Describe the anatomical structure of dicot root and compare it with monocot root. OR Describe an experiment to demonstrate light is necessary for the process of photosynthesis with clean diagram.

Anatomical Structure of Dicot Root and Comparison with Monocot Root

Anatomical Structure of Dicot Root

The dicot root exhibits a well-defined radial vascular arrangement with distinct primary and secondary growth. The structure can be described from the outermost to the innermost layers:

1. Epidermis

   • Single-layered outermost covering.
   • Cells are rectangular with thickened outer walls.
   • May bear root hairs for increased absorption.

2. Cortex

   • Composed of parenchymatous cells arranged in layers.
   • Contains exodermis (a protective layer just beneath the epidermis).
   • Endodermis marks the boundary between the cortex and stele.
     • Cells have Casparian strips (suberin deposits) to regulate water and nutrient flow.

3. Pericycle

   • A single layer of cells just inside the endodermis.
   • Gives rise to lateral roots and secondary vascular tissues (in dicots).

4. Vascular Bundle (Stele)

   • Arranged in a ring (radial vascular system).
   • Consists of:
     • Xylem: Tetrarch (4 arms) or pentarch (5 arms), arranged in a cross.
     • Phloem: Located between xylem arms.
   • Pith (central parenchyma) is well-developed in dicot roots.

5. Secondary Growth (in older dicot roots)

   • Vascular cambium develops between xylem and phloem.
   • Produces secondary xylem (wood) and secondary phloem.
   • Cork cambium (phellogen) forms a protective periderm (cork and phelloderm).

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Comparison of Dicot Root and Monocot Root

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Experiment to Demonstrate Light is Necessary for Photosynthesis

Objective

To show that light is essential for photosynthesis by comparing the production of starch in a leaf kept in the dark and one exposed to light.

Materials Required

• A healthy potted plant (e.g., Mimosa pudica or Coleus)
• Black paper or aluminum foil
• A beaker or test tube
• Iodine solution (Lugol’s iodine)
• Alcohol (70% ethanol)
• Water
• Boiling water bath
• Forceps

Procedure

1. Destarch the Plant

   • Keep the plant in a dark room for 24–48 hours to remove all stored starch.
   • This ensures that any starch detected later is newly synthesized.

2. Expose Part of a Leaf to Light

   • Select a mature leaf and cover half of it with black paper or aluminum foil, ensuring the covered part receives no light.
   • Leave the plant in sunlight for 4–6 hours.

3. Test for Starch

   • Carefully remove the leaf and place it in a beaker of boiling water for 2–3 minutes to kill cells and soften the leaf.
   • Transfer the leaf to a test tube containing alcohol and heat gently in a water bath until the leaf becomes bleached (colorless).
   • Rinse the leaf with water to remove alcohol.
   • Place the leaf on a white tile and add a few drops of iodine solution.
   • Observe the color change:
     • Blue-black indicates the presence of starch (photosynthesis occurred).
     • Brown/yellow indicates no starch (no photosynthesis).

Expected Observations

• The exposed (lighted) part of the leaf turns blue-black (starch present).
• The covered (dark) part remains brown/yellow (no starch).

Conclusion

Light is essential for photosynthesis, as starch (a photosynthetic product) is only produced in the illuminated part of the leaf.