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Morphology of Flowering Plants - Biology Chapter 5

Morphology of Flowering Plants

Explore the structural organization and diverse forms of flowering plants through their roots, stems, leaves, flowers, and fruits.

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Chapter Overview

Brief Introduction

Angiosperms (flowering plants) show enormous diversity in external structure or morphology, yet all are characterized by roots, stems, leaves, flowers and fruits. This chapter explores the standard technical terms and definitions used to describe these structures and their possible variations as adaptations to different environments.

Learning Objectives

  • Understand the morphology of different plant parts
  • Identify root systems and their modifications
  • Study stem characteristics and their adaptations
  • Analyze leaf structure and venation patterns
  • Explore flower structure and inflorescence types
  • Learn about fruit and seed morphology

Key Topics Covered

  • The Root System
  • Stem Structure and Modifications
  • Leaf Morphology and Phyllotaxy
  • Inflorescence Types
  • Flower Structure and Symmetry
  • Fruit Types and Seed Structure
  • Description of Important Families
  • Floral Diagrams and Formulas

Interactive Chapter Index

The Root System

Explore the underground part of flowering plants, its regions, and different types of root systems.

The Stem

Study the ascending part of the plant axis that bears branches, leaves, flowers and fruits.

The Leaf

Understand leaf structure, venation patterns, types, and phyllotaxy arrangements.

The Inflorescence

Learn about the arrangement of flowers on the floral axis in racemose and cymose patterns.

The Flower

Discover the reproductive unit of angiosperms with its four whorls and various symmetries.

The Fruit and Seed

Examine the mature ovary and its development into different fruit types with seeds.

Full Chapter Notes

5.1 The Root

The root is the underground part of the flowering plant that forms the root system. Roots originate from the radicle of the embryo and have several important functions including absorption of water and minerals, anchorage, storage of food, and synthesis of plant growth regulators.

Types of Root Systems:

  • Tap root system: Found in dicots, develops from the radicle (primary root) with secondary and tertiary branches (mustard plant)
  • Fibrous root system: Found in monocots, primary root is short-lived and replaced by numerous roots from the stem base (wheat plant)
  • Adventitious roots: Roots arising from parts other than the radicle (grass, Monstera, banyan tree)
Types of Root Systems
Figure 5.2: Different types of roots: (a) Tap (b) Fibrous (c) Adventitious

Regions of the Root:

  1. Root cap: Thimble-like structure protecting the tender apex
  2. Region of meristematic activity: Small cells with dense protoplasm that divide repeatedly
  3. Region of elongation: Cells undergo rapid growth increasing root length
  4. Region of maturation: Cells differentiate and mature, some form root hairs for absorption
Q: What are the main differences between tap root and fibrous root systems?

5.2 The Stem

The stem is the ascending part of the axis bearing branches, leaves, flowers and fruits. It develops from the plumule of the embryo and is characterized by nodes and internodes. Stems are generally green when young and often become woody and dark brown with age.

Key Features of Stems:

  • Bears nodes (points where leaves are born) and internodes (portions between nodes)
  • Contains buds (terminal or axillary) that may develop into branches
  • Main functions include spreading branches, conducting water and minerals, photosynthesis (in young stems), storage, support, and vegetative propagation
Note: The stem can be distinguished from roots by the presence of nodes and internodes, multicellular hairs, and being positively phototropic (grows toward light).
Q: How can you distinguish a stem from a root based on morphological features?

5.3 The Leaf

The leaf is a lateral, generally flattened structure borne on the stem at nodes. It develops from shoot apical meristems and is arranged in an acropetal order (older at base, younger at tip). Leaves are the most important vegetative organs for photosynthesis.

Parts of a Leaf:

  • Leaf base: Attaches leaf to stem, may have stipules (small leaf-like structures)
  • Petiole: Stalk that holds the blade to light, allows fluttering
  • Lamina (blade): Green expanded part with veins and veinlets, including midrib
Structure of a Leaf
Figure 5.4: Structure of a leaf: (a) Parts of a leaf (b) Reticulate venation (c) Parallel venation

Venation Patterns:

  • Reticulate: Veinlets form a network (most dicots)
  • Parallel: Veins run parallel to each other (most monocots)

Types of Leaves:

  • Simple leaf: Lamina is entire or incisions don't reach midrib
  • Compound leaf: Incisions reach midrib, breaking it into leaflets
    • Pinnately compound: Leaflets present on common axis (rachis) like neem
    • Palmately compound: Leaflets attached at common point like silk cotton

Phyllotaxy (Leaf Arrangement):

  • Alternate: Single leaf at each node (mustard, sunflower)
  • Opposite: Pair of leaves at each node (Calotropis, guava)
  • Whorled: More than two leaves at node forming whorl (Alstonia)
Q: How is a pinnately compound leaf different from a palmately compound leaf?

