• Written By Priyanka Srivastava
  • Last Modified 22-06-2023

Respiratory Organs Of Animals: Important Details


Respiratory Organs Of Animals: What is respiration? Respiration is one of the life processes, which involves the oxidation of food in the cells. Respiration involves the exchange of gases. But how does this process occur in different animals? It occurs through respiratory organs. What are the respiratory organs in aquatic animals? Respiratory organs in different animals are different and it is a very interesting topic for the students to learn.

What should be the criteria that a respiratory organ should have? How do simple and complex organisms carry out this process? Read through the article to find out more about common features of respiratory organs in aquatic and terrestrial animals, the evolution of respiratory organs in different animals and much more!

Respiratory Organs Definition: Different Types of Respiratory Organs in Animals

Respiration generally involves the oxidation of food in the cells by using oxygen taken from the environment with the production of energy, carbon dioxide and water. Energy is stored in the bonds of ATP for use in biological activities. Organs that are involved in gaseous exchange during respiration are called respiratory organs. Like in humans, a pair of lungs are present, and in fish, gills are present, which are involved in the gaseous exchange.

Important features for all Respiratory Organs

Check out common features of respiratory organs in aquatic and terrestrial animals below.

  1. The surface of the respiratory organs should be moist.
  2. It should be thin.
  3. It should be highly vascularised.
  4. It should have a large surface area to get enough oxygen.

Different Respiratory Organs in Different Animals

1. Amoeba

Respiratory organ- Cell membrane

  1. Cell membrane or plasma membrane is the respiratory structure in Amoeba.
  2. With other functions, the plasma membrane also participates in the respiration process as it is a thin, moist membrane and selectively permeable.
  3. It does not let all the components from the outside environment get in. It provides a large surface area to get enough oxygen.
  4. By the process of simple diffusion, gaseous exchange occurs. As Amoeba is a unicellular organism, oxygen easily diffuses to the entire cell for respiration.

Fig: Cell membrane in Amoeba

Respiratory process

Oxygen is present in the water. By the process of simple diffusion, oxygen enters the cell membrane of the Amoeba, and after the process of respiration, \({\rm{C}}{{\rm{O}}_{\rm{2}}}\) is evolved, which is given out through the cell membrane by the process of simple diffusion. Through this process of respiration, energy is released.

2. Earthworm

Respiratory organ – Skin

  1. Gaseous exchange in Earthworms occurs through the skin.
  2. This type of respiration is also called cutaneous respiration.
  3. The skin of the earthworm is thin and moist and has a good supply of blood. So, the respiratory organ of the earthworm is its skin which absorbs oxygen needed for respiration.

Respiratory process

Oxygen from the atmosphere is absorbed through the skin, and then it is diffused to the blood, and through blood, it is transported to all parts of the body. When oxygen reaches each cell, respiration takes place, during which carbon dioxide is evolved, which is expelled out of the body through the skin by the diffusion process.

Fig: Respiration in Earthworm

3. Insects like Grasshoppers

Respiratory organ- Trachea

  1. In insects like grasshoppers, cockroaches, houseflies and mosquitoes, respiration takes place through the tracheal system.
  2. It is a network of tubes that frame the entire body of the insect.
  3. The trachea is open to the exterior through the microscopic pores called spiracles which are arranged on either side of the body segments.
  4. Each spiracle leads into a cavity, called the tracheal tubes, from which branches arise. Air enters the body through these spiracles.
  5. Tracheoles, the minute branches of the trachea, reach each and every cell of the body and each cell gets oxygen directly.

Fig:  Tracheal system in grasshopper

Respiratory process

Alternate contraction and expansion of the abdomen expel and take air in the tracheal system. When the abdomen expands, inspiration takes place. And when the abdomen contracts, the air is expelled through the spiracles.

4. Fish

Respiratory organ- Gills

  1. Gills are the respiratory organs in fish.
  2. Gill filaments are the units of the gills. Plate-like lamella is arranged on each filament.
  3. Lamella is characterized by blood capillaries that can extract oxygen from the water flowing between lamellae.
  4. These lamellae provide a large surface area.
  5. Gills have arches that provide structural support. Through these, the blood vessels run.
  6. Rakers in the gills run along the arches, which do not allow food to pass through the gills.

Fig: Gills in fishes

Respiratory process

Fish use dissolved oxygen from water. Water enters the mouth of fish, which is then passed through the gills where the dissolved oxygen is extracted by gills, and the water goes out through gill slits. Blood absorbs oxygen from the gills, which is carried to all parts of the body of the fish. Then after respiration, carbon dioxide is produced, which is brought to the gills through the blood and is expelled out of the body into the water.

