Quick Revision Notes

Class: 11 Biology

Chapter: Anatomy of Flowering Plants (MP Board)

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1. Introduction & The Tissues

Anatomy is the study of internal structures of plants. A tissue is a group of cells having a common origin and usually performing a common function.

A. Meristematic Tissues (विज्योतक ऊतक)

Cells have the capacity to divide actively.

• Apical Meristems: Present at root and shoot apices; responsible for primary growth (increase in length).
• Intercalary Meristems: Located between mature tissues; occurs in grasses and helps regenerate parts removed by grazing.
• Lateral Meristems (Secondary Meristems): Cylindrical meristems (e.g., Fascicular cambium, Cork cambium); responsible for secondary growth (increase in girth/thickness).

B. Permanent Tissues (स्थायी ऊतक)

Cells have lost the capacity to divide and have attained maturity.

1. Simple Permanent Tissues (सरल स्थायी ऊतक): Made of only one type of cells.

   • Parenchyma: Living, thin-walled cells. Functions: Photosynthesis, storage, secretion.
   • Collenchyma: Living, unevenly thickened corners (pectin deposition). Function: Mechanical support to growing parts (young stem, petiole).
   • Sclerenchyma: Dead, highly thick walls (lignified). Function: Mechanical support. Divided into fibers and sclereids (stone cells).

2. Complex Permanent Tissues (जटिल स्थायी ऊतक): Made of more than one type of cells working as a unit.

   • Xylem (दारू): Conducts water and minerals from roots to stem and leaves.
     • Elements: Tracheids, Vessels, Xylem parenchyma (living), Xylem fibers (dead).
     • Note: Gymnosperms lack vessels in xylem.
   • Phloem (वाही / पोषवाह): Conducts food materials from leaves to other parts.
     • Elements: Sieve tube elements, Companion cells, Phloem parenchyma, Phloem fibers.
     • Note: Gymnosperms have albuminous cells and sieve cells (no sieve tubes and companion cells).

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2. The Tissue System

Based on structure and location, plant tissue systems are of three types:

1. Epidermal Tissue System (बाह्यत्वचीय ऊतक तंत्र):

   • Outer covering of the plant body.
   • Includes epidermal cells, stomata, and epidermal appendages (trichomes and hairs).
   • Stomata: Structures in epidermis of leaves regulating transpiration and gaseous exchange. Guard cells enclose the stomatal pore (bean-shaped in dicots, dumbbell-shaped in monocots).

2. Ground Tissue System (भरण ऊतक तंत्र):

   • All tissues except epidermis and vascular bundles.
   • Consists of parenchyma, collenchyma, and sclerenchyma.
   • In leaves, the ground tissue is called Mesophyll (photosynthetic).

3. Vascular Tissue System (संवहन ऊतक तंत्र):

   • Consists of Xylem and Phloem arranged in Vascular Bundles.
   • Radial: Xylem and phloem arranged in alternate radii (e.g., Roots).
   • Conjoint: Xylem and phloem situated along the same radius (e.g., Stems and Leaves).
     • Open: Cambium present between xylem and phloem -> Secondary growth possible (Dicot stem).
     • Closed: Cambium absent -> No secondary growth (Monocot stem).

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3. Anatomy of Dicotyledonous and Monocotyledonous Plants

A. Dicot Root vs. Monocot Root

Feature	Dicot Root	Monocot Root
Vascular Bundles	Usually 2 to 4 (Diarch to Tetrarch)	Polyarch (usually more than six)
Cambium	Developed later (Secondary growth occurs)	Absent (No secondary growth)
Pith	Small or inconspicuous	Large and well-developed

B. Dicot Stem vs. Monocot Stem

Feature	Dicot Stem	Monocot Stem
Vascular Bundles	Arranged in a ring	Scattered throughout the ground tissue
Bundle Sheath	Absent	Present (Sclerenchymatous)
Hypodermis	Collenchymatous	Sclerenchymatous
Secondary Growth	Present	Absent

C. Dicot Leaf (Dorsiventral) vs. Monocot Leaf (Isobilateral)

Feature	Dicot Leaf	Monocot Leaf
Stomata	More on lower epidermis (Hypostomatic)	Equal on both surfaces (Amphistomatic)
Mesophyll	Differentiated into Palisade and Spongy parenchyma	Undifferentiated (Uniform mesophyll)
Bulliform Cells	Absent	Present (help in curling of leaves to minimize water loss)

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4. Secondary Growth (द्वितीयक वृद्धि)

Increase in girth (diameter) of stems and roots, typical of dicots and gymnosperms. Driven by two lateral meristems:

1. Vascular Cambium:

   • Forms a ring of meristematic tissue between xylem and phloem.
   • Cuts off cells inwards towards the center to form Secondary Xylem (Wood).
   • Cuts off cells outwards to form Secondary Phloem.
   • Spring Wood / Early Wood: Lighter in color, vessels with wider cavities formed in spring.
   • Autumn Wood / Late Wood: Darker in color, vessels with narrower cavities formed in winter.
   • Annual Rings: Combination of spring and autumn wood of one year; used to estimate the age of a tree (Dendrochronology).
   • Heartwood (Duramen): Central dark-colored dead wood, filled with resins/tannins; non-functional in water conduction, provides mechanical support.
   • Sapwood (Alburnum): Peripheral light-colored living wood; actively conducts water and minerals.

2. Cork Cambium (Phellogen):

   • Develops in the cortex region.
   • Cuts off cells internally to form Secondary Cortex (Phelloderm).
   • Cuts off cells externally to form Cork (Phellem).
   • Periderm: Phellem (Cork) + Phellogen (Cork cambium) + Phelloderm (Secondary cortex).
   • Bark: All tissues outside the vascular cambium (includes secondary phloem and periderm).
   • Lenticels: Lens-shaped openings in the periderm that permit gaseous exchange between internal tissues and the atmosphere.