Flowering Plant Biology and Physiology

A complete set of vocabulary flashcards covering plant anatomy, tissue systems, water and sugar transport, mineral nutrition, sensory systems, hormone signaling, defense mechanisms, and flowering plant reproduction.

Calyx

The outermost floral whorl consisting of sepals that protect the flower before it opens.

Corolla

The floral whorl located to the inside of sepals, composed of petals that attract pollinators.

Perianth

The collective term for the non-reproductive envelope of a flower, comprising the calyx and corolla.

Stamen

The male reproductive organ of a flower, consisting of an anther and a filament.

Anther

The pollen-producing structure at the tip of a stamen.

Filament

The stalk portion of a stamen that elevates the anther.

Carpel

The defining female reproductive organ of angiosperms, consisting of a stigma, style, and ovary containing one or more ovules.

Stigma

The receptive surface at the apex of a carpel that receives pollen.

Style

The elongated stalk of a carpel that elevates the stigma above the ovary.

Ovary

The enlarged basal portion of a carpel containing ovules, which typically develops into a fruit.

Perfect Flower

A bisexual flower that possesses both stamens and carpels.

Imperfect Flower

A unisexual flower that possesses either stamens or carpels, but not both.

Monoecious

A plant species that has separate staminate and carpellate flowers on the same individual plant ("one house"), such as corn.

Dioecious

A plant species that has staminate and carpellate flowers on different individual plants ("two houses"), such as Cannabis.

Pollen Grain

The microgametophyte (male gametophyte) of flowering plants, enclosed in a protective wall containing sporopollenin.

Sporopollenin

A highly resistant chemical polymer that forms the outer cell wall of pollen grains.

Double Fertilization

A process in angiosperms where one sperm fuses with the egg to form a diploid ($2n$) zygote, while a second sperm fuses with two polar nuclei to form triploid ($3n$) endosperm.

Endosperm

A triploid ($3n$) nutritive tissue formed inside angiosperm seeds that nourishes the developing embryo.

Micropyle

The small pore in an ovule through which the pollen tube enters to deliver sperm cells.

Aggregate Fruit

A fruit that develops from a single flower containing many separate carpels, such as a blackberry.

Multiple Fruit

A fruit that develops from an inflorescence of many individual flowers with many carpels, such as a pineapple.

Simple Fruit

A fruit that develops from a single flower with a single carpel or several fused carpels, such as a cherry.

Phototropin

A blue-light photoreceptor in guard cells that activates proton pumps to stimulate stomatal opening.

Phytochrome

A photoreceptor protein that absorbs red ($\sim 660\,\text{nm}$) and far-red ($\sim 735\,\text{nm}$) light, acting as a molecular switch via reversible conformational changes.

$$P_{fr}$$

The active far-red-absorbing conformation of phytochrome that triggers biological responses such as seed germination and photomorphogenesis.

Photoperiodism

Any physiological response of an organism that is controlled by the relative lengths of light and dark periods (photoperiod).

Long-Day Plant

A plant that flowers in midsummer when nights are shorter than a specific critical length.

Short-Day Plant

A plant that flowers in spring or autumn when nights are longer than a specific critical length.

Florigen (FT)

The Flowering Locus T protein synthesized in leaves that travels to the shoot apical meristem to trigger the transition to flowering.

Etiolation

A growth response in seedlings grown in darkness, characterized by excessive stem elongation, pale color, and lack of chloroplast development.

Photomorphogenesis

The transition of a seedling to normal structural development (shortened stem and photosynthetic greening) induced by red light converting phytochrome to $P_{fr}$.

Statolith Hypothesis

The model explaining root gravitropism, wherein dense starch-filled amyloplasts (statoliths) settle to the bottom of root cap cells due to gravity, activating pressure receptors.

Thigmomorphogenesis

A change in plant growth and body form induced by mechanical stress, such as wind or repeated touch.

Thigmotropism

A directional growth or bending response of a plant structure in contact with a solid object, commonly observed in vine tendrils.

