Respiration can be defined as the process by which an organism takes in oxygen and releases carbon dioxide, one in which the circulating medium of the organism (e.g., the blood) comes into contact with air or dissolved gases. Either way, this means more or less the same thing as breathing.
The process of Respiration of two types they are: (1) Aerobic respiration:- In this case free oxygen is used in oxidizing the stored does and as a result of this water and carbon dioxide are formed as end products. In this type of respiration about 674 cal. Of energy is released.
(2) Anaerobic respiration:- Certain cacti, many tissues of higher plants, fleshy fruits etc. respire by means of this kind of respiration i.e. they respire in the absence of free oxygen. Here, incomplete oxidation of stored food tales place with the formation of ethyl alcohol, carbon dioxide and even some organic acids e.g. malic acid, citric acid, oxalic acid, tartaric acid. In this type of respiration only 23 cal. Of energy is released.
Anaerobic respiration is of two types:
- Alcoholic fermentation
- Lactic acid fermentation
Respiratory process is different among Humans, Plants and Animals.
 The Human respiration Process
Human respiration is a process by which oxygen is received into the body and carbon dioxide is expelled. Oxygen is a vital component of human survival and is needed for several types of cellular respiration, while carbon dioxide is poisonous to humans. The Lungs are the human organs of respiration. Human body have two lungs, with the left being divided into two lobes and the right into three lobes. Together, the lungs contain approximately 1500 miles (2,400 km) of airways and 300 to 500 million alveoli, having a total surface area of about 75 m2 in adults — roughly the same area as a tennis court. Furthermore, if all of the capillaries that surround the alveoli were unwound and laid end to end, they would extend for about 620 miles.
The lung capacity depends on the person's age, height, weight, sex, and normally ranges between 4,000 and 6,000 cm3 (4 to 6 L).
Respiration of oxygen includes four stages:
- Ventilation from the ambient air into the alveoli of the lung.
- Pulmonary gas exchange from the alveoli into the pulmonary capillaries.
- Gas transport from the pulmonary capillaries through the circulation to the peripheral capillaries in the organs.
- Peripheral gas exchange from the tissue capillaries into the cells and mitochondria.
The skeletal muscles of the thoracic cavity are used to in the process of respiration by contracting and forcing air in and out of the lungs. The two muscles primarily involved are the external intercostal muscles and the diaphragm, which is the sheet of muscle separating the thoracic and abdominal cavities. These muscles will contract when breathing out and expand while breathing in in order to allow air flow in and out of the lungs.
Upon entering through either the oral or nasal cavities (Nasal breathing of respiration process refers to the state of inhaling and exhaling through the nose) the oxygen from the ambient air will travel through the pharynx, trachea, left and right bronchi, secondary and tertiary bronchi, bronchioles, and finally arive at the alveoli. The alveoli is the site of the gas exchange of oxygen for carbon dioxide. The oxygen will move to the blood stream in order to be used in cellular respiration, while the carbon dioxide will then travel out in expiration. Some oxygen is still expelled with the carbon dioxide, however.
 The Plant respiration Process
The respiratory system is the biological system of any organism that engages in gas exchange. Even trees have respiratory systems, taking in carbon dioxide and emitting oxygen during the day, consuming carbon dioxide and producing oxygen constantly.
Plant respiration is limited by the process of diffusion. Plants take in carbon dioxide through holes on the undersides of their leaves known as stomata. However, most plants require little air. Most plants have relatively few living cells outside of their surface because air (which is required for metabolic content) can penetrate only skin deep. However, most plants are not involved in highly aerobic activities, and thus have no need of these living cells.
 The Animal respiration Process
Like humans, Animals also respire with their lungs. But, not all animals have lungs. For example, fish have gills, that is how they respire. frogs breath though their skin and that is how they respire. All mammals (animals with hair) have lungs though, so they breath respire like Humans.