Tag: tissues: plant tissues

Sclereids are present in fruit walls of nuts, the grit of guava and pear, seed coats of legumes. So, the correct answer is (d).

Parenchyma tissue possess cells with a wide lumen. In aquatic plants, parenchyma cells possess large air cavities, which provide buoyancy to the plant. It enables the plant to float. Hence, option B is incorrect. 
Collenchyma tissue contains cell with wide lumen. Hence, option C is incorrect.  
Tracheids possess spacious lumen, which extends throughout the length. Hence, option D is incorrect. 
Sclerenchyma tissue possess long and narrow cells with narrow lumen. Hence, option A is correct.  

A. sclerenchyma fibers are long, narrow spindle-shaped sclerenchyma cells having tapering end walls.

B. phloem fibers are sclerenchyma fibers present in the phloem, also called bast fibers.

C. libriform fibers are the typical xylem fibers with thick walls and simple pits.

D. fiber tracheids are xylem fibers intermediate between tracheids and typical sclerenchyma fibers.

so the correct answer is ‘phloem fibers’.

Sclereids are a reduced form of sclerenchyma cells with highly thickened, lignified cellular walls that form small bundles of durable layers of tissue in most plants. Although sclereids are variable in shape, the cells are generally isodiametric, prosenchymatic, forked, or elaborately branched. They can be grouped into bundles, can form complete tubes located at the periphery, or can occur as single cells or small groups of cells within parenchyma tissues. An isolated sclereid cell is known as an idioblast. Sclereids are typically found in the epidermis, ground tissue, and vascular tissue. The presence of numerous sclereids form the cores of apples and produce the gritty texture of guavas. 

Sclerenchyma cells are characterized by relatively thick, lignified secondary cell walls. All plant cells initially have only a primary wall made predominantly of cellulose. As sclerenchyma develops, a secondary wall with a high proportion os lignin is deposited inside a primary wall.

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.