A group of cells that are similar in structure and work together to achieve a particular function is called tissue.
Or you can say a group of cells having common origin, similar structure and performing a definite function is called a tissue.
Organs are formed by the functional grouping together of multiple tissue.
All living organisms are made of cells.
In Unicellular organisms, a single cell performs all basic functions.
For example: Amoeba
In Amoeba, a single cell carries out movement,intake of food and respiratory gases, respiration and excretion.
But in Multi-cellular organisms there are millions of cells.Most of these are specialized to carry out a few functions. Each specialized function is taken up by a different group of cells.
Since these cells carry out only a particular function,they do it very efficiently. In human beings muscle cells contract and relax to cause movement,nerve cells carry messages, blood flows to transport oxygen,food,hormone and waste materials and so on.
In plants, vascular tissues conduct food and water from one part of the plant to other parts. So multi-cellular organisms show division of labor.
Cells specializing in one function are often group together in the body. This means that a particular function is carried out by a cluster of cells,called a tissue,is arranged and designed so as to give the highest possible efficiency of function.
Blood,phloem and muscles are all example of tissues.
Is there any difference between Plant and Animal tissue?
There are noticeable difference between plant tissues and animal tissues.
Plants are fixed they don’t move from one place to other which provides them structural strength.Most of these tissues are dead,since dead cells provide mechanical strength as easily as live ones and need less maintenance. The growth in plants are limited in certain regions.
On the other hand animals move around in search of food etc. They consume more energy as compare to plants.Most of there tissues are living. Cell growth in animals is more uniform.
They are grouped into two basic types.
Meristematic tissues: Meristematic tissues are group of cells, which have the ability to divide.
This tissue consists of small, cubodial densely packed cells, which keeps on dividing to form new cells. These tissues are capable of stretching, enlarging and differentiate into other types of tissues as they mature. Meristematic tissues give rise to permanent tissues.
Permanent tissues:The tissues, which are derived from the Meristematic tissues, are called as permanent tissues.
They are the tissues, which have lost their ability to divide as they have attained their mature form.
They are grouped into four basic types.
Epithelial tissue: Covers body surfaces and lines body cavities
Muscular tissues: Enables movement of structures within the body and movement of the entire person/animal
Connective tissues: Binds and Supports body parts
Nervous tissue: Enables responses to stimuli and coordinates bodily functions.