Biology · Anatomy of Flowering Plants · NEET
They occur in the endodermis, which is the innermost single layer of the root cortex. NEET 2018 asked this exact question and the answer is Endodermis - not cortex, not pericycle, not epidermis. The endodermal cells are barrel-shaped and fit together with no air gaps, and the Casparian strip runs along their radial and tangential walls.
Their job is to block the apoplast pathway. Water normally moves freely through cell walls and spaces (apoplast) without entering any cell. The Casparian strip is water-proof, so at the endodermis water is forced to leave the wall and cross a living cell membrane (symplast). This lets the root control and check every mineral before it reaches the xylem, and it stops back-flow of water out of the stele.
They are made of suberin, a waxy, water-impermeable material. NCERT says the endodermal walls have 'a deposition of water-impermeable, waxy material suberin in the form of casparian strips.' Do not write cutin or lignin - the exam answer is suberin.
Because suberin does not let water pass. When water travelling through the cell walls (apoplast) reaches the endodermis, the suberin band seals the wall route. The only way forward is through the plasma membrane into the cytoplasm (symplast). Since the membrane is selectively permeable, the plant can now select which ions enter, which is why the endodermis acts as a barrier and checkpoint.
Passage cells are a few endodermal cells opposite the protoxylem that stay thin-walled and do not get the full suberin deposit. They allow water and minerals to pass directly into the xylem. They are the 'open gates' in the endodermal barrier and are mostly seen in older roots.
The endodermis is the innermost layer of the cortex, but everything inside the endodermis (pericycle, vascular bundles, pith) forms the stele. So the endodermis is the boundary line - it belongs to the cortex but marks where the stele begins. This is why NEET 2016 said cortex lies between epidermis and stele.
Casparian strips occur in
Match List-I with List-II: A. Conjunctive tissue B. Casparian strips C. Subsidiary cells D. Starch sheath | I. Specialised cells near guard cells II. Endodermal cells rich in starch III. Tissue between xylem and phloem IV. Endodermal cells with suberin deposition
Try the real previous-year questions from this chapter — each with the answer and a full solution.
In the dicot stem, the innermost cortex layer is the endodermis, but it stores starch and is called the starch sheath. Well-developed Casparian strips are a feature of the root endodermis, not the stem.
Yes. Both dicot and monocot roots have an endodermis with Casparian strips. Monocot roots keep a strongly suberised endodermis with passage cells, since they usually have no secondary growth.
Both are waxy and water-proof. Suberin forms Casparian strips (endodermis) and cork; cutin forms the cuticle on the epidermis. NEET often swaps them, so remember suberin = inside (endodermis/cork), cutin = outside (cuticle).
They give the plant control. By blocking the apoplast, they force water through living cells so the plant can select minerals and stop leakage of water and ions back out of the stele. This is key to safe, one-way uptake of nutrients.
