NEET Practice Questions (MCQs) with Answers & Solutions

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).

The vascular bundles in Hordeum vulgare (barley) plant are scattered in ground tissues, many in number and vary in size-smaller towards periphery and bigger towards centre of the ground tissue, oval or rounded in outline, conjoint, collateral and closed.

Guard cells help in transpiration. Each stomatal opening is surrounded by two specialized epidermal cells, called guard cells. Because of their small size guard cells are rapidly influenced by turgor change and thus regulate the opening and closing of stomata.

Sorghum (family-Poaceae) is a monocot plant.The leaves of monocot do not contain palisade parenchyma,because the mesophyll of monocot leaf is not differentiated into palisadeand spongy parenchyma,all being thin walled, chlorophyllous and irregularly compactly arranged with fewer intercellular spaces.

In hydrophytes, vascular tissue and mechanical tissue are reduced. Cuticle is either completely
absent or if present, it is thin and poorly developed.In xerophytes, cuticle is heavy, well-developed.
Vascular tissue and mechanical tissue are well-developed and differentiated. In mesophytes, cuticle in aerial part is moderately developed. Vascular and mechanical tissues are fairly developed and well differentiated.

Histogen theory for shoot apical meristem has been proposed by Hanstein (1870). It advocates that there are three distinct meristematic zones (layers) called dermatogens periblem and plerome. The dermatogens is the outermost histogen giving rise to epidermis, periblem is the middle one producing the cortex and plerome is the innermost resulting in central cylinder (ie, vascular tissues).

Cock cambium (phellogen) is the secondary lateral meristem found in outer cortical region. Its cells divide periclinally cutting off cells towards the outside (forming cork or phellem) and inside (forming secondary cortex or phelloderm).

(b) The increase in the diameter or thickness is due to the formation of secondary tissues as a result of the activities od vascular cambium and cork cambium. this secondary growth is characteristic of dicot stem root.