Tissue NCERT Class 11 Notes
Tissues are categorized as −
Plant Tissue
Animal Tissue
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| Tissue |
♦️Plant Tissue
Following are the major types of plant tissue −
➖Meristematic Tissues
➖Permanent Tissues
▪️Simple Permanent Tissues
➖Parenchyma
➖Collenchyma
➖Sclerenchyma
➖Epidermis
▪️Complex Permanent Tissue
➖Xylem
➖Phloem
▪️Meristematic Tissue
➖Meristematic tissue mainly consists of actively dividing cells, and helps in increasing the length and thickening the stems of the plant.
➖Meristematic tissue, is common, present in the primary growing regions of a plant, for example, in the tips of stems or roots.
➖Depending on the region (where the meristematic tissues are found); meristematic tissues are classified as apical, lateral, and intercalary (see the image given below).
➖Apical meristem (as shown in the above image) is present at the growing tips of stems and roots and helps in their growth.
➖Lateral Meristem is found in the stem or root region and helps in their growth.
➖Intercalary meristem is found at the base of the leaves or internodes (on twigs) and helps in growth.
🔸Permanent Tissue
Cells of meristematic tissue later differentiate to form different types of permanent tissue.
Permanent Tissue is further categorized as −
➖Simple Permanent Tissue and
➖Complex Permanent Tissue
🔸Simple Permanent Tissue
Simple Permanent Tissue is further categorized as −
➖Parenchyma
➖Collenchyma
➖Sclerenchyma
➖Epidermis
🔸Parenchyma tissue provides support to plants and also stores food.
🔸Sometimes, parenchyma tissue contains chlorophyll and performs photosynthesis, in such a condition, it is known as collenchyma.
🔸The collenchyma tissue provides flexibility to plants and also provides mechanical support (to plants).
🔸The large air cavities, which are present in the parenchyma of aquatic plants, give buoyancy to the plants and also help them float, are known as aerenchyma.
🔸The Sclerenchyma tissue makes the plant hard and stiff. For example, the husk of a coconut is made up of sclerenchymatous tissue.
🔸The cells of Sclerenchyma tissue normally are dead.
🔸The outermost layer of cells is known as the epidermis.
🔸The epidermis is usually made up of a single layer of cells.
🔸The entire surface of a plant has the outer covering of the epidermis, which protects all the parts of the plant.
🔷Complex Permanent Tissue
Complex tissue, normally, consists of more than one type of cells which work together as a unit.
Complex tissues help in transportation by carrying organic material, water, and minerals up and down in the plants.
🔸Complex Permanent Tissue is categorized as;
➖Xylem
➖Phloem
🔸Xylem, normally, consists of the tracheid, vessels, xylem parenchyma, and xylem fibers.
🔸Xylem is accountable for the conduction of water and mineral ions/salt.
🔸Phloem, normally, is made up of four types of elements namely −
➖Sieve tubes
The sieve tube is the conducting element of the phloem. It is formed from a vertical series of elongated cells, interconnected by perforations in their walls in areas known as sieve plates. The perforations may be restricted to the smaller areas, and sieve fields, several of which are contained in each sieve plate.
➖Companion cells
Companion cells apparently function with the enucleate sieve tube elements and die when they break down.
➖Phloem fibers
Phloem fibers are important elements of plant architecture by providing mechanical strength and support to a plant in general and to phloem in particular. These fibers are abundantly formed in the long but narrow stems of many fiber crops.
➖Phloem parenchyma
Phloem parenchyma cells called transfer cells and border parenchyma cells, are located near the finest branches and terminations of sieve tubes in leaf veinlets, where they also function in the transport of foods.
🔸Phloem tissue transports food from leaves to other parts of the plant.
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