Question

Sunken stomata are characteristics of
A. Cycas
B. Pinus
C. Taxus
D. All of the above

Answer 1

Hint: Stomata are the tiny openings present on the undersurface of most of the leaves. They are also found on the stems as well as some other surfaces and function to control the rate of gaseous exchange. The opening is also known as stomatal opening and they are guarded by two specialized cells known as the guard cells.

Complete answer:
Stomata are the minute pores which are guarded by a pair of cells known as the guard cells. The stomatal aperture regulates the entry as well as the exit of gases from the epidermis of the leaves during gaseous exchange. Air enters and exits the plants through these tiny pores by the process of diffusion and also water vapors are also released by the plants through the stomata.
In some plants such as in the gymnosperms and the plants growing in the arid and dry conditions. The stomata are present deep inside the layer of epidermis and are known as sunken stomata. They appear to be embedded deeply and sunken inside. The stomata is present in a pit like structure which protects the loss of water vapors from the air currents and helps to reduce the water loss from the leaf surfaces. The deeply embedded stomata are also protected from the sunlight as they are not exposed directly to the sun. In different species of gymnosperm plants such as Pinus, Cycas and Taxus, the stomata are sunken to varying degrees.
In Pinus, the leaves appear as needles in structure and it has a thick waxy layer of the cuticle. The stomatal pores are microscopic pores and are arranged in the form of rows. The stomata appear to be present beneath the surface cells and so, are often known as the sunken stomata.
In Cycas, the stomata are present below the guard cell and it creates a sunken stomatal complex. The stomata are sunken to various measures and the stomatal pits are always formed by two layers of epidermal cells.
In Taxus leaves, the stomata are highly sunken and are arranged in rows. They are limited only to the abaxial surfaces and are guarded above by the guard cells.

Hence, the correct answer is option (D).

Note: In gymnosperms, the leaves are needle shaped and are covered with a covering known as the cuticle. The stomata are found on the underside of the leaves and they are found to be sunken to deep layers of the epidermis. In gymnosperm, species such as Pinus, Cycas, and Taxus show deeply sunken stomata. The sunken stomata help to reduce the loss of water from the surface of the leaves.