Q.50 The schematic depicts an unexpanded plant cell within a hypocotyl with the
arrangement of cellulose microfibrils marked on its cell wall.
Which one of the following shapes would most likely result from the expansion of
this cell if the pattern of the cellulose fibrils does not change?

The cell will elongate in the direction perpendicular to the cellulose microfibrils, so the most likely expanded shape is the tall, vertically elongated cell shown in option A.​

Concept behind the question

Cellulose microfibrils in the primary cell wall act as rigid hoops that resist stretching along their own length, so expansion occurs mainly in the axis perpendicular to their orientation. When microfibrils are arranged transversely around a cylindrical cell (i.e., encircling it), they restrict radial widening and promote longitudinal elongation, producing a long, column‑like cell.​

In the given schematic, the fibrils on the sides of the unexpanded cell are drawn horizontally, i.e., transversely to the long axis of the hypocotyl, so the cell will elongate vertically while keeping almost the same width.​

Detailed analysis of each option

Option A

• The sides still show horizontal cellulose microfibrils, and the cell has become a tall rectangle without much increase in width.

• This matches the rule that transversely oriented microfibrils in hypocotyl epidermal cells favor expansion in the long axis and restrict lateral expansion.​

• Therefore, option A is correct because it shows anisotropic growth: strong elongation parallel to the hypocotyl axis with microfibril pattern unchanged.

Option B

• The cell in B is expanded mainly in width and not in height, giving a squat, broad brick‑like shape.

• Such radial swelling would occur if microfibrils were oriented longitudinally (parallel to the long axis), which would resist elongation but allow lateral expansion, the opposite of what is drawn in the original figure.​

• Because the given pattern is transverse, option B contradicts the expected growth direction and is therefore incorrect.

Option C

• In C the cell looks larger overall, but the increase in height and width is roughly similar, suggesting more isotropic expansion.

• Isotropic or nearly uniform expansion would require a more random or crossed orientation of cellulose microfibrils, not the strictly parallel transverse array that is shown and specified to remain unchanged.​

• As the question states that the pattern of cellulose fibrils does not change, option C is not consistent with the biomechanics of the wall.

Option D

• Option D shows a spherical cell with a criss‑crossed, random microfibril network on the surface.

• A spherical shape implies completely isotropic expansion in all directions, which only occurs when cellulose microfibrils lose a preferred orientation and become more or less randomly arranged.​

• Since the original cell has clearly ordered transverse fibrils that remain unchanged, option D is clearly wrong for this question.

SEO‑oriented introduction (using keyphrase)

In plant development, the relationship between cellulose microfibrils and plant cell expansion in hypocotyl cells is a classic concept tested in CSIR NET and other competitive exams. This problem uses a schematic to link the orientation of cellulose microfibrils with the final shape of an expanding plant cell, and understanding this link helps in predicting anisotropic versus isotropic growth patterns.​