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Simple Permanent Tissues

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Simple Permanent Tissues - Lesson Summary

Tissues are a group of cells similar in structure and functions. There are two main types of plant tissues — meristematic tissues and permanent tissues. Meristemetic tissues undergo active cell division while the permanent tissues do not undergo any division.

Permanent plant tissue is a group of cells, which are complete in growth and usually incapable of meristematic activity.  Permanent tissue is of two types—simple permanent tissues, where all cells are similar in structure and function, and complex permanent tissues, which are composed of different types of cells.
 
There are three types of simple permanent tissues —parenchyma, collenchyma and sclerenchyma.
 
Parenchyma is the most common ground tissue. It performs functions such as photosynthesis, storage and secretion. The cells of parenchyma have the same dimensions or the same length, width and height, which mean that they are isodiametric. Parenchymatous cells are of different shapes such as sphere, oval, round, polygonal or elongated. The cell walls are thin and made up of cellulose. Parenchymatic cells may be closely packed or have small intercellular spaces between them.
 
The second type of simple permanent tissue is collenchyma. It is found in the layers below the epidermis of dicotyledonous plants. This layer is either homogeneous or in patches. Collenchyma provides mechanical support to the growing parts of a plant, such as a young stem or the petiole of a leaf. The cells of collenchyma are thick at the corners due to cellulose, hemicellulose and pectin deposits. They may be oval, spherical or polygonal in shape, and there is no intercellular space between them. These cells often contain chloroplasts and assimilate food by the photosynthetic processes.
 
The third type of simple permanent tissue is sclerenchyma, which consists of long, narrow cells with thick lignified cell walls. In fact, the term sclerenchyma has been derived from the Greek word ‘scleros,’ which means hard. Sclerenchyma provides stiffness or mechanical support to plant organs. The cell walls of sclerenchyma have a few or many pits. These cells are generally dead and without any protoplasts. Based on the variation in form, structure, origin and development, sclerenchyma tissue can be of two types—fibres and sclereides.
 
Fibres are narrow, elongated, spindle-shaped, thick-walled cells with pointed ends. They usually occur in groups in various parts of the plant. Sclereids are short and thick-walled cells generally spherical, oval or cylindrical in shape. They are extremely lignified, and have narrow cavities or lumen. They occur in the hard covering of seeds, the shells of nuts, and the pulp of fruits like guava, pear and sapota. Simple permanent tissues are very essential as they provide protection, storage, support and strength to the plant. 

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