Class 11 Biology Notes Chapter 5 (Morphology of flowering plants) – Biology Book

Alright class, let's delve into the fascinating world of plant forms. Chapter 5, 'Morphology of Flowering Plants', is crucial not just for understanding the plant kingdom but also frequently tested in various government examinations. Morphology, as you know, is the study of the external structure, form, and relative position of different plant organs.

Here are the detailed notes focusing on key concepts for your preparation:

Chapter 5: Morphology of Flowering Plants - Detailed Notes

1. Introduction:

• Flowering plants (Angiosperms) exhibit a vast range of structures.
• Morphology deals with the study of these external forms and features.
• A typical flowering plant consists of a Root System (usually underground) and a Shoot System (usually aerial).

2. The Root System:

• Develops from the elongation of the radicle of the embryo.
• Functions: Anchorage, absorption of water and minerals, storage of reserve food material, synthesis of plant growth regulators.
• Types of Root Systems:
  • Tap Root System: Primary root (direct elongation of radicle) grows deep into the soil, bearing lateral roots of several orders (secondary, tertiary, etc.). Characteristic of dicotyledonous plants (e.g., Mustard, Gram).
  • Fibrous Root System: Primary root is short-lived and replaced by numerous large roots originating from the base of the stem. Characteristic of monocotyledonous plants (e.g., Wheat, Grass).
  • Adventitious Roots: Roots arising from parts of the plant other than the radicle (e.g., from stem, leaves). Examples include grass, Monstera, banyan tree.
• Regions of the Root: (From apex upwards)
  • Root Cap: Thimble-like structure protecting the tender root apex. Secretes mucilage for lubrication.
  • Region of Meristematic Activity: Small region of actively dividing cells, just above the root cap.
  • Region of Elongation: Cells proximal to the meristematic region undergo rapid elongation and enlargement, responsible for root growth in length.
  • Region of Maturation: Cells differentiate and mature. Root hairs (unicellular epidermal extensions) arise from this region, increasing surface area for absorption.
• Modifications of Root: Roots modify to perform functions other than absorption and anchorage.
  • Storage: Tap roots (Carrot, Turnip), Adventitious roots (Sweet Potato).
  • Support:
    • Prop Roots: Hanging structures supporting branches (Banyan tree - Ficus benghalensis).
    • Stilt Roots: Supporting roots arising from lower nodes of the stem (Maize, Sugarcane).
  • Respiration: Pneumatophores (Respiratory roots) grow vertically upwards from roots in swampy areas to get oxygen (e.g., Rhizophora growing in mangroves).

3. The Shoot System:

• Consists of the stem, leaves, flowers, and fruits. Develops from the plumule of the embryo.

4. The Stem:

• Ascending part of the axis, bearing branches, leaves, flowers, and fruits.
• Characterized by the presence of nodes (regions where leaves arise) and internodes (portion between two nodes).
• Bears buds, which can be terminal (apical) or axillary (in the axil of leaves). Buds develop into branches or flowers.
• Functions: Spreading out branches; bearing leaves, flowers, fruits; conduction of water, minerals, and photosynthates; storage of food; support; protection; vegetative propagation.
• Modifications of Stem:
  • Underground Stems (Storage & Perennation):
    • Rhizome: Horizontal stem (Ginger, Turmeric).
    • Tuber: Swollen end of underground branch, has 'eyes' (axillary buds) (Potato).
    • Corm: Vertical, condensed stem (Zaminkand, Colocasia).
    • Bulb: Highly reduced stem with fleshy leaves (Onion, Garlic).
  • Sub-aerial Stems (Vegetative Propagation):
    • Runner: Creeping stems with long internodes (Grass, Strawberry).
    • Stolon: Slender lateral branch arising from base of main axis, arches downwards (Mint, Jasmine).
    • Offset: Lateral branch with short internodes, rosette of leaves above, tuft of roots below (Pistia, Eichhornia).
    • Sucker: Lateral branch originating from basal underground part, grows obliquely upwards (Banana, Pineapple, Chrysanthemum).
  • Aerial Stems (Specialized Functions):
    • Stem Tendrils: Slender, spirally coiled structures for climbing, develop from axillary buds (Gourds - cucumber, pumpkins, watermelon; Grapevines).
    • Thorns: Woody, straight, pointed structures for protection, modified axillary buds (Citrus, Bougainvillea).
    • Phylloclade: Flattened (Opuntia) or cylindrical (Euphorbia) green stems performing photosynthesis in arid regions (leaves reduced to spines). Contains chlorophyll.
    • Cladode: Green stem of limited growth (usually one internode long) performing photosynthesis (Asparagus - leaves reduced to scales). Note: NCERT uses Phylloclade for Asparagus too, but traditionally Cladode is used. Stick to NCERT examples.

