Tag: tissues: plant tissues

A. Cortical fibres are the extraxylary fibres present in cortex.

B. Sclereides are excessively thick walled short sclerenchyma cells.

C. Xylary fibres are the sclerenchyma fibres present in the xylem.

D. Phloem fibres are the sclerenchyma fibres present in the phloem.

So the correct answer is ‘sclereids’.

Sclerenchyma tissue possesses long, narrow cells with thickened walls. They possess secondary walls made of lignin. Lignin is a chemical substance, which acts as cement and hardens them. Therefore, option B is correct. 

• Simple permanent tissues are a group of cells with the same origin, structure and function are called simple permanent tissues.
•  Parenchyma, collenchyma, and sclerenchyma are simple tissue which coordinates to perform a similar function.

Collenchyma, is the simple permanent mechanical tissue, formed of living cells. 

Sclerenchyma, is the simple permanent mechanical tissue, formed of dead cells.

Aerenchyma, is a type of parenchyma, simple permanent tissue, formed of living cells.

Xylem is a simple complex permanent tissue formed of the majority of dead cells. 

So, the correct answer is ‘Sclerenchyma’.

Sclerenchyma cells possess pits and plasmodesmata where cell walls are not lignified or thickened. Plasmodesmata aid in cytoplasmic connections in adjacent cells through which transportation of substances occur. Therefore, option D is correct.

The plant tissues commonly found in fruit walls of nuts and pulp of some fruits like guava are termed as sclereids. 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. The presence of numerous sclereids form the cores of apples and produce the gritty texture of pears. 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.
Thus, the correct answer is option C.

• Sclerenchyma makes plant hard and stiff. The cells of the tissue are dead. They are long and narrow. For example, coconut. The cells of this tissue are dead and its wall is thickened with a chemical substance Lignin. (Lignin is a chemical substance which acts as cement). 
• Sclerenchyma is present in the stems, around the vascular bundle in the veins of the leaves and the hard covering of seeds and nuts. It provides strength to the plant parts.

Lignin is a component of the secondary cell walls of sclerenchyma. Two types of sclerenchyma cells exists- fibres and sclereids. Their walls consist of cellulose, hemicellulose and lignin. Sclerenchyma cells are the principal supporting cells in plant tissues that have ceased elongation.