🔬 Introduction to Plant Organisation 🔬

• Flowering plants (Angiosperms) exhibit a remarkable level of structural organisation.
• This organisation is divided into two main aspects: Morphology and Anatomy.
• Morphology: Study of external features and forms of organisms.
• Anatomy: Study of the internal structure of organisms.
• Understanding both is crucial to comprehend plant function and adaptation.

🌱 Morphology of Flowering Plants: Overview 🌱

• A typical flowering plant consists of a root system and a shoot system.
• The root system is underground, primarily for absorption and anchorage.
• The shoot system is above ground, comprising stem, leaves, flowers, and fruits.
• Each part performs specific functions essential for the plant’s survival and reproduction.
• Variations in morphology reflect adaptations to different environments.

🌿 The Root System 🌿

• Primary function: Absorption of water and minerals from the soil.
• Provides proper anchorage to the plant parts.
• Stores reserve food material (e.g., carrot, radish).
• Synthesizes plant growth regulators.
• Types:
  • Tap Root System: Primary root with lateral branches (e.g., Dicot plants like Mustard).
  • Fibrous Root System: Arises from the base of the stem (e.g., Monocot plants like Wheat).
  • Adventitious Roots: Arise from parts other than the radicle (e.g., Banyan tree – prop roots, Maize – stilt roots).

🔍 Regions of the Root 🔍

• Root Cap: Thimble-like structure protecting the root apex during growth.
• Region of Meristematic Activity: Cells are small, thin-walled, and divide rapidly.
• Region of Elongation: Cells rapidly increase in length, responsible for root growth.
• Region of Maturation: Cells differentiate and mature. Root hairs develop here.
• Root Hairs: Fine, delicate, thread-like structures for water absorption.

🔄 Modifications of Root 🔄

• Storage Roots: Store food (e.g., Radish, Carrot, Turnip – tap roots; Sweet potato – adventitious roots).
• Prop Roots: Hanging structures providing support (e.g., Banyan tree).
• Stilt Roots: Provide support by growing obliquely from lower nodes of stem (e.g., Maize, Sugarcane).
• Pneumatophores: Roots coming out of ground to help in respiration in marshy areas (e.g., Rhizophora).
• Nodulated Roots: Bear nodules with nitrogen-fixing bacteria (e.g., Pea, other legumes).

🌳 The Stem 🌳

• Ascending part of the axis, bearing branches, leaves, flowers, and fruits.
• Develops from the plumule of the embryo.
• Characterized by the presence of nodes and internodes.
• Nodes: Points where leaves or branches arise.
• Internodes: Portions between two nodes.
• Bears terminal (apical) and axillary buds.

🔄 Modifications of Stem 🔄

• Underground Stems (for storage): Rhizome (ginger), Tuber (potato), Corm (colocasia), Bulb (onion).
• Tendrils: Slender, spirally coiled structures for climbing (e.g., cucumber, grapevines).
• Thorns: Woody, pointed structures for protection (e.g., Bougainvillea, Citrus).
• Phylloclade: Flattened or cylindrical green stems for photosynthesis (e.g., Opuntia).
• Runners, Stolons, Suckers: For vegetative propagation (e.g., Grass, Jasmine, Mint).

🍃 The Leaf 🍃

• Flattened, thin, green structure borne on the stem, originating from the nodal meristem.
• Main site of photosynthesis.
• Parts:
  • Leaf base: Attaches leaf to stem.
  • Petiole: Stalk of the leaf, helps hold the blade to light.
  • Lamina (Leaf Blade): Broad, green part, with veins and veinlets.
• Possesses axillary bud in its axil.

🕸️ Venation and Phyllotaxy 🕸️

• Venation: Arrangement of veins and veinlets in the lamina.
  • Reticulate Venation: Net-like (e.g., Dicot leaves like China rose).
  • Parallel Venation: Veins run parallel (e.g., Monocot leaves like Grass).
• Phyllotaxy: Pattern of arrangement of leaves on the stem or branch.
  • Alternate: Single leaf at each node (e.g., China rose).
  • Opposite: Pair of leaves at each node (e.g., Guava).
  • Whorled: More than two leaves at each node (e.g., Alstonia).

🌸 Inflorescence 🌸

• The arrangement of flowers on the floral axis.
• Racemose Inflorescence: Main axis continues to grow, flowers borne laterally in acropetal succession (older flowers at base, younger at apex). E.g., Radish.
• Cymose Inflorescence: Main axis terminates in a flower, limited growth. Flowers borne in basipetal succession (older at apex, younger at base). E.g., Jasmine.
• Determines the overall appearance and pollination strategy of a plant.

