Notes Class 11 Chapter 9 Biology Maharashtra Board

Morphology of Flowering Plants

9.1 Angiosperms

Angiosperms, or flowering plants, are the dominant group within the plant kingdom due to their adaptability to various environmental conditions. They exhibit significant morphological diversity in both external and internal structures, enabling them to perform essential functions. Angiosperms belong to the phanerogams, characterized by the presence of flowers, fruits, and seeds.

Classification Based on Habitat

Angiosperms are classified based on their habitat as follows:

Hydrophytes: Grow in aquatic environments (e.g., Hydrilla).
Xerophytes: Thrive in arid regions with minimal rainfall (e.g., Opuntia).
Psammophytes: Found in sandy soils (e.g., Elymus).
Lithophytes: Grow on rocks (e.g., Cladopus, Dalzellia, Couchidium).
Halophytes: Adapted to saline soils (e.g., Rhizophora).

9.2 Morphology

Morphology studies the form and structure of plants. Angiospermic plants consist of vegetative structures (root, stem, leaf) and reproductive structures (flower, fruit, seed). These structures vary to suit the plant’s habitat and function.

A. Root

Roots are the descending axis of the plant, typically growing beneath the soil surface. They are positively geotropic (grow towards gravity) and hydrotropic (attracted to water) but negatively phototropic (avoid light) and aerotropic (avoid air). Roots are non-green, cylindrical, and lack nodes and internodes.

Typical Root Structure

A root comprises several regions:

Root Cap: A parenchymatous, multicellular structure covering the root apex, secreting mucilage to lubricate soil passage. It contains starch granules aiding graviperception. Single in most plants, multiple in Pandanus, or replaced by root pockets in hydrophytes (e.g., Pistia, Eichhornia).
Meristematic Region (Region of Cell Division): A 1 mm long growing point with compactly arranged, actively dividing cells responsible for longitudinal root growth.
Region of Elongation: Above the meristematic region, cells here elongate rapidly, increasing root length and aiding mineral absorption.
Region of Root Hairs (Piliferous Zone): Contains tubular, unicellular root hairs from the epiblema, increasing surface area for water absorption. Root hairs are short-lived, replaced every 10-15 days.
Region of Maturation (Differentiation): The major portion of the root, with thick-walled, impermeable cells forming tissues for fixation and conduction. Lateral roots develop here.

Functions of Roots

Primary Functions: Anchorage, water and mineral absorption, and conduction to the stem.
Secondary Functions: Storage, support, or specialized functions in modified roots.

Types of Roots

Roots are classified based on origin:

Tap Root (True Root):
- Develops from the radicle during seed germination.
- Consists of a primary root with secondary and tertiary branches.
- Common in dicotyledonous plants (e.g., Pea, Bean, Sunflower).
Adventitious Root:
- Arises from parts other than the radicle (e.g., stem base, nodes, leaves).
- Forms a fibrous root system in monocots (e.g., Maize, Wheat, Sugarcane).
- Used for vegetative propagation in some plants (e.g., Euphorbia).

Modifications of Roots

Roots may undergo structural changes for specialized functions, termed metamorphosed roots.

1. Modifications of Tap Root:

Food Storage:
- Fusiform: Swollen in the middle, tapering at both ends (e.g., Radish).
- Conical: Broad at the base, narrowing towards the apex (e.g., Carrot).
- Napiform: Highly swollen base, abruptly narrowing at the apex (e.g., Beet).
Respiratory Roots (Pneumatophores):
- Found in halophytes (e.g., Rhizophora) in saline, waterlogged soils.
- Negatively geotropic, growing vertically upwards with lenticels for gaseous exchange.