5. The Leaf:

• Lateral, generally flattened structure borne on the stem at the node. Develops from the shoot apical meristem. Arranged in acropetal order (younger leaves at the apex).
• Main vegetative organ for photosynthesis.
• Parts of a Leaf:
  • Leaf Base: Attaches leaf to stem. May bear two lateral small leaf-like structures called stipules. In legumes, the leaf base may swell (pulvinus), responsible for sleep movements. In monocots, the leaf base expands into a sheath covering the stem partially or wholly.
  • Petiole: Stalk connecting the lamina to the stem. Allows lamina to flutter in wind (cooling, bringing fresh air).
  • Lamina (Leaf Blade): Green, expanded part with veins and veinlets. Midrib is the prominent central vein. Veins provide rigidity and act as channels for transport.
• Venation: Arrangement of veins and veinlets in the lamina.
  • Reticulate Venation: Veinlets form a network. Characteristic of dicots.
  • Parallel Venation: Veins run parallel to each other within the lamina. Characteristic of monocots.
• Types of Leaves:
  • Simple Leaf: Lamina is entire or incised, but incisions do not touch the midrib.
  • Compound Leaf: Incisions of the lamina reach up to the midrib (or petiole), breaking it into multiple leaflets.
    • Pinnately Compound: Leaflets present on a common axis called the rachis (represents midrib) (e.g., Neem).
    • Palmately Compound: Leaflets attached at a common point (tip of the petiole) (e.g., Silk Cotton).
• Phyllotaxy: Pattern of arrangement of leaves on the stem or branch.
  • Alternate: Single leaf arises at each node in an alternate manner (e.g., China rose, Mustard, Sunflower).
  • Opposite: Pair of leaves arise at each node, opposite to each other (e.g., Calotropis, Guava).
  • Whorled: More than two leaves arise at a node and form a whorl (e.g., Alstonia).
• Modifications of Leaves:
  • Tendrils: For climbing (e.g., Peas).
  • Spines: For defence, reduced surface area (e.g., Cacti).
  • Storage Leaves: Fleshy leaves store food (e.g., Onion, Garlic).
  • Phyllode: Petioles expand, become green and synthesise food (e.g., Australian Acacia).
  • Insectivorous Leaves: Modified to trap insects (e.g., Pitcher plant, Venus-fly trap).

6. The Inflorescence:

• Arrangement of flowers on the floral axis (peduncle).
• Types:
  • Racemose: Main axis continues to grow, flowers borne laterally in acropetal succession (older flowers at base, younger at apex). Indefinite growth.
  • Cymose: Main axis terminates in a flower, hence limited growth. Flowers borne in basipetal succession (older flower at apex, younger towards base).

