Tag: botany

Lignin is a class of complex organic polymers that form key structural materials in the support tissues of vascular plants and some algae. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity and do not rot easily. Chemically, lignins are cross-linked phenolic polymers. As a biopolymer, lignin is unusual because of its heterogeneity and lack of a defined primary structure. Its most commonly noted function is the support through strengthening of wood (mainly composed of xylem cells and lignified sclerenchyma fibres) in vascular plants.

Bast is the term used for the fibres of phloem. These fibres are tough and resistant with a narrow lumen and secondary walls deposited with lignin. These are dead elongated cells of sclerenchyma tissue. Examples include jute fibres. 

Pericycle is the outermost layer of the stele. Stele is composed of all tissues inside of the endodermis. Structure of pericycle differs in monocots and in dicots. In dicots, pericycle is in the form of isolated strips of sclerenchyma cells, which are lignified. Each patch is associated with phloem of vascular bundle. Such, pericycle is called as hard bast. 
Epiblema are special epidermal cells present in rootlets. They are specially adapted for absorbing liquids. Phellem is outermost layer of cork cambium which is suberised. 
Astrosclereids is a type of sclereid which is a large, radially branched structure. 
Thus, the correct answer is option C.

Hypodermis is present in both dicot and monocot stems. In case of dicots, the hypodermis is made up of collenchyma cells and those present in monocots is made up of sclerenchymatous cells.

Macrosclereids are elongated sclereids. Sclereids are the reduced form of sclerenchyma. It is usually found in the outer layer of seed coat of legumes. These cells are responsible for restricting water uptake by hard seeded legumes. 

The cortex of the root and shoot is formed from the periblem. The cortex is the outermost layer on the stem or roots of plants. Cork which is used commercially as bottle stoppers, bulletin boards, coasters, insulation, sealing for lids, flooring, gaskets for engines etc. is obtained from Quercus suber, commonly called as the cork oak, a medium-sized, evergreen oak tree. Since the vessel elements are absent in most gymnosperms, the tracheids form the main elements of xylem that help in transporting water and minerals.

Sclereids are reduced form of sclerenchyma cells with thick and lignified walls. Grittiness in pear is due to the presence of stone cells called as sclereids. The presence of numberous brachy sclereids makes the texture of pear gritty. The brachy sclereids are isodiametric in shape.

Stereome is a mechanical tissue which is formed due to polysaccharide deposition. This is seen in sclerenchyma, collenchyma and all non-living cells of vascular tissues. The deposition of polysaccharides thickens the cell walls in all the three tissue types. Collenchyma is formed due to the deposition of cellulose and is a living tissue. Sclerenchyma is formed due to the deposition of lignin and is a dead permanent tissue.

• Sclerenchyma cells are simple permanent tissue which is composed of dead cells and has secondary cell walls thickened with cellulose and usually impregnated with lignin. It serves two major functions protection and support.

Victoria regia belongs to the genus of water-lilies, from the family Nymphaeceae and inhabits in the still waters of all the rivers of the South American continent. These are characterized by the presence of  very large green leaves that are orbiculate, peltate, flat with their margin elevated all around and floating on water surface. The leaves borne on long foot stalks  are radiately and reticulately ribbed and the venation of lamina corrugated involute. A cross section reveals the presence of stellate sclerenchyma cells. The sclerenchyma cells with thick nonelastic walls provide the strength and support for these vast leaves