Plant Biology and Botany Key Terms: Leaves, Fruits, Hormones, and Cell Structures (MIDTERM ONLY)

Abaxial

Facing away from the apex of a plant (often used to denote the lower surface of a leaf).

Abscisic acid

A plant hormone that promotes dormancy in seeds and buds.

Abscission zone

The area at the base of a leaf, flower, fruit, or branch containing tissues that play a role in the controlled separation of a plant part from the plant body.

Achene

A dry, indehiscent fruit formed from a single carpel and containing a single ovule (and seed) that is not fused to the fruit wall.

Actin filament

A helical protein filament, 5 to 7 nanometers thick, composed of globular actin molecules; a major constituent of the cytoskeleton of all eukaryotic cells; also called microfilament.

Actinomorphy, adj. Actinomorphic

[Gk. aktis, ray, of light, + morphé, form]; Pertaining to a type of flower that can be divided into two equal halves in more than one longitudinal plane, also called radially-symmetrical or regular; see also zygomorphic.

Adaxial

Facing toward the apex of a plant (often used to denote the upper surface of a leaf).

Adventitious

A structure that arises from an unusual place (such as roots or buds that arise from tissue other than the apical meristem).

Aerobic respiration

The release of energy from sugars or other substrates by consuming O2 commonly undertaken by mitochondria in eukaryotic organisms.

Aggregate fruit

A collection of small simple fruits derived from a single flower with several free (unfused) pistils.

Alternation of generations

Related to the sporic meiosis life cycle in eukaryotes where diploid and haploid generations alternate; in plants, these are designated as sporophyte (diploid) and gametophyte (haploid) individuals.

Angiosperm

[Gk. angion, a vessel, + sperma, a seed]: Literally, a seed enclosed in a vessel (carpel), thus one of a group of plants whose seeds are borne within a mature ovary (fruit); evolutionary lineage designated as flowering plants

Annual

A plant whose complete life cycle occurs within a single growing season.

Anther

The location of microsporangia within a flower, forms part of the stamen; bears pollen sacs.

Anticlinal

Plant cell walls that run perpendicular to the surface of the plant; in development, a type of cell division where the new cell wall is formed perpendicular to the surface of a plant.

Apical dominance

A process in plants where the shoot apical meristem controls lateral growth and complexity of the canopy by limiting or suppressing axillary meristem growth via auxin; the extent of apical dominance can have strong effects on the overall shape of the plant or canopy.

Apical meristem

The meristem at the tip of the root or shoot in a vascular plant, engaged in growth in length.

Archaea

A phylogenetic domain of prokaryotes consisting of the methanogens, most extreme halophiles and hyperthermophiles, and Thermoplasma.

Artificial classification

A system that arranges organisms by convenience using a few characters and providing limited information. This type of classification does not have to include or reflect evolutionary history.

Auxin

A major plant hormone that acts as a plant-growth regulator and is generated through meristem activity; effects of auxin are concentration- and tissue-dependent.

Axillary meristem (axillary bud)

A small shoot apical meristem situated in the axil of the leaf, formed during primary growth; an axillary meristem may begin growth as a branch to increase the complexity of the plant canopy or remain dormant as a bud.

Bacteria

The phylogenetic domain consisting of all prokaryotes that are not members of the domain Archaea.

Berry

A many-seeded (usually) fleshy fruit. All parts of the pericarp are fleshy at maturity.

Biodiversity

A term blending of two words biological and diversity to reflect "the variability among living organisms from all sources, including, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part: this includes diversity within species, between species and of ecosystems" according to the UN Convention on Biological Diversity.

Biennial

A plant that normally requires two growing seasons to complete its life cycle. Flowering and fruiting occur in its second year.

Binomial nomenclature

The process of giving a species two names. In scientific nomenclature, this is represented as a genus and species or specific epithet.

Biomass

The total living matter of a given system.

Bract

Leaf-like structures that occur on a flowering stem below a flower or inflorescence; may become modified to provide protection for the flower or fruit, or brightly coloured mimicking petals.

Bryophtya

A lineage of simple green plants, such as liverworts, hornworts, and mosses, that lack vascular tissue. The gametophyte phase is dominant in this group.

Bundle sheath

Layer or layers of cells surrounding a vein (vascular bundle); may consist of parenchyma or sclerenchyma cells, or both.

Calyx

[Gk. kalyx, a husk, cup]; The sepals collectively; the outermost flower whorl.

Cambium

[L. cambiare, to exchange]: A meristem that gives rise to parallel rows of cells; commonly applied to the lateral meristems (vascular cambium and the cork cambium).

Capsule

A many-seeded dry, dehiscent fruit from an ovary consisting of more than one carpel.

Carpel

The fundamental unit of the ovary bearing the ovules (and megasporangia); an ovary may consist of one or more carpels.

Caryopsis

A specialized achene where the pericarp layers are fused with the seed coat, typical of plants from the grass family (Poaceae).

