• Unicellular organisms - Single cell performs all basic functions. e.g. Amoeba

Multi-cellular organisms – Most of the cells are specialize to carry our a few functions. e. g. Human beings

In human

• Muscles – movement

• Nerve cells – carry messages

• Blood – transport – food, oxygen, hormone, waste materials

• In multicellular organism - DIVISION OF LABOUR

• TISSUE – A group of cells similar in structure that work together to perform a particular function.

PLANT TISSUE

• I) Meristematic tissue

• II) Permanent tissue

Meristematic tissue Permanent tissue

Cells devide repeatedly Cells are derived from meristematic tissue & normally do not devide

Undifferentiated Fully differentiate

Small Variable in shape and size

Intercellular spaces generally absent

Intercellular spaces are present

Vacuole absent Large vacuoles in mature cells

Name Location Function

Apical meristems

Growing tips (Apex) of roots and stems

Elongation

Lateral meristems (Cambium)

Beneath the bark, in vascular bundles of dicot stems

Increase in diameter

Intercalary meristems

Base of the leaves / internode

Increase of length

Classification of Plant TissuesPlant Tissue

Meristmatic Permanent

Apical Lateral Intercalary Simple Complex

Parenchyma

Collenchyma

Sclerenchyma

Phloem

Xylem

Mature cells incapable of cell division

Below bark,

Cambium, in dicot roots and stems

Internodes

of stem

Cells are capable of cell division and have toipotency

Tips of root and stem

II) PARMANENT TISSUE • i) Simple permanent tissue

• ii) Complex permanent tissue

Simple permanent tissue

Parenchyma Collenchyma Sclerenchyma

Location Soft parts of plat – Cortex of root, ground tissues in stem, mesophyll of leaves

Below the epidermis of dicot stem and petiole (Absent in monocot)

In stem around vascular bundle, roots, veins of leaves, hard covering of seeds and nuts

Nature • Cells are isodiametric i.e. equally expanded on all sides

• They may be oval, round, polygonal or elongated

• Nucleus is present and hence living

• The cell walls are thin and made of cellulose

Cytoplasm is dense with a single large vacuole

Intercellular spaces may be present

May contain chlorophyll. Parenchyma which contain chlorophyll are called chlorenchyma.

• The cells are elongated and are circular, oval or polygonal in cross-section

Cell wall is unevenly thickened with cellulose at the corners against the intercellular spaces

Nucleus is present and hence the tissue is living

• Vacuoles are small

Intercellular spaces are generally absent

• If they contain chlorophyll they are known as chlorenchyma

• The cells are long, narrow, thick and lignified, usually pointed at both ends

• The cell wall is evenly thickened with lignin and sometimes is so thick that the cell cavity or lumen is absent

Nucleus is absent and hence the tissue is made up of dead cells

They have simple, often oblique pits in the walls

• The middle lamella i.e. the wall between adjacent cells is conspicuous

Function Store and

assimilate food Give mechanical

strength by maintaining turgidity

Prepare food if chlorophyll is present

Store waste products like tanin, gum, crystals and resins

Provide mechanical support to the stem

Allows easy bending in various parts of the plant without actually breaking it

Gives mechanical support to the plant by giving rigidity, flexibility and elasticity to the plant body.