Tag: permanent tissues and their types

A. Sclerenchyma is known as the supporting tissue of the plants which make the plant hard and stiff as their cell wall is made up of cellulose, hemicellulose and lignin.

Parenchyma cells are thin-walled, flexible and loosely packed cells. They are often alive at maturity. Their shape changes as per function. They are filler tissue in soft parts of a plant. 
Collenchyma cells are thin-walled with some areas of secondary thickening. They provide extra structural support and flexibility to plant. Coconut husk is not made of collenchymatous cells. 
In many aquatic plants, parenchyma cells have large air cavities to give buoyancy to the plant and enable them to float in water. Such parenchyma cells are called as aerenchyma.
Sclerenchyma is dead, long, thin narrow cells. Walls of sclerenchyma cells are lignified, which make them thick. This tissue makes the plant hard and stiff. Coconut husk is very hard and is made of such thickened, lignified cells. Such cells make it very hard to pull out the coconut husk.

Answer B: Lignin

• Parenchyma cells are alive, thin-walled cells. They are present in soft parts of the plant. But pear fruit has hard parts inside, which give it a gritty texture. Therefore, option B is incorrect. 
• Collenchyma cells are thin-walled with some areas of secondary thickening. They provide extra structural support and flexibility to plant. Therefore, option C is incorrect.
• Aerenchyma cells are present in an aquatic plant. Such cells have large air cavities, which enable the plant to float in water. 
• Sclereid is a reduced form of sclerenchyma, which has thickened lignified walls. In pear fruit, sclereid cells are present in bundles, which give a gritty texture to the fruit. Such cells are also called "stone cells" because of their hardness.

the sclerenchyma tissue is present in stems, around vascular bundles, in the veins of leaves and in the hard covering of seeds and nuts. It is the tissue which makes the plant hard and stiff due to the presence of lignin in the cell wall. The cells of this tissue are dead. So, the correct answer is "sclerenchyma".

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.