7. The Flower:

• Reproductive unit in angiosperms, meant for sexual reproduction.
• A modified shoot where the shoot apical meristem changes to floral meristem. Internodes do not elongate, axis gets condensed.
• Borne on a stalk (pedicel) or sessile. Swollen end of pedicel is the thalamus or receptacle, upon which floral whorls are arranged.
• Floral Whorls: Calyx, Corolla, Androecium, Gynoecium.
  • Accessory Whorls: Calyx and Corolla (non-essential).
  • Essential Whorls: Androecium (male) and Gynoecium (female).
• Perianth: When calyx and corolla are not distinct (e.g., Lily). Individual units called tepals.
• Bracts: Reduced leaf found at the base of the pedicel. Flowers with bracts are bracteate, without are ebracteate.
• Symmetry:
  • Actinomorphic (Radial): Can be divided into two equal radial halves in any radial plane passing through the centre (e.g., Mustard, Datura, Chilli). Symbol: ⊕
  • Zygomorphic (Bilateral): Can be divided into two similar halves only in one particular vertical plane (e.g., Pea, Gulmohur, Bean, Cassia). Symbol: %
  • Asymmetric (Irregular): Cannot be divided into two similar halves by any vertical plane (e.g., Canna).
• Insertion of Floral Whorls on Thalamus (Ovary Position):
  • Hypogynous: Gynoecium occupies the highest position; other parts below it. Ovary is superior (e.g., Mustard, China Rose, Brinjal).
  • Perigynous: Gynoecium situated in the centre; other parts on the rim of the thalamus almost at the same level. Ovary is half-inferior (e.g., Plum, Rose, Peach).
  • Epigynous: Margin of thalamus grows upward enclosing the ovary completely and getting fused with it; other parts arise above the ovary. Ovary is inferior (e.g., Guava, Cucumber, Ray florets of Sunflower).
• Parts of a Flower:
  • Calyx: Outermost whorl, composed of sepals. Generally green, leaf-like, protective function in bud stage.
    • Gamosepalous: Sepals united.
    • Polysepalous: Sepals free.
  • Corolla: Composed of petals. Usually brightly coloured to attract insects for pollination.
    • Gamopetalous: Petals united.
    • Polypetalous: Petals free.
    • Shape varies: tubular, bell-shaped, funnel-shaped, wheel-shaped.
  • Aestivation: Mode of arrangement of sepals or petals in floral bud with respect to other members of the same whorl.
    • Valvate: Sepals/petals just touch each other at the margin, without overlapping (e.g., Calotropis).
    • Twisted: One margin overlaps the next one, and so on (e.g., China rose, Lady's finger, Cotton).
    • Imbricate: Margins overlap one another but not in any particular direction (e.g., Cassia, Gulmohur).
    • Vexillary (Papilionaceous): Five petals; largest (standard) overlaps two lateral petals (wings), which in turn overlap the two smallest anterior petals (keel) (e.g., Pea, Bean flowers - characteristic of Fabaceae family).
  • Androecium: Composed of stamens (male reproductive organ). Each stamen consists of a stalk (filament) and an anther (usually bilobed, each lobe having two chambers - pollen sacs containing pollen grains). A sterile stamen is called a staminode.
    • Adhesion (Union with other whorls):
      • Epipetalous: Stamens attached to petals (e.g., Brinjal).
      • Epiphyllous: Stamens attached to perianth (e.g., Lily).
    • Cohesion (Union among stamens):
      • Monadelphous: Stamens united into one bundle or tube (e.g., China rose).
      • Diadelphous: Stamens united into two bundles (e.g., Pea - 9+1).
      • Polyadelphous: Stamens united into more than two bundles (e.g., Citrus).
    • Variation in filament length within a flower (e.g., Salvia, Mustard).
  • Gynoecium: Female reproductive part, composed of one or more carpels. Each carpel has three parts: stigma (receptive surface for pollen), style (connects stigma to ovary), and ovary (enlarged basal part containing ovules).
    • Apocarpous: More than one carpel, free (e.g., Lotus, Rose).
    • Syncarpous: More than one carpel, fused (e.g., Mustard, Tomato).
    • Placentation: Arrangement of ovules within the ovary.
      • Marginal: Placenta forms a ridge along the ventral suture; ovules in two rows (e.g., Pea).
      • Axile: Placenta is axial; ovules attached in a multilocular ovary (e.g., China rose, Tomato, Lemon).
      • Parietal: Ovules develop on inner wall of ovary or peripheral part. Ovary one-chambered but becomes two-chambered due to false septum (replum) (e.g., Mustard, Argemone).
      • Free Central: Ovules borne on central axis; septa absent (e.g., Dianthus, Primrose).
      • Basal: Placenta develops at the base of ovary; single ovule attached (e.g., Sunflower, Marigold).

8. The Fruit:

• Mature or ripened ovary, developed after fertilisation. Characteristic feature of flowering plants.
• If formed without fertilisation, it is parthenocarpic (e.g., Banana).
• Consists of pericarp (fruit wall) and seeds.
• Pericarp may be dry or fleshy. If fleshy, differentiated into outer epicarp, middle mesocarp, and inner endocarp.
• Types (Focus on NCERT examples):
  • Drupe: Develops from monocarpellary superior ovary, one-seeded. Pericarp differentiated into thin epicarp, fleshy mesocarp, stony hard endocarp (e.g., Mango, Coconut). In coconut, mesocarp is fibrous.
  • Other types exist (Berry, Pepo, Hesperidium, Pome, Legume, Capsule, Caryopsis etc.) but Drupe is detailed in NCERT Ch 5.

