A group of cells that work together to perform a particular function.
Plant Tissues
◼ A tissue is an organization of cells that work together as a functional unit.
◼ Parenchyma cells make up parenchyma tissue, which is a simple tissue.
◼ Xylem and phloem are complex tissues; they are composed of a number of different cell types.
◼ Tissues are grouped into tissue systems that extend throughout the body of the plant to form the various organs of the plant.
◼ There are three plant tissue systems: vascular, dermal, and ground.
| Tissue | Cell Types | Function | Locations |
| Vascular tissue | Xylem is made up of vessels and tracheids Phloem is made up of sieve cells and companion cell |
Xylem transports water Phloem transports sugars |
In stems, leaves, and roots |
| Epidermal tissue | Parenchyma | Protect plant tissues and prevent water loss |
Outer layer of stems, roots, and leaves |
| Ground tissue | Parenchyma Collenchyma Sclerenchyma |
Makes up bulk of plant mass |
Stems, roots, leaves |
| Meristematic tissue | Parenchyma | Divide to produce new growth |
Tips of shoots Tips of roots In buds In a ring around the stem in woody plants |
The tissues of a plant are organized into three tissue systems: the dermal tissue system, the ground tissue system, and the vascular tissue system.
MERISTEMATIC TISSUE
Nature-cells of meristems divide continuously & help in increasing the length, girth of the plant. These cells show the following characteristics:
1. The cells of meristematic tissue are similar in structure & have thin cellulose cell walls.
2. The meristematic cells may be spherical, oval, polygonal or rectangular in shape.
3. The meristematic cells are compactly arranged & do not contain any intercellular space between them.
4. Each meristematic cell contains dense or abundant cytoplasm & a single large nucleus.
5. The meristematic cells contain few vacuoles or no vacuoles at all.
Occurrence-Meristematic tissues are growth tissues & are found in those regions of the plant that grow. According to their position in the plant, meristems are apical, lateral & intercalary.
Function-the main function of meristematic tissue is to continuously form a number of new cells.
Epidermis:
• It is usually present in the outermost layer of the plant body such as leaves, flowers, stem & roots.
• Epidermis is one cell thick & is covered with cuticle.
• Cuticle is a water proof layer of a waxy substance called cutin which is secreted by epidermal cells.
• Cuticle possess variable thickness in plants such as it is more thicker in xerophytic plants.
• Cells of epidermis are elongated & flattened & do not contain any intercellular space between them.
• Their inner contents are similar to parenchyma cells.
❑ The main function of epidermis is to protect the plant from desiccation & infection.
❑ In fact, cuticle of epidermis helps to reduce water loss by evaporation from the plant surface as well as helping in preventing the entry of pathogens.
Cork/Periderm:
• As plants grow older, the outer protective tissue undergoes certain changes.
• A strip of secondary meristem, called phellogen or cork cambium replaces epidermis of stem.
• Cork cambium is a simple tissue having only one type of cells.
• The cells of cork cambium are rectangular & their protoplasrs are vacuolated & contain tannins & chloroplasrs.
• Cork cambium gives off new cells on its both sides, thus, forming cork on the outer side & the secondary cortex or phelloderm on the inner side.
• The layer of cells which is cut by cork cambium on the outer side ultimately becomes several layered thick cork or the bark of trees.
• Cells of cork are dead & compactly arranged without intercellular spaces.
• The walls of cork cells are heavily thickened by deposition of an organic substance, called suberin.
• Suberin makes these cells impermeable to water & gases. • The cork cells do not contain protoplasm but are filled with resin or tannins.
• In case of onion bulb too, in the skin of onion the cell walls become thick & water proof due to addition of suberin.
❑ Cork is protective in function. Cork cells prevent desiccation, infection & mechanical injury.
