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Anatomy of Flowering Plants - Tissue systems in dicots and monocots

Grade 11CBSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The Tissue System is categorized into three types: Epidermal, Ground (Fundamental), and Vascular tissue systems.

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Epidermal Tissue System: Consists of epidermal cells, stomata, and epidermal appendages (trichomes and hairs). The epidermis is covered by a waxy layer called the cuticle to prevent H2OH_2O loss.

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Ground Tissue System: All tissues except epidermis and vascular bundles. It includes parenchyma, collenchyma, and sclerenchyma. In leaves, it is called mesophyll and contains chloroplasts for the reaction: 6CO2+6H2O→lightC6H12O6+6O26CO_2 + 6H_2O \xrightarrow{light} C_6H_{12}O_6 + 6O_2.

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Vascular Tissue System: Consists of complex tissues, xylem and phloem. In Dicots, cambium is present between xylem and phloem (Open vascular bundles). In Monocots, cambium is absent (Closed vascular bundles).

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Dicot Root: Typically shows diarch to tetrarch vascular bundles. Endodermis contains suberized Casparian strips. Pith is small or inconspicuous.

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Monocot Root: Characterized by polyarch xylem bundles (usually >6> 6). Pith is large and well-developed. No secondary growth occurs.

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Dicot Stem: Vascular bundles are arranged in a ring (eustele). Hypodermis is collenchymatous. Endodermis is often called a 'starch sheath'.

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Monocot Stem: Vascular bundles are scattered in the ground tissue (atactostele). Each bundle is surrounded by a sclerenchymatous bundle sheath. Hypodermis is sclerenchymatous.

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Dicot (Dorsiventral) Leaf: Mesophyll is differentiated into palisade parenchyma (upper) and spongy parenchyma (lower). Stomata are usually more numerous on the abaxial (lower) epidermis.

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Monocot (Isobilateral) Leaf: Mesophyll is not differentiated. Bulliform cells are present in the adaxial epidermis of grasses to help in leaf rolling during water stress (H2OH_2O deficit).

📐Formulae

Open Vascular Bundle=Xylem+Cambium+Phloem\text{Open Vascular Bundle} = \text{Xylem} + \text{Cambium} + \text{Phloem}

Closed Vascular Bundle=Xylem+Phloem (No Cambium)\text{Closed Vascular Bundle} = \text{Xylem} + \text{Phloem (No Cambium)}

Stele=Pericycle+Vascular Bundles+Pith\text{Stele} = \text{Pericycle} + \text{Vascular Bundles} + \text{Pith}

Water Potential (ψw) influence on Bulliform cells: ψw decrease→Flaccidity→Inward rolling\text{Water Potential (}\psi_w\text{) influence on Bulliform cells: } \psi_w \text{ decrease} \rightarrow \text{Flaccidity} \rightarrow \text{Inward rolling}

💡Examples

Problem 1:

A transverse section of a plant organ shows scattered vascular bundles, each surrounded by a sclerenchymatous bundle sheath, and a lack of pith. Identify the organ.

Solution:

The organ is a Monocot Stem.

Explanation:

In Monocot stems, the vascular system is 'atactostele', meaning bundles are scattered. The presence of a sclerenchymatous bundle sheath and the absence of a distinct pith (due to scattered bundles) are diagnostic features of monocotyledonous stems.

Problem 2:

How can you distinguish between a Dicot root and a Monocot root based on the number of xylem bundles?

Solution:

Dicot roots have fewer xylem bundles (2 to 4, i.e., diarch to tetrarch), while Monocot roots have many (>6> 6, i.e., polyarch).

Explanation:

The vascular arrangement in roots is radial. The count of protoxylem poles distinguishes the two; dicots follow the condition n≤4n \leq 4 (usually), whereas monocots follow n>6n > 6 where nn is the number of xylem bundles.

Tissue systems in dicots and monocots Revision - Class 11 Biology CBSE