NEET Biology - Unit 2- Morphology and modifications- Study Notes - New Syllabus

Morphology and Modifications of Flowering Plants

📌 Introduction

The term morphology is derived from Ancient Greek:

• Morphe meaning form
• Logos meaning study

Morphology is the study of:

• External form of plants
• Internal structure of plants
• Ontogenic development of the plant body and its organs

Flowering plants are terrestrial organisms and live in two contrasting environments:

• Below the ground → water and mineral absorption
• Above the ground → light and CO₂ absorption

To efficiently acquire these resources, plants evolved three basic organs:

• Root
• Stem
• Leaf

These organs together form:

• Root system → develops from radicle of seed
• Shoot system → develops from plumule of seed

🌿 The Root

📌 Definition

The root is a plant organ that:

• Anchors the plant in soil
• Absorbs water and minerals
• Often stores food materials

🌱 Types of Root Systems

1. Tap Root System

• Found in dicot plants
• Develops from elongation of radicle
• Primary root gives rise to secondary and lateral roots
• Helps in strong anchorage
• Example: Mustard

2. Fibrous Root System

• Found in monocot plants
• Primary root dies early
• Many roots arise from base of stem
• Roots are adventitious
• Example: Wheat, maize

🔄 Modification of Roots

Roots may modify to perform special functions other than absorption.

For Support 

• Buttress roots → large trees in tropical regions
• Stilt roots → maize
• Prop roots → banyan tree

For Storage of Food

Tap roots of:

• Carrot
• Turnip

Adventitious roots of:

• Sweet potato

For Respiration

• Pneumatophores or air roots
• Found in mangroves
• Grow vertically upward to absorb oxygen

🌾 The Stem

Definition

• Develops from plumule
• Bears nodes and internodes
• Supports leaves, flowers, and fruits

Functions of Stem

• Supports aerial plant parts
• Positions leaves for maximum photosynthesis
• Helps in pollination and fruit dispersal

Modification of Stem

Stems may modify for:

• Storage
• Vegetative reproduction

Examples of modified stems:

• Rhizome
• Stolon
• Tuber

These are often mistaken as roots but are actually modified shoots.

🍃 The Leaf

Definition

The leaf is the main photosynthetic organ of vascular plants.

Features of Leaf

• Arises from node
• Bears a bud in its axil
• Developed from apical meristem
• Arranged in acropetal order

Structure of Leaf

• Lamina → flat blade
• Petiole → stalk connecting leaf to stem

Venation

Arrangement of veins in leaf:

Phyllotaxy

Arrangement of leaves on stem:

• Alternate
• Opposite
• Whorled

Modification of Leaves

Leaves may modify for special functions:

• Tendrils → climbing (pea)
• Spines → protection (cactus)
• Fleshy leaves → storage (onion, garlic)
• Insectivorous leaves → nutrition (pitcher plant, Venus flytrap)

🌸 The Flower

Definition

• Shoot apical meristem becomes floral meristem
• Leaves are replaced by floral parts

Flower is the reproductive unit of angiosperms.

Structure of Flower

• Pedicel → stalk of flower
• Receptacle (Thalamus) → swollen part bearing floral whorls

Floral Whorls

1. Calyx

• Outermost whorl
• Made of sepals
• Gamosepalous → fused
• Polysepalous → free

2. Corolla

• Made of petals
• Brightly colored
• Gamopetalous → fused
• Polypetalous → free

3. Androecium

• Male reproductive part
• Made of stamens

Each stamen has:

• Filament
• Anther

4. Gynoecium

• Female reproductive part
• Made of carpels

Each carpel has:

• Stigma
• Style
• Ovary

Aestivation: Arrangement of sepals or petals in floral bud with respect to other members of the same whorl.

Inflorescence: Arrangement of flowers on floral axis is called inflorescence.

🍎 The Fruit 

Definition

A fruit is a mature ovary formed after fertilization.

Fruit formed without fertilization → Parthenocarpic fruit

Fruit Development

• Ovary wall becomes pericarp
• Pericarp may be:
  • Dry
  • Fleshy

🌰 The Seed

Definition

The ovule after fertilization develops into a seed.

Seed Structure

• Seed coat
• Embryo, consisting of:
  • Radicle
  • Embryonal axis
  • One or two cotyledons

📐 Floral Diagram and Floral Formula

📌 Importance

Used to describe a flowering plant in a short and systematic manner.

Plant description includes:

• • Habit
  • Vegetative characters
  • Floral characters
  • Floral diagram and floral formula use standard symbols to represent flower structure.

Symbols and their description in floral formula

📦 Quick Recap 
Morphology studies form and structure of plants
Root, stem, and leaf are basic organs
Roots modify for support, storage, respiration
Stems modify for storage and reproduction
Leaves modify for protection, climbing, nutrition
Flower is reproductive organ
Fruit develops from ovary
Seed develops from ovule
Floral diagram and formula simplify plant description