Botany

Tissue and Plant Tissue

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.

 

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