Tissues-Notes

1.  Plant tissues- On the basis of dividing capacity, plant tissues are of two types-

       (a)  Meristematic tissue

       (b)  Permanent tissue

(a)  Meristematic tissue- It consists of actively dividing cells. Meristematic tissues have three types.

       •   Apical meristem- present at the growing tips of stems and roots and helps in increasing the length of stem and roots

       •   Intercalary meristem- Present at the base of the leaves. It is required for longitudinal growth of plants.

       •   Lateral meristem- present on the lateral side of stem and roots and helps to increase the length of stem and roots.

(b)  Permanent tissue- It is formed from the meristematic tissues, the cells in this tissue lose the ability to divide. They are further divided into –

       •   Parenchyma- It is composed of unspecialized living cells with relatively thin cell walls, intercellular space, present in soft part of the plants.

       •   Collenchyma- Composed of living and elongated cells with cell walls irregularly thickened at the corners. There is no inter-cellular space. It helps in bending of leaves and stems.

       •   Sclerenchyma- It is composed of long narrow, thick-walled cells. It is made of dead cells and there are no inter-cellular cells.

       •   Complex permanent tissue- It is made up of more than one type of cells.

2.  Animal tissues- Animal tisues are divided into four types based on the functions performed by them.

       (a)  Epithelial tissues- They form the covering of the external surfaces, internal cavities and organs of the animal body. These are various types of epithelial tissues-

                     •   Simple squamous epithelium

                     •   Cuboidal epithelium

                     •   Columnar epithelium

       (b)  Connective tissues- They connect various organs of the body. They are divided into:-

                     •   Areolar tissue

                     •   Adipose tissue

                     •   Dense regular connective tissue

                     •   Skeletal tissue

       (c)  Muscular tissue- Muscular tissue provides movement to the body. They are divided into three types:

                     •   Striated/skeletal/voluntary muscles

                     •   Smooth/involuntary muscles

                     •   Cardiac muscles

       (d)  Nervous tissue- These are present in brain, spinal cord and nerves. Neurons are cells of nervous tissue which consist of a cell body, axon and dendrite.