Organisation of cells plant tissues

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Concept #1 Plant tissues-Meristematic tissue

Learning objectives

1. In Angiosperms, there are different tissues to perform different functions such as growth,absorption, photosynthesis, protection and conduction of water and minerals.
2. Plant tissues are mainly classified into two major groups based on their function as Meristematic and Permanent tissue.
3. Meristematic tissue help in the growth of the plant.
4. Permanent tissues perform various functions such as absorption, photosynthesis, protection and conduction of water and minerals.

Notes for teachers

The growth of plants occurs only in certain specific regions. This is because the dividing tissue, also known as meristematic tissue, is located only at these points. Depending on the region where they are present,meristematic tissues are classified as apical,lateral and intercalary. New cells produced by meristem are initially like those of meristem itself, but as they grow and mature, their characteristics slowly change and they become diferentiated as components of other tissues. Apical meristem is present at the growingtips of stems and roots and increases thelength of the stem and the root. The girth ofthe stem or root increases due to lateral meristem (cambium). Intercalary meristem is the meristem at the base of the leaves or internodes (on either side of the node) or twigs.
Cells of the meristematic tissues show the following features:

• The cells have thin walls.
• The cells divide actively and cause growth.
• The cells are closely arranged without any intercellular spaces between them.
• The cells have large nucleus and lack chloroplasts.
• Vacuoles are either small or absent.

Activities

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Concept #2-Permanent tissues-Simple permanent tissues

Learning objectives

• Cells of meristematic tissue differentiate to form different types of permanent tissue.
• Simple permanent tissue consists of same kind of cells performing common functions.
• They form a major part of the plant body and perform several functions like storage and support.

Notes for teachers

Permanent tissues in plants are divided into simple permanent and complex permanent tissues.Simple permanent tissues are again divided into three types. They are Parenchyma,Collenchyma and Sclerenchyma.
PARENCHYMA TISSUE:
Cells formed by meristematic tissue take up a specific role and lose the ability to divide. As a result,they form a permanent tissue. This processof taking up a permanent shape,size and function is called differentiation. Cells of meristematic tissue differentiate to form different types of permanent tissue.
Parenchyma, in plants, tissue typically composed of living cells that are thin-walled, unspecialized in structure, and therefore adaptable, with differentiation, to various functions. Parenchyma may be compact or have extensive spaces between the cells. It is often called ground, or fundamental, tissue and makes up the mesophyll (internal layers) of leaves and the cortex (outer layers) and pith (innermost layers) of stems and roots; it also forms the soft tissues of fruits. Cells of this type are also contained in xylem and phloem as transfer cells and, with both xylem and phloem as bundle sheaths, the cells that surround the vascular strands.

Parenchyma tissue

Parenchyma tissue is composed of loosely packed thin wall cells so that large spaces between cells(intercellular spaces) are found in this tissue. This tissue provides support to plants and also stores food. In some situations, it contains chlorophyll and performs photosynthesis, and then it is called chlorenchyma. In aquatic plants like pistia and lotus, large air cavities are present in parenchyma to give buoyancy to the plants to help them float.Such a parenchyma type is called aerenchyma. The parenchyma of stems and roots also stores nutrients and water.

COLLENCHYMA TISSUE:
The flexibility in plants is due to another permanent tissue, collenchyma. It allows easy bending in various parts of a plant (leaf,stem,petiole) without breaking. It also provides mechanical support to plants. We can find this tissue in leaf stalks below the epidermis.The cells of this tissue are living, elongated and irregularly thickened at the corners. There is very little intercellular space.The cell wall is made up of cellulose and pectin.

SCLERENCHYMA:
Sclerenchyma is the tissue which makes the plant hard and stiff. We have seen the husk of a coconut. It is made of sclerenchymatous tissue. The cells of this tissue are dead. They are long and narrow as the walls are thickened due to lignin (a chemical substance which acts as cement andhardens them). Often these walls are so thick that there is no internal space inside the cell. This tissue is present in stems, around vascular bundles, in the veins of leaves and in the hard covering of seeds and nuts. It provides strength to the plant parts.
The cell wall of sclerenchyma cells in plants like jute and hemp contain elongated, thread like thick walled cells called fibres.Since fibres are flexible and elastic they are used in coir industries to make gunny bags and ropes.

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Concept #3

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Concept #4

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