Respiratory System in Unicellular Organisms, Insects, Fish, Tadpole and Toad

RESPIRATORY SYSTEM IN UNICELLULAR ORGANISMS


[Photo credit: Dr.Tsukii Yuuji]


Unicellular organisms have no special respiratory organs, as well as aquatic animals such as Amoeba and Paramecium. Oxygen that dissolves in water diffuses into the body while carbon dioxide goes out of the body through the
entire body surface. The cell membrane acts as the respiratory surface. 

Oxygen concentration in water more than the one in the body, leading to the diffusion of the oxygen into all parts of the body. As well, the carbon dioxide concentration in the body is more than that of the water, leading to the diffusion of the carbon dioxide out of the body. This process is made possible by simple diffusion. 

The surface area to volume ratio of these organisms are high, hence diffusion through the body surface is enough to satisfy its gaseous exchange needs.


RESPIRATORY SYSTEM IN INSECTS



Insects generally use the tracheal system for gaseous exchange. Insects have tiny openings in their abdomen, known as spiracles. Gaseous exchange occurs through the spiracles. The spiracles lead to tracheae. These tracheae divide into tracheoles. 

Breathing occurs in insects by the insects compressing their body dorso-ventrally (i.e inwards from both sides along its entire body) and then relaxes it. When their body is compressed, they become flattened and air moves out of the tracheae through the spiracles. When they relax their body, air moves in through the tracheae.


RESPIRATORY SYSTEM IN FISH

The gill is the organ, used by fish for respiration. The gills are found in both sides of the head region. They are arranged in gill chamber. They ma be in three or four. Each gill consists of gill filament, gill raker and gill arch. The gill chamber is externally closed by operculum. The function of the constituents are:

• gill filament: This is the place where gaseous exchange takes place
• gill raker: This helps to stop food particles from entering the gill chamber
• gill arch: The gill filaments are build on this.

The process of gaseous exchange in fish is as follows:

For the fish to breath, it closes it operculum, opens its mouth and lowers the floor of the mouth. Water then rush into its mouth. The water contains oxygen. The fish then closes its mouth, raises the the floor of the mouth, then the water rush into the gill chamber and move across the gill filaments. After this, oxygen in the water diffuses into the gill filament while carbon dioxide diffuses out of the body into the water. 

For the water, which contains the dissolved carbon dioxide to pass out of the fish, the fish opens its operculum. 

For another breathing to occur, the fish repeats the above process.

RESPIRATORY SYSTEM IN TADPOLE

By tadpole, we refer to young toad. The gills are used by tadpoles for gaseous exchange. External gills are developed by tadpoles, through which gaseous exchange occur by diffusion. The respiratory medium is water. Oxygen dissolved in water moves in the tadpole and carbon dioxide move out through simple diffusion. The ratio of body sure face to volume of tadpoles are large, which makes simple diffusion possible and easy.

As the tadpole develops, the external gills disappear. It then develops internal gills under the operculum or spout. When this occurs, the process of gaseous exchange is now similar to that of fish.

RESPIRATORY SYSTEM IN TOAD

Three different respiratory organs are used by toads for gaseous exchange. The respiratory organs are: mouth, skin and lungs. 

1. Respiration in Toad through the mouth (Mouth or Buccal Respiration)

When toads are on land, they have the ability of breathing through the mouth. The process is as follows:

The toad closes its mouth, opens its nostrils, and lowers the flor of the mouth, to breath in air. As a result of this, the air pressure within the mouth becomes low, hence allowing air to be drawn in through the nostrils. The nostrils and glottis are then closed. 

To get rid of carbon dioxide from the body, the toad raises the floor of the mouth, making the air pressure inside the mouth to increase. As a result, the nostrils are opened and carbon dioxide is breathed out to the environment.

The mouth serves as an efficient respiratory organ because:

1. It has large surface area.
2. It has a thin mucus for easy diffusion.
3. It is well supplied with blood capillaries.

2. Respiration in Toad through the skin (Skin or Cutaneous Respiration)

Both on land and in water, the toad can respire through the skin. Oxygen can diffuse into the blood of the capillaries through the entire skin. The diffused oxygen is then passed to cells and tissues within the body. Carbon dioxide are also removed by diffusion through the entire skin.

The toad's skin serves as an efficient respiratory organ because:

1. It has a large surface area and thin covering.
2. It is moist due to continuous secretions from mucus gland.
3. It is well vascularized, i.e, well supplied with blood capillaries.

3. Respiration in Toad through the lungs (Lungs or Pulmonary Respiration)

When on land, the toad can carry out gaseous exchange with its lungs. How it works is similar to that of mouth or buccal respiration. 

For the toad to breath in, it closes its mouth, keeps its nostrils opened, and lowers the floor of the mouth. As a result, the air pressure in the mouth is lowered, hence making air containing oxygen to be breathed in through the nostrils. The nostrils are then closed, keeping the glottis opened, and the air is forced into the lungs through the glottis, larynx and the lungs. 

Oxygen then diffuses into the blood of the capillaries while carbon dioxide diffuses out into the lungs, where it is sent out. When the toad lowers its mouth, keeping the nostrils closed, carbon dioxide is drawn from the lungs into the glottis. The mouth floor is then raised severally, pumping out the air containing carbon dioxide out of the lungs, and finaly forces it out through the nostrils.

Categories: Biology, Respiration, Respiratory System