2. Modifications of Adventitious Roots:

Food Storage:
- Simple Tuberous: Swollen, irregular roots (e.g., Sweet Potato).
- Fasciculated Tuberous: Cluster of thick, fleshy roots (e.g., Dahlia, Asparagus).
- Beaded (Moniliform): Swellings at intervals like beads (e.g., Indian Spinach).
- Nodulose: Enlarged tips forming nodules (e.g., Curcuma amada).
Mechanical Support:
- Prop Roots/Columnar Roots: Arise from branches, grow downwards, and thicken to support heavy branches (e.g., Banyan tree).
- Stilt Roots: Obliquely growing roots from lower nodes for support (e.g., Maize, Sugarcane, Pandanus).
- Climbing Roots: Arise from nodes to attach to supports (e.g., Betel leaf, Money plant).
- Clinging Roots: Tiny roots with sticky tips for attachment to walls (e.g., English Ivy).
- Plank Roots/Buttresses: Plank-like extensions at the base of large trees (e.g., Silk cotton, Pipal).
Buoyant Roots: Inflated, spongy roots in aquatic herbs for buoyancy (e.g., Jussiaea repens).
Special Functions:
- Epiphytic Roots: Hygroscopic roots in epiphytes (e.g., Vanda) with velamen tissue to absorb moisture from air.
- Sucking Roots (Haustoria): Microscopic roots in parasitic plants (e.g., Cuscuta, Viscum) to absorb nutrients from the host.

B. Stem

The stem is the ascending axis of the shoot system, developing from the plumule. It is positively phototropic, negatively geotropic, and negatively hydrotropic. Stems bear nodes, internodes, buds (axillary, apical), leaves, and flowers. Young stems are green and photosynthetic.

Functions of Stem

Primary Functions: Support branches, leaves, flowers, and fruits; conduct water, minerals, and food.
Secondary Functions: Storage, perennation, vegetative propagation, or photosynthesis in modified stems.

Modifications of Stem

Stems modify to perform additional functions, categorized as:

1. Underground Stem:

Develop below soil, store food, aid perennation, and enable vegetative propagation.
Rhizome: Prostrate, thickened, brownish stem growing horizontally or obliquely (e.g., Ginger, Turmeric). Shows sympodial (lateral bud growth) or monopodial (terminal bud growth) patterns.
Stem Tuber: Swollen tips of underground branches with nodes and “eyes” (e.g., Potato).
Bulb: Reduced, discoid stem with fleshy leaves storing food. Types include tunicated (e.g., Onion) and scaly/compound tunicated (e.g., Garlic).
Corm: Swollen, spherical internode with nodes and axillary buds (e.g., Colocasia).

2. Sub-Aerial Stem:

Weak stems growing over or slightly below the ground for perennation and propagation.
Trailer: Spreads over the ground, either procumbent or decumbent (e.g., Euphorbia, Tridax).
Runner: Narrow, horizontal branches producing new crowns (e.g., Cynodon).
Stolon: Slender lateral branch bending to produce new shoots (e.g., Mentha).
Sucker: Non-green, runner-like branch from underground roots (e.g., Chrysanthemum).
Offset: One-internode-long runners in rosette plants (e.g., Eichhornia, Pistia).

3. Aerial Modification:

Thorn: Modified apical or axillary bud, reducing transpiration and protecting against animals (e.g., Citrus, Bougainvillea).
Phylloclade: Leaf-like, fleshy stem for photosynthesis (e.g., Opuntia, Casuarina).
Cladodes: One-internode-long photosynthetic branches (e.g., Asparagus).
Cladophylls: Leaf-like structures with floral buds (e.g., Ruscus).
Stem Tendrils: Thin, coiled structures for support (e.g., Passiflora, Vitis).
Bulbils: Fleshy axillary buds for vegetative propagation (e.g., Dioscorea).

C. Leaf

Leaves are flattened, green appendages developing from leaf primordia at nodes. They are exogenous, show limited growth, and lack apical buds. Leaves perform photosynthesis and transpiration.

Typical Leaf Structure

A leaf consists of:

Leaf Base (Hypopodium): Attaches the leaf to the stem, may be pulvinus, sheathing, or ligulate.
Petiole (Mesopodium): Connects the lamina to the base, aiding light exposure and conduction. Leaves with petioles are petiolate; without are sessile.
Lamina (Epipodium): Flat, green part for photosynthesis, gaseous exchange, and transpiration. May be dorsiventral (Dicots) or isobilateral (Monocots).