5.4 The Inflorescence

An inflorescence is the arrangement of flowers on the floral axis. A flower is a modified shoot where the shoot apical meristem changes to floral meristem. When a shoot tip transforms into a single flower, it is called solitary.

Types of Inflorescence:

  • Racemose: Main axis continues to grow, flowers borne laterally in acropetal succession (youngest at top)
  • Cymose: Main axis terminates in a flower, growth limited, flowers in basipetal order (youngest at base)
Types of Inflorescence
Figure 5.7: Racemose and cymose inflorescence patterns
Q: Differentiate between racemose and cymose inflorescence.

5.5 The Flower

The flower is the reproductive unit in angiosperms, meant for sexual reproduction. A typical flower has four whorls arranged on the thalamus or receptacle: calyx, corolla, androecium (male), and gynoecium (female).

Flower Characteristics:

  • Symmetry:
    • Actinomorphic (radial) - can be divided into equal halves in any radial plane (mustard, datura)
    • Zygomorphic (bilateral) - can be divided into similar halves only in one plane (pea, gulmohur)
    • Asymmetric - cannot be divided into equal halves (canna)
  • Floral appendages: Trimerous (3), tetramerous (4), or pentamerous (5)
  • Bracts: Reduced leaf at base of pedicel (bracteate or ebracteate)
Parts of a Flower
Figure 5.10: Parts of a flower

Position of Floral Parts:

  • Hypogynous: Gynoecium occupies highest position, ovary superior (mustard, brinjal)
  • Perigynous: Gynoecium at center, other parts on rim at same level, ovary half inferior (plum, rose)
  • Epigynous: Thalamus encloses ovary completely, ovary inferior (guava, cucumber)

Parts of a Flower:

  1. Calyx: Outermost whorl of sepals (green, protective)
    • Gamosepalous (united) or polysepalous (free)
  2. Corolla: Whorl of petals (brightly colored to attract pollinators)
    • Gamopetalous (united) or polypetalous (free)
    • Shapes: tubular, bell-shaped, funnel-shaped, wheel-shaped
  3. Androecium: Male reproductive part (stamens)
    • Each stamen has filament and bilobed anther with pollen sacs
    • May be epipetalous (attached to petals) or epiphyllous (attached to perianth)
    • Union types: monadelphous (one bundle), diadelphous (two bundles), polyadelphous (many bundles)
  4. Gynoecium: Female reproductive part (carpels)
    • Each carpel has stigma, style and ovary
    • Apocarpous (free carpels) or syncarpous (fused carpels)
    • Placentation types: marginal, axile, parietal, basal, central, free central
Q: What are the different types of placentation found in flowering plants?

5.6 The Fruit and Seed

The fruit is a mature or ripened ovary, developed after fertilization. If formed without fertilization, it's called parthenocarpic fruit. The fruit consists of a wall (pericarp) and seeds.

Fruit Structure:

  • Pericarp: Fruit wall, may be dry or fleshy
    • Fleshy pericarp differentiated into epicarp (outer), mesocarp (middle), endocarp (inner)
  • Drupe: Develops from monocarpellary superior ovary, one-seeded (mango, coconut)
    • Mango: Distinct epicarp, fleshy mesocarp, stony endocarp
    • Coconut: Fibrous mesocarp

Seed Structure:

Ovules develop into seeds after fertilization. A seed consists of a seed coat and embryo.

  • Dicotyledonous seed:
    • Seed coat with testa (outer) and tegmen (inner)
    • Hilum (scar) and micropyle (pore)
    • Embryo with two cotyledons, embryonal axis, radicle and plumule
    • May be non-endospermous (bean, pea) or endospermic (castor)
  • Monocotyledonous seed:
    • Generally endospermic (except orchids)
    • Seed coat fused with fruit wall in cereals (maize)
    • Endosperm with aleurone layer
    • Embryo with one cotyledon (scutellum), plumule (covered by coleoptile), radicle (covered by coleorhiza)
Q: Compare the structure of dicot and monocot seeds.

