Thin-Walled large cells present in the leaf epidermis, and capable of contraction and expansion are?
A) Guard Cells
B) Subsidiary Cells
C) Gland Cells
D) Bulliform Cells

Hint:The epidermis is a single layer of cells that covers the leaves, flowers and roots and stems of plants. It forms a boundary between the plant and the external environment. The epidermis serves several functions like it protects against water loss, regulates gas exchange, secretes metabolic compounds and absorbs water and mineral nutrients.

Complete answer:
The epidermis of most leaves shows the upper and lower surfaces have somewhat different construction and may serve different functions. Woody stems and some other stem structures such as potato tubers produce a secondary covering called the periderm that replaces the epidermis as the protective covering.

The epidermis is the outermost cell layer of the primary plant body. In some older works the cells of the leaf epidermis have been regarded as specialized cells but the established modern preference has long been to classify the epidermis as dermal tissue whereas parenchyma is classified as ground tissue. The epidermis is the main component of the dermal tissue system of leaves and also stem, flower and roots; it is usually transparent cells.

Guard cells modified epidermal cells present in the stomata. They perform transpiration. Cell walls with varying thickness can contract and expand subsidiary cells afford a cushioning effect for the adjoining cells from the stomatal expansion and contractions. Subsidiary cells epidermal cells present around the guard cells in stomata. They perform transpiration. Gland cells are the cells which secrete substances, bulliform cells the large thin walled epidermal cells present in the adaxial epidermis of grass leave. They are involved in the contraction or rolling and expansion or unrolling of leaf lamina.

Hence the correct answer is option ‘A’.

Note:The cells of the epidermis are structurally and functionally variable. Most plants have an epidermis that is a single cell layer thick. In plants with secondary growth the epidermis of roots and stems is usually replaced by a periderm.