Notes for B3.2.10 Distribution of tissues in a transverse section of the root of a dicotyledonous plant - IB | RevisionDojo
B3.2.10 Distribution of tissues in a transverse section of the root of a dicotyledonous plant Notes
Overview of Dicotyledonous Roots
Dicotyledonous plants (commonly called dicots), such as beans, sunflowers, and oak trees, have roots with a distinct tissue organization.
Unlike dicot stems, where vascular bundles are scattered near the periphery, the vascular tissues in dicot roots are concentrated at the center.
This centralized arrangement reinforces the root, allowing it to push through the soil effectively.
Dicot vs monocot root
Root Tissue Layers
1. Epidermis: The Outer Shield
Single-layered, thin-walled cells without cuticle (allows water absorption).
Root hairs extend from some cells to massively increase surface area for absorption.
Tip
Root hairs are short-lived but vital for maximizing water and nutrient uptake.
Be sure to identify them when examining microscope slides of root sections.
2. Cortex: The Storage and Transport Zone
Made of parenchyma cells (loosely packed for gas exchange).
Stores starch for energy.
Transports water & minerals to vascular tissue.
Ends in the endodermis, a single-cell layer controlling water entry into the vascular cylinder.
Contains the Casparian strip – a waterproof barrier that forces water through cell membranes, ensuring selective uptake.
Example
The Casparian strip acts like a security checkpoint, ensuring that only essential nutrients enter the vascular tissue while harmful substances are kept out.
This is critical for maintaining the plant’s health.
3. Vascular Cylinder (Stele): The Transport Hub
Pericycle (outer ring of cells) – generates lateral roots.
Xylem (center, star-shaped) – thick-walled water transport vessels.
Phloem (between xylem arms) – thin-walled sugar transport cells.
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Questions
Recap questions
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Question 1
Recap question
Why does the epidermis of a root lack a cuticle, unlike many aerial plant surfaces?
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Note
Root Tissue Layers Overview
The root is organized into concentric layers, each with specific functions:
Epidermis
Cortex
Endodermis
Pericycle
Vascular tissue (xylem and phloem)
TipWhen examining root cross-sections under a microscope, try to identify these layers from outermost to innermost.