5.8 Semi-technical Description of a Typical Flowering Plant

Flowering plants are described using a standard sequence of morphological features:

  1. Habit (herb, shrub, tree, etc.)
  2. Vegetative characters (root, stem, leaf)
  3. Floral characters (inflorescence, flower parts)
  4. Floral diagram and formula

Floral Formula Symbols:

  • Br: Bracteate
  • K: Calyx
  • C: Corolla
  • P: Perianth
  • A: Androecium
  • G: Gynoecium
  • G̲: Inferior ovary
  • ♂: Male
  • ♀: Female
  • ⚥: Bisexual
  • ✳: Actinomorphic
  • ↓: Zygomorphic

Fusion indicated by brackets, adhesion by line above symbols.

Floral Diagram and Formula
Figure 5.16: Floral diagram with floral formula (example: Brassicaceae family)

5.9 Description of Some Important Families

The Solanaceae family (potato family) is widely distributed in tropics, subtropics and temperate zones.

Solanaceae Characteristics:

  • Vegetative:
    • Plants mostly herbs, shrubs, rarely small trees
    • Stems: herbaceous, aerial, erect, branched
    • Leaves: alternate, simple, exstipulate, reticulate venation
  • Floral:
    • Inflorescence: solitary or cymose
    • Flower: bisexual, actinomorphic
    • Calyx: 5 united sepals, persistent
    • Corolla: 5 united petals
    • Androecium: 5 stamens, epipetalous
    • Gynoecium: bicarpellary, syncarpous, superior ovary, axile placentation
    • Fruit: berry or capsule
    • Floral formula: ⚥ ✳ K(5) C(5) A5 G(2)
  • Economic importance: Food (tomato, potato), spice (chilli), medicine (belladonna), ornamentals (petunia)
Solanum nigrum plant
Figure 5.17: Solanum nigrum (makoi) plant showing flowering twig, flower, and floral parts

Chapter Summary

Key Takeaways:

  • Flowering plants show enormous variation in shape, size, structure and habitat
  • Root system is either tap root (dicots) or fibrous (monocots), with various modifications
  • Stems bear nodes and internodes, with various adaptations for different functions
  • Leaves show variation in shape, size, margin, apex and venation patterns
  • Flowers are modified shoots arranged in inflorescences (racemose or cymose)
  • Flower symmetry can be actinomorphic, zygomorphic or asymmetric
  • Fruits develop from ovary, seeds from ovules after fertilization
  • Floral characteristics form basis for classification and identification

NCERT Solutions

Question 1: How is a pinnately compound leaf different from a palmately compound leaf?

A pinnately compound leaf differs from a palmately compound leaf in the following ways:

Feature Pinnately Compound Palmately Compound
Arrangement Leaflets arranged on a common axis (rachis) Leaflets attached at a common point (tip of petiole)
Midrib Rachis represents the midrib No rachis present
Examples Neem Silk cotton

Question 2: Explain with suitable examples the different types of phyllotaxy.

Phyllotaxy refers to the pattern of arrangement of leaves on the stem or branch. The three main types are:

  1. Alternate: A single leaf arises at each node in alternate manner.
    • Example: China rose, mustard, sunflower
  2. Opposite: A pair of leaves arise at each node and lie opposite to each other.
    • Example: Calotropis, guava
  3. Whorled: More than two leaves arise at a node and form a whorl.
    • Example: Alstonia

Question 3: Define the following terms: (a) aestivation (b) placentation (c) actinomorphic (d) zygomorphic (e) superior ovary (f) perigynous flower (g) epipetalous stamen

  1. Aestivation: The mode of arrangement of sepals or petals in floral bud with respect to other members of same whorl.
  2. Placentation: The arrangement of ovules within the ovary.
  3. Actinomorphic: Flowers that can be divided into two equal radial halves in any radial plane passing through center (radial symmetry).
  4. Zygomorphic: Flowers that can be divided into two similar halves only in one particular vertical plane (bilateral symmetry).
  5. Superior ovary: Ovary that occupies the highest position in hypogynous flowers, with other floral parts below it.
  6. Perigynous flower: Flower where gynoecium is situated in center and other parts on rim of thalamus at same level (ovary half inferior).
  7. Epipetalous stamen: Stamens attached to petals (e.g., brinjal).