5. Frogs

Fig: Frogs

Respiratory organs

Frogs can respire through:

  1. Skin– Skin in frogs, is thin, moist and highly vascularised. Blood vessels present in the skin increases its surface area for the exchange of gases in water. Respiration through skin takes place when a frog is in water. Outside water, mucus is secreted by the mucus gland in the skin, which keeps the skin of the frog moist. During hibernation and aestivation, cutaneous respiration takes place.
  2. Lungs–  Frogs respire through the lungs when they are on land. Frogs have lungs, but they do not have ribs and diaphragm like us. Instead, they have mouths, nostrils, and gullets to move air in and out and regulate air pressure.
  3. Lining of the mouth– It is also used as a respiratory structure when they are at rest on land as it is a thin, moist, vascularised structure. This is also called buccopharyngeal respiration.
  4. Gills– Tadpoles of frogs can respire through gills. Gills are external when newly hatched but eventually get inside the body with the growth of the tadpole. Frogs respire through gills only at the larval stage. Water flows over the gills for the exchange of gases.

Fig: Different Respiratory Organs in Frogs

Respiratory process

During respiration, there occurs an exchange of gases, i.e. oxygen is taken in, and carbon dioxide is thrown out of the body. This process gives energy to the frog and tadpole for different biological activities.

6. Humans

Respiratory organ – Lungs

  1. In humans, respiration occurs through the lungs.
  2. The human respiratory system is divided into two major components- the respiratory tract and respiratory organs.
  3. The respiratory tract consists of external nares, nasal chambers, internal nares, pharynx, larynx, trachea, bronchi and bronchioles. Bronchi and bronchioles lie within the lungs while other parts lie outside the lungs.
  4. Respiratory organs are a pair of lungs. Lungs lie in the thoracic cavity on the sides of the heart.
  5. Each lung is covered by two membranes called pleura.
  6. Between two pleura, a narrow space exists called the pleural cavity, which is filled with pleural fluid. This fluid lubricates the pleura. This avoids the friction between the two pleura when there is contraction and expansion of the lungs.
  7. The left lung has two lobes, and the right lung has three lobes.
  8. The trachea is divided into bronchi and bronchioles inside the lungs, which end up in alveolar sacs.
  9. The alveoli have a very thin wall composed of thin, moist, nonciliated, squamous epithelium. It is surrounded by collagen and elastin fibres that provide flexibility to alveoli, enabling them to expand and recoil easily during breathing. There are numerous alveoli.

Fig: Respiratory System in Humans

Respiratory process

We breathe in air through our nostrils, and that air enters our respiratory tract. The respiratory tract serves as a passageway for the fresh air to flow from outside to the lungs. Air containing oxygen enters through the nose to the trachea, which leads to the lungs. Inside lungs, air containing oxygen enters bronchi, bronchioles and finally the alveolar sac. In this sac, gaseous exchange occurs. Alveolar sacs increase the surface area of the lung. Oxygen is taken up by blood and is transported to all cells of the body where oxidation of food occurs, and then carbon dioxide is released, which is transported to the lungs back by blood and is then expelled out through exhalation.

Respiratory Structure for the Exchange of Gases in Different Groups of Animals

Students are also interested in the evolution of respiratory organs in different animals. Check out the respiratory structure for the exchange of gases in different groups of animals below.

Animal groupRespiratory Structure
ProtozoanPlasma membrane
CnidariansBody surface
PlatyhelminthesBody surface
NemathelminthesBody surface
ArthropodsGills, trachea, book lungs, book gills
MolluscsGills, pulmonary sac
EchinodermataDermal branchiae, tube feet
ChordataGills, Lungs


In this article, we learnt about different respiratory organs in different animals including respiratory organs in aquatic animals. Respiratory organs should be moist, thin, highly vascularised and should have a large surface area for the exchange of gases. Respiratory organs in simple organisms like Amoeba is the cell membrane through which gaseous exchange occurs. In earthworms, the exchange of gases occurs through the skin, while in fish, the respiratory organ is the gill. In frogs, respiration can take place through either skin or lungs, depending on which medium it is present. If a frog is inside the water, then an exchange of gases occurs through the skin, and when it is on land, it occurs through the lungs. Tadpoles of frogs respire through gills. In insects like grasshoppers, tracheal respiration takes place. In humans, respiration occurs through the lungs. Respiration is an essential life process as the required energy is released through respiration and stored as ATP.

Frequently Asked Questions (FAQs) on Respiratory Organs in Animals

Q.1. Which animal has a skin respiratory organ?
Ans: Earthworms have skin as their respiratory organ.

Q.2. What is the main function of the lungs in a human body?
Ans: Lungs are involved in gaseous exchange during the respiration process.

Q.3. What are the respiratory organs of amphibians?
Ans: Respiratory organs of amphibians like frogs can be either skin, lungs or gills.

Q.4. What are the respiratory organs of mammals?
Ans: Respiratory organs of mammals are the lungs.

Q.5. What are the respiratory organs in fishes?
Ans: Respiratory organs in fishes are gills.

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