🌼 The Flower 🌼

• The reproductive unit in angiosperms.
• A modified shoot where apical meristem changes to floral meristem.
• Consists of four whorls arranged on a swollen receptacle (thalamus).
• Outer two whorls (calyx, corolla) are accessory; inner two (androecium, gynoecium) are reproductive.
• Variations in floral parts aid in identification and classification.

🌻 Parts of a Flower (Floral Whorls) 🌻

• Calyx: Outermost whorl, sepals (green, protective).
• Corolla: Petals (brightly colored, attract pollinators).
• Androecium: Male reproductive part, stamens (filament + anther).
• Gynoecium (Pistil): Female reproductive part, carpels (stigma + style + ovary).
• Ovary: Contains ovules, develops into fruit.
• Ovule: Develops into seed after fertilization.

🌱 Placentation 🌱

• The arrangement of ovules within the ovary.
• Marginal: Ovules on the ridge forming a single row (e.g., Pea).
• Axile: Ovules attached to central axis in a multilocular ovary (e.g., Lemon, Tomato).
• Parietal: Ovules on the inner wall of ovary or peripheral part (e.g., Mustard, Argemone).
• Basal: Single ovule at the base of the ovary (e.g., Sunflower, Marigold).
• Free Central: Ovules borne on central axis, septum absent (e.g., Dianthus, Primrose).

🍎 The Fruit 🍎

• Mature or ripened ovary, developed after fertilization.
• A characteristic feature of flowering plants.
• Protects the seeds and aids in their dispersal.
• Consists of pericarp (fruit wall) and seeds.
• Types:
  • Simple fruits: Develop from a single flower with a single ovary (e.g., Mango, Tomato).
  • Aggregate fruits: Develop from a single flower with multiple separate ovaries (e.g., Custard apple).
  • Multiple fruits: Develop from an entire inflorescence (e.g., Pineapple, Mulberry).
  • False fruits: Formed from parts other than the ovary (e.g., Apple, Cashew).

🌰 The Seed 🌰

• Fertilized ovule, develops into a new plant.
• Consists of seed coat and embryo.
• Embryo: Composed of an embryonal axis and one or two cotyledons.
• Cotyledons: Store food (in non-albuminous seeds) or absorb food (in albuminous seeds).
• Micropyle: Small pore in seed coat, allows water and oxygen during germination.
• Provides nourishment and protection to the developing embryo.

🔬 Anatomy of Flowering Plants: Introduction 🔬

• Plant anatomy deals with the internal structure of plants.
• Study of plant tissues and their organisation.
• Tissues are groups of cells having a common origin and usually performing a common function.
• Plants have various tissues organised into tissue systems.
• This internal structure reveals how plants perform vital functions like transport and support.

🌱 Plant Tissues: Meristematic Tissue 🌱

• Composed of actively dividing cells.
• Responsible for plant growth.
• Types:
  • Apical Meristem: Present at root and shoot apices, responsible for primary growth (increase in length).
  • Intercalary Meristem: Located between permanent tissues, responsible for growth in grasses and monocots.
  • Lateral Meristem: Cylindrical meristem (e.g., vascular cambium, cork cambium), responsible for secondary growth (increase in girth).
• Cells are typically small, isodiametric, with dense cytoplasm and prominent nucleus.

🌿 Plant Tissues: Permanent Tissue (Simple) 🌿

• Cells are fully differentiated and have lost the power of division.
• Formed from meristematic tissue.
• Types (composed of only one type of cell):
  • Parenchyma: Living, thin-walled, isodiametric cells. Functions: photosynthesis, storage, secretion.
  • Collenchyma: Living, thickened at corners, provide mechanical support to young stems and petioles.
  • Sclerenchyma: Dead, highly thickened lignified walls. Functions: mechanical support. (Fibers and Sclereids).

💧 Plant Tissues: Permanent Tissue (Complex) 💧

• Composed of more than one type of cells, working together as a unit.
• Function: Transport of water, minerals, and food.
• Types:
  • Xylem (Wood): Conducts water and minerals from roots to leaves. Composed of tracheids, vessels, xylem parenchyma, xylem fibers.
  • Phloem (Bast): Translocates food from leaves to other parts. Composed of sieve tube elements, companion cells, phloem parenchyma, phloem fibers.
• Also known as vascular tissues.

