Explain the different Modes of Respiration.

Modes of Respiration.

For simple animals such as sponges, jellyfish, flatworms and roundworms, respiration is primarily through diffusion of oxygen through the moist tissues of the animal with carbon dioxide diffusing outward i.e. they respire through their body surfaces and do not have any specialized respiratory organs. But in more complex invertebrates, there exist specialized surfaces for gas exchange and a circulatory system that transports oxygen more readily than that possible by simple diffusion.

Due to low metabolic demands, the animals like protozoans and flatworms carry simple diffusion. Similarly, having very modest metabolic demands, the sufficient gas exchange takes place in the absence of circulatory system or respiratory pigments in sponges and corals. They maintain a circulation of water by cilia over the surfaces of cells which line their canal systems.

The animals having efficient circulatory systems and readily permeable vascular skins, gas exchange occurs through the integument. Respiration by skin is called cutaneous respiration.

Skin is the only respiratory organ in most annelids including such that earthworms, leeches. Many amphibians like frog and fish respires through skin during emergencies. The giant salamander cryptobranchus alleganiensis is the largest aquatic amphibian relying exclusively on integumentary breathing.

In large and more complex organisms, the metabolic rates are high, thus they required specialized respiratory organs. The organs include gills and lungs and have a thin respiratory surface to help in gas exchange. Those that have respiratory surface turned out forming an evagination. These are called gills. Those that have respiratory surface turned in forming an invagination. These are called lungs. Fish and the larval stage of amphibians respiration is through gills. Adult amphibiang, reptiles, birds and mammals all use lungs for respiration.

Generally gills are for breathing in water and lungs for breathing in air. Insects respire through the small openings on its body surface which are connected to small tubes called trachea. These branched into tracheal trees and spread throughout the body. The gases diffuse through these branches directly into the cells.