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Old meristematic cells lose the capacity to divide and transform into permanent tissues. This process of taking up a permanent shape, size, and function is called differentiation.

These are cells which have lost their capacity to divide but are specified to provide strength, flexibility and elasticity to the plant. These tissues can be further classified into simple permanent, complex permanent and special tissues.

Simple permanent can be categorized into parenchyma, collenchyma and sclerenchyma based on their function.

Parenchyma- they are live cells. They are usually loosely packed. This tissue provides support to plants and also stores food. In some situations it contains chlorophyll and performs photosynthesis and then it is called chlorenchyma. Parenchyma which contains large air cavities in aquatic plants is called aerenchyma. The aerenchyma helps in buoyancy.

Collenchyma – These are elongated living cells with small intercellular spaces. Their cell walls are made up of cellulose and pectin. Collenchyma occurs in the peripheral regions of stems and leaves to provide mechanical support and flexibility in plants.

Sclerenchyma – These are long, dead cells with a deposit of lignin in their cell wall. They have no intercellular spaces. Sclerenchyma occurs around the vascular tissues in stems, in the veins of leaves, and in the hard covering of seeds and nuts. They provide strength to the plant.

Epidermis aids in protection against loss of water, mechanical injury and invasion by parasitic fungi. Since it has a protective role to play, cells of epidermal tissue form a continuous layer without intercellular spaces. Epidermis of the leaf contains small pores called stomata. These are necessary for gases exchange and transpiration.

Cork – This is the outer protective tissue which replaces the epidermal cells in older roots and stems. Cork cells are dead and lack intercellular spaces. Their cell walls are thickened by suberin which makes them impermeable to water and gas molecules.

These are the tissues present only in animals. Different types of animal tissues are epithelial tissue, connective tissue, muscle tissue and nervous tissue.

The cells of striated muscles are in the form of long, unbranched fibres. Cells are multinucleate. Light and dark bands (striations) are present on muscle fibres; which gives the name striated muscles. Striated muscles are found in those organs where voluntary movement is possible, 

e.g. hands, legs, back, neck, etc.

Complex permanent tissue comprises of conducting tissues called xylem and phloem. Xylem is useful in transport of water and soluble substances. Xylem consists of tracheids, vessels, fibres and xylem parenchyma. Transport of minerals and water is unidirectional in xylem. Phloem is useful in transport of food molecules. Phloem comprises of sieve tubes, sieve cells, companion cells, phloem fibres and phloem parenchyma. Phloem is unlike xylem in that materials can move in both directions in it.

MUSCULAR TISSUE 

• Movements are brought about in our body with the help of muscular tissues. 

• They are long fibre-like cells called muscle fibres. 

• They are capable of contraction or relaxation.

Intercalary meristems is located in the leaves and internodes at the intercalary position. These help to increase the length of the internode. It is found in grass, monocots, and pines. It is a part of apical meristem and adds to the height of the plant.

(a) They are responsible for root and stem elongation, resulting in an increase in the height of the plant (primary growth). 

(b): They cause an increase in the diameter and girth of stems or roots (secondary growth).

Characteristic features of Meristematic tissues are:

• The meristematic cells may be round, oval, polygonal or rectangular in shape.
• Their cell walls are thin, elastic and made up of cellulose.
• They are closely arranged without intercellular spaces.
• They have dense cytoplasm with large nucleus.

A neuron consists of a cell body with a nucleus and cytoplasm, from which long thin half like parts arise.

Simple tissues consist of cells that are structurally and functionally similar. They are made up of only one type of cells. Simple tissues are of three types namely parenchyma, collenchyma and sclerenchyma.

Parenchyma – they are living cells and walled, soft in nature due to the presence of thin-walled cells 

Collenchyma – These are characterized by uneven thick-walled living cells. 

Sclerenchyma – They have cells with thickened lignified walls, providing them strength and making them waterproof.

The growth of plants occurs only in certain specific regions. This is because the dividing tissue also known as meristematic tissue (Meristos – divisible) is located only at these points.

Three features of cardiac muscles are:

(i) Cardiac muscles are involuntary muscles that contract rapidly, but do not get fatigued.

(ii) The cells of cardiac muscles are cylindrical, branched, and uninucleate.

(iii) They control the contraction and relaxation of the heart.

Plant tissues are of two main types, viz. 

(i) meristematic tissue and 

(ii) permanent tissue.

Functions of areolar tissue:

(i) It helps in supporting internal organs.

(ii) It helps in repairing the tissues of the skin and muscles

In multicellular organisms, the body system is based on the division of labour. It means the cells performing a specific function are grouped together to form a particular tissue. The different tissues are organized in a way to provide highest efficiency in functioning of the body.

A group of cells that are similar in structure and /or work together to achieve a particular function from a tissue.