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Areolar tissue is connective tissue which hold organs in place and attaches epithelial tissue to other underlying tissues.

The cells of parenchyma have thin cell wall. They are loosely packed; with lot of intercellular spaces between them. They are living cells. They are generally present in all organs of a plant. They are oval or spherical or rectangular or cylindrical in shape. The cell wall is made of cellulose and pectic materials. Parenchyma makes the largest portion of a plant body. Parenchyma mainly works are packing material in plant parts. The main function of parenchyma is to provide support and to store food. In some plant parts, parenchyma has chlorophyll as well. In that case, parenchyma carries out photosynthesis and is then termed as chlorenchyma. In aquatic plants, large air cavities are present in parenchyma. This provides buoyancy to the plant, and then the parenchyma is known as aerenchyma.

Xylem vessels have perforations at the end and are placed one above the other like a long pipe line. They are seen in the xylem of angiosperms. They conduct water, mineral nutrients and also provide mechanical strength to the plant body.

Tracheids are elongated, tapering cells with blunt ends. They have lignified secondary wall. They are the chief water conducting elements in Pteridophytes and Gymnosperms.

Companion cells are thin walled elongated specialized Parenchyma cells. They are associated with sieve elements. They have a prominent nucleus and cytoplasm. They help the sieve tube in conduction of food materials in angiosperms.

Animal tissues are of four types:

(i) epithelial tissue, 

(ii) connective tissue, 

(iii) muscular tissue and 

(iv) nervous tissue.

The fibres of sclerenchyma associated with phloem are called phloem fibres.

They are also called bast-fibres. They give mechanical support to the plant. Among the four types of phloem cells, phloem fibres are the only dead tissues.

The outer protective layer or bark of a tree is known as the cork. It is made up of dead cells.

Therefore, it protects the plant against mechanical injury, temperature extremes, etc. It also prevents the loss of water by evaporation.

Phloem consists of sieve tubes, companion cells, phloem fibres and phloem parenchyma.

(i) Intercalated discs- They form the zig zag thickening in cardiac muscles.

(ii) Lignin, since the thickening in sckerenchyma is due to lignin.

Skeletal muscles are involved in this case. Since skeletal muscles are involved in voluntary body movements. These are the muscles which will help in carrying weights and will get tired.

In complex organisms, different tasks are carried out by different organs and organ systems. Tissues are the first step towards division of labour in complex organisms.

Following are the various types of tissues found in plants:

● Meristematic tissue: These tissues are further subdivided into apical meristem, intercalary meristem, and lateral meristem.

● Permanent tissue: This is further subdivided into simple permanent tissue and complex permanent tissue. 

● Simple permanent tissue: Parenchyma, collenchyma, sclerenchyma, epithelial tissue are various types of simple permanent tissue.

● Complex permanent tissue: Xylem and phloem are various types of complex permanent tissue.