Plant Biology: Shoot & Stem Systems

Comprehensive flashcards covering shoot system functions, meristems, vascular anatomy, phyllotaxis, leaf structure, abscission, flower development genetic models, and modified shoot organs based on the reference study guide.

Shoot System

The above-ground plant structure that exhibits greater complexity than roots, featuring specialized organs and vascular architecture for support and conduction.

Shoot Apical Meristem (SAM)

A terminal meristem lacking a protective cap that initiates leaf primordia and bud primordia, protected by overarching young leaf primordia.

Tunica

The outer cell layer(s) of the shoot apical meristem undergoing anticlinal division to expand the outer tissue sheet.

Corpus

The internal cell mass beneath the tunica in the shoot apical meristem undergoing periclinal division to build tissue volume.

Anticlinal Division

Cell division occurring perpendicular to the tissue surface.

Periclinal Division

Cell division occurring parallel to the tissue surface.

Internode

The region of a stem between nodes where leaves attach, along which growth occurs during stem elongation.

Intercalary Meristem

A meristem situated at the base of internodes in many monocots that drives rapid stem elongation.

Woody Plant Stem Vasculature

Vascular arrangement characterized by a continuous vascular cylinder embedded within ground tissue.

Eudicot Herb Stem Vasculature

Vascular arrangement consisting of a ring of discrete vascular bundles surrounding a central pith and bounded externally by the cortex.

Monocot Stem Vasculature

Vascular arrangement consisting of vascular bundles complexly scattered throughout the ground tissue matrix.

Open Vascular Bundle

A vascular bundle retaining an active fascicular cambium, enabling secondary growth and lateral expansion.

Closed Vascular Bundle

A vascular bundle entirely enclosed by a sclerenchyma sheath and lacking cambium, making it incapable of secondary growth.

Leaf Trace

An extension of a stem vascular bundle that diverges out into a leaf petiole.

Leaf Trace Gap

A parenchymatous gap created in the stem's vascular cylinder immediately above the point where a leaf trace departs.

Phyllotaxis

The geometric arrangement of leaves along a stem axis.

Alternate & Spiral Phyllotaxis

Leaf arrangement featuring a single leaf per node, emerging in a spiral path around the stem.

Distichous Phyllotaxis

Leaf arrangement featuring a single leaf per node, aligned strictly in two opposite vertical rows.

Opposite Phyllotaxis

Leaf arrangement featuring two leaves attached at each node on opposite sides.

Decussate Phyllotaxis

Leaf arrangement featuring opposite leaf pairs rotated 90 degrees relative to adjacent upper and lower pairs.

Whorled Phyllotaxis

Leaf arrangement featuring three or more leaves attached simultaneously at a single node.

Auxin Maximum

A localized accumulation of auxin generated by PIN1 efflux transporters that signals leaf primordium initiation.

Auxin Sink

The physiological state of a growing leaf primordium that depletes nearby auxin to maintain precise spacing between adjacent primordia.

PIN1

Directional efflux transporters that mediate localized accumulation of auxin to direct leaf initiation.

Blade (Lamina)

The main photosynthetic flat portion of a leaf.

Petiole

The stalk connecting the leaf blade to the stem.

Stipules

Basal protective structures located at the base of a leaf petiole.

Simple Leaf

A leaf featuring an undivided blade.

Compound Leaf

A leaf possessing a blade divided into distinct leaflets.

Axillary Bud

A bud positioned exclusively at the leaf axil on the stem, used as a key diagnostic marker to distinguish leaves from leaflets.

Palisade Parenchyma

Columnar, densely packed cells on the adaxial side of leaf mesophyll that serve as the primary photosynthetic site.

Spongy Parenchyma

Loosely packed cells with extensive gas spaces located on the abaxial side of leaf mesophyll.

Reticulate Venation

Netted leaf vein pattern characteristic of eudicots.

Parallel Venation

Parallel leaf vein pattern characteristic of monocots.

Kranz Anatomy

Specialized leaf anatomy in C4 plants featuring chloroplast-rich bundle sheath cells surrounded by mesophyll cells.

Leaf Abscission

The highly regulated process of leaf shedding at the petiole base involving nutrient remobilization, enzyme digestion of middle lamellae, and suberin deposition.

Leaf Scar

A mark on a twig remaining after leaf abscission, sealed by protective suberin deposition.

Bundle Scars

Markings within a leaf scar representing severed vascular traces.

Terminal Bud Scale Scars

Rings on a dormant twig that indicate annual primary growth increments.

Calyx (Sepals)

The outermost floral whorl consisting of green protective organs.

Corolla (Petals)

The floral whorl consisting of petals that serve to attract pollinators.

Androecium (Stamens)

The male reproductive floral whorl composed of stamens, each consisting of an anther and a filament.

Gynoecium (Carpels)

The innermost female reproductive floral whorl composed of carpels enclosing ovules.

ABC Model of Floral Development

A genetic model where combinatorial expression of homeotic MADS-box genes determines organ identity: Class A alone forms sepals, Class A+B forms petals, Class B+C forms stamens, and Class C alone forms carpels.

Cladophyll

A flattened, leaf-like photosynthetic stem (e.g., Asparagus, cladodes).

Tendril

A coiling structural organ derived from a leaf or stem that provides climbing support.

Thorn

A sharpened, woody modified branch arising from axillary buds (stem origin).

Spine

A hard, pointed modified leaf or stipule (leaf origin, e.g., cactus spines).

Prickle

An outgrowth of outer tissue (epidermis/cortex) without vascular connections that detaches easily (e.g., rose "thorns").

Carnivorous Trap

A modified leaf lamina specialized for prey capture (e.g., Sarracenia, Sundew).

Tuber

A fleshy, enlarged underground storage stem bearing "eyes" (buds) (e.g., Potato).

Bulb

A structure consisting of fleshy storage leaves clustered on a compressed stem plate (e.g., Onion).

Rhizome

A horizontal underground stem with clear nodes, scales, and adventitious roots (e.g., Ginger).

Stolon (Runner)

A horizontal above-ground runner stem that roots at nodes (e.g., Strawberry).