Casparian strip

[after Robert Caspary, German botanist]: A band-like region of primary wall containing suberin and lignin; found in anticlinal-radial and transverse-walls of endodermal and exodermal cells.

Cell wall

The rigid outermost layer of the cells found in plants, some protists, and most prokaryotes. A primary cell wall (with cellulose) is created in all plant cells. A secondary cell wall (with lignin) may be formed on the inside of the primary wall to add structural support.

Cellulose

The chief component of cell walls in plants and some protists; an insoluble complex carbohydrate formed of microfibrils of glucose molecules attached end to end.

Chalaza

[Gk. chalaza, small tubercle]: The region of an ovule or seed where the funiculus unites with the integuments and nucellus. This may often be the larger end of the send.

Chilling requirement

The minimum period of cold weather needed to break bud or seed (embryo) dormancy. It is often expressed in chill hours, which can be calculated in different ways, all of which essentially involve adding up the total amount of time in a winter spent at certain temperatures.

Chlorophyll

A fundamental pigment in chloroplasts that absorbs red and blue wavelengths of light, and reflects green wavelengths. There are two types: chlorophyll a and chlorophyll b.

Chloroplast

A plastid organelle in which chlorophyll and other pigments are located, contains thylakoids and is the site of photosynthesis. Chloroplasts occur in plants and algae.

Cladoptosis

Some tree species abscise shoots rather than individual leaves forming an abscission zone and shedding the entire branch.

Class

A taxonomic category between phylum and order in rank. A class contains one or more orders, and belongs to a particular phylum.

Cline

A continuous or graded series of changes in some characteristics within a species, often correlated with a gradual change in climate or another geographical factor.

Coleoptile

[Gk. koleos, sheath, + ptilon, feather]: The sheath enclosing and protecting the apical meristem and leaf primordia of the grass embryo; often interpreted as the first leaf.

Coleorhiza

[Gk. koleos, sheath, + rhiza, root]: The sheath enclosing and protecting the radicle in the grass embryo.

Complete flower

A flower that fully develops all four floral whorls, even if whorls are somewhat reduced.

Compound

A structure made of up or divided into similar repeating parts or units; often referring to a leaf or inflorescence.

Cone scale

The structure in seed cones, derived from a modified leaf, that bears an ovule (or ovules) on its surface. Cone scales are typically flattened, dry and woody, as the scales of pine (Pinus) cones. However, they may be soft and fleshy, as in junipers (Juniperus), or leathery as in eastern arborvitae (Thuja occidentalis).

Coniferous tree

A gymnosperm cone-bearing tree; many species occur in the Pinaceae.

Cork cambium

The lateral meristem that forms the periderm, producing cork (phellem) toward the surface (outside) of the plant and phelloderm toward the inside; common in stems and roots of gymnosperms and woody angiosperms. Also called phellogen.

Corolla

[L. corona, crown]; The petals collectively; usually a conspicuously coloured flower whorl.

Corrosion cavity

A central space within the female gametophyte of gymnosperm seeds. During development, the primary suspensor cells elongate to push the embryo deep into the food-laden female gametophyte. As this happens, the corrosion cavity forms around the embryo.

Cortex

Ground-tissue region of a stem or root bounded externally by the epidermis and internally by the vascular system; a primary-tissue region; also used to refer to the peripheral region of a cell protoplast.

Cotyledon

[Gk. kotyledon, cup-shaped hollow]: The embryonic or seed leaf; generally absorbs food in monocotyledons and stores food in other angiosperms. Eudicots and many basal angiosperms will have two cotyledons, monocots will have one cotyledon, and gymnosperms can have variable numbers of cotyledons.

Critical photoperiod

The length of day or light period in a 24-hour cycle required to induce/inhibit flowering or budset. For example, when the day length is longer than the critical daylength, long-day plants are induced to flower and short-day plants never flower.

Cultigen

A plant species or variety known only in cultivation, especially one with no known wild ancestor.

Cultivar

A variety of plant found only under cultivation. Cultivars are registered with the International Code of Nomenclature for Cultivated Plants (ICNCP).

Cultural ecosystem service

Non-material benefits that people obtain and value as part of being human, including inspiration, cultural identity, spiritual experience, sense of home/place, tourism and recreation.

Cuticle

A waxy, water impermeable layer on the outer wall of epidermal cells, formed of cutin and wax. Occurs primarily on tissues (such as aerial tissues) that can desiccate.

Cyanobacteria

Organisms in Kingdom Bacteria that first evolved the photosynthetic pathway involving chlorophyll for light capture and Rubisco for CO2 fixation.

Cypsela

A dry, indehiscent fruit formed from an inferior ovary with two fused carpels and only containing one seed, typical of the sunflower family (Asteraceae).

Cytoplasm

The fluid or gel-like living matter of a cell, exclusive of the nucleus.

