Plant Anatomy Plant Tissues MCQs for NEET — Botany Questions with Answers

The presence of protoxylem helps distinguish a dicot stem from a dicot root. Protoxylem elements are arranged in an exarch pattern (towards the center) in roots, while in stems, they are arranged in an endarch pattern (towards the periphery).

(a) In dicot stems, the cells of cambium present between primary xylem and primary phloem is the intrafasicular cambium. The cells of medullary rays, adjoining these intrafascicular cambium become
meristematic and form the interfascicular cambium. Xylem parenchyma are living and thin-walled and their cell walls are made up of cellulose. In dicot roots the innermost layer of the cortex is called endodermis. Next to endodermis lies a few layers of thick-walled parenchymatous cells called as pericycle.

(b) Plants have stomata and lenticels involved in gaseous exchange. In stems the living cells are organised in thin layers inside and beneath bark. They have openings called lenticels. Transpiration is the evaporative loss of water by plants. It occurs mainly through stomata in leaves. Food transport occurs by the vascular tissue phloem from a source to a sink. Photosynthesis is a physico-chemical process by which they use light energy to derive re synthesis of organic compounds.

The cork cambium or phellogen cells divide periclinally cutting off cells towards the outside and inside. The cells cut off towards the out side become suberized and dead. These are compactly packed in radial rows without intercellular spaces and form cork or phellem. Cork is impervious to water due to suberin and provides protection to underlying tissues. The cells cut off from cork cambium towards inside add to the cortex and are called secondary cortex cells or phelloderm cells.

Companion cells are characteristic elements of phloem tissue associated with the sieve tubes (sieve elements) in the angiosperms. The siever tubes and companion cells are related ontogenically as they develop from the same mother cell. The companion cells and sieve tubes maintain close cytoplasmic connections through plasmodesmata.

In dicot stems, cambium is present between phloem and xylem. Such vascular bundles, because of the presence of cambium, posses the ability to form secondary xylem and phloem tissues and hence, are called open vascular bundles. On the contrary, vascular bundles in monocots have no cambium. Hence, they do not form secondary tissues, and are referred to as closed.

In monocot stem like Zea mays, vascular bundles, the lowermost protoxylem vessels and xyylem parenchyma cells dissolve forming a water containing schizolysigenous cavity called protoxylem cavity or lacuna or lysigenius cavity. Protoxylem cavity and protophloem may be absent in the smaller vascular bundles in maize.

All tissues except epidermis and vascular bundles constitute the ground tissue or fundamental tissue. It consists of simple tissues such as parenchyma, collenchyma and sclerenchyma. It includes cortex, pericycle, medullary rays. In leaves the ground tissue consists of mesophyll.

The guard cells of stomata in land plants are specialised epidermal cells which contain chloroplasts. In rest of epidermal cells, chloroplasts are absent. But chloroplasts of guard cells are capable of poor photosynthesis as there is absence of NADP reductase enzyme.

Intercalary meristems are the portions of apical meristerns, which are separated from the apex during the growth of axis and formation of permanent tissues . It is present mostly at the base of node (eg, Mentha viridis), base of internode (eg, stern of many monocots viz, wheat, paddy, grasses; pteridophytes like Equisetum) or at the base of leaf (eg, Pinus).