Botany MCQs for NEET — Practice Questions with Answers

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.

In plant conducting tissue xylem has an important integral cell as xylem vessel which is without nucleus. The phloem has a row of sieve tubes which are also without nucleus at maturity.

(d) Anomocytic stomata lacking subsidiary cells surrounding the guard cells. Anisocytic stomata is characterized by the presence of three subsidiary cells of which one is distinctly smaller than the
other two. Paracytic stomata is accompanied on either side by one or more subsidiary cells which lie
parallel to the long axis of the pore and guard cells. Perigenous stomata shows an independent origin of the guard cells and the subsidiary cells.

(a) In dicotyledonous stems, a thin strip of primary meristem is present in between the xylem and phloem, which is termed as fascicular or vascular cambium. The cambium cells are rectangular and thin walled. Cambium is one layered. In monocot stem cambium is absent.

(d) Epidermis is the outer most covering of the plant which is in direct contact with the external environment. It is single layered or multilayered structure that helps in protection, absorption, excretion, gaseous exchange, transpiration and secretion. The epidermis is derived from dermatogen which is the outer most initial of the shoot apex.

Cork cambium is a secondary lateral meristem that may arise from permanent living cells of hypodermis or outer cortex. It is composed of a single layer of meristematic cells. Its cells divide tangentially and periclinally towards the outer face and produce cork cells. These cells are compactly arranged and have thin cellulose walls in the beginning. As they mature there is a gradual loss of living matter and cells get elongated radially, vertically of tangentially. The cell walls become thick because of development of fatty substance called suberin, which is impervious to water.