 10, 11

substrate specificity The ability of an enzyme to distinguish one substrate from similar substrates. 10

succession A more-or-less predictable sequence of changes over time of the species that occur in an area. 26

summer wood In secondary xylem, the wood formed late in the season, usually with few or no vessels in angiosperms, or with narrow tracheids in gymnosperms. Also called late wood. Alternative: spring wood. 8

superior ovary An ovary located above the sepals, petals, and stamens; those appendages are hypogenous. Alternatives: inferior and half-inferior ovary. 9

suspensor In seed plant embryos, the stalk of cells that pushes the embryo into the endosperm. 9, 22

symbiotic relationship A relationship in which two or more organisms live closely together. 19

sympatric speciation Speciation that occurs within a limited geographic range; populations are separated by biotic reproductive barriers, not by physical differences. Alternative: allopatric speciation. 17

sympetally The condition of having the petals of a flower fused together into a tube. 23

symplast The protoplasm of all the cells in a plant are interconnected by plasmodesmata; the entire mass is the symplast or symplasm. See apoplast. 3, 12

sympodial branching A branching pattern in which what appears to be one main shoot (the trunk) is actually a series of lateral branches, each of which displaces the apex of the shoot that bears it. Alternatives: monopodial and pseudomonopodial branching. 21—23

synapsis (pl.: synapses) The pairing of homologous chromosomes during zygotene of prophase I of meiosis. Synapsis precedes crossing-over. 4

synaptonemal complex In prophase I of meiosis, after homologous chromosomes have paired (undergone synapsis), a protein complex, the synoptonemal complex, holds them together. It is composed of a central element connected by fine fibers to the lateral elements that actually connect to DNA. 4

synergid In the egg apparatus of an angiosperm megagametophyte, there is an egg and one or two adjacent cells, synergids; the pollen tube enters one of the synergids. 9

syngamy The fusion of a sperm and an egg. 9

T

TATA box In the promotor region of many genes, a region rich in thymine- and adenine-containing nucleotides, believed important for RNA polymerase binding. 15

taxis A response in which a cell swims toward or away from a stimulus. 14

taxon A term that refers to any taxonomic group such as species, genus, family, and so on. 18

teleology The interpretation that objects and processes have a purpose, such as, “The purpose of most leaves is photosynthesis,” in contrast to a statement of fact, such as, “Most leaves carry out photosynthesis.” 1, 18

telome In a plant with dichotomous branching, the last two twigs produced by the last bifurcation. 21

telome theory The theory that leaves (megaphylls) of arthrophytes, ferns, and seed plants evolved from branch systems (telomes) by overtopping, planation, and webbing. 21

telophase The fourth and last phase of mitosis, during which the chromosomes decondense, the nucleolus and nuclear envelope reform, the spindle depolymerizes, and the phragmoplast appears. 4

telophase I The fourth phase of meiosis I, similar to telophase of mitosis. However, in many organisms, telophase I and prophase II are often shortened or eliminated, and full nuclei are not formed between meiosis I and II. 4

telophase II A phase of meiosis II, similar to telophase of mitosis. 4

temperate virus A virus whose genome has been incorporated into the host’s genome, being replicated simultaneously with host DNA; the virus produces few or no symptoms. 15

tendril An organ that attaches a vine to a support by wrapping around it. It may be a modified leaf, leaflet, or shoot. Example: grape. 5, 6

tension wood See reaction wood. 8

tepal Refers to members of a perianth when it is not certain if they are really sepals or petals. 9

terminal bud A bud located at the extreme apex of a shoot; usually present only in winter as a dormant bud. Alternative: axillary bud. 5

test cross A cross involving one parent known to be homozygous recessive for the trait being considered. 16

testa (pl.: testas) Synonym for seed coat. 9

tetrads During meiosis I, after homologs have paired and condensed sufficiently, the four chromatids are visible as a tetrad. 4

tetrahydrocannabinol (THC) The psychoactive chemical in marijuana (Cannabis sativa). 24

tetraploid Refers to four full sets of chromosomes within a single nucleus. 4, 16

tetraspores In red algae, the spores produced by meiosis in the tetrasporophyte. 19

tetrasporophyte In red algae, the diploid generation equivalent to a sporophyte generation in other algae. 19

thallophyte An old, rarely used term to distinguish organisms that are not embryophytes; algae and fungi. 2, 19, 20

thallus In plants, algae, and fungi, a simple body that lacks vascular tissues and the complex organs of vascular plants. 2, 20

theory After a hypothesis has been confirmed by numerous observations or experiments, it is considered to be a theory. 1

thermogenic respiration Respiration in which electron transport is uncoupled from ATP synthesis, so heat is generated. Synonym: cyanide-resistant respiration. 11

thigmotropic response A tropic response with touch as the stimulus. 14

threshold The level or intensity of stimulus that must be present during the presentation time in order for an organism to perceive it. 14

