Plant Structures: Roots and Adaptations

Key Plant Structures and Adaptations

• Roots are specialized structures in terrestrial plants that grow downwards due to positive geotropism and serve multiple functions.
• Taproots have one main root with smaller lateral roots, common in dicots and gymnosperms, while monocots often develop a new root from the stem's lower part.
• Adventitious roots emerge from the stem's lower part or above-ground structures, anchoring plants like corn with prop roots.
• Fibrous roots consist of many same-sized roots branching from the stem, as seen in onions, crabgrass, and various monocots.
• The root cap, or calyptra, is a protective yellow/brown structure at the root tip, safeguarding the meristematic zone.
• The epidermis is the root's outermost layer, made of single-layer cells, featuring root hairs from epidermal tissue.
• The cortex is composed of large, thin-walled parenchyma cells, storing starch and transporting water/minerals.
• The endodermis separates the cortex from vascular bundles, with gate cells facilitating material exchange.
• Vascular tissue, including the pericycle, forms lateral roots/cambium and contains xylem/phloem vessels in the plant's core.
• Stems connect roots and leaves, exhibiting vascular tissue in regular or irregular arrangements.
• Herbaceous stems are soft, non-woody stems in herbs, maintained by turgor pressure, and covered by a water loss-preventing cuticle.
• Lenticels are specialized areas on the cork cambium that facilitate gas exchange, similar to stomata in leaves.
• Phloem vessels are elongated structures from roots to leaves with cytoplasmic guard cells, sieve plate elements, and parenchyma cells.
• Sieve tubes have sieve plate tubes connecting closely packed sieve tube elements.
• Xylem vessels extend from roots to leaves, made of tracheids, schlerenchyma, and parenchyma cells, located in the core of the plant.
• Stolons are slender, horizontal stem branches above or below ground, seen in plants like strawberries.
• Rhizomes resemble underground stolons, but are thick, fleshy "roots" found in irises, cannas, and water lilies.
• Tubers, like potatoes, are swollen underground stems with sprouting "eyes".
• Corms grow vertically, unlike stolons/rhizomes, giving rise to gladiolus, crocus, and tuberous begonias.
• Bulbs are short stems encased in fleshy scales (modified leaves). Layered bulbs (onions/garlic) feature concentric rings, while scaly bulbs (lily) have fleshy scales.
• Water-storing stems specialize in water storage, becoming fat, common in spurge, purslane, and milkweed.
• Leaves develop from lateral buds, with dicotyledons having a leaf stalk and blade for efficient sunlight absorption.
• Hydrothodes are located at leaf edges to facilitate guttation in humid conditions where transpiration is limited.
• Guttation is the excretion of excess water as droplets in humid environments when root water uptake exceeds the amount used.
• The cuticle layer is a waxy, transparent coating that prevents water loss while allowing sunlight penetration.
• Epidermal layers form the leaf's surface, lacking chloroplasts, and are non-photosynthetic.
• Palisade parenchyma consists of vertically-ordered, cylindrical cells below the upper epidermis that are adapted for high rates of photosynthesis.
• Spongy parenchyma, located above the lower epidermis, features loosely packed photosynthetic cells with air spaces.
• Vascular bundles consist of xylem and phloem to transport water/nutrients between root and leaf.
• Stomata are incomplete cuticular coverings on leaf surfaces that, when open, allow for transpiration and gas exchange.

Multiple Choice Completion

• The plant body consists of a root system and a shoot system.
• The root system is typically located below ground, while the shoot system includes a vertical stem with leaves, flowers, and fruits containing seeds.
• Roots exhibit positive geotropism as a specialized structure.
• Roots and stems have external appearance classifications.
• Plants have taproot and fibrous root systems.
• Roots lack leaves, nodes, internodes, and chloroplasts, whereas stems possess these structures.
• Adventitious roots develop from the lower stem portion.
• A germinating root is composed of the root cap, zone of cell division, zone of elongation, and the zone of maturation.
• In the zone of elongation, cells specialize and lengthen.
• Root hairs originate from epidermal tissue.
• Parenchyma cells in the cortex region store starch and transport water and minerals.
• The cortex and vascular bundles are separated by an endodermal layer.
• The pericycle, found beneath the endodermis, develops into lateral roots and contributes to meristematic activity.
• Mature, non-woody stems are referred to as herbaceous stems.
• Phloem vessels consist of cytoplasmic guard cells, non-nucleated sieve plate elements, and parenchyma cells.
• Xylem vessels comprise tracheids, schlerenchyma, and parenchyma cells.
• Plants like strawberries reproduce through stolons during springtime.
• Irises, cannas, and water lilies have thick, fleshy "roots" that are actually rhizomes.
• Tubers, such as the potato, sprout from the potato's eyes.
• Gladiolus, crocus and tuberous begonias arise from corms, which are stem nodes
• Onions and garlic exist as layered bulbs.
• Lily bulbs are examples of scaly bulbs with fleshy bulb scales.
• Water-storing plants such as spurge, purslane, and milkweed have water-storing stems.
• Dicotyledon leaves are divided into a leaf stalk and blade.
• A thick cuticle layer covers each leaf.
• A leaf cut in cross-section reveals the cuticle layer, epidermal layers, mesophyll layer, and vascular bundles.
• The mesophyll layer includes palisade parenchyma and spongy parenchyma.
• There is a mesophyll layer between the upper and lower epidermis.
• Xylem and pholem vessels are part of vascular bundles.

