Describe in detain meristematic tissues, Parenchyma , collenchyma and sclerenchyma tissues.


Group of cells is called tissue. Group of cells may be similar or dissimilar with common origin and perform identical function.

Meristematic tissue

Meristos = divided. These are composed of cells that are in a state of division or retain the power of dividing. These cells are essentially alike being either spherical, oval or polygonal in shape without any intercellular spaces, their walls thin and homogenous; the protoplasm abundant and active with large nuclei and the vacuoles small or absent.

Meristematic tissues may be apical and lateral. The apical meristem lies at the apex of the stem and the root and gives rise to primary permanent tissues while the lateral meristem e.g.: Cambium lies among masses of permanent tissues and gives rise to secondary permanent tissues.

Permanent Tissues are composed of cells that have lost the power o dividing, having attained their definite form and size. They may be living or dead and thin walled or thick walled. Permanent tissues are formed by differentiation of the cells of the meristems (apical and lateral) and may be primary and secondary.
The primary permanent tissues are derived from the apical meristems of growing region and the secondary permanent tissues from lateral meristems.

(1)        Parencnhyma
It is kind of simple tissue. It consists of collection of cells which are more or less are equally expanded on all sides. Typical parenchymatous cells are oval, spherical or polygonal in shape. Their walls are thin and made up of cellulose. These are living. Parenchyma is of universal occurence in all soft parts of plants. Its function is storage of food material.
It manufactures sugar and starch.

(2)        Collenchyma
This tissue consists of somewhat elongated cells with the corners or intercellular spaces much thickened with a deposit of cellulose and pectin. In T.S of stem cells look circular or oval. Their walls are provided with simple pits. Collenchyma occurs in few layers under the skin (epidermis) of herbaceous dicotyledons e.g.: sunflower and gourd. It is absent from root and monocots. The cells are living and contain some chloroplasts. Being flexible in nature collenchyma gives tensile strength to the stem. It manufactures sugar and starch. Its functions are mechanical and vital.

(3)        Schlerenchyma
Scleros = hard.
Schlerenchyma consists of very long, narrow, thick walled and lignified cells pointed at both ends. They are fibre like and are called schlerenchymatous fibres or simply fibres. They have simple often oblique pits in their walls. These cells are many in number in plants and occur in patches. They are dead cells and serves as mechanical function and give strength and rigidity to plant body and thus enable it to withstand various strains. Their average length is 1 to 3 mm but in fibre yielding plants such as hemp, Indian hemp, Decan hemp, jute. Such fibres are of commercial importance. Sometimes here and there in the plant body special types of sclerenchyma may be developed. These are known as stone or sclerotic cells. Cells are thick walled and are irregular in shape or slightly elongated. Some cells occur in hard seeds, nuts and stony fruits.

Comments

Post a Comment

Popular posts from this blog

Compare the anatomy of Bifacial and Isobilateral leaves

BIFACIAL LEAF: It is also called dorsiventral leaf. This leaf is more strongly illuminated on upper surface than on lower surface. This unequal illumination induces a difference in the internal structure between upper and lower sides. Its internal structure shows: (1)        Upper Epidermis This is single layer of cells with thick cuticle which checks excessive evaporation of water from the surface. It does not contains chloroplasts, stomata are also absent. (2)        Lower Epidermis This is also single layer but with a thin cuticle. It bears many stomata, two guard cells of which contain some chloroplast, none are present in the epidermal cells. Internal to each stomata is large cavity called respiratory cavity. Lower epidermis of leaf is meant for exchange of gases (oxygen and carbon dioxide) between the atmosphere and the plant body. Excess water also evaporates from lower epidermis. (3)...
Read more

osmoregulation in terrestrial and aquatic animals

Mechanism of osmoregulation is very important for all groups of animals whether inhibting land or water. Unlike plant cells, animal cells when placed in hypotonic solution burst due to the continuous absorption of water. On the contrary they would shrink and die if constantly placed in hypertonic solution. Normally uptake and loss of water are in balance for proper survival of cell. (1)        Osmoregulation in terrestrial animals: Terrestrial animals are more likely to loose water by evaporation through their permeable surfaces exposed to amsophere. Among various animal groups only Arthropods and vertebrates became the most successful land dwellers. They have developed number of strategies to maintain osmoregulation of their body fluid. (a) Water proof external coverings: To prevent water loss through external surfaces, vertebrates like reptiles, birds and mammals have water proof keratinized epidermis. Similarly the insects have developed...
Read more

Autobiographical elements in A Farewell to Arms

Introduction Some, literature can be satisfactorily read and discussed taking the author into account. Other literature seems inseparable from the person who created it. To an extraordinary degree Hemingway and what he has written exist in a synergetic relationship, reinforcing and fulfilling each other; he has created a personal legend which serves as an ambience in which we read him. Autobiographical Touches The novel A Farewell to Arms autobiographical elements. The love-affair between Fredric and Barkley, the hero’s injury in the battlefield, his despair and frustration, the hero’s separate peace with life are some of the characteristics of Hemingway’s life. Hemingway himself had received the injury caused by the mortar-shell at Fossalta, and he was admitted into the Milan hospital for recuperation in the late summer and autumn of 1918. He fell in love with the nurse in the Milan hospital. Carlos Baker has thrown light on this fact. In A Farewell to Arms Hemingway was d...
Read more