Organ is a distinct body part that performs a special function. Each organ is mixed with a contradictory tissues. The meaning of 'organ' 'voice means that are not blinding each other.The cell is the smallest composition that displays all the characteristics of life. The community of the same function cells are called tissue. The organ is a huge structure. It is accompanied by two or more tissues that can be seen with the naked eye. A group of organs collaborating to perform a similar body function are the named as organ system. For example esophagus, stomach, liver etc organs are together formed the digestive system. The organs of the circulatory system are the heart, arteries, veins and capillaries. The body parts needed to grow in leaves, stems, root and root are for the growing organs in plants. Flowering are reproductive organs too.
Organs especially in animals are full of diversity. It is because of the natural selection by generations. If organs are a little and simple in structure, they may gave different functions. But usually for different functions, different organs or part5s are available. It is very much relevant in the case of humans which are at the peak level of evolution. The most simplest form of digestive organs are seen in protozoa and sponges. In earthworms, organs are somewhat advanced. In humans and other animals, due to evolutionary high, there are different organs in different organ systems.
In body, the position of organs are at right places. The shape, structure and formation of every organs are according to there function. The different types of functional principles which are started at the time of zygote development controls symmetry and formation of organs by continuous natural selection. Symmetry are of two types. One is Radial or Axial symmetry which is seen at plants and other lower animals and the second is Bilateral symmetry which is seen in arthropods and vertebrates. The external bilateral symmetry is not applicable in internal organs mostly. In some protozoans, Spherical symmetry is also seen.
Each tissues helps to form a organ have different functions and positions. One special tissue have the prime function of the organ. The other tissues helps for the tissue to attain the specific function.
In different animals which live in different conditions have differentiation in organ structure. For example, the moving organs in watery animals are fins and wings in the cases of birds. The different parts of different animals may have common structures. For example, arms of humans, wings of birds and flippers of whales have same structures. Many times the functions are also same. Human hand, Wings of birds and front legs of dear are doing many functions in same time.
There are having rudimentary organs in the body. For example, Vermiform Appendix, Caecum etc.
There are having unimportant organs are also in the body. They are named according to the person who discovered it. For example, Jacobson's organ which unimportant in humans but important in cows used for smell.