9. The Seed:

• Final product of sexual reproduction, fertilised ovule. Made up of a seed coat and an embryo.
• Embryo: Consists of an embryonal axis and one (monocotyledons - e.g., Wheat, Maize) or two (dicotyledons - e.g., Gram, Pea) cotyledons.
• Seed Coat: Outer protective layer, developed from ovule integuments. Has outer testa and inner tegmen. Hilum is a scar where seed was attached to fruit. Micropyle is a small pore above hilum.
• Endosperm: Food-storing tissue formed during double fertilisation.
  • Albuminous/Endospermic Seed: Retain endosperm at maturity (e.g., Wheat, Maize, Barley, Castor, Coconut, Sunflower).
  • Non-albuminous/Exalbuminous Seed: Endosperm completely consumed during development; food stored in cotyledons (e.g., Pea, Groundnut, Bean).
• Structure of Dicotyledonous Seed (e.g., Bean, Gram): Seed coat, hilum, micropyle. Embryo: embryonal axis (with plumule and radicle) and two fleshy cotyledons.
• Structure of Monocotyledonous Seed (e.g., Maize): Seed coat fused with fruit wall (pericarp). Bulky endosperm. Embryo small, situated in a groove at one end of endosperm. Consists of one large, shield-shaped cotyledon (scutellum), and a short axis with plumule (covered by coleoptile) and radicle (covered by coleorhiza). Aleurone layer: Proteinaceous layer separating embryo from endosperm.

10. Semi-Technical Description of a Typical Flowering Plant:

• Requires specific symbols and a sequence (Floral Formula and Floral Diagram - though detailed family descriptions are later, the concept is introduced).
• Symbols: Br (bracteate), K (calyx), C (corolla), P (perianth), A (androecium), G (gynoecium), G (superior ovary), G (inferior ovary), ♂ (male), ♀ (female), ⚥ (bisexual), ⊕ (actinomorphic), % (zygomorphic). Fusion indicated by brackets (), adhesion by a line above symbols.

Importance: Understanding morphology is fundamental for plant identification, classification, and understanding evolutionary relationships and adaptations.

Multiple Choice Questions (MCQs):

1. Which type of root system is characteristic of most dicotyledonous plants?
   a) Fibrous root system
   b) Adventitious root system
   c) Tap root system
   d) Prop root system

2. Pneumatophores are modifications of roots found in plants growing in:
   a) Desert areas
   b) Swampy areas
   c) Temperate regions
   d) Alpine regions

3. A potato tuber is a modified:
   a) Root for storage
   b) Stem for storage
   c) Leaf for storage
   d) Fruit

4. Phyllotaxy refers to the arrangement of:
   a) Flowers on the floral axis
   b) Veins in the leaf lamina
   c) Leaves on the stem
   d) Ovules in the ovary

5. In a flower with a superior ovary (hypogynous condition), the gynoecium is located:
   a) Below all other floral whorls
   b) At the same level as other floral whorls
   c) Above all other floral whorls
   d) Enclosed completely by the thalamus

6. Vexillary aestivation, characterized by standard, wings, and keel petals, is typically found in the flowers of:
   a) China rose
   b) Pea
   c) Mustard
   d) Lily

7. When stamens are united into more than two bundles, the condition is called:
   a) Monadelphous
   b) Diadelphous
   c) Polyadelphous
   d) Epipetalous

8. Axile placentation is observed in:
   a) Pea and Bean
   b) Mustard and Argemone
   c) Dianthus and Primrose
   d) China rose, Tomato, and Lemon

9. The edible part of a mango fruit is the:
   a) Epicarp
   b) Mesocarp
   c) Endocarp
   d) Seed

10. In a maize grain (monocot seed), the proteinaceous layer separating the embryo from the endosperm is called the:
    a) Scutellum
    b) Coleoptile
    c) Coleorhiza
    d) Aleurone layer

Answer Key:

1. c) Tap root system
2. b) Swampy areas
3. b) Stem for storage
4. c) Leaves on the stem
5. c) Above all other floral whorls
6. b) Pea
7. c) Polyadelphous
8. d) China rose, Tomato, and Lemon
9. b) Mesocarp
10. d) Aleurone layer

Study these notes thoroughly. Focus on the definitions, types, modifications, and especially the examples provided, as they are frequently asked. Good luck with your preparation!