Phloem vs Xylem

• Phloem Vessels:*
• Elongate from roots to leaves, near the stem's outer section.
• Consist of cytoplasmic guard cells, non-nucleated sieve plate elements, support cells, and parenchyma cells.
• Sieve tube elements are closely packed.
• Sieve plate tubes connect phloem vessels.
• Transports the organic molecules of photosynthesis.
• Transport rate is slower than xylem.
• Xylem Vessels:*
• Stretch from the roots to the leaves, situated in the core of the plant.
• Consist of tracheids, schlerenchyma, and parenchyma cells.
• The cells located at the outer portion of the parenchyma are nonliving
• Xylem cells enlarge and connect together forming pipe-like structures.
• Transports water and minerals absorbed by roots.
• The transport rate is rapid, and it occurs against gravity.

Palisade vs Spongy Parenchyma

• Palisade Parenchyma:*
• Composed of long, cylindrical, tightly packed cells.
• Located directly below the upper epidermis.
• High rate of photosynthesis due to numerous chloroplasts.
• Spongy Parenchyma:*
• Consists of loosely arranged cells with air spaces, creating a sponge-like appearance.
• Located above the lower epidermis layer.
• Contains fewer chloroplasts than palisade parenchyma.

Stolon vs Rhizome

• Stolon:*
• Slender stem-branches running horizontally above or below ground.
• Have nodes capable of forming roots and new plants.
• Strawberries are example plants
• Rhizome:*
• Underground stolons-like.
• Each stolon can radiate several stems from the plant's center.
• The thick, fleshy "roots" of irises, cannas, and water lilies.

Plant Functions and Importance

• Root:*
• Anchors the plant.
• Transports water and minerals.
• Some store materials.
• Root Cap:*
• Protects the meristematic zone.
• Zone of Cell Division:*
• Actively dividing meristematic region.
• Meristematic Region:*
• Involved in root extension and cap renewal.
• Zone of Maturation:*
• Differentiating region forming phloem, xylem, etc.
• Parenchyma Cells:*
• Store starch and transport materials.
• Gate Cells:*
• Facilitate material exchange in the cortex and core.
• Stem:*
• Connects roots and leaves.
• Root Hair:*
• Differentiating region forming phloem, xylem.
• Lenticel:*
• Facilitates gas exchange.
• Phloem Vessels:*
• Transports photosynthetic products/nitrogenous compounds.
• Sieve Tube:*
• Composed of cytoplasmic guard cells and sieve plate elements.
• Xylem Vessels:*
• Transports water and minerals.
• Cuticle Layer:*
• Transparent and prevents water loss.
• Stomata:*
• Provides gas exchange and water regulation.
• Vascular Bundles:*
• Transports water and organic materials.

Causes For

• Highly branched roots: have a larger surface area, due to root hairs and branches.
• Few cells bordering xylem vessels do not thicken to create a passageway.
• Slower transportation rate in phloem due to living vessels.
• Corms grow vertically, unlike stolons/rhizomes.
• Water-storing stems become fat by water accumulation.
• Wide surface area in leaf allows absorption of large amounts of light.
• Desert plants minimize water loss via needle-shaped leaves.
• Stomata are buried in lower epidermis to prevent water loss.
• Transparent cuticle allows sunlight, but prevents water loss.
• High Chloroplast Concentration leads to a high rate of photosynthesis
• The variation in the thickness of the inner vs outter walls, allows the stroma

Root Adaptations and Germinating Root Parts

• Tap and fibrous roots obtain water in different ways: taproots reach deep, and fibrous roots collect rainwater near the surface.
• Germinating root parts include the root cap (protection), the zone of cell division (growth), the zone of elongation (specialization), and the zone of maturation (differentiation).
• The epidermis is the root's outermost layer. Cortex stores starch and transports materials. The endodermis regulates exchange, and vascular tissue forms lateral roots/cambium.
• mesophyll layer: includes palisade and
• spongy parenchyma cells.

Leaf Structure

• Cuticle layer: waxy, prevents water loss.
• Epidermal layers: surface made of non-photosynthetic layer.
• Mesophyll Layer: palisade and spongy parenchyma, photosynthetic.
• Vascular bundles: transport water and nutrients.