Dumbbell shaped stomata can be traced in:

a. Monocot leaves

b. Dicot leaves

c. Gymnosperms

d. Both (a) and (c)

Stomata are tiny pores found in the epidermis of leaves, stems, and sometimes other parts of plants. These pores play a crucial role in gaseous exchange between the plant and the atmosphere. Each stomatal pore is surrounded by a pair of specialized parenchymatous cells known as guard cells. These guard cells regulate the size of the stomatal opening. Together, the guard cells, the stomatal pore, and subsidiary cells form the stomatal aperture.

Air enters the plant through these pores by diffusion and takes in carbon dioxide, which is essential for photosynthesis (the process by which plants make their food). As a result, oxygen is produced as a by-product, which diffuses out of the plant into the atmosphere. Water vapor also escapes through the stomata in a process called transpiration.

In vascular plants, the number, shape, and size of stomata vary significantly. In dicots, the stomata are kidney-bean shaped and are arranged irregularly on the leaf surface. The number of stomata is usually greater on the lower surface of the leaf compared to the upper surface.

Thus, the correct answer is Option A.