A student observes the transverse section of a leaf under a microscope and notes the following features: (a) The mesophyll is not differentiated into palisade and spongy parenchyma. (b) The upper epidermis possesses some large, empty, and colourless cells along the veins. Identify the likely group of plants to which this leaf belongs, and the primary function of the specialised cells mentioned in feature (b).

Step-by-step solution

The presence of an undifferentiated mesophyll (no distinct palisade and spongy parenchyma) is a characteristic feature of an isobilateral leaf, which is typically found in monocotyledonous plants. The large, empty, and colourless cells on the upper (adaxial) epidermis are bulliform cells. In grasses (monocots), these cells help in minimising water loss during water stress by becoming flaccid, which causes the leaves to curl inwards. Therefore, the leaf belongs to a monocotyledonous plant, and the specialised cells