BIO 102 - Botany Midterm Reviewer: Roots, Stems, and Leaves

Flashcards testing concepts in root, stem, and leaf morphology, anatomy, development, and specialized functions based on BIO 102 lecture material.

What is the origin, structure, and typical depth of a taproot system?

A taproot system originates from the enlarged radicle (embryonic root), consists of one main root with smaller lateral roots, and grows deep vertically in the soil.

Why are fibrous roots also classified as adventitious roots?

Fibrous roots are called adventitious because they arise directly from stem tissue at the base of the plant rather than from a pre-existing root or embryonic radicle.

Which plant groups typically possess taproot systems, and which possess fibrous root systems?

Taproot systems are mostly found in dicots and gymnosperms, whereas fibrous root systems are mostly found in monocots.

Why are storage taproots usually classified as biennials?

Storage taproots store food reserves during their first year of growth (Year 1) and utilize that stored food to reproduce during their second year (Year 2).

What is the key function of the root cap and what substance does it secret?

The root cap protects the root apical meristem, aids downward orientation, and secretes slime or mucigel to lubricate the root's passage through soil.

What is the role of the quiescent center in the root tip?

It is a small, slowly dividing zone inside the meristem that serves as a reserve of healthy cells to reactivate and repair the root tip if it becomes damaged.

In which root region do root hairs form, and why are they absent from the elongation zone?

Root hairs form exclusively in the maturation/differentiation zone; they do not form in the elongation zone because they would be sheared off as cells push through the soil.

What are the structural features and average lifespan of root hairs?

Root hairs are short-lived, unicellular extensions of epidermal cells that die within $4\text{--}5\text{ days}$.

What is the Casparian strip, where is it located, and how does it affect water transport?

The Casparian strip is a suberin band located on the radial and transverse walls of endodermal cells that blocks the apoplastic pathway, forcing water and dissolved minerals to pass selectively through the plasma membrane.

What are passage cells in the root endodermis?

Passage cells are unsuberized endodermal cells located directly opposite the protoxylem that allow selective movement of water and solutes.

Which primary root structures originate from the pericycle?

The pericycle gives rise to lateral roots and contributes to the vascular cambium during secondary growth.

How do the symplast and apoplast pathways differ in transporting water to the stele?

The symplast pathway moves water cell-to-cell through continuous living cytoplasm via plasmodesmata; the apoplast pathway moves water through interconnected cell walls until blocked by the Casparian strip.

How do monocot and dicot (eudicot) roots differ in protoxylem arrangement, pith presence, and stele type?

Monocot roots have many protoxylem groups (>10, polyarch), a central parenchymatous pith, and a siphonostele; dicot roots have few protoxylem groups (2–5), no pith (metaxylem at center), and a protostele.

What do the terms monarch, diarch, triarch, and polyarch describe?

They describe the number of protoxylem groups present in a root (1, 2, 3, or many, respectively).

How do fusiform, napiform, and conical storage roots differ in shape?

Fusiform roots are spindle-shaped (swollen middle, tapering both ends, e.g., radish); napiform roots are top-shaped (spherical base sharply tapering to apex, e.g., turnip, beet); conical roots have a broad base tapering gradually to apex.

What are pneumatophores and what function do they serve?

Pneumatophores are spongy roots that grow upward above water or soil to facilitate gas exchange (e.g., in black mangrove/Avicennia).

How do prop roots differ from stilt roots?

Prop roots are aerial roots arising from high stem branches that grow vertically downward into the soil (e.g., banyan tree); stilt roots emerge obliquely from lower stem nodes (e.g., Pandanus).

What are haustoria in parasitic plants?

Haustoria are peg-like projections produced by parasitic plants that penetrate host vascular tissue (xylem and phloem) to extract water, minerals, and carbohydrates.

What is the difference between hemiparasitic and holoparasitic plants?

Hemiparasites (e.g., mistletoe) possess chlorophyll and can photosynthesize, taking mainly water/minerals from host; holoparasites (e.g., dodder, Rafflesia) lack chlorophyll and depend entirely on the host for nutrition.

What is the structural difference between ectomycorrhizae and endomycorrhizae?

Ectomycorrhizae form a fungal mantle surrounding the root surface with hyphae remaining outside cells (e.g., in pine, oak); endomycorrhizae feature fungal hyphae that penetrate into root cortical cells.

How do beneficial root nodules differ from harmful root knots?

Root nodules are mutualistic structures housing nitrogen-fixing Rhizobium bacteria in legumes; root knots are damaging galls caused by parasitic nematodes (e.g., Meloidogyne spp.).

What information does the distance between bud scale scars on a twig provide?

The distance between consecutive bud scale scars marks one year's linear growth of the twig.

What are bundle scars and where are they located?

Bundle scars are small dark dots located inside a leaf scar that represent broken vascular strands that extended into the leaf petiole.

Which primary tissues develop from the protoderm, procambium, and ground meristem?

Protoderm develops into the epidermis; procambium produces primary xylem and primary phloem; ground meristem produces the cortex and central pith.

How do protoxylem and metaxylem differ in wall structure and timing of function?

Protoxylem forms early during elongation with extensible annular/helical secondary walls; metaxylem forms later after elongation stops with non-extensible pitted/reticulate walls for permanent conduction.

What tissues are produced inward and outward by the vascular cambium?

