Test: The Tissue System (May 2) - NEET MCQ

A typical stoma is microscopic and usually consists of two kidney-shaped guard cells surrounding a pore. The guard cells are usually much smaller in size as compared to other epidermal cells. In some species the guard cells are surrounded by subsidiary cells or accessory cells which differ morphologically from the other epidermal cells. Guard cells possess few small chloroplasts, they are bean or kidney shaped in most dicots and dumb-bell shaped in most monocots.

Trichomes are unicellular or multicellular, branched or unbranched outgrowths which are strictly epidermal in origin. Being the outermost layer trichome is protective in nature. With the help of cuticle it checks the rate of water loss from aerial parts. Trichomes present on the surface of some seeds and fruits help in their dispersal.

Ground tissue system includes all the tissues of plant body except epidermal tissue system and vascular tissues. It forms the bulk of body and consists of mainly parenchymatous, collenchymatous, sclerenchymatous, glandular and laticiferous tissues.

 The vascular bundles which contain both xylem and phloem together on the same radius are called conjoint collateral vascular bundles. In gymnosperms and dicot stems a strip of vascular cambium occurs between phloem and xylem of each vascular bundle. It is called intrafascicular for fascicular) cambium. This strip of vascular cambium layer produces secondary tissues. Such vascular bundles are described as open. In monocot stems vascular bundles do not have a strip of vascular cambium. They are termed as closed.

The given figure represents radial vascular bundles. Here xylem and phloem occur in the form of separate bundles called xylem bundles and phloem bundles. The two types of bundles usually alternate with each other. They occur on different radii. Radial bundles are characteristic of monocot and dicot roots. 

Solution: 
They do not form secondary tissues. Explanation: Monocotyledonous vascular bundles are referred to as closed because they do not have cambium and, as a result, cannot form secondary tissues.

Open vascular bundles possess cambium between phloem and xylem, which enables them to form secondary xylem and phloem tissues.

In amphivasal or laptocentric vascular bundles, xylem surrounds phloem e.g., Dracaena, Yucca. When phloem surrounds xylem it is amphicribal or hadrocentric type of vascular bundles, e.g. Hydrilla, Selaginella.

Protoderm (Gk. Protos-first, derma-skin) in the outer layer of apical meristem that given rise to epidermal tissues epidermal tissue system is derived from protoderm. Ground tissue system is derived partly from periblem and partly from plerome. Vascular tissue system is derived from procambium.

Diacytic (caryophyllaceous) type of stomata are surround by 2 subsidiary cells. Diacytic subsidiary cells are arranged at right angles to the stomata cells e.g., saponaria.