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In the given figure, which component has thin outer walls and highly thickened inner walls?
Inner wall facing aperture is thick and inelastic; outer wall is thin and elastic. This asymmetric structure belongs uniquely to Guard Cells!
The stomatal apparatus consists of the stomatal aperture (pore), two guard cells flanking the pore, and surrounding specialized subsidiary cells derived from epidermal tissue.
In dicots, guard cells are bean-shaped or kidney-shaped. The outer walls of guard cells (away from the stomatal pore) are thin, while the inner walls (facing and bordering the stomatal pore) are highly thickened and inelastic. Cellulose microfibrils are oriented radially rather than longitudinally, facilitating aperture opening when guard cells become turgid.
The question asks which component possesses thin outer walls and highly thickened inner walls. This is the hallmark anatomical definition of guard cells.
Diagnose every choice: Know exactly why the right option works and why distractors fail.
Typical epidermal cells are parenchymatous with a thin layer of cytoplasm lining the cell wall and a large central vacuole, without differential inner/outer wall thickenings.
Subsidiary cells are modified epidermal cells in close proximity to guard cells that provide mechanical and ionic support; they do not possess thickened inner walls.
Guard cells have thin outer walls and highly thickened inner walls bordering the stomatal pore, allowing bowing outward upon turgor increase.
The stomatal pore is an extracellular aperture/opening, not a cellular component with walls.
Students often confuse subsidiary cells with guard cells because both form part of the stomatal apparatus.
"Each stoma is composed of two bean-shaped cells known as guard cells. The outer walls of guard cells (away from the stomatal pore) are thin and the inner walls (towards the stomatal pore) are highly thickened."
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