11th Class Biology Breathing and Exchange of gases (Animal Respiration) Respiratory Organs

(1) Skin : Respiration by skin is called cutaneous respiration. Skin is the only respiratory organ in most annelids (earthworm and leeches) and an additional respiratory organ in amphibians (Toads and frogs). Skin should be thin, moist, naked, permeable and well vascular for respiration. For cutaneous respiration animal should have large surface area then its volume and should have relatively inactive life to minimize the use of oxygen. Some marine annelids such as sandworms (nereis) have parapodia (locomotory appendages) for respiration. In frog 100% cutaneous respiration during hibernatin. In all marine snakes 20% respiration by skin.

(2) Tracheae : In insects, peripatus centipedes and millipedes tracheae are found for respiration. Tracheae are complex system of whitish, shining, intercommunicating air tubules. Tracheae are ectodermal air tubes. In cockroaches, three pairs of longitudinal tracheal trunks are present all along the length of body which are further connected with each other with the help of transverse branches. The main tracheae give off smaller tracheae whose branch repeatedly form a network of trachioles throughout the body. Trachea internally lined by chitinous cuticle called intima, which spirally thickened to form taenidae. Trachioles without taenidae, trachioles lined by trachein protein. From each tracheal trunk three branches come out. The dorsal branch is supplied to the dorsal muscles where as ventral one to nerve cord and ventral muscles and middle one to the alimentary canal.

(3) Book lungs and book gills : Spiders ticks, mites and scorpion (belongs to class arachnida) have book lungs for respiration. In scorpion 4 pairs of book lungs are present. A book lung is a chamber containing a series of thin vascular, parallel lamellae arranged like the pages of book. Book gills are found in marine king crab or horse shoe crab.

(4) Gills : Aquatic animals such as prawn, unio, fishes, sea stars and tadpoles respire by gills. Respiration by gills called bronchial respiration. Gills are of two types -

(i) External gills : External gills are found in arenicola (lug worm), larvae of certain insects e.g. damsel fly and some amphibians e.g. necturus, siren, proteus, frog tadpole first develop external gills which are replaced by internal gills later.

(ii) Internal gills : The internal gills may be phyllobranch (prawn), monopectionata (pila) eulamellibrach (unio), lamellibranch, fillibranch (pisces). In all fishes, gills are hemibranch or demibranch and holobranch. In gills, gill lamellae are found which have capillary network. Water is drawn into gills \[\to \] blood flowing in the capillaries of gill lamellae absorb oxygen from water and release \[C{{O}_{2}}\to \] water containing \[C{{O}_{2}}\] is thrown out from gills. The 80% of \[{{O}_{2}}\] of incoming water is absorbed.

Oxygen content of respiratory media

(5) Buccopharyngeal lining : Frog breathes by buccopharyngeal lining of buccopharyngeal cavity. This is called buccopharyngeal respiration.

Respiratory organs of animals