Leaf Venation

Venation is the arrangement of veins and veinlets in the lamina, responsible for conduction and structural support. Types include:

Reticulate: Net-like pattern (common in Dicots).
Parallel: Veins run parallel (common in Monocots).

Types of Leaves

Based on lamina incision:

Simple Leaf: Entire, undivided lamina.
Compound Leaf:
- Pinnately Compound: Leaflets on a rachis (e.g., Cassia, Rosa).
- Palmately Compound: Leaflets attached at the petiole tip (e.g., Citrus, Oxalis).

Modifications of Leaves

Leaves modify for specialized functions:

Leaf Spines: Entire leaf, margin, or stipule modified into spines for protection or reduced transpiration (e.g., Opuntia, Acacia).
Leaf Tendrils: Leaf or leaflet modified into coiled structures for support (e.g., Lathyrus, Pisum sativum).
Leaf Hooks: Terminal leaflets modified into curved hooks (e.g., Bignonia unguis cati).
Phyllode: Flattened, leaf-like petiole for photosynthesis (e.g., Acacia auriculoformis).

Phyllotaxy

Phyllotaxy is the arrangement of leaves on the stem to optimize light exposure:

Alternate: Single leaf per node (e.g., Mango).
Opposite Decussate: Pair of leaves at each node, consecutive pairs at right angles (e.g., Calotropis).
Opposite Superposed: Pair of leaves at each node, consecutive pairs aligned (e.g., Jamun).
Whorled: Multiple leaves per node (e.g., Nerium).

D. Inflorescence

Inflorescence is a specialized axis bearing flowers in a definite manner, consisting of a peduncle and flowers. It increases pollination chances and enhances plant attractiveness.

Types of Inflorescence

Racemose:
- Unlimited peduncle growth with a free apical bud.
- Older flowers at the base, acropetal succession.
- Centripetal opening in disc-shaped peduncles (e.g., Mustard).
Cymose:
- Limited peduncle growth, apical meristem forms a flower.
- Oldest flower at the apex, basipetal succession.
- Centrifugal opening in compressed peduncles (e.g., Hibiscus).

E. Flower

A flower is a modified shoot for sexual reproduction, arising axillary or terminally. The thalamus, with four nodes and three condensed internodes, bears floral whorls.

Floral Characteristics

Bracteate/Ebracteate: With/without bracts.
Pedicellate/Sessile: With/without pedicel.
Symmetry:
- Actinomorphic: Radial symmetry (e.g., Hibiscus).
- Zygomorphic: Bilateral symmetry (e.g., Sweet pea).
Completeness:
- Complete: All four whorls present.
- Incomplete: Missing one or more whorls.
Sex:
- Perfect (Bisexual): Both androecium and gynoecium present.
- Imperfect (Unisexual): Only one reproductive whorl (staminate or pistillate).
- Neuter: No reproductive whorls (e.g., Marigold ray florets).
Plant Types:
- Monoecious: Male and female flowers on the same plant (e.g., Maize).
- Dioecious: Male and female flowers on different plants (e.g., Papaya).

Insertion of Floral Whorls

The position of floral whorls relative to the gynoecium:

Hypogynous: Ovary superior, other whorls below (e.g., Mustard). Denoted as G in floral formula.
Perigynous: Ovary semi-superior, whorls at the same level (e.g., Rose). Denoted as G.
Epigynous: Ovary inferior, other whorls above (e.g., Sunflower). Denoted as G.

