Chapter 31: Plant Structure, Growth and Reproduction

Comprehensive vocabulary flashcards covering plant morphology, tissue systems, primary and secondary growth, cellular specialization, root symbioses, and angiosperm reproduction from Chapter 31.

Monocot

An angiosperm lineage characterized by one cotyledon, parallel leaf veins, scattered vascular bundles lacking vascular cambium, fibrous roots, and floral organs arranged in multiples of three.

Eudicot

A flowering plant clade comprising approximately $75\%$ of all angiosperms, defined by tricolpate pollen grains, two cotyledons, branched leaf venation, ringed vascular bundles, and floral organs in multiples of four or five.

Pith

The internal ground tissue located centrally relative to the vascular bundles in a plant stem or root.

Cortex

The ground tissue located external to the vascular cylinder, occupying the region between vascular tissues and the epidermis.

Endodermis

The innermost cellular layer of the root cortex that acts as a sensory filter between soil and the stele, forcing water and solutes through the symplast, preventing vascular backflow, storing starch, and blocking pathogens.

Middle lamella

A pectin-rich layer situated between adjacent plant cells that cements their primary cell walls together.

Plasmodesmata

Microscopic open channels traversing adjoining plant cell walls that facilitate cytoplasmic exchange and direct intercellular transport of materials.

Parenchyma

The most predominant and metabolically active plant cell type, characterized by thin, flexible primary cell walls; capable of photosynthesis, biosynthesis, starch storage, and regenerating entire plants through totipotent differentiation.

Collenchyma

Elongated plant cells possessing unevenly thickened, pectin- and water-rich primary cell walls that provide flexible structural support to actively growing plant organs.

Sclerenchyma

Plant supporting cells featuring rigid, thick secondary cell walls reinforced with lignin; they are non-elongating, metabolically inactive, and dead at functional maturity.

Tracheids

Elongated, slender, water-conducting xylem cells with tapered ends and lignified secondary walls that align and convey fluids through pits.

Vessel elements

Short, wide, less tapered water-conducting cells in xylem tissue that align end-to-end with open perforations in their end walls to form continuous transport tubes.

Sieve-tube elements

Living food-conducting phloem cells arranged into continuous columns that lack most cytoplasmic organelles at maturity and permit fluid transport via perforated end walls called sieve plates.

Companion cells

Nucleated cells linked to sieve-tube elements by numerous plasmodesmata that synthesize and transport vital proteins and metabolic support to adjacent sieve-tube members.

Lignin

The second most abundant natural polymer on Earth; a non-carbohydrate polymer that thickens and reinforces secondary cell walls in vascular plants, giving structural rigidity necessary for vertical growth.

Root hairs

Tubular, microscopic extensions of root epidermal cells that massively expand the total root surface area for water and mineral nutrient absorption.

SYM genes

Signaling genes that mediate symbiotic molecular recognition between plant hosts and mutualists (rhizobia and mycorrhizal fungi) and coordinate root nodule organogenesis in legumes.

Infection thread

An inward tubular invagination of the plant root hair cell wall and plasma membrane through which rhizobia bacteria navigate from an infection pocket into the root cortical tissue.

Endomycorrhizal (AMF) Fungi

Fungal mutualists colonizing approximately $80\%$ of vascular plants that penetrate root epidermal cells via a hyphopodium to form branching, tree-like intracellular nutrient exchange organs called arbuscules.

Ectomycorrhizal (ECM) Fungi

Fungal mutualists associated primarily with woody trees and shrubs that form an outer fungal sheath (mantle) over root tips and an intercellular network between epidermal and cortical cells called the Hartig net without penetrating cell interiors.

Cuticle

A waxy extracellular layer covering epidermal surfaces of leaves and stems that functions as a hydrophobic barrier preventing excessive water loss and gas movement.

Stomata

Microscopic pores distributed predominantly across the lower leaf epidermis that regulate photosynthetic gas exchange and water transpiration through guard cell activity.

Guard cells

Specialized paired epidermal cells flanking each stoma that undergo reversible changes in turgor pressure to open or close the pore.

Indeterminate growth

A growth pattern characteristic of plants wherein active meristems enable continuous growth and development throughout the organism's lifespan under favorable environmental conditions.

Apical meristem

Undifferentiated mitotic tissue situated at the tips of roots and shoots responsible for primary growth, facilitating plant elongation.

Root cap

A thimble-shaped mass of protective cells covering the root apical meristem that shields dividing tissue from abrasive soil damage during growth.

Zone of elongation

The region of primary growth in a root or shoot where newly produced cells absorb water and expand lengthwise, physically pushing the tip forward.

Zone of differentiation

The developmental root region where cells complete maturation and undergo specialized gene expression to form distinct dermal, ground, and vascular tissues.

Vascular cambium

A cylindrical lateral meristem one cell layer thick situated between primary xylem and primary phloem that generates secondary xylem (wood) inwardly and secondary phloem outwardly.

Cork cambium

A lateral meristem developing from cortical parenchyma cells that produces dense, suberin-impregnated, dead cork cells outwardly to replace the shed epidermis.

Annual growth rings

Concentric boundaries in secondary xylem cross-sections formed by the contrast between large, thin-walled early spring vessels and smaller, thicker-walled late summer xylem cells.

Heartwood

The centrally located, darker-colored older secondary xylem of a tree trunk that has ceased water transport due to resin deposition and provides mechanical rigidity and decay resistance.

Sapwood

The peripheral, younger, lighter-colored band of secondary xylem surrounding heartwood that actively conducts water and mineral nutrients.

Wood rays

Radial bands of parenchyma cells extending through secondary xylem that store nutrients, assist in wound repair, and facilitate lateral transport of fluids across a stem.

Sporophyte

The diploid ($2n$) spore-producing multicellular generation in the plant alternation of generations life cycle; constitutes the dominant, conspicuous phase in all vascular plants.

Gametophyte

The haploid ($n$) gamete-producing multicellular phase in the plant life cycle; forms the dominant phase in bryophytes but is reduced and microscopic within seed plants.

Stamen

The pollen-producing male reproductive organ of a flower consisting of a terminal anther supported by a slender filament.

Carpel (Pistil)

The female reproductive organ of a flower composed of a receptive stigma, an elongated style, and a basal ovary enclosing one or more ovules.

Pollen tube

A slender cellular extension produced by a germinating pollen grain that digests through the style to deliver two sperm cells directly into the ovule.

Double fertilization

A reproductive mechanism unique to angiosperms in which two sperm nuclei from a single pollen tube enter the embryo sac: one fertilizes the egg to yield a diploid ($2n$) zygote, while the other fuses with the two polar nuclei to produce triploid ($3n$) endosperm.

Endosperm

Nutritive triploid ($3n$) seed tissue generated during double fertilization that nourishes the developing angiosperm embryo until germination and photosynthetic competence.

Fruit

A specialized reproductive structure formed from a ripened, mature flower ovary that encases seeds to protect them and promote their dispersal.