Anatomy of Flowering Plants

The study of internal structure of plants is termed anatomy.
Plants consist of cells, which are the basic structural unit, organized into tissues, which in turn are organized into organs.
Different organs exhibit variations in internal structure.
Within angiosperms (flowering plants), monocots and dicots exhibit anatomical differences.
Adaptations in internal structure are present to cope with diverse environments.

Tissues vary depending on their location in the plant body; their structure and function are influenced by this location.
There are three main types of tissue systems based on structure and location: - Epidermal Tissue System - Ground Tissue System - Vascular Tissue System

Function: Forms the outermost covering of the entire plant body.
Components: - Epidermal Cells: Elongated, compactly arranged forming a single layer, with a small amount of cytoplasm and a large vacuole. - Stomata: Structures that regulate transpiration and gaseous exchange. Each stoma has two guard cells which control its opening and closing. - Epidermal Appendages: Includes hair-like projections known as trichomes, which can be unicellular (root hairs) or multicellular (stem hairs). - Cuticle: A waxy layer covering the epidermis, prevents water loss (absent in roots).
Guard Cells: - Bean-shaped cells surrounding the stomatal pore; exhibit different shapes in grasses (dumb-bell shaped). - Inner walls thickened to assist in regulation; bear chloroplasts.
Stomatal Apparatus: Consists of guard cells, stomatal pore, and occasionally accompanying subsidiary cells.

Encompasses all tissues except epidermis and vascular bundles.
Composed of simple tissues: - Parenchyma: Thin-walled cells found in cortex and medullary rays. - Collenchyma: Provides mechanical support with thicker cell walls. - Sclerenchyma: Comprises thick-walled, supportive cells.
Mesophyll: Specific to leaves, made up of chlorophyll-containing cells involved in photosynthesis.

Comprises two complex tissues: phloem and xylem.
Vascular Bundles: Formed by the arrangement of xylem and phloem; categorized based on presence of cambium: - Open Vascular Bundles: Found in dicots (presence of cambium allows secondary growth). - Closed Vascular Bundles: Found in monocots (lack cambium).
Arrangement Types: - Radial Arrangement: Xylem and phloem alternate along different radii (common in roots). - Conjoint Arrangement: Xylem and phloem lie along the same radius (typical in stems and leaves, with phloem external to xylem).

To better comprehend tissue organization, transverse sections of mature organs (roots, stems, leaves) are analyzed.

Transverse section reveals:
- Outer Layer: Epiblema with unicellular root hairs. - Cortex: Comprised of several layers of parenchyma with intercellular spaces. - Endodermis: Innermost cortex layer, barrel-shaped cells possessing Casparian strips (water-impermeable material). - Pericycle: Layer inside the endodermis, responsible for lateral root formation. - Pith: Small or inconspicuous. - Conjunctive Tissue: Parenchyma cells between xylem and phloem. - Development of cambium between xylem and phloem is seen. - Stele: All tissues inside the endodermis, comprising pericycle, vascular bundles, and pith.

Similar anatomy to dicot root.
Characteristics include: - More than six xylem bundles (polyarch). - Well-developed pith. - No secondary growth.

Transverse section shows: - Epidermis: Thin cuticle, presence of trichomes and stomata. - Cortex: Multiple layers with three sub-zones including: - Hypodermis: Colenchymatous for mechanical support. - Cortical Layers: Parenchymatous, rounded, with intercellular spaces. - Endodermis: Rich in starch, referred to as starch sheath. - Pericycle: Located inner to endodermis, above phloem in sclerenchymatous patches. - Medullary Rays: Parenchyma cells located between vascular bundles. - Vascular Bundles: Arranged in a characteristic ring (common in dicots), open, endarch protoxylem. - Pith: Comprised of rounded parenchymatous cells with large intercellular spaces.

Anatomy:
- Sclerenchymatous hypodermis. - Scattered vascular bundles each with a bundle sheath. - Conspicuous parenchymatous ground tissue. - Vascular bundles are conjoint and closed; peripheral ones smaller than central ones. - Absence of phloem parenchyma and presence of water-containing cavities within bundles.

Transverse section reveals: - Epidermis: Covers both surfaces of the leaf, typically with more stomata on the abaxial surface (lower surface). - Mesophyll: Composed of chloroplast-containing parenchyma, arranges into: - Palisade Parenchyma: Elongated, vertically arranged cells. - Spongy Parenchyma: Loose arrangement with air cavities for gas exchange. - Vascular System: Includes vascular bundles in veins and midrib, dependent on vein size and thickness.

Features: - Stomata are present on both surfaces. - Mesophyll not differentiated into palisade and spongy parenchyma. - Modification of adaxial epidermal cells into bulliform cells for water management (turgidity influences leaf position). - Parallel Venation seen in uniform vascular bundle sizes.

Plants exhibit various tissue types: meristematic (apical, lateral, intercalary) and permanent (simple, complex).
Functions include food assimilation and storage, water and mineral transportation, and mechanical support.
The three tissue systems include functional details about epidermal, ground, and vascular tissues.
Notable differences between monocot and dicot structures highlight evolutionary adaptations.
Secondary growth primarily occurs in dicot roots and stems.

Draw illustrations showing anatomical differences between (a) Monocot root and Dicot root, (b) Monocot stem and Dicot stem.
Observe a transverse section of a young stem and determine if it is monocot or dicot, including reasoning.
Identify plant material with the following features: (a) Conjoint, scattered vascular bundles surrounded by sclerenchymatous sheath, (b) Absence of phloem parenchyma.
Describe the stomatal apparatus and include a labelled diagram of stomata.
Name three basic tissue systems in flowering plants and list the tissues under each system.
Discuss the utility of studying plant anatomy.
Describe the internal structure of a dorsiventral leaf using labelled diagrams.