Define the term ‘tissue’.

Tissue is the group of cells similar in structure that work together to achieve a particular function. For example - blood, bone , xylem and phloem etc

Multi-cellular organisms show division of labour because a particular function is carried out by a cluster of cells (tissue) at a definite place in the body. The tissue is arranged and designed so as to give the highest possible efficiency of function.

Simple tissues are made of one type of cells which coordinate to perform a common function. For example parenchyma, epidermis etc

Complex tissues are made of more than one type of cells. All these coordinate to perform a common function. For example Vascular tissues. 

A group of cells that are similar in structure and/or work together to achieve a particular function forms a tissue. For example phloem, blood etc.

Xylem formed of four types of elements. They are (i) tracheids (ii) vessels (iii) xylem parenchyma (iv) xylem phloem.