CHAPTER – 6

TISSUES

DEFINITION

A group or collection of similar cells performing or help to perform same function and arise from the same origin are called tissues.

The tissues are of different types depending on the functions of the organism, they are mainly of two categories PLANT TISSUES and ANIMAL TISSUES.

PLANT TISSUES

Plants perform functions which are different from animals and also their structure is different , hence they have tissues which are different from animals. They are further classified into many sub categories which is shown in the table below:

MERISTEMATIC TISSUE

• The main characteristic of this tissue is that it is responsible for the growth of plants.

• The cells of this tissue continuously divide and later differentiate ( i.e. get converted ) into permanent tissue.

Characteristics of the cells/ tissue• The cells are made of thin & elastic cell wall

made of cellulose.• The cells may be round , oval, polygonal or

rectangular in shape.• They are compact, having no intercellular

space.• There is a large nucleus and abundant

cytoplasm.• The protoplasm contains very few or no

vacuoles at all.

This tissue occurs at specific regions of the plant body

• This is so because in plant body growth occurs only at these regions.

• Hence , on the basis of this there are 3 types of meristem :

1. APICAL MERISTEM 2. INTERCALARY MERISTEM 3. LATERAL MERISTEM

APICAL MERISTEM

As the name suggests this tissue is present at the apex of the main & lateral shoots and roots.

This tissue gives the plant body a linear growth.

LATERAL MERISTEM

This tissue lies on the sides of the plant body.

It lies under the bark of the plant in form of cork cambium.

It gives the plant it’s width or girth.

INTERCALARY MERISTEM

This tissue is present at the base of the nodes, internodes, leaves etc.

They are also present in between the permanent tissue.

They give the plant growth in length.

PERMANENT TTISSUE• These tissues arise from the meristematic

tissue.• The cells of this tissue gradually loose their

power to divide and acquire a definite shape, size and function.

• These tissues may be living or dead.• There are 2 types of permanent tissues1. Simple permanent tissue2. Complex permanent tissue.

SIMPLE PERMANENT TISSUE

• This tissue comprises of same type of cells which perform the same function and all arise from the same origin. There are three categories of simple permanent tissues: Parenchyma, Collenchyma, & Sclerenchyma.

THE THREE SIMPLE PERMANENT TISSUES

PARENCHYMA• Characteristics: a) The cells are living.b) The cells are thin walled.c) There may or may not be

intercellular spaces. d) They are the most

unspecialized cells.e) No depositions are seen, the

cell wall consists only of cellulose.

f) There is a prominent nucleus, cytoplasm & vacuoles.

• There are some special types of parenchyma tissues : • Storage parenchyma : The cells enlarge to store

nutrients & water.• Aerenchyma : Air cavities are present in the

parenchyma tissue to provide buoyancy to the aquatic plants.

• Chlorenchyma : These parenchyma cells have presence of chlorophyll & hence can perform the function of photosynthesis.

Parenchyma tissue is found generally in all parts of the plant body. It forms the Ground tissue in leaves, stem, roots & fruits etc.

Functions of parenchyma :

a) To store materials such as starch, proteins, hormones etc and waste products such as gum, tannin, resin etc.

b) Parenchyma cells perform the metabolic activities of the plant.

c) Forms the packaging tissue between the specialized tissue.

d) By providing turgidity , they provide mechanical strength.

e) Chlorenchyma helps in performing photosynthesis.

COLLENCHYMA

• Characteristics:a) It has cells which are

somewhat elongated.b) The cell walls are thin

except at the angular region ( where the cells join). The thickenings are caused due to deposition of cellulose or pectin.

c) There is o or less intercellular space.

d) The cells are living, have distinct nucleus & dense protoplasm.

e) They often contain chlorophyll.

• Functions : a) Providing mechanical

strength is the primary function.

b) Provide flexibility.c) Photosynthesis, as they

contain chlorophyll.

They are present below the epidermis in dicot stems and leaves. They absent in dicot roots and all parts of monocot plants.

SCLERENCHYMA