Tag: permanent tissues and their types

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.

Fibres and sclereids are two types of sclerenchyma cells. The fibres are generally long, slender cells occurring in bundles. Their walls are thickened by lignin and the principal cell wall material is cellulose. Sclereids are the reduced form of sclerenchyma cells with thickened, lignified walls. So, the correct option is 'lignin, lignin'.

Cork (phellem) is not considered as living tissue. It is a water-resistant, protective tissue that displaces the stem epidermis during the secondary growth phase. A mature cork cell is non-living and has cell walls that are composed of a waxy substance that is highly impermeable to gasses and water called as suberin. Generally, the phloem together with the cork cells is considered to comprise the outer bark. The epidermis cell is a single-layered group of cells that covers plants leaves, flowers, roots, and stems. It forms a boundary between the plant and the external environment. The epidermis serves several functions, it protects against water loss, regulates gas exchange, secretes metabolic compounds and absorbs water and mineral nutrients. Cortex and pericycle are not the protective tissues. 
Thus, the correct answer is option D.

The ground tissue of plants is the supporting tissue which helps the specialized one to carry their function efficiently. The ground tissue includes parenchyma, sclerenchyma, and collenchyma.
Collenchyma cells have thin primary walls with some areas of secondary thickening. Collenchyma provides extra structural support, particularly in regions of new growth.
Sclerenchyma cells have thick lignified secondary walls and often die when mature. Sclerenchyma provides the main structural support to a plant. Ground tissue is a simple tissue. Xylem and phloem come under vascular bundles.
Thus, the correct answer is option A.

The bundle sheath of monocot leaf is made of parenchyma but just above and below the vascular bundles are found sclerenchymatous cells up to epidermis. The bundle sheath of dicot leaf made of parenchyma. Just above and below the vascular bundle, some parenchymatous cells or collenchymatous cells are present up to epidermis. Grass belongs to monocot so, contains sclerenchymatous bundle sheath. Sunflower, banyan and mango are dicot so, contains parenchymatous or collenchymatous bundle sheath. 
Thus, the correct answer is option C.

Companion cells are specialised type of parenchyma cells. The metabolic functioning of sieve-tube members depends on a close association with the companion cells, a specialized form of parenchyma cell. All of the cellular functions of a sieve-tube element are carried out by the (much smaller) companion cell, a typical nucleate plant cell except the companion cell usually has a larger number of ribosomes and mitochondria. The cytoplasm of a companion cell is connected to the sieve-tube element by plasmodesmata.