🗺️ Tissue Systems 🗺️

• Plant tissues are organised into three main tissue systems:
• Epidermal Tissue System: Outermost covering of the plant body.
  • Composed of epidermal cells, stomata, and epidermal appendages (trichomes, root hairs).
  • Functions: Protection, prevention of water loss, gas exchange.
• Ground Tissue System: All tissues except epidermis and vascular bundles.
  • Composed of parenchyma, collenchyma, sclerenchyma.
  • Functions: Photosynthesis, storage, support.
• Vascular Tissue System: Xylem and phloem. Arranged in vascular bundles. Functions: Conduction.

🌱 Anatomy of Dicot Root 🌱

• Epidermis: Outermost layer, often bears root hairs.
• Cortex: Inner to epidermis, consists of several layers of parenchyma cells.
• Endodermis: Innermost layer of cortex, having Casparian strips (impermeable to water).
• Vascular Bundles: Radial arrangement (xylem and phloem bundles separated by parenchyma).
• Xylem is tetrarch (four xylem arms) to hexarch (six xylem arms).
• Small or inconspicuous pith.

🌾 Anatomy of Monocot Root 🌾

• Similar to dicot root in many respects (epidermis, cortex, endodermis).
• Possess more than six xylem bundles (polyarch condition).
• Large and well-developed pith.
• Does not undergo secondary growth (no cambium).
• Examples: Maize, Wheat roots.
• The number of xylem bundles is a key distinguishing feature.

🌳 Anatomy of Dicot Stem 🌳

• Epidermis: Outermost protective layer, with a cuticle and sometimes trichomes.
• Cortex: Hypodermis (collenchymatous), cortical layers (parenchymatous), and endodermis (starch sheath).
• Vascular Bundles: Conjoint (xylem and phloem together), collateral (xylem towards inside), and open (cambium present between xylem and phloem).
• Arranged in a ring.
• Well-developed pith.

🌽 Anatomy of Monocot Stem 🌽

• Epidermis: Outermost layer with a cuticle.
• Hypodermis: Sclerenchymatous.
• Ground Tissue: Large, continuous parenchymatous ground tissue without distinct cortex/endodermis/pericycle.
• Vascular Bundles: Conjoint, collateral, and closed (no cambium).
• Scattered throughout the ground tissue, larger bundles towards periphery.
• Lack secondary growth.

🍃 Anatomy of Dicot Leaf (Dorsiventral) 🍃

• Typically found in dicotyledonous plants, showing distinct upper (adaxial) and lower (abaxial) surfaces.
• Epidermis: Upper and lower epidermis, lower epidermis has more stomata.
• Mesophyll: Tissue between upper and lower epidermis.
  • Palisade Parenchyma: Elongated cells, vertically arranged, rich in chloroplasts (upper side).
  • Spongy Parenchyma: Irregularly shaped cells with air spaces (lower side).
• Vascular Bundles: Vary in size, surrounded by bundle sheath cells.

🌾 Anatomy of Monocot Leaf (Isobilateral) 🌾

• Found in monocotyledonous plants, appearing similar on both sides.
• Epidermis: Both upper and lower epidermis may have equal numbers of stomata.
• Mesophyll: Not differentiated into palisade and spongy parenchyma. All cells are parenchymatous.
• Vascular Bundles: Parallel venation, bundles of similar size (except midrib), bundle sheath present.
• Presence of Bulliform cells (motor cells) on the adaxial epidermis, helping in leaf rolling during water stress.

🌳 Secondary Growth 🌳

• Increase in girth of the plant due to activity of lateral meristems.
• Occurs in dicot stems and roots, but not in monocots.
• Involves:
  • Vascular Cambium: Forms secondary xylem (wood) inwards and secondary phloem outwards.
  • Cork Cambium (Phellogen): Forms cork (phellem) outwards and secondary cortex (phelloderm) inwards.
• Results in the formation of annual rings (growth rings) in wood, useful for determining plant age.

📚 Summary of Plant Organisation 📚

💡 Problem-Solving Tips & Exam Guidance 🎯

• Distinguish between morphological and anatomical features.
• Master the different types of roots, stems, and leaves and their modifications.
• Practice drawing and labeling diagrams of dicot/monocot root, stem, and leaf anatomy.
• Understand the functions of different plant tissues and tissue systems.
• Focus on the distinguishing features of monocots vs. dicots in anatomy.
• Know the process and significance of secondary growth.

🌟 Conclusion 🌟

• Flowering plants exhibit a complex and highly organised structure.
• Morphology describes external features, while anatomy reveals internal arrangements.
• Roots, stems, and leaves are fundamental organs, each with specialised functions.
• Tissues and tissue systems form the intricate network enabling plant life.
• Understanding plant structure is key to appreciating their physiology and ecology.