Thigmonasty

A rapid, non-directional plant movement in response to touch driven by action potentials and turgor pressure changes rather than growth.

Auxin (IAA)

A major plant hormone produced in shoot tips that enforces apical dominance, stimulates adventitious root formation, and inhibits leaf abscission.

Ethylene ($\text{CH}_2=\text{CH}_2$)

A gaseous plant hormone that promotes fruit ripening, leaf abscission, and stem elongation.

Abscisic Acid (ABA)

A plant hormone that maintains seed dormancy and induces stomatal closure in response to water stress.

Hypersensitive Response (HR)

A rapid local plant defense mechanism triggered by pathogen recognition, leading to localized cell death, cell wall fortification, and toxin production.

Systemic Acquired Resistance (SAR)

A slow-acting, plant-wide systemic defense response mediated by methyl salicylate (MeSA) that protects uninfected tissues from subsequent pathogen attack.

Systemin

A peptide hormone released from damaged plant cells during herbivore attack that moves systemically to induce jasmonic acid synthesis.

Jasmonic Acid (JA)

A plant defense hormone synthesized in response to systemin that triggers the transcription of proteinase inhibitor genes.

Proteinase Inhibitors

Defensive proteins produced by plants that inhibit digestive enzymes in herbivores, causing illness and deterring feeding.

Macronutrients

Essential chemical elements required by plants in large amounts, such as Nitrogen (N), Phosphorus (P), and Potassium (K).

Micronutrients

Essential chemical elements required by plants in small quantities, typically serving as enzyme cofactors.

Limiting Nutrient

An essential element whose scarce supply limits plant growth and productivity.

Mobile Nutrients

Nutrients (such as N, P, K, and Mg) that a plant can retranslocate from older tissues to younger growing regions, causing deficiency symptoms to appear first in older leaves.

Immobile Nutrients

Nutrients (such as Fe and Ca) that remain bound in older plant tissues and cannot be retranslocated, causing deficiency symptoms to appear first in younger leaves.

Leghemoglobin

An iron-rich, oxygen-binding protein present in legume root nodules that buffers free oxygen levels to protect the oxygen-sensitive enzyme nitrogenase.

Rhizobia

Species of nitrogen-fixing bacteria that form a symbiotic, nodule-forming relationship with the roots of legume plants.

Haustoria

Specialized nutrient-absorbing structures produced by parasitic plants that penetrate the host plant's vascular tissue.

Epiphyte

A non-parasitic plant that grows anchored on another plant and absorbs water and mineral nutrients from rain, air, and organic debris.

Carnivorous Plant

A photosynthetic plant adapted to nutrient-poor environments (such as bogs) that traps and digests insects to obtain nitrogen.

Water Potential ($\Psi_w$)

The potential energy of water in a specific environment relative to pure water at standard conditions, measured in megapascals (MPa).

Solute Potential ($\Psi_s$)

The component of water potential that reflects the osmotic tendency of water to move in response to solute concentration; pure water has $\Psi_s = 0\,\text{MPa}$.

Pressure Potential ($\Psi_p$)

The component of water potential resulting from physical hydrostatic pressure or tension exerted on water inside cells.

Turgor Pressure

The outward hydrostatic pressure exerted by the fluid protoplast against the cell wall of a plant cell.

Symplast

The continuous network of interconnected plant cell cytoplasm linked by plasmodesmata.

Apoplast

The continuous system of cell walls, intercellular spaces, and dead xylem lumens outside plasma membranes.

Casparian Strip

A waxy ring of suberin embedded in the endodermal cell walls that blocks passive apoplastic transport into the vascular cylinder.

Transpiration

The evaporation of water from mesophyll cell walls followed by diffusion out through open stomata.

Cohesion-Tension Theory

The accepted model for xylem transport, stating that water is pulled upward through continuous xylem columns by transpirational pull, cohesive hydrogen bonding between water molecules, and adhesion to cell walls.

Translocation

The long-distance movement of sugars, amino acids, and other organic solutes through phloem from source regions to sink regions.