The vascular cambium produces secondary xylem (wood) toward the inside and secondary phloem (inner bark) toward the outside.

What three components form the periderm in woody plant stems?

The periderm consists of the cork cambium (phellogen), cork (phellem), and phelloderm.

What is the difference between intrafascicular and interfascicular cambium?

Intrafascicular cambium originates within a vascular bundle between primary xylem and phloem; interfascicular cambium develops from parenchyma cells located between adjacent vascular bundles.

How does vascular bundle arrangement differ between herbaceous eudicot stems and monocot stems?

Herbaceous eudicot stems feature vascular bundles arranged in a distinct ring around a central pith (eustele); monocot stems feature vascular bundles scattered throughout ground tissue (atactostele).

Why are monocot vascular bundles considered 'closed'?

Monocot vascular bundles are closed because they lack vascular cambium, which prevents them from undergoing secondary growth.

How do sapwood and heartwood differ in appearance and function?

Sapwood is younger, lighter-colored outer wood that actively conducts water and minerals; heartwood is older, darker central wood with plugged vessels that provides structural support only.

What is the anatomical definition of hardwood vs. softwood?

Hardwood refers to the wood of woody eudicots (containing both xylem fibers and vessel elements); softwood refers to the wood of gymnosperms/conifers (containing tracheids only, lacking vessels).

How do springwood (early wood) and summerwood (late wood) differ structurally?

Springwood develops when water is abundant and features large vessel elements with thin walls; summerwood develops later with smaller vessels and thicker cell walls that provide structural strength.

What is the structural difference between a bulb and a corm?

A bulb consists mostly of fleshy, food-storing leaf bases attached to a small stem (e.g., onion); a corm consists mostly of a solid, swollen stem tissue covered by thin papery scale leaves (e.g., gladiolus).

Why are potato 'eyes' proof that a potato tuber is a modified stem rather than a root?

Potato 'eyes' are axillary buds situated at nodes, which are defining structural characteristics of stems that are absent in true roots.

What anatomical distinction separates thorns, spines, and prickles?

Thorns are modified stems arising from axillary buds; spines are modified leaves; prickles are non-vascular outgrowths of epidermal or cortical tissue.

What are cladophylls (cladodes) and phylloclades?

Cladophylls are flattened, leaf-like photosynthetic stems with nodes bearing scale leaves (e.g., Asparagus); phylloclades are flattened or fleshy green stems that replace leaves reduced to spines (e.g., Opuntia).

What is a pulvinus and how does it generate leaf movement?

A pulvinus is a swollen, cushion-like motor organ at the base of a leaf or leaflet that induces movement via reversible turgor changes in flexor and extensor cells.

What single rule determines whether a leaf is simple or compound?

An axillary bud is present in the axil of the whole leaf petiole, but is NEVER present in the axil of an individual leaflet.

How do leaf venation patterns correlate with monocots and dicots?

Monocots predominantly exhibit parallel venation, whereas dicots (eudicots) exhibit netted (reticulate) venation.

How do serrate, dentate, and crenate leaf margins differ in tooth shape?

Serrate margins have sharp forward-pointing teeth; dentate margins have sharp outward-pointing teeth; crenate margins have rounded teeth.

What distinguishes a sagittate leaf base from a hastate leaf base?

Both are arrowhead-shaped, but sagittate basal lobes point downward or backward toward the petiole, whereas hastate basal lobes point outward or sideways.

What is a peltate leaf?

A peltate leaf is a shield-shaped leaf where the petiole attaches directly to the lower surface of the blade rather than at the blade margin (e.g., lotus).

How do upper and lower epidermal layers differ in a typical eudicot leaf?

The upper epidermis has a thicker cuticle and generally lacks stomata; the lower epidermis has a thinner cuticle and contains abundant stomata for gas exchange.

What are the structural and functional differences between palisade and spongy mesophyll?

Palisade mesophyll consists of densely packed columnar cells rich in chloroplasts optimized for light absorption; spongy mesophyll consists of loosely arranged cells with large air spaces optimized for gas diffusion.

What are bulliform cells and what is their role in monocot leaves?

Bulliform cells are large, thin-walled epidermal cells in monocot leaves that lose turgor during drought, causing the leaf blade to roll or fold to minimize transpiration.

What sequence of physiological events causes stomata to open under blue light?

Blue light activates proton pumps $\rightarrow$ Protons ($H^+$) are pumped out of guard cells $\rightarrow$ Potassium ($K^+$) and Chloride ($Cl^-$) ions enter guard cells down the gradient $\rightarrow$ Solute concentration increases $\rightarrow$ Water enters by osmosis $\rightarrow$ Guard cells become turgid and bow outward, opening the pore.

How does guttation differ from stomatal transpiration and dew?

Guttation is the exudation of liquid water droplets from hydathodes driven by positive root pressure at night; transpiration is water vapor loss through stomata; dew is ambient moisture condensing directly from the air onto surfaces.

What is the stomatal distribution on the upper vs. lower epidermis of an apple ($Malus\,sylvestris$) leaf?

Apple leaves have approximately $400\text{ stomata/mm}^2$ on the lower epidermis and $0$ stomata on the upper epidermis.

What precise stimulus triggers the active trap closure of a Venus flytrap ($Dionaea\,muscipula$)?

A trigger hair must be touched twice (or two separate trigger hairs touched once) within a time window of approximately $20\text{ seconds}$.