How does Breathing takes place in Animals?

Every animal in nature breath either through lungs, gills, skin or spiracles. 

Mammals like birds and 

reptiles breathe through their lungs. Lung is an organ of the body that facilitates the breathing process.

When we talk about mammals, human beings can be considered as the best example. Breathing process in human beings involve lungs, nose, diaphragm and ribs. The process of breathing in air is called inspiration and the process of breathing out air is called expiration. When a person takes air through the nose, the nose hair works as a filter protecting the inside of the body from the dust coming alongside the air. The diaphragm in the chest helps in drawing the air during the breathing process. The ribs moves up and diaphragm moves down to facilitate the breathing process and as the pressure in the lungs decreases, the air rushes into the lungs. That's how breathing takes place particularly in mammals.

Now, the breathing process in birds and reptiles take place differently. As birds have small holes near their beaks which helps in breathing. Reptiles and birds do not have diaphragm like mammals, they only use ribs in their process of breathing. 

Fish and other animals that live in water use gills for their breathing process. Gills consists of threadlike structures called filaments. Each filament contains a capillary network that provides a large surface area for exchanging oxygen and carbon dioxide. As the water passes over to the gills, the oxygen is taken in and carbon dioxide is released to the water. Water is then passed out of the gills through gill slits. 

Breathing through skin and spiracles take place in frogs. Frogs have very thin skin which allows the gases to pass through it. When the frog is underwater, it uses its skin for breathing. When the frog is on land, it uses its lungs to breath. 

The organisms like mosquito, grasshopper and cockroach do not have lungs or gills for breathing. Their blood does not carry oxygen. They use spiracles for breathing. Spiracles are connected to air tubes called trachea. Trachea is in turn connected to the smaller tubes, these smaller tubes are further connected with the body cell. This connection facilitates the breathing process in these organisms.