Introduction to Respiration, Respiratory Organs in Animals, Practice Problems and FAQs

You all know about your respiratory organ. Right?

Please enter alt text

Fig: Lungs

Yes, there are two lungs in the chest area. They are the respiratory organs in human beings. It facilitates breathing. But which lungs structure aids in this respiration?

Alveoli, indeed. They are the sac-like structures present in lungs. You know, each of your lungs has roughly 300 million alveoli, which are balloon-like structures that replace carbon dioxide waste in your blood with oxygen.

Do you think the organs for respiration are the same in all organisms? Do you have any idea about the respiratory organs of butterflies, moths or cockroaches? Let us understand about the different types of respiratory organs in animals in this article.

Table of contents

Breathing
Difference between breathing and cellular respiration
Respiratory organs
Invertebrates
Vertebrates
Practice Problems
FAQs

Breathing

Breathing helps you to take in the oxygen your cells require while also allowing you to eliminate carbon dioxide as waste. When we exhale, we also exhale a lot of water which is also a byproduct of cellular respiration.

Breathing is considered as the process of exchanging oxygen from the atmosphere with carbon dioxide produced by the cells through cellular respiration. Inhalation (to breathe in) and expiration (to breathe out) are two aspects of breathing (exhale or to breathe out). The process during which food is broken down with the help of oxygen to give energy is called cellular respiration.

Fig: Respiration

Difference between breathing and cellular respiration

Breathing	Cellular respiration
Oxygen is inhaled and carbon dioxide is exhaled out of the lungs	Breakdown of food using oxygen to produce energy which is used by cells to carry out cellular function
No energy is produced during the process	Energy is released in the form of ATP
Takes place in respiratory organs	Takes place in cells
Physical process	Biochemical process

Respiratory Organs

Organs used in the process of respiration are known as respiratory organs. Different animals have different organs depending upon their two main features as follows:

Habitat

It is the place where an animal lives. For example, reptiles live on land, respire through lungs, while fishes live in water, have gills to respire.

Level of organisation

Breathing mechanisms vary according to the level of organisation. For example, poriferans have cellular level of respiration.

Types of respiratory organs

In Invertebrates

Porifera - Sponges

In sponges the exchange of gases occurs by simple diffusion through the body surface. It occurs across cell membranes as they are unicellular organisms. Sponges are dependent on the dissolved oxygen in the water passing through the spongocoel. Oxygen-containing water enters the body of the sponge through small pores, called ostia. Water is circulated throughout its body by the action of cells called choanocytes. The choanocyte cells have flagella that move around and push water through the sponge. Water goes out through the opening called the osculum.

Fig: Respiration in sponges

In other invertebrates

Cnidarians - Hydra	Diffusion occurs through their body surface	Fig: Hydra
Platyhelminthes - Flatworms	Diffusion occurs through their body surface	Fig: Flatworms
Annelida - Earthworms	Diffusion occurs through their body surface	Fig: Earthworms
Aquatic arthropods - Horseshoe crab	Gaseous exchange occurs through book gills	Fig: Horseshoe crab
Arthropods - Terrestrial	Gas exchange occurs through tracheal tubes	Fig: Insects
Mollusca - Snail	Gas exchange occurs through feather-like gills inside the mantle cavity	Fig: Snail

In vertebrates

Fishes

In these organisms the gaseous exchange occurs through gill slits.

Fig: Eel

In reptiles, amphibians, mammals and birds

In these organisms the gaseous exchange takes place through lungs.

Fig: Major respiratory organs higher classes of vertebrates

Practice Problems

Q1. Branchial respiration is seen in __________________________.

Fishes
Aquatic arthropods
Molluscs
All the above

Solution: Branchial respiration is the respiration through gills. It is observed in fishes, aquatic arthropods like horseshoe crabs, molluscs like snails etc.

Q2. In chordates, which group has multiple organs for respiration?

Amphibians
Mammals
Urochordates
Cyclostomates

Solution: In chordates, amphibians can respire through skin, lungs and buccopharyngeal cavity.

Q3. Frogs respire through which organ, when they are submerged in water?

Nostrils
Lungs
Skin
Buccal cavity

Solution: When frogs are submerged in water, they use only their skin for breathing. On land, the buccal cavity and the two lungs are used for breathing.

Q4. Select the incorrect statement from the given below:

Amoeba gets oxygen mainly by simple diffusion through their cell membrane from the surrounding water
Elephants snorkel when under water
The principle of countercurrent flow facilitates efficient respiration in gills of fishes
Whales and dolphins do not have lungs

Solution: Whales and dolphins are mammals and they have lungs as their respiratory organs, just like human beings. They need to rise to the surface of the water to inhale and exhale oxygen through their blowholes. Blow holes are normally surrounded by muscles which keep the hole closed when the whale or dolphin is under water. It opens it when the animal is reaching near the surface for breathing.

FAQs

Q1. Which are the respiratory processes in adult frogs?
Answer: Adult frogs have three different types of gaseous exchange mechanisms as follows:

Cutaneous respiration - Frog do cutaneous respiration during hibernation and aestivation.
Buccopharyngeal respiration - It happens with the help of the buccopharyngeal cavity via the nasal chamber and external nares when the frog is on land or partially immersed in water.
Pulmonary respiration - It happens with the help of the lungs.

Identify the respiratory organs in the following organisms.

Tadpole
Scorpion
Spider
Mollusc

Answer: Book lungs are present in terrestrial arthropods such as scorpions and spiders. Gills are present in aquatic arthropods, molluscs and fishes. Internal gills are found in the tadpole larvae of the frog.

Q3. Do human beings show cutaneous respiration?
Answer: Cutaneous respiration is the respiration that happens through the skin. Some annelids like earthworm, leeches and amphibians like frogs can respire through skin. Frogs show this method mainly during hibernation and aestivation. They can respire through lungs and the buccopharyngeal cavity also. Lungs are the respiratory organs in human beings. We can perspire (sweating) through lungs.

Q4. What do you know about the countercurrent mechanisms in fish?
Answer: Countercurrent means a current flowing in a direction opposite to another. The flow of blood and water in opposite directions make respiration in fishes efficient. When the water enters through the mouth, it is highly oxygenated. Let us assume it has 100 ppm of oxygen in it. The time it reaches the other end of the body through the gills, it would have given up most of its oxygen to the blood. This results in a drop in the level of blood. For example, we can assume it as 20 ppm. Hence the blood, which flows in the opposite direction has 20 ppm of oxygen, and as it flows through the blood vessels, it once again gains oxygen, and by the time it reaches the opening of the operculum where water enters, it would have gone up to 80 ppm. Thus, in this countercurrent mechanism, there is a constant gradient that is created which helps oxygen diffusion to happen more effectively in fishes. Here if the blood and water flow in the same direction in fishes then both blood and water would have the same concentration of oxygen, which means that there won't be any gradient created for diffusion to take place.