[Biology Class Notes] on Sclerenchyma Pdf for Exam

Sclerenchyma Definition Biology – In-Plant Sclerenchyma is the supportive Tissue, which is composed of various hard woody cells. Sclerenchyma cells once matured are usually the dead cells that have heavily thickened secondary walls containing lignin. These cells are found in the non-growing region of the Plants like bark and the mature stems, and these cells are rigid and non-stretchable in nature. Sclerenchyma is one of the three ground and fundamental Tissues found in the Plant. 

 

Define Sclerenchyma Tissue – These are composed of dead cells, which have thickened walls containing lignin and highly cellulose content from 60 – 80 percent.

 

Sclerenchyma Diagram

 

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Classification of Sclerenchyma

Sclerenchyma cells are mainly divided into two types Fibers and sclereids 

 

Fibers

They are greatly elongated cells having long and tapering ends which interlock to provide mechanical support to the Plant. Fibers usually occur in the bundles and they can be found almost everywhere on the Plant body including the stem, roots, and vascular bundles of the leaves. Most of these Fibers include seed hairs, leaf Fibers, and bast Fibers, and these are an important source of the raw material for the textile industry and also for other oven goods. Fibers are further Classified into two groups: Xylary Fibers and extra Xylary Fibers. 

 

Sclereids

They are defined as mechanical Tissue having features like, they occur in a group or single, and they are found associated with the Plant vascular Tissue Xylem and phloem. The thickening of the cell wall in sclereids is non-uniform and it also contains a number of simple pits, with round apertures, and usually, the cells of the Sclerenchyma consist of the narrow lumen. It is sometimes known as the stone cells and it is also responsible for the gritty texture of pears and guava. Based on the shape of the cell, sclereids are further subdivided into four subClasses. 

It is also known as the “Malpighian cell”. Macrosclereids appear elongated and columnar in shape and they occur usually, in the outer epidermal cells of seed. An example of the Macrosclereids is the seed coat of Pisum species. 

It is also known as the “Bone cells”. Osteosclereids appear very similar to the shape of a bone of hourglass with enlarged, lobed, and columnar cells. And it is lobed towards the end. They are commonly found below the epidermal layer like the hypodermis of seeds and leaves of certain plants belonging to the category of xerophytes. Some of the examples are Leaves of Hakea species. 

It is also known as “Stellate cells” and it appears to be star-like, deeply lobed with the radiating arms from the central body. The radiating arms are usually pointed, irregular, and varied in number. Astroscelerids mainly occur from the upper to lower epidermis of the leaf. Some of the examples of it are Leaves of Thea, Olea, etc.

It is also known as the “Grit cells” and it deeply resembles parenchymatous cells, and its symmetry is roughly isodiametric. They are mainly present in the fleshy portions of fruit. Some of the examples of the Brachyscelerids are flesh of pear fruit, where the brachysclereids form grit and also refer to a stone cell.

It is also known as “Needle-like cells’ ‘ and it seems to appear hair-like that is more elongated and branched cells stretching towards the intercellular space. Trichosclereids are present in the specialized Tissues of leaves and roots some of the examples of this are aerial roots of Monstera sp, leaves of olive and water-lily, etc. 

It is also known as “Fibre-like cells” and it appears to be a very elongated, sparingly-branched and uncommon kind of cell. They are mainly found in the specialized Tissues of leaves. An example of filiform sclereid is the leaves of Olea.

 

What is the Function of Sclerenchyma?

Some of the important functions of the Sclerenchyma are given below – 

Location of Sclerenchyma 

Some of the locations where Sclerenchyma is found are present in the stems around the vascular bundles, in the veins of the leaves, and the hard covering of the fruit, seed, and nuts. Coconut husk is also made up of the same kind of Tissue. 

 

Sclerenchyma Structure 

The cells of the Sclerenchyma are usually long, narrow, pointed at both ends. They are uniformly thickened by the deposition of lignin without any space in between the cells. To understand and visualize the structure of Sclerenchyma refer to the Sclerenchyma diagram. 

 

Did You Know?

Is Sclerenchyma also found in humans? Yes, only some of the Sclerenchyma cells are found in the human body, not all the cells. As humans mainly depend on the skeleton for support and flexibility and on complex organs to perform life functions.