Question 4: Differentiate between (a) Racemose and cymose inflorescence (b) Apocarpous and syncarpous ovary

(a) Differences between racemose and cymose inflorescence:

Feature Racemose Cymose
Main axis growth Unlimited (indeterminate) Limited (determinate)
Flower arrangement Acropetal (youngest at top) Basipetal (youngest at base)
Opening sequence From base to apex From apex to base

(b) Differences between apocarpous and syncarpous ovary:

Feature Apocarpous Syncarpous
Carpels Free from each other Fused together
Ovary chambers Multiple (equal to number of carpels) Single or divided into locules
Examples Lotus, rose Mustard, tomato

Question 5: Draw the labelled diagram of the following: (i) gram seed (ii) V.S. of maize seed

(i) Gram seed (dicotyledonous seed):

  • Seed coat with testa and tegmen
  • Hilum and micropyle visible
  • Embryo with two large cotyledons
  • Embryonal axis with plumule and radicle

(ii) V.S. of maize seed (monocotyledonous seed):

  • Seed coat fused with fruit wall
  • Large endosperm with aleurone layer
  • Embryo with single shield-shaped cotyledon (scutellum)
  • Plumule covered by coleoptile, radicle by coleorhiza

Question 6: Take one flower of the family Solanaceae and write its semi-technical description. Also draw their floral diagram.

Semi-technical description of Datura (Solanaceae):

  1. Habit: Herbaceous plant
  2. Root: Tap root system
  3. Stem: Erect, branched, herbaceous
  4. Leaf: Simple, alternate, exstipulate, reticulate venation
  5. Inflorescence: Solitary and axillary
  6. Flower:
    • Bracteate, bisexual, actinomorphic, hypogynous
    • Calyx: 5 sepals, gamosepalous, valvate aestivation
    • Corolla: 5 petals, gamopetalous, plicate aestivation
    • Androecium: 5 stamens, epipetalous, alternate to petals
    • Gynoecium: Bicarpellary, syncarpous, superior ovary, axile placentation
  7. Fruit: Spiny capsule

Floral formula: ⚥ ✳ K(5) C(5) A5 G(2)

Question 7: Describe the various types of placentations found in flowering plants.

The main types of placentation are:

  1. Marginal: Placenta forms ridge along ventral suture, ovules borne in two rows (pea)
  2. Axile: Placenta axial, ovules attached to it in multilocular ovary (china rose, tomato)
  3. Parietal: Ovules develop on inner wall of ovary, one-chambered becomes two-chambered by false septum (mustard)
  4. Basal: Placenta develops at base of ovary, single ovule (sunflower)
  5. Free central: Ovules borne on central axis, septa absent (Dianthus, Primrose)

Question 8: What is a flower? Describe the parts of a typical angiosperm flower.

Flower: The flower is the reproductive unit in angiosperms, meant for sexual reproduction. It is a modified shoot where the shoot apical meristem changes to floral meristem.

Parts of a typical angiosperm flower:

  1. Calyx: Outermost whorl of sepals, usually green, protective function
  2. Corolla: Whorl of petals, usually brightly colored to attract pollinators
  3. Androecium: Male reproductive part consisting of stamens
    • Each stamen has filament and anther (with pollen sacs producing pollen)
  4. Gynoecium: Female reproductive part consisting of carpels
    • Each carpel has stigma (receives pollen), style (connects stigma to ovary), and ovary (contains ovules)

These parts are arranged on the thalamus or receptacle. Flowers may be bisexual (both androecium and gynoecium) or unisexual (only one reproductive whorl).

Question 9: Define the term inflorescence. Explain the basis for the different types of inflorescence in flowering plants.

Inflorescence: The arrangement of flowers on the floral axis is termed as inflorescence.

Basis for different types: Inflorescences are classified based on:

  1. Growth pattern of main axis:
    • Racemose: Main axis continues to grow indefinitely, producing flowers laterally
    • Cymose: Main axis terminates in a flower, limiting growth
  2. Sequence of flower opening:
    • Acropetal: Older flowers at base, younger at apex (racemose)
    • Basipetal: Older flowers at apex, younger at base (cymose)
  3. Position of flowers:
    • Terminal or axillary
    • Solitary or clustered

Question 10: Describe the arrangement of floral members in relation to their insertion on thalamus.

