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Structural Organisation in Animals and Plants - Anatomy of Flowering Plants (Tissues, Secondary Growth)

Grade 11ICSEBiology

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

🔑Concepts

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Classification of Meristematic Tissues: Based on position, they are categorized into Apical Meristem (increases length), Intercalary Meristem (internodal growth), and Lateral Meristem (increases girth via secondary growth).

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Simple Permanent Tissues: Comprise Parenchyma (thin-walled, storage), Collenchyma (living mechanical tissue with pectin deposition at corners), and Sclerenchyma (dead, lignified cells for structural strength).

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Complex Permanent Tissues: Xylem consists of Tracheids, Vessels, Xylem Parenchyma, and Xylem Fibres for water transport. Phloem consists of Sieve tube elements, Companion cells, Phloem Parenchyma, and Phloem Fibres for translocation of solutes.

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Dicot vs. Monocot Stem: Dicot stems possess a ring-like arrangement of vascular bundles which are 'Open' (contain cambium), whereas monocot stems have scattered 'Closed' vascular bundles (no cambium).

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Secondary Growth: This process occurs primarily in dicotyledonous plants through the activity of the vascular cambium and cork cambium (PhellogenPhellogen). It results in the formation of secondary xylem (wood) and secondary phloem.

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Heartwood and Sapwood: Heartwood is the central, dark, non-functional part of the secondary xylem filled with tannins and resins, while Sapwood is the peripheral, lighter, functional part involved in water conduction.

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Periderm Formation: During secondary growth, the PhellogenPhellogen (cork cambium) produces PhellemPhellem (cork) towards the outside and PhellodermPhelloderm (secondary cortex) towards the inside.

📐Formulae

Periderm=Phellem (Cork)+Phellogen (Cork Cambium)+Phelloderm (Secondary Cortex)\text{Periderm} = \text{Phellem (Cork)} + \text{Phellogen (Cork Cambium)} + \text{Phelloderm (Secondary Cortex)}

1 Annual Ring=1 Spring wood (Early wood)+1 Autumn wood (Late wood)\text{1 Annual Ring} = \text{1 Spring wood (Early wood)} + \text{1 Autumn wood (Late wood)}

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

Bark=All tissues exterior to the vascular cambium (Periderm + Secondary Phloem)\text{Bark} = \text{All tissues exterior to the vascular cambium (Periderm + Secondary Phloem)}

💡Examples

Problem 1:

A cross-section of a dicot stem shows 2525 distinct annual rings. If the tree grew in a temperate region, what is the estimated age of the tree and which tissue layer is responsible for these rings?

Solution:

The estimated age is 2525 years. The tissue responsible is the Secondary Xylem produced by the Vascular Cambium.

Explanation:

In temperate regions, the activity of the vascular cambium varies with seasons. One annual ring consists of one layer of spring wood and one layer of autumn wood, representing one year of growth. Since there are 2525 rings, the age is 2525 years.

Problem 2:

Distinguish between the vascular bundles of a Dicot root and a Monocot root based on the number of xylem bundles (XX).

Solution:

Dicot Root: X=2 to 4X = 2 \text{ to } 4 (Diarch to Tetrarch); Monocot Root: X>6X > 6 (Polyarch).

Explanation:

Dicot roots typically have fewer xylem bundles (usually 2-4), whereas monocot roots are characterized by a polyarch condition where the number of xylem bundles is significantly higher, often exceeding 6.

Anatomy of Flowering Plants (Tissues, Secondary Growth) Revision - Class 11 Biology ICSE