Cytoskeleton

The flexible network within cells, composed of microtubules and actin filaments, or microfilaments.

Deciduous

[L. decidere, to fall off]: Shedding of leaves at the onset of a season unfavourable for growth (such as extended cold or drought).

Dehiscent fruit

A dry type of fruit opening spontaneously at maturity to release seeds.

Dichotomous

Forked branching via a subdivision of the apex to form two branches of the same size. A primitive form of branching.

Dictyosome

See Golgi body.

Dioecy, adj. Dioecious

An organism that split sexes between individuals; evolved to promote outcrossing during sexual reproduction; see also monoecious.

Diploid

Having two sets of chromosomes (two copies of each type of chromosome); the 2n (diploid) chromosome number is characteristic of the sporophyte generation.

Division

See Phylum.

Domain

The taxonomic category above the kingdom level; the three domains are Archaea, Bacteria, and Eukarya.

Dormancy

A state in a seed or bud where tissues are alive but do not actively grow or develop (i.e. "arrested growth"); typically a very low metabolic rate is maintained.

Drupe

A fleshy fruit at maturity containing a hardened endocarp surrounding a single seed; endocarp and seed form the stone (or pyrene).

Ecosystem

A major interacting system that involves both living organisms and their physical environment.

Ecotype

[Gk. oikos, house, + L. typus, image]: A locally adapted variant of an organism, differing genetically from other ecotypes.

Embryophyta

The supergroup of plants consisting of bryophytes (non-vascular) and tracheophytes (vascular plants), both of which produce embryos; a synonym for plants.

Endemic

Native or restricted to a certain country or area.

Endocarp

The innermost layer of the pericarp or fruit wall.

Endodermis

[Gk. endon, within, + derma, skin]: A single layer of cells forming a sheath around the vascular cylinder in roots, some stems and conifer needles; the endodermal cells are characterized by a waxy Casparian strip within the radial and transverse cell walls. In roots and stems of seed plants, the endodermis is the innermost layer of the cortex.

Endoplasmic reticulum

A complex, three-dimensional membrane system of indefinite extent present in eukaryotic cells, dividing the cytoplasm into compartments and channels. Those portions that are densely coated with ribosomes are called rough endoplasmic reticulum, and other portions with fewer or no ribosomes are called smooth endoplasmic reticulum.

Endosperm

The triploid (3n) nutritive tissue within the seeds of flowering plants, developed from the double fertilization process where the second sperm from a pollen grain fertilizes a double-nucleate cell within the megagametophyte.

Enzyme

A protein that is capable of speeding up specific chemical reactions by lowering the required activation energy, but is unrelated itself in the process; a biological catalyst.

Epicotyl

The upper portion of the axis of an embryo or seedling, above the cotyledons (seed leaves) and below the next leaf or leaves.

Epidermis

A primary tissue and the outermost layer of cells of the leaf and of young stems and roots.

Epigeous germination

[Gk. epi, upon, + ge, the Earth]: Type of seed germination in which the cotyledons are carried above ground level (i.e. cotyledons are exposed above the soil)

Epigynous

A term referring to point of attachment of the stamens, corolla and calyx above an ovary within a flower; also called an inferior ovary.

Ethylene

A plant hormone involved in germination by stimulating gibberellin production and hypocotyl growth in seeds, as well as maturing of plant organs like flowers and ripening of fruit.

Eudicotyledons

One of the major classes of angiosperms; formerly grouped with the magnoliids, a diverse group of archaic flowering plants, as dicots; members of the Eudicotyledons are known as eudicot.

Eukarya

The phylogenetic domain containing all eukaryotic organisms.

Evapotranspiration

A term blending of two words evaporation and transpiration reflecting the combined process of water evaporating from surfaces and loss of water vapour directly from plant tissues.

Evergreen

Plants that maintain leaves throughout each season (do not undergo an annual/seasonal shedding of leaves).

Evolutionary theory

A scientific theory that explains the observations of variation among living organisms and provides a mechanism for change in organisms over time (via natural selection, mutation, genetic drift, and gene flow).

Exocarp

The outermost layer of the pericarp or fruit wall.

Family

A taxonomic group between order and genus in rank; the ending of family names in animals and heterotrophic protists is -idae; in all other organisms it is -aceae. A family contains one or more genera, and each family belongs to an order.

Fertile hybrid

A species is defined as 'organisms that produce fertile offspring' but this is sometimes limited as some organisms do not always reproduce sexually, and some hybrids are fertile. Sometimes classification can be complicated by: variation within a species.

Fertilization

Fusion of haploid egg and sperm gametes to produce a new diploid individual in eukaryotic sexual reproduction.

Fiber

An elongated, tapering generally thick-walled sclerenchyma cell of vascular plants functioning in support; its walls may or may not be lignified; it may or may not have a living protoplast at maturity.

Filament

The stalk supporting an anther, part of the stamen.