Pressure-Flow Model

The mechanism of phloem transport explaining bulk sap flow driven by a turgor pressure gradient generated between active phloem loading at sources and unloading at sinks.

Phloem Loading

The process by which sugars produced in source cells are transported into companion cells and sieve-tube elements.

Shoot System

The above-ground structural system of a plant consisting of stems, leaves, and reproductive structures.

Root System

The below-ground structural system of a plant responsible for anchorage, water absorption, nutrient uptake, and storage.

Phenotypic Plasticity

The capacity of an individual organism's morphology or structure to alter in response to changing environmental conditions.

Taproot System

A root system composed of a prominent main vertical root (taproot) with smaller lateral roots branching off.

Fibrous Root System

A root system consisting of a dense network of numerous similarly sized roots originating near the stem base, typical of monocots.

Root Cap

A thimble-shaped layer of cells protecting the root apical meristem that lubricates soil passage and perceives gravity.

Rhizome

A horizontal underground stem that serves as a storage organ and enables asexual reproduction.

Stolon

A horizontal above-ground stem (runner) that produces cloned plantlets at nodes.

Tuber

An enlarged underground stem modified for carbohydrate storage, such as a potato.

Petiole

The stalk that connects a leaf blade to the plant stem.

Blade

The broad, flattened portion of a leaf specialized for light absorption and photosynthesis.

Primary Cell Wall

The outer cell wall layer formed by growing plant cells, rich in cellulose and pectin, which provides flexible support.

Secondary Cell Wall

A thick, rigid cell wall layer reinforced with lignin deposited inside the primary wall of certain mature specialized plant cells.

Plasmodesma

A microscopic, membrane-lined cytoplasmic channel passing through cell walls to connect adjacent plant cells.

Amyloplast

A non-pigmented plastid specialized for starch synthesis and storage, which also functions as a statolith in gravity perception.

Chromoplast

A plastid containing carotenoid pigments that impart yellow, orange, or red colors to ripe fruits and flower petals.

Tonoplast

The selective membrane enclosing the central vacuole in a plant cell.

Cuticle

A waxy hydrophobic coating secreted by epidermal cells on aerial plant organs to minimize water loss and block pathogens.

Trichomes

Hair-like outgrowths of epidermal cells that reduce transpiration, reflect light, or secrete chemical defenses.

Parenchyma

A versatile simple ground tissue composed of thin-walled primary cells active in photosynthesis, carbohydrate storage, and tissue repair.

Collenchyma

A simple ground tissue composed of living cells with unevenly thickened primary cell walls that provide flexible structural support to growing shoots.

Sclerenchyma

A simple ground tissue composed of dead cells with thick, lignified secondary cell walls (sclereids and fibers) that provide rigid support.

Xylem

A complex vascular tissue composed of tracheids, vessel elements, fibers, and parenchyma that conducts water and dissolved mineral ions upward from roots.

Tracheids

Long, slender xylem conducting cells with tapered ends, lignified secondary cell walls, and pits for water movement.

Vessel Elements

Short, wide xylem conducting cells stacked end-to-end with open perforation plates that allow rapid water passage in angiosperms.

Phloem

A complex vascular tissue comprising sieve-tube elements and companion cells that transports sugars, amino acids, and signal molecules throughout the plant.

Sieve-Tube Element

An elongated phloem conducting cell in flowering plants that lacks a nucleus at maturity and is connected end-to-end by perforated sieve plates.

Companion Cell

A specialized parenchyma cell joined to a sieve-tube element by plasmodesmata that provides metabolic support and regulates phloem loading.

Apical Meristem

A cluster of undifferentiated stem cells located at shoot tips (SAM) and root tips (RAM) that drives primary growth and organ formation.

Vascular Cambium

A cylinder of lateral meristematic tissue that produces secondary xylem (wood) toward the interior and secondary phloem toward the exterior.

Cork Cambium

A lateral meristem that produces cork cells toward the outside and phelloderm toward the inside, forming the protective periderm.