CBSE Class 9 Science Tissue Exam Notes

CBSE Class 9 Science Tissue Exam Notes. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

Tissue

"A tissues may be defined as a group or collection of similar or dissimilar cells that perform a common function & have a common origin."

PLANT TISSUE

 Classification of Plant Tissues :

• A plant body is made up of different kinds of tissue. They are basically of two types - Meristamatic & permanent

 Meristematic tissue :

• Meristematic tissues may be defined as a group or collection of living cells which ar located specific locations and divide continuously to add new cells to the plant body.

 Characteristics of meristematic tissues :

• The cells of meristematic tissues are similar in structure and have thin and elastic primary cell walls made up of cellulose.

• These meristematic cells may be rounded, oval, polygonal or rectangular in shape 

• They are compactly arranged without intercellular spaces between them 

• Each cell contains dense or abundant cytoplasm and a large prominent nucleus.

• The dense protoplasm of meristematic cell contains few small vacuoles or no vacuoles at all.

 Apical meristem :

• This meristem is located at the growing apices of main and lateral shoots and roots. These cells are responsible for linear growth of an organ. Example root apical meristem and shoot apical meristem 

 Lateral meristem :

• This meristem consists of initials which divide mainly in one plane and cause the organ to increase in diameter and girth. The lateral meristem usually occurs on the sides both in stem and root. Lateral meristem is of two types, i.e., in the form of cork cambium and in vascular bundles of dicots in the form of vascular cambium. The activity of this cambium results in the formation of secondary growth.

 Intercalary meristem :

• This meristem is located in between the regions of permanent tissues. The intercalary meristem are usually persent at the base of node, base of internode or at the base of the leaf. They are responsible for growth of leaves and internodes.

Permanent Tissues  

Definition :

• These tissues are derived from the meristematic tissues but their cells have lost the ability of division and have attained their different forms.

They are of these types-Simple and Complex.

Simple Permanent Tissues :

• These tissues are made up of cells which are structurally and functionally similar. These are of three types -

Parenchyma Collenchyma

Sclerenchyma Protective tissue

Parenchyma :

• The parenchyma tissue is composed of living cells which are variable in thin morphology and physiology but generally having thin wall and a polyhedral shape and concern with vegetative activities of the plant.

•  They have inter cellular spaces between them.

• They act as storage for food and water.

Types of Parenchyma : Aerenchyma :

• In hydrophytes, the intercellular space between cells become wide & filled with air.

• Such a parenchymatous tissue having large air spaces is called Aerenchyma.

• These help in gaseous exchange and provide buoyancy to plant.

Chlorenchyma :

• When parenchyma is richly supplied with chloroplasts, it is called chlorenchyma. 

• They are found in leaf mesophyll, sepals, phylloclades, phyllodes, cladodes etc. It is photosynthetic in function and posses chlorophyll.

Collenchyma :

• It was discovered and coined by schleiden (1839). 

• The cells are living with intercellular space in between the cells or junctional places filled with cellulose and pectin.

• Generally they are longer than parenchyma

• Usually they are known as living mechanical tissue owing to their supportive functions. 

• It provides flexibility and strength to young plant organ.

• They were discovered and coined by Mettenius (1805).

• The cells are long, narrow, pointed at ends, thick walled and lignified. They are the dead cells.

• It impart hardness to plant parts and give mechanical strength.

 Protective Tissue :

• It includes epidermis and cork.

Epidermis :

• It is usually present in the outermost layer of the plant body such as leaves, flowers, stem and roots.

• Epidermis is one cell thick and is covered with cuticle.

• Cuticle is a water proof layer of a waxy substance called cutin which is secreted by epidermal cells.

• The main function of epidermis is to protect the plant from desication and infection.

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