Based on the position of floral parts (calyx, corolla, androecium) in relation to the ovary on thalamus, flowers are of three types:

  1. Hypogynous:
    • Gynoecium occupies highest position
    • Other parts situated below it
    • Ovary superior
    • Example: Mustard, brinjal
  2. Perigynous:
    • Gynoecium situated in center
    • Other parts on rim of thalamus at same level
    • Ovary half inferior
    • Example: Plum, rose
  3. Epigynous:
    • Thalamus margin grows upward enclosing ovary completely
    • Other parts arise above ovary
    • Ovary inferior
    • Example: Guava, cucumber

Practice Questions

1. Which of the following is NOT a characteristic of the root?

Correct Answer: c) Presence of nodes and internodes

Explanation: Nodes and internodes are characteristic of stems, not roots. Roots have root cap, region of meristematic activity, elongation zone, maturation zone, and may form root hairs.

2. The type of placentation seen in tomato is:

Correct Answer: b) Axile

Explanation: Tomato has axile placentation where the placenta is axial and ovules are attached to it in a multilocular ovary. This is characteristic of the Solanaceae family.

3. Which of the following represents the floral formula of family Solanaceae?

Correct Answer: b) ⚥ ✳ K(5) C(5) A5 G(2)

Explanation: The Solanaceae family has bisexual (⚥), actinomorphic (✳) flowers with 5 united sepals (K(5)), 5 united petals (C(5)), 5 stamens (A5), and bicarpellary syncarpous superior ovary (G(2)).

1. What are adventitious roots? Give two examples of plants with adventitious roots.

Answer:

Adventitious roots are roots that arise from parts of the plant other than the radicle. They may develop from stems, leaves or other plant parts.

Examples:

  1. Grass - roots arise from the base of stem
  2. Banyan tree - roots arise from branches and grow downward
  3. Monstera - aerial roots arise from nodes
2. Differentiate between reticulate and parallel venation with examples.

Answer:

Feature Reticulate Venation Parallel Venation
Pattern Veinlets form a network Veins run parallel to each other
Plant type Dicotyledonous plants Monocotyledonous plants
Examples Mango, rose, sunflower Grass, wheat, maize
1. Describe the various modifications of roots in plants with suitable examples.

Answer:

Roots undergo various modifications to perform specialized functions other than absorption and anchorage:

  1. Storage roots: Become swollen to store food
    • Tap root: Conical (carrot), fusiform (radish), napiform (turnip)
    • Adventitious roots: Tuberous (sweet potato)
  2. Respiratory roots (pneumatophores): Grow upward above ground for respiration in waterlogged soils (mangroves like Rhizophora)
  3. Prop roots: Adventitious roots that provide additional support (banyan, maize)
  4. Stilt roots: Adventitious roots arising from lower nodes for support (sugarcane, Pandanus)
  5. Climbing roots: Help plant climb (ivy, money plant)
  6. Parasitic roots (haustoria): Penetrate host plant to absorb nutrients (Cuscuta)
  7. Nodular roots: Have nitrogen-fixing bacteria (legumes like pea, gram)
  8. Photosynthetic roots: Green roots that perform photosynthesis (Tinospora, orchids)
2. Describe the structure of a typical flower with a neat labeled diagram. Explain the different types of symmetry found in flowers.

Answer:

Structure of a typical flower:

A typical flower has four whorls arranged on the thalamus:

  1. Calyx: Outermost whorl of sepals, usually green, protective
  2. Corolla: Whorl of petals, usually brightly colored to attract pollinators
  3. Androecium: Male reproductive part consisting of stamens
    • Each stamen has filament (stalk) and anther (produces pollen)
  4. Gynoecium: Female reproductive part consisting of carpels
    • Each carpel has stigma (receives pollen), style (connector), and ovary (contains ovules)

The flower is attached to the stem by pedicel. The swollen end of pedicel is called thalamus or receptacle.

Types of flower symmetry:

  1. Actinomorphic (radial symmetry):
    • Can be divided into two equal radial halves in any radial plane passing through center
    • Example: Mustard, datura, chilli
  2. Zygomorphic (bilateral symmetry):
    • Can be divided into two similar halves only in one particular vertical plane
    • Example: Pea, gulmohur, bean
  3. Asymmetric (irregular):
    • Cannot be divided into two similar halves by any vertical plane
    • Example: Canna

Interactive Flashcards

What are the main types of root systems in flowering plants?

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The three main types are:

  1. Tap root system: Develops from radicle with primary, secondary and tertiary roots (dicots like mustard)
  2. Fibrous root system: Primary root short-lived, replaced by many roots from stem base (monocots like wheat)
  3. Adventitious roots: Arise from parts other than radicle (grass, banyan tree)
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