thylakoids The photosynthetic membranes of chloroplasts. 3, 10

ti plasmid A plasmid from the bacterium Agrobacterium tumefaciens; this is a commonly used vector for recombinant DNA studies in plants. 15

tinsel flagellum A flagellum covered with many minute hairlike projections. Alternative: whiplash flagellum. 19

tolerance range The range of environmental conditions in which an organism can live and reproduce. 25

tonoplast The vacuolar membrane. 3

trace element See essential element. 13

tracheary element A term refering to either or both types of xylem-conducting cell: tracheids and vessel elements. 5

tracheid A xylem-conducting cell; tracheids tend to be long and tapered, and they never have a perforation—a complete hole in the primary wall—as vessel elements do. 5, 12, 23

trans-acting factor Molecules that affect the activity of a gene but which are not part of the DNA strand that contains the gene; trans-acting factors must diffuse to the DNA from some other location in a cell. Alternative: cis-acting factor. 15

transamination The transferral of an amino group from one molecule to another; important in the synthesis of amino acids. 13

transcription The “reading” of DNA by RNA polymerase with the simultaneous production of RNA. 15

transduction In a receptive tissue after the perception of a stimulus, transduction is the change that allows the tissue to communicate that the stimulus has occurred. 14

transfer cells Cells involved in rapid short-distance transfer of material; they have transfer (labyrinthine) walls. 12

transfer wall In transfer cells, walls whose inner surface is highly convoluted, thus increasing the surface area of the plasma membrane and the number of molecular pumps present. Synonym: labyrinthine wall. 12

transformation theory The theory that vascular plants arose from algae that had an alternation of isomorphic generations, each of which was gradually transformed into the types of sporophytes and gametophytes present today. Compare: interpolation theory. 21

translation In protein synthesis, the utilization of mRNA to guide the incorporation of amino acids into protein. 15

translocation Long-distance transport of water and nutrients by xylem and phloem. 12

transpiration Loss of water vapor through the epidermis. transcuticular transpiration Loss through the cuticle. transstomatal transpiration Loss through stomata. 6, 12

transposable element A region of DNA that codes for enzymes that catalyze the release of the element and its insertion into a different site in the DNA. See also transposon and insertion sequence. 16

transposon A large transposable element that carries, in addition to the insertion sequence, other genes that code for proteins not directly associated with transposition. 16

trans-unsaturated fatty acid, usually just called a trans-fat An unsaturated fatty acid (it has one or more carbon—carbon double bonds) and the two hydrogens at the double bond are on opposite sides of the molecule. Trans-unsaturated fatty acids are synthetic, not natural, and they are not healthful. Compare: cis-unsaturated fatty acid. 24

tricarboxylic acid cycle Synonym for citric acid cycle and Krebs cycle. 11

trichome A plant hair; often restricted to structures that contain only cells derived from the epidermis. 5

tricolpate pollen Pollen that has three germination pores as opposed to just one; tricolpate pollen is a synapomorphy that unites eudicots. 23

triglyceride A type of lipid consisting of three fatty acids bound to one molecule of glycerol. 11

triploid A nucleus that contains three sets of chromosomes. 16

tropic response A growth response oriented with regard to the stimulus. Synonym: tropism. 14

true fruit A fruit that developed only from carpel tissue, not containing any other tissue. Alternative: accessory fruit. 9

trumpet hyphae In some brown algae, the phloem-like cells that conduct photosynthate through the alga. 19

tuber A short, fleshy, horizontal stem, involved in storing nutrients but not in migrating laterally. Example: potato. 5

tubulin See microtubules. 3

turgid Filled with water to such a degree that the surface of the cell or plant is firm. 12

turgor pressure The pressure with which a protoplast presses against the cell wall when a cell is turgid. 12

tylosis (pl.: tyloses) After a vessel stops conducting because of cavitation, adjacent cells may push cytoplasm into the vessel through pits, plugging the vessel. 8

type specimen A single specimen that is the absolute standard for the species and its scientific name. 18

U

uniaperturate pollen Pollen that has only a single germination pore. This is an ancestral condition (a symplesiomorphy) for the angiosperms. 23

uniform distribution In ecology, the distribution of individuals in the habitat such that they are evenly spaced, as in an orchard, rather than being clumped or occurring at random. 25

unilocular sporangium In brown algae, a multinucleate, coenocytic sporangium where meiosis occurs. Alternative: plurilocular gametangia. 19

uniparental inheritance Inheritance of genes from just one parent, the most common case for plastid and mitochondrial genes; sperm cells typically do not contribute these organelles to the zygote. Alternative: biparental inheritance. Synonym: maternal inheritance. 16

uniseriate Consisting of just one row; often used for things that consist of one layer. 5

upright cell In rays in secondary xylem, cells that are taller than long; they typically have extensive cross-field pitting. Alternative: procumbent cell. 8

