Types of respiration

Types of respiration

(iii) Types of respiration : It is of two types

(a) Aerobic respiration : It occurs in the presence of molecular oxygen. The oxygen completely oxidises the food to carbon dioxide and water, releasing large amount of energy. The organisms showing aerobic respiration, are called aerobes. It is found in most of animals and plants. Aerobic respiration is of two main types direct and indirect.

(1) Direct respiration : It is the exchange of environmental oxygen with the carbon dioxide of the body cells without special respiratory organs and without the aid of blood. It is found in aerobic bacteria,protists, plants, sponges, coelenterates, flatworms, roundworms and most arthropods.

Protists : Amoeba proteus is about 0.25 mm. Wide and has a large surface area to volume ratio. Diffusion of gases occurs over the entire surface via cell membrane, and is enough to fulfill its metabolic requirements.

Coelenterates : In Hydra and Obelia, practically all cells are in contact with the surrounding water. Each cell can exchange gases sufficient for its own needs through the cell membrane adjacent to water.

Flatworms : Planaria can also exchange gases sufficient for its needs by diffusion over its body surface. This is facilitated by its very thin body which increases the surface area to volume ratio.

(2) Indirect respiration : It involves special respiratory organs, such as skin, buccopharyngeal lining, gills and lungs, and needs the help of blood. The respiration in the skin, buccopharyngeal lining, gills and lungs is respectively called cutaneous buccopharyngeal, bronchial and pulmonary respiration. Cutaneous respiration takes place in annelids, some crustaceans, eel fish, amphibians and marine snakes. It occurs both in water and in air. Buccopharyngeal respiration is found in certain amphibians such as frog and toad. It occurs in the air. Branchial respiration is found in many annelids, most crustaceans and mollusks, some insect larvae, echinoderms, all fishes and some amphibians. It occurs in water only. Pulmonary respiration is found in snails, pila, some amphibians and in all reptiles, birds and mammals. It takes place in

air only.

(b) Anaerobic respiration : It occurs in the absence of molecular oxygen and is also called fermentation. In this, the food is only partially oxidised so only a part of energy (5%) is released and of energy remains trapped in the intermediate compounds. It is found in lower organisms like bacteria and yeast. It is also found in certain parasitic worms (Ascaris, Taenia) which live in deficient medium. The organism showing anaerobic respiration, are called anaerobes. These involve one of following reactions.

Certain body tissues of even aerobes also show anaerobic metabolism e.g., during the vigorous contraction of skeletal muscle fibres. In this, the glucose is metabolised into the lactic acid in anaerobic conditions. The rapid formation and accumulation of lactic acid are responsible for muscle-fatigue. The mammalian RBCs shows anaerobic respiration as these lack the mitochondria. In lens of eye and cornea of eye respiration is anaerobic because these structures are a non vascular. Anaerobic respiration appeared first in primitive organisms because there was absence of O₂ in primitive atmosphere.

Difference between aerobic and anaerobic respiration