What is Permanent Tissues, Types, and Functions? Class 9th Science
Permanent tissues are those tissue which has lost the power of cell division. Cells of ‘permanent tissues’ are matured, assume a definite shape, size and function. On the basis of constituents call, permanent tissues are classified into three types: simple, complex and secretory or special tissues. Permanent tissues are of two types:
Simple tissues and Complex tissues
(i) Simple tissues: This type of tissue is composed of the same type of cells.
These are again of four types:
(a) Parenchyma simple tissues: Cells of parenchyma tissues are live. They are oval, elongated and loosely packed with large inter-cellular space, forming basic packing of tissue and are found throughout the plant body.
Functions of parenchyma:
They provide mechanical support to the plant body.
They store food and nutrients in vacuoles.
Chlorenchyma: Parenchyma with chlorophyll which performs photosynthesis is called as chlorenchyma.
Aerenchyma: In aquatic plants, cells of parenchyma have large air cavities to give buoyancy to the plant and is called aerenchyma.
(b) Collenchyma simple Tissues: Cells of collenchyma are live. They are oval and elongated and tightly packed with no inter-cellular spaces. They are found below epidermis in leaves and stem.
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Functions of collenchymas tissues:
They provide mechanical support to plant.
They also provide flexibility to plants so that they can bend without breaking.
(c) Sclerenchyma Simple Tissues: Cells of sclerenchyma are dead. They are narrow and elongated. The cell wall in sclerenchyma is composed of lignin which makes it hard. Sclerenchyma is found around vascular bundles, veins of leaves in the hard covering of seeds and nuts. For exampleSclerenchyma tissues are found in the coconut husk.
Functions of sclerenchyma:
They help to makes parts of plant hard and stiff.
Also provides mechanical strength.
(d) Protective tissues: They protect the plant body by forming an outer layer.
There are two types of protective tissues:
- Epidermis Simple Tissues: Epidermis tissue covers the entire body of the plant. They protect the plant from injury, germs and water loss.
Cells of epidermal tissue form a continuous layer without intercellular spaces.
Stomata are small openings on epidermal layer of leaf and soft part of the stem to facilitate the gaseous exchange and transpiration in plants. Each stoma is composed of two guard cells which regulate the opening and closing of stomata.
In desert plants, epidermis and cutin (a waterproof waxy substance secreted by epidermis) are thicker to reduce the loss of water due to transpiration.
- Cork Simple Tissues: These types of tissue consist of dead cells with no intercellular spaces. They form the outer layer of old tree trunks.
Cork cells have a chemical called suberin in their walls that makes them impervious to gases and water.
Cork tissue protects plants from injuries, germs and water loss.
Cork being light in weight is used for making several products like bottle stoppers and shuttle cork.
(ii) Complex tissues: Group of different type of cells performing a common task together is named as complex tissues.
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Complex tissues are of two types:
(a) Xylem (b) Phloem
(a) Xylem: This is the tissue that transports water and nutrients from root to upper parts of the plant. It is composed of four types of cells i.e., tracheid, vessel, xylem parenchyma and xylem sclerenchyma (fiber).
- Tracheids are long elongated cells with the tapered ending. Tracheid cells are dead. Tracheid transports water through pits.
- The vessel is a pipe like structure. Vessels are dead and have lignified thick cell wall. Upper and lower portion of the cell wall is absent.
- Parenchyma’s are living cells. They store food and nutrients.
- Sclerenchyma’s (fibers) are dead cells. They provide mechanical support to plant.
(b) Phloem: Phloem is the tissue that transports food from the site of photosynthesis to different parts of plants.
It is composed of four types of cell i.e. sieve cells, companion cells, phloem parenchyma, phloem fiber or blast fiber. All types of cells are live except phloem fibers.
- Sieve cells are elongated and have a thin cell wall. They have cytoplasm but no nucleus and other organelles. These cells are responsible for transportation of food and nutrients
2. Companion cells have cytoplasm, nucleus, and other organelles. They perform the tasks required for sieve cells for a living.
3. Phloem parenchyma store food.
4. Phloem fibers have a thick cell wall and they provide mechanical support to plant.
Read more articles on Plant and Animal tissue – Muscular tissue, epithelial tissue, nervous tissue.
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