Anatomy of Flowering Plants: Class 11 NCERT Complete Guide

Introduction to Anatomy of Flowering Plants

Anatomy of flowering plants studies the internal structure of their organs like roots, stems, and leaves. Class 11 NCERT covers these in detail to help students understand how plants perform vital functions such as transport, support, and photosynthesis.

Key plant tissues include:

• Parenchyma: Fundamental tissue with thin walls and intercellular spaces.
• Collenchyma: Provides flexible support.
• Sclerenchyma: Offers mechanical strength.
• Xylem: Conducts water and minerals.
• Phloem: Transports food from leaves to other parts.

Understanding these tissues lays the foundation for studying plant physiology and growth.

Structure and Function of Stomata

Stomata are tiny pores mainly found on the epidermis of leaves but also on stems and other aerial parts. Each stoma is bordered by two guard cells that regulate its opening and closing, controlling gas exchange and transpiration.

• Guard cells shape: Bean-shaped in dicots, dumb-bell shaped in monocots.
• Chloroplasts: Present in guard cells, aiding in turgor changes.
• Opening mechanism: Guard cells absorb water, become turgid, and curve to open the pore.
• Closing mechanism: Loss of water makes guard cells flaccid, closing the pore.

This regulation balances CO2 intake for photosynthesis and water loss through transpiration, crucial for plant survival.

Diagram:

Vascular Bundles: Open vs Closed

Vascular bundles are the transport systems in plants, consisting of xylem and phloem tissues. They are classified as open or closed based on the presence of cambium.

• Open vascular bundles: Have cambium between xylem and phloem, allowing secondary growth. Found in dicot stems.
• Closed vascular bundles: Lack cambium, so no secondary growth. Found in monocot stems.

This distinction helps identify plant types and understand their growth patterns.

Secondary Growth in Dicot Stems

Secondary growth increases the girth of stems and roots and is typical in dicots. It occurs due to the activity of lateral meristems like the vascular cambium and cork cambium.

• Vascular cambium: Produces secondary xylem (wood) inward and secondary phloem outward.
• Cork cambium: Produces cork cells, forming the protective outer bark.

Annual rings: Formed by variations in xylem growth during seasons, visible in cross-sections of woody stems. Counting these rings estimates the plant's age.

Worked example: If a tree shows 50 dark and 50 light rings, its age is calculated as:

$$ \text{Age} = \frac{50 + 50}{2} = 50 \text{ years} $$

This growth is absent in monocots, which lack cambium.

Phloem: Structure and Function

Phloem is the conducting tissue responsible for transporting food from leaves to other parts of the plant. It consists of:

• Sieve tubes: Long tubes with sieve plates for food conduction.
• Companion cells: Assist sieve tubes with metabolic functions.
• Phloem parenchyma and fibers: Provide support and storage.

Note: Gymnosperms lack sieve tubes and companion cells, differing from angiosperms.

Phloem transport is bidirectional and driven by pressure flow, essential for distributing nutrients and supporting growth.

Parenchyma Tissue Characteristics

Parenchyma is the most common plant tissue, characterized by:

• Isodiametric cells with thin, cellulose walls.
• Loosely packed arrangement with intercellular spaces.
• Functions include storage, photosynthesis, and wound repair.

Parenchyma cells retain the ability to divide and differentiate, playing a vital role in plant growth and healing.