(Structure, Classification and Function of Parenchyma)
What is simple tissue?
Ø The tissue (a group of cells with particular function) composed of single type of cells.
Ø Three types of simple tissue system in plants:
What are the characteristics of Parenchyma (Parenchymatous Cells)?
Ø Parenchyma is a simple permanent tissue.
Ø They are living cells which contains plenty of water.
Ø Cells are nucleated with prominent nucleus.
Ø They are thin walled cells.
Ø Cell wall composed of cellulosic primary cell wall only.
Ø No lignin deposition in the cell wall of parenchyma.
Ø Parenchymatous cells are relatively undifferentiated
Ø Parenchyma is the least specialized along simple permanent tissues in plants.
Ø Parenchyma usually occupies in the ground tissue of stem, root, leaves, petiole and fruits.
Ø They are also found in xylem and phloem as xylem parenchyma and phloem parenchyma respectively.
Ø The parenchyma of ground tissue is originated from the ground meristem.
Learn more: Classification of Meristems
Ø Parenchyma of the xylem and phloem are originated from the cambium.
What are the Different Types of Parenchyma?
Ø Different types of parenchymatous cells occur in plants.
Ø Classification of parenchyma in plants is based on two criterions: (1) Function and (2) Shape.
Ø Based on functions the parenchyma is classified into Seven categories, they are:
(4). Vascular Parenchyma
(5). Medullary Parenchyma
(6). Conjunctive Parenchyma
(7). Armed Parenchyma
Ø They are the parenchymatous cells with chloroplasts.
Ø Chlorenchyma usually present in the mesophyll tissue of leaves.
Ø They are also present in the outer cortex young stem.
Ø The green colour of young stem and aerial roots are due to the presence of chlorenchyma.
Ø Chlorenchymatous cells are usually loosely packed with many intercellular spaces.
Ø Function of chlorenchyma: photosynthesis
Ø They are parenchyma cells with plenty of intercellular spaces.
Ø The huge intercellular spaces appear as large air cavities.
Ø Air cavities of aerenchyma can store air.
Ø Aerenchyma is a characteristic of aquatic plants.
Ø In aquatic plants, aerenchyma assists in floating.
Ø They provide buoyancy to the plants to balance in the water.
Ø Respiratory gases (CO2 or O2) stored in aerenchyma can be utilized by the plants when required.
Ø They are elongated and narrow sized parenchyma.
Ø They possess interpenetrating tapering (pointed) ends.
Ø Prosenchyma is usually present in the vascular tissues of higher plants.
(4). Vascular parenchyma
Ø They are the parenchyma cells occur in the vascular tissue of plants.
Ø They provide nourishment to the vascular tissues.
Ø They can also store ergastic substances like resins, tannins etc.
Ø Axial parenchyma and ray parenchyma of wood are best examples.
Ø Parenchymatous cells in heart wood (old secondary xylem) forms tyloses which can block the vessels cavities and can prevent the water flow through them.
Lear more: Tyloses formation and its Functions in Wood
(5). Medullary parenchyma:
Ø Medullary parenchyma occurs in the medullary ray of primary vascular tissue of stem.
Ø They are radially elongated cells with very thin walled cells.
Ø They allow radial condition of water and minerals.
Ø They can also store starch grains.
(6). Conjunctive parenchyma:
Ø They form the conjunctive tissue of the stele of roots.
Ø In most of the monocots, the conjunctive tissue becomes sclerenchymatous during maturation.
(7). Armed parenchyma:
Ø They are star shaped parenchymatous cells with many spiny projections to the interior of the cells.
Ø Armed parenchyma is found in the mesophyll of some gymnosperm.
Ø Example: mesophyll cells of Pinus leaf (needle).
Based on shape in cross section (C.S. or T.S.), parenchyma is classified into two categories, they are:
(1). Angular Parenchyma
(2). Circular Parenchyma
(1). Angular parenchyma
Ø In angular parenchyma, the cells are angular and polygonal in outline.
Ø This parenchyma is usually compactly packed without any intercellular spaces.
(2). Circular parenchyma
Ø In circular parenchyma, the cells are circular (round) in outline.
Ø They are usually loosely packed with plenty of intercellular spaces.
What are the Functions of Parenchyma?
@. Parenchyma forms the fundamental ground tissue system in plants.
@. Parenchymatous cells can store water.
@. They can store food materials as starch grains, protein grains or oil droplets.
@. Chlorenchyma of leaves and young stem assist in photosynthesis.
@. Aerenchyma in aquatic plants provides buoyancy.
@. Parenchyma can store ergastic substances.
@. Parenchyma in secondary wood form tyloses.
@. All meristematic cells are parenchymatous cells
@. Parenchyma can be easily differentiated into secondary meristem (Eg. cork cambium).
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