Test: Anatomy of Flowering Plants - Assertion and Reasoning - NEET MCQ

Root apical meristem is subterminal because of the presence of a protective terminal root cap over it.

Histogen theory, which proposes that the three principal tissues of the root-vascular cylinder, cortex, and epidermis-originate from three groups of initial cells, or histogens, in the apical meristem-plerome, periblem, and dermatogen respectively. A fourth histogen, the calyptrogen, produces the root cap.

The root apex and shoot apex are meristematic in nature. These meristematic tissues are embryonic in origin. They are primary in origin because it develops from embryonic tissues and primary in function because they form the primary structure of the plant cell, the root apex and shoot apex, that live till the death of the whole plant. Hence, plants have the feature of indefinite growth.

Growth in plants is mostly restricted to specialised regions of active cell division called meristems. The meristems which occur at the tips of roots and shoots and produce primary tissues are called apical meristems. They cause growth in length. The meristem which occurs between mature tissues is known as intercalary meristem, commonly located at the bases of leaves, above the nodes (e.g., grasses) or below the nodes (e.g., mint). These help in elongation of the organs. Both apical meristems and intercalary meristems are primary meristems because they appear early in life of a plant and contribute to the formation of the primary plant body.

Secondary meristem is the meristem that occurs in the mature regions of roots and shoots of many plants, particularly those that produce woody axis and appear later than primary meristem. These are cylindrical meristems. Fascicular vascular cambium, interfascicular cambium and cork cambium are examples of lateral meristems. These are responsible for producing the secondary tissues.

Higher plants have root and shoot apices where the cells are in state of continuous division. Here, they can grow indefinitely. Such regions are not found in animals.

Quiescent centre is found in the centre of the root apex. Cell divisions are very few in the quiescent centre as there is very little synthesis of new proteins, RNAs and DNA. Quiescent centre may function as reserve meristem.

Intercalary meristems are intercalated inbetween the permanent tissues. The activities of these meristems also add to the length of the plant or its organs. They originate from the apical meristems when their portions get detached due to the growth of the organs. For example, in the grasses when the internodes complete their elongation, some cells at the base retain their meristematic activity and function as intercalary meristems. They lie just above the node.

Apical and intercalary meristems always increase the height of plants and lateral meristem is responsible for secondary growth and doesn't occur in monocots.

Intercalary meristems are intercalated in between the permanent tissues. They may be present either at the base of the internode as in the stems of various grasses and wheat; or at the base of the leaf as in Pinus; or at the base of a node as in mint (Mentha viridis).

Collenchyma cells are elongated cells with irregularly thick cell walls that provide support and structure. Their thick cell walls are composed of the compounds cellulose and pectin. These cells are often found under the epidermis, or the outer layer of cells in young stems and in leaf veins

Aerenchyma is a spongy tissue that forms spaces or air channels in the leaves, stems and roots of some plants, which allows exchange of gases between the shoot and the root.

Collenchyma is made up of living cells with unevenly thickened cell wall. Their cell wall is made up of cellulose and pectin. Collenchyma are present beneath the epidermis of young stem, petioles and midrib of leaves, etc. These are absent in underground tissues and leaves and stems of monocots.

The tissues in which the cells of which have lost the capacity to divide and have attained a permanent shape, size and function due to morphological, biochemical and physiological differentiation are permanent tissues. Permanent tissues can be classified as simple, complex and special on the basis of composition. A simple permanent tissue is that tissue which is made up of similar permanent cells that carry out the same function or have the same structure. Simple permanent tissues are of three types-parenchyma, collenchyma and sclerenchyma.

Sclerenchyma is the supporting tissue in plants. Two types of sclerenchyma cells exist: fibers and sclereids. Their cell walls consist of cellulose, hemicellulose and lignin. Sclerenchyma provides the main structural support to a plant.

Secretory cells are specialized parenchyma cells that produce nectar, oil, etc. Idioblasts are specialized non-green large-sized parenchyma cells which possess inclusions or ingredients like tannins, oils, crystals, etc.

Sclerenchyma consists of long narrow cells with thick lignified cell walls having a few or numerous pits. They are usually dead and without protoplasm.

Organs of aquatic plants are made of a special parenchyma tissue known as aerenchyma. It consists of a network of parenchyma cells which enclose very large air cavities. These air cavities store gases and make the aquatic plants light and buoyant. Collenchyma is simple permanent tissue with pectocellulose thickening in its wall and no intercellular gaps.

Sclerenchyma is a simple supportive tissue with highly thick-walled cells with little or no protoplasm. Sclerenchyma is of two types: sclerenchymatous fibres and sclereids. Sclereids dead sclerenchymatous cells that are highly thickened with very narrow cavities. They are lignified and extremely thick walled. Sclereids are broader as compared to the fibres being isodiametric polyhedral, spherical, oval, short or cylindrical. They may also be branched. Sclereids may occur singly or in groups. The various types of sclereids are stone cells or Brachysclereids, Macroslereids, Osteosclereids. Astrosclereids, filiform sclereids and trichosclereids, etc. Sclereids are found in grit of guava, sapota, apple, pear, epidermal covering of some legume, seeds, etc.

Xylem is the water conducting tissue. It consists of living cells like parenchyma and dead cells like tracheary elements