What is a Tissue?
Organs such as stem, roots in plants and stomach, heart and lungs in animals are made up of different kinds of tissues. A group of similar cells that work together to do the same job is called tissue or tissue is a group of cells similar in structure and function. They are derived from the same layer of cells in the embryo. Tissues combine to form organs. An organ is made up of different kinds of tissues, which work in a co-operative and co-ordinate manner to perform a specific function inside the body. Example: blood, bone, cartilage, epithelial tissue, connective tissues are some examples of animal tissues whereas parenchyma, collenchyma, xylem, phloem and ground tissue are examples of plant tissues. The study of tissues is called histology. A group of cells with similar origin, structure and function is called tissue, e.g. bone, muscle in animals and meristem in tips of root and shoot in plants.
The Plant Tissues:
The plant tissues are of two types; meristematic and permanent.
Meristematic tissues are formative tissues add new cells to the plant body. They contribute towards growth in length and width of the plant. These are made up of actively dividing cells full of cytoplasm and large nuclei. Vacuoles are either small or absent. The cells are small, rounded, oval or polygonal with thin walled. The cells lack spaces between them (lack intercellular spaces). There are three types of meristems;
It is found at the tip of stems and roots and is responsible for growth in length of the plant.
It is found at the base of leaves, internodes or below the nodes and responsible for the intermodal growth.
Lateral meristem (cambium):
It is present within the vascular bundles plants and increases thickness of the plant. Cambium is present in the cortex of dicot plants.
They are composed of cells that cease to divide. Permanent tissues are derived from meristematic tissues. These tissues form the bulk of the plant body. The cells of permanent tissues may be living or dead and small and thin walled. Cytoplasm is much less and nucleus is small and cells do not divide. There are two types of permanent tissues;
Simple permanent tissues:
Simple tissue is made up of only one type of cells. Common simple tissues are parenchyma, collenchyma and sclerenchyma.
Complex permanent tissues:
Complex tissue is made up of more than one type of cells working together as a unit. Common examples are xylem and phloem.