V

vacuole A membrane-bounded (tonoplast) space larger than a vesicle which stores material, either dissolved in water or as a crystalline or flocculent mass. 3

vacuole membrane Synonym for tonoplast. 3

valence electrons The electrons that actually participate during a chemical reaction. 10

variegation A pattern of spots, stripes, or patches in leaves or other organs, caused by plastid mutations. 16

vascular bundle A column of vascular tissue, typically both xylem and phloem together, but in leaves sometimes consisting of only one or the other. 5

vascular cambium The meristem that produces secondary vascular tissues—secondary xylem (wood) and secondary phloem (inner bark). 8

vascular cryptogams The vascular plants that do not produce seeds, such as lycopods, horsetails, and ferns. Alternative: spermatophytes. 21

vascular plant A plant that has vascular tissues, such as flowering plants, conifers, ferns, and others. Synonym: tracheophyte. Compare: non-vascular plants and bryophytes. 2

vector Pieces of DNA that are used to insert experimental, recombinant DNA into bacteria or eukaryotes. 15

vegetarian diet A diet centered mostly or exclusively on foods derived from plants (vegetables, fruits, grains, sugars) and excluding or minimizing any food derived from an animal. Some vegetarian diets exclude meat but include eggs or milk (an ovo-lacto-vegetarian diet); others avoid all animal products (a strict vegetarian diet). 23

vegetative Refers to phenomena or parts of a plant not involved in sexual reproduction. 9

vegetative cell In the pollen grain of seed plants, the cell or cells that do not give rise to the sperm cells; the cell that is not the generative cell. 9, 22

vegetative organ An organ (a set of tissues) that are not involved in reproduction. Familiar vegetative organs are leaves, roots, and stems. 2

venation The pattern of veins in a tissue or organ. 5, 6

vernalization The cold treatment necessary for biennials to initiate flowering. 14

vesicle A small space enclosed by a single membrane. Vesicles are similar to vacuoles, but smaller, generally being unresolvable by light microscopy. 3

vessel In xylem, a column of vessel elements interconnected by pairs of perforations. 5

vessel element (vessel member) A xylem conducting cell that has one or two perforations—a complete large hole in the primary wall that permits water to flow easily from one vessel member to another. 5, 23

vesselless (primitively, secondarily) A plant that lacks vessels is vesselless. If it is part of a clade that has never had vessels, it is primitively vesselless, but if one of its ancestors had vessels but has since lost them, it is secondarily vesselless. 23

violaxanthin A xanthophyll pigment in brown algae. 19

W

water potential The chemical potential of water; a measure of the ability of a substance to absorb or release water relative to another substance. Components: osmotic potential, pressure potential, matric potential. 12

webbing In the telome theory of the origin of megaphylls, the concept that the lamina originated by the production of parenchyma cells between the telomes. 21

whiplash flagellum A flagellum that has a smooth surface. Alternative: tinsel flagellum. 19

whole wheat flour Flour produced by grinding entire fruits of wheat; it contains bran (the dried fruit wall) along with the endosperm and germ (embryo); enzymes in the germ will cause whole wheat flour to become rancid if not kept perfectly dry. White flour lacks bran and germ. 24

whorl A set of leaves or flower parts, all attached to the stem or receptable at the same level. 5, 6

wood Secondary xylem. 8

wood fiber In textiles and the manufacture of paper, a wood fiber is one extracted from wood. Synonym: xylary fiber. If wood of eudicots is used, then the fibers are actually fibers in the botanical sense (single cells with narrow pits), but if conifer wood is used, then the “wood fibers” are actually tracheids. 24

woody plant A plant that undergoes secondary growth by means of a vascular cambium which produces secondary xylem (wood) and secondary phloem. Alternative: herbaceous plant. 2, 5, 8

X

xerophyte A plant adapted to desert conditions. 5, 6, 27

xylary fiber See wood fiber. 24

xylem The water- and mineral-conducting portion of vascular tissues, containing either tracheids or vessel elements or both; parenchyma, fibers, and sclereids are also frequent components of xylem. Alternative: phloem. 2, 5

Z

zeatin A natural cytokinin. 14

zero growth isocline On a graph of predator—prey relationships, the zero growth isocline is the line that indicates the sizes of predator and prey populations that are stable. If the predator population is sparser than that of the line, the prey population will increase; if predator populations are greater than the line, the prey population decreases. 26

zone of elongation Region of a root tip, just proximal to the root apical meristem, where cells undergo pronounced elongation. 7

zoospore A spore capable of swimming. 19

zygomorphic flower A bilaterally symmetrical flower. Alternative: regular flower (actinomorphic). 9, 23

zygote The diploid cell formed as the result of the fusion of two gametes. 4, 9, 19, 20

zygotene See prophase I. 4