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Types of Permanent Tissues
Permanent tissues consist of cells that have undergone a loss of the ability to divide either temporarily or permanently. These tissues originate from the division and differentiation of meristematic tissues. Notably, the cells within permanent tissues typically do not undergo further division. These tissues exhibit diversity and can be categorized into three main types:
- Simple Permanent Tissue (Homogeneous Tissue)
- Complex permanent Tissues (Heterogeneous Tissue)
- Special Tissues (Secretory Tissue)
1.0Simple Permanent Tissue
This tissue is made up of structurally similar types of cells or only one type of cells (homogeneous) that perform a common function. Simple tissues are of three types : Parenchyma, Collenchyma and Sclerenchyma.
- Parenchyma: Living tissue, considered primitive and the first differentiated tissue.
Characteristics :
- Thin-walled cells with pectin-cellulose composition.
- Universal tissue found in various plant organs.
- Major components in organs like cortex, pericycle, pith, etc.
Functions :
- Storage, photosynthesis, and secretion.
- Idioblast cells store waste materials.
- Chlorenchyma conducts photosynthesis.
Modifications :
- Prosenchyma provides strength.
- Aerenchyma provides buoyancy.
- Stellate parenchyma offers mechanical support.
- Chlorenchyma contains chloroplasts for photosynthesis.
- Mucilage parenchyma stores water.
- Collenchyma: Living mechanical tissue, present in young dicot stems.
Characteristics :
- Elongated cells with localized deposition of pectin, cellulose, and hemicellulose.
- Absence of intercellular spaces.
- Often contains chloroplasts.
Occurrence :
- Stems of herbaceous dicotyledons.
- Forms hypodermis, providing flexibility.
- Found in leaf margins and petioles.
Functions :
- Provides tensile strength.
- Supports growing parts of the plant.
- Photosynthesis in chloroplast-containing cells.
- Sclerenchyma: Primary mechanical tissue with dead cells at maturity.
Characteristic :
- Long, narrow cells with thick, lignified walls.
- Pits contribute to rigidity.
Types :
- Sclereids: Small, diverse shapes, common in fruit walls, seed coats, and leaves.
- Sclerenchymatous Fibers: Longest cells with thick walls, providing structural support.
2.0Complex Permanent Tissues
Complex permanent tissues in plants are composed of cells that have lost their ability to divide and are specialized for specific functions. These tissues are derived from meristematic tissues, which are responsible for the growth and development of the plant. Unlike meristematic tissues, complex permanent tissues do not undergo cell division. There are two main types of complex permanent tissues in plants: xylem and phloem.
- Xylem : The primary function of xylem is to transport water, minerals, and nutrients from the roots to the other parts of the plant.
Components :
- Tracheids: Elongated, tapering cells with lignified walls that transport water.
- Vessels: Larger, tube-like structures formed by the fusion of cells called vessel elements. Vessels provide efficient water conduction.
- Xylem Fibers: Long, thick-walled cells that provide mechanical support.
- Xylem Parenchyma: Living cells that play a role in storage and lateral conduction of water.
- Phloem : The primary function of phloem is to transport organic nutrients, primarily sugars produced during photosynthesis, from the leaves to other parts of the plant.
Components:
- Sieve Tube Elements: Elongated cells that form tubes for the transport of food materials. Sieve plates at the ends of these cells allow the movement of nutrients.
- Companion Cells: Associated with sieve tube elements and assist in the loading and unloading of substances in the phloem.
- Phloem Fibers: Provide mechanical support to the plant.
- Phloem Parenchyma: Living cells involved in storage and lateral conduction of nutrients.
3.0Special Tissues
The special type of permanent tissues in plants is called "secretory tissues." These tissues are involved in the production and secretion of various substances, such as resins, latex, essential oils, and nectar.
- Glandular Tissues : Found in the epidermis of various plant organs, such as leaves, stems, and flowers. They secrete substances like resins, mucilage, and oils that may have protective or defensive roles.
- Lactiferous tissues : Lactiferous tissues in plants are specialized structures that produce, store, and transport latex, a milky or sticky fluid containing various chemical compounds.