Anatomy of Flowering Plants 🌿 - Biology Class 11th - Handwritten Notes 📖 [PDF]📚

Anatomy of flowering plants deals with the internal structure of plant organs such as roots, stems, and leaves. It helps us understand tissue organization, adaptations, and functional modifications that enable survival and growth.

Plant Tissues

1. Meristematic Tissues

Definition: Groups of undifferentiated, actively dividing cells that form new tissues.

Characteristics

• Thin cell wall, dense cytoplasm, prominent nucleus.
• No intercellular spaces, vacuoles absent or small.
• Responsible for growth.

Types (Based on Position)

1. Apical meristem: At tips of roots and shoots; causes primary growth.
2. Intercalary meristem: At internodes/base of leaves (e.g., grasses); responsible for regrowth.
3. Lateral meristem: Along sides (cambium, cork cambium); responsible for secondary growth.

Types (Based on Origin)

• Protoderm → epidermis.
• Procambium → vascular tissue.
• Ground meristem → ground tissue (cortex, pith).

2. Permanent Tissues

Formed after meristematic tissues lose the power of division and differentiate.

(A) Simple Permanent Tissue

Made of similar cells.

1. Parenchyma

• Living, thin-walled, intercellular spaces present.
• Functions: storage, photosynthesis, secretion.
• Modified forms: Aerenchyma (air spaces in aquatic plants), Chlorenchyma (contains chlorophyll).

2. Collenchyma

• Living, thickened at corners (cellulose + pectin).
• Provides flexibility + mechanical support.
• Found in petiole and margin of dicot leaves.

3. Sclerenchyma

• Dead, thick lignified walls, no protoplasm.
• Types: Fibres (elongated), Sclereids (irregular, e.g., in nutshells).
• Provides mechanical strength.

(B) Complex Permanent Tissue

Made of different types of cells working together.

Xylem (water conduction)

Compongnts:

• Tracheids – elongated, dead, with pits.
• Vessels – tubular, dead, main water-conducting element in angiosperms.
• Xylem fibres – support.
• Xylem parenchyma – living, stores food.
• Direction of flow: unidirectional (roots → stem → leaves).

Phloem (food conduction)

Components:

• Sieve tube elements – elongated, sieve plates at ends.
• Companion cells – living, control sieve tube activity.
• Phloem parenchyma – storage.
• Phloem fibres – support (dead).

Direction of flow: bidirectional (up & down the plant).

(C) Secretory Tissues

• Laticifers – produce latex (opium, rubber).
• Glandular cells – secrete oils, resins, gums, nectar.

Anatomy of Monocot and Dicot Plants

1. Dicot Root (e.g., Bean, Mustard)

• Epidermis (with root hairs).
• Cortex – parenchymatous, endodermis with Casparian strips.
• Pericycle – gives rise to lateral roots.
• Vascular bundles – radial, xylem exarch (protoxylem towards periphery).
• Xylem: tetrarch (4 arms).
• Pith – small or absent.

2. Monocot Root (e.g., Maize)

• Similar to dicot but with key differences:
• Xylem: polyarch (many arms, 6+).
• Pith: large and well-developed.
• Secondary growth: absent.

3. Dicot Stem (e.g., Sunflower)

Epidermis: single layer with cuticle, sometimes trichomes.

Cortex: collenchyma (hypodermis) + parenchyma.

Endodermis: starch sheath.

Stele:

• Vascular bundles – conjoint, collateral, open, arranged in a ring.
• Cambium present → secondary growth occurs.

Pith: large and well-developed.

4. Monocot Stem (e.g., Maize)

• Epidermis: single layer with cuticle.
• Hypodermis: sclerenchymatous.
• Ground tissue: large, not differentiated into cortex and pith.
• Vascular bundles: scattered, conjoint, collateral, closed (no cambium).
• Bundle sheath present.
• Secondary growth: absent.

5. Dicot Leaf (Dorsiventral Leaf, e.g., Sunflower)

Epidermis: upper (adaxial) and lower (abaxial) with stomata (more on lower).

Mesophyll:

• Palisade parenchyma (upper, photosynthetic).
• Spongy parenchyma (lower, air spaces).

Vascular bundles: reticulate venation, surrounded by bundle sheath.

6. Monocot Leaf (Isobilateral Leaf, e.g., Maize)

• Both surfaces similar (adaxial and abaxial).
• Mesophyll not differentiated into palisade and spongy.
• Vascular bundles parallel, surrounded by sclerenchymatous bundle sheath cells.

Secondary Growth

• Occurs in dicot stem and root, not in monocots.
• Vascular cambium produces secondary xylem (wood) inside, secondary phloem outside.
• Cork cambium produces cork (outer bark) and secondary cortex (phelloderm).
• Annual rings form due to activity of cambium → used in dendrochronology.