Floral Parts

Calyx (K):
- Outermost whorl of sepals, usually green, photosynthetic, and protective.
- Gamosepalous: Fused sepals (e.g., China rose).
- Polysepalous: Free sepals (e.g., Brassica).
- Modified forms: Petaloid (e.g., Mussaenda) or pappus (e.g., Tridax).
Corolla (C):
- Second whorl of petals, often colorful to attract pollinators.
- Polypetalous: Free petals (e.g., Rose).
- Gamopetalous: Fused petals (e.g., Datura).
Perianth (P):
- Undifferentiated calyx and corolla, termed tepals.
- Polyphyllous: Free tepals.
- Gamophyllous: Fused tepals.
- Sepaloid (green) or petaloid (colorful) tepals (e.g., Lily).
Androecium (A):
- Male reproductive whorl of stamens, each with anther, filament, and connective.
- Polyandrous: Free stamens.
- Cohesion:
  - Adelphy: Fused filaments, free anthers.
  - Syngenesious: Fused anthers, free filaments (e.g., Sunflower).
  - Synandrous: Fused filaments and anthers (e.g., Cucurbita).
- Adhesion: Epipetalous (e.g., Datura) or epiphyllous (e.g., Lily).
Gynoecium (G):
- Female reproductive whorl of carpels (pistils), each with stigma, style, and ovary.
- Syncarpous: Fused carpels (e.g., Datura).
- Apocarpous: Free carpels.
- Placentation:
  - Marginal: Ovules on fused margins (e.g., Pea).
  - Axile: Ovules on central axis (e.g., China rose).
  - Parietal: Ovules on inner wall (e.g., Papaya).
  - Basal: Single ovule at base (e.g., Sunflower).
  - Free Central: Ovules on unattached central axis (e.g., Dianthus).

Aestivation

The arrangement of sepals, petals, or tepals in the bud:

Valvate: Edges touching without overlapping.
Imbricate: Overlapping irregularly.
Contorted: Twisted, overlapping in one direction.
Vexillary: Large petal (vexillum) encloses others (e.g., Pea).

Epicalyx

Additional sepal-like structures outside the calyx, characteristic of Malvaceae (e.g., Ladies finger).

F. Fruit

Fruits develop from the ovary after fertilization, or without (parthenocarpic fruits, e.g., Banana). Fruits are classified as:

True Fruit: Develops only from the ovary (e.g., Mango).
False Fruit (Pseudocarp): Develops from other floral parts (e.g., Apple).

Fruit Structure

Pericarp: Protective wall, divided into epicarp, mesocarp, and endocarp in fleshy fruits.
Types:
1. Simple Fruits: From one ovary.
  - Dry Fruits: Thin pericarp, dehiscent (e.g., Pea) or indehiscent (e.g., Maize).
  - Fleshy Fruits: Thick pericarp, e.g., berry (Tomato) or drupe (Coconut).
2. Aggregate Fruits: From multiple ovaries of one flower (e.g., Strawberry, Custard apple).
3. Composite Fruits: From multiple ovaries of an inflorescence (e.g., Pineapple, Fig).

G. Seed

Seeds develop from fertilized ovules, consisting of:

Seed Coat: Outer testa and inner tegmen, with a hilum scar.
Embryo: Contains radicle, plumule, cotyledons, epicotyl, and hypocotyl.
Endosperm: Nutritive tissue, present (endospermic, e.g., Castor) or absent (non-endospermic, e.g., Pea).

9.3 Study of Important Families

Fabaceae (Pea Plant)

Habit: Herbs, shrubs, or trees; erect climbers with root nodules.
Leaves: Pinnately compound, alternate phyllotaxy.
Inflorescence: Racemose-raceme.
Flower: Bisexual, zygomorphic, gamosepalous calyx (imbricate), polypetalous corolla (vexillary), diadelphous androecium [(9)+1], monocarpellary gynoecium with marginal placentation.
Fruit: Legume.
Seeds: Non-endospermic.

Floral Formula:

Solanaceae (Datura Plant)

Habit: Herbs, shrubs, or small trees; tap root system.
Stem: Erect, woody, branched, sometimes hairy; tuber in potato.
Leaves: Simple, alternate, reticulate venation.
Inflorescence: Cymose-solitary.
Flower: Bisexual, actinomorphic, gamosepalous calyx (valvate, persistent), gamopetalous corolla (contorted), epipetalous androecium, bicarpellary syncarpous gynoecium with axile placentation.
Fruit: Berry or capsule.
Seeds: Endospermic.