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Plant Tissues

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Plant Tissues - Lesson Summary

Plants are stationary, and hence are provided with some tissues made up of dead cells, which provide mechanical strength.  They have to withstand unfavourable conditions like strong winds, storms, floods etc.

Tissue:  A group of cells, that are similar in structure and work together to achieve a particular function, forms a tissue.  Different types of plant tissues include meristematic and permanent tissues.

Meristematic tissue:  Meristematic tissues are the tissues which have the ability to grow by rapid division.  They help in the primary growth of the plant.  Increase in length and increase in diameter of the plant are brought about by these meristematic cells.  Meristematic cells are living, cubical cells with a large nucleus.  These cells are closely packed with no intercellular spaces.  Depending on the region where the meristematic tissues are present, they are classified as apical, lateral and intercalary meristems.

    •  Apical meristem is present at the apical or growing tips of stems and roots.  Apical meristem increases the length of the plant.
    •  Lateral meristem is present in the radial portion of the stem or root.  Lateral meristem increases the girth of the plant.
    •  Intercalary meristem occurs at the base of the leaves or at the internodes.  Intercalary meristem increases the length of the internode.

Old meristematic cells lose the capacity to divide and transform into permanent tissues. This process of taking up a permanent shape, size, and function is called differentiation.

Permanent tissues:  The cells which have lost their capacity to divide but are specified to provide strength, flexibility and elasticity to the plant. These tissues can be further classified into simple permanent, complex permanent and special tissues.

    •  Simple permanent can be categorized into parenchyma, collenchyma and sclerenchyma based on their function.
    •  Complex permanent tissue comprises of xylem and phloem. Xylem is useful in transport of water and soluble substances. Xylem is made up of tracheids, vessels, fibres and xylem parenchyma. Phloem is useful in transport of food molecules. Phloem comprises of sieve tubes, sieve cells, companion cells, phloem fibres and phloem parenchyma.

Parenchyma – These are living, polygonal cells with a large central vacuole, and have intercellular spaces between them.  Parenchymatous cells form the ground tissue and pith.

    •  Parenchyma containing chloroplasts are called chlorenchyma.  The chlorenchyma help in photosynthesis.
    •  Parenchyma which contain large air cavities are called aerenchyma.  The aerenchyma help in buoyancy.
    •  Some parenchymatous cells act as storage cells for starch in fruits and vegetables.

Collenchyma – These are elongated living cells with small intercellular spaces.  Their cell walls are made up of cellulose and pectin.   Collenchyma occur in the peripheral regions of stems and leaves to provide mechanical support and flexibility in plants.

Sclerenchyma – These are long, dead cells with a deposit of lignin in their cell wall.  They have no intercellular spaces.  Sclerenchyma occur around the vascular tissues in stems, in the veins of leaves, and in the covering of seeds and nuts.  They provide strength to the plant.

Xylem – This tissue helps in the transport of water and dissolved substances throughout the plant.  The different components of the xylem include tracheids, vessels, xylem parenchyma and xylem fibres.  Tracheids and xylem fibres are made up of lignin, which provides mechanical support to the plant.

Phloem – This tissue helps in the transport of food throughout the plant.  The different elements of phloem include sieve tubes, companion cells, phloem parenchyma and phloem fibres.

Protective tissues:  These offer protection to the plant.  They include the epidermis and cork.

Epidermis – A layer of cells making up an outer covering of all the structures in the plant.  The layer epidermis is perforated by the stomata at certain places.  The stomata help in gaseous exchange and loss of water.

Cork – This is the outer protective tissue which replaces the epidermal cells in older roots and stems. Cork cells are dead and lack intercellular spaces.  Their cell walls are thickened by suberin which makes them impermeable to water and gas molecules.


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