How Sclerenchyma Supports Plant Structure and Strength
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.
Macrosclereids
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.
Osteosclereids
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.
Astrosclereids
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.
Brachysclereids
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.
Trichosclereids
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.
Filiform Sclereids
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 -
Sclerenchyma provides mechanical support to the Plant.
And it provides hardness to the Plant.
It provides a protective covering around the seeds and nuts of the Plant.
It takes part in the conductive system of the Plant.
Sclerenchyma acts as a component vascular Tissue system.
They form the hypodermis of the xerophytes and prevent the loss of water.
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.
FAQs on Sclerenchyma: Definition, Classification & Functions
1. What is sclerenchyma tissue in plants?
Sclerenchyma is a type of simple permanent plant tissue composed of cells that are typically dead at maturity. Its primary role is to provide mechanical strength and rigidity to the plant. The cells have thick, lignified secondary walls, which makes them hard and supportive.
2. What are the main functions of sclerenchyma?
The main functions of sclerenchyma tissue are:
Structural Support: It provides a rigid framework to the plant, helping it to stand upright and withstand environmental stresses like strong winds.
Protection: It forms a hard, protective layer around seeds and nuts, such as the shell of a walnut or the husk of a coconut.
Conduction: Sclerenchyma fibres are part of the vascular tissues (xylem) and help support the water-conducting elements.
Hardness: It imparts hardness and a gritty texture to certain plant parts, like the pulp of pears and guavas.
3. How is sclerenchyma tissue classified?
Sclerenchyma tissue is mainly classified into two types based on their shape, structure, and origin:
Fibres: These are long, narrow, and needle-like cells with tapering ends. They occur in bundles and provide significant tensile strength. Examples include the fibres of jute and flax.
Sclereids (Stone Cells): These are short, irregularly shaped cells that are extremely hard. They are found in nutshells, seed coats, and are responsible for the gritty texture in the pulp of some fruits.
4. Why are sclerenchyma cells dead when they mature?
Sclerenchyma cells are dead at maturity because they undergo a process of heavy secondary thickening. During this process, their cell walls become uniformly coated with a hard, waterproof substance called lignin. This lignification makes the cell wall impermeable to water and nutrients. Consequently, the living content of the cell, the protoplast, cannot survive and eventually degenerates, leaving behind a hollow, rigid structure designed purely for support.
5. How does sclerenchyma differ from parenchyma and collenchyma?
Sclerenchyma, parenchyma, and collenchyma are all simple permanent tissues, but they differ in key aspects:
Living/Dead Cells: Sclerenchyma consists of dead cells at maturity, whereas parenchyma and collenchyma consist of living cells.
Cell Wall: Sclerenchyma has a thick, rigid cell wall with uniform lignin deposition. Collenchyma has unevenly thickened walls with pectin, providing flexibility. Parenchyma has thin, uniform cellulosic walls.
Primary Function: The primary function of sclerenchyma is rigid mechanical support. Collenchyma provides flexible support to growing parts, while parenchyma is involved in storage, photosynthesis, and secretion.
6. Where can you find sclerenchyma tissue in a typical plant?
Sclerenchyma tissue is found in parts of the plant that have stopped growing and require hardness and rigidity. Common locations include:
In the stems, often surrounding the vascular bundles.
In the veins of leaves, providing them with a rigid framework.
In the hard outer coverings of seeds and nuts.
In the roots to provide anchoring support.
7. What causes the gritty texture when eating a pear or guava?
The characteristic gritty texture you feel when eating a pear or guava is caused by clusters of sclereids, which are also known as stone cells. These are a type of sclerenchyma cell. They are short, hard, and irregular in shape, and they are scattered throughout the soft, fleshy pulp of the fruit, creating tiny, hard specks that feel gritty on the tongue.
8. Is xylem a type of sclerenchyma?
No, xylem is a complex permanent tissue, not a type of sclerenchyma. However, xylem does contain sclerenchyma cells as one of its components. Specifically, xylem is made up of four elements: tracheids, vessels, xylem parenchyma, and xylem fibres. These xylem fibres are a type of sclerenchyma that provide structural support to the water-conducting xylem tissue.
