All animals take in oxygen for oxidation of organic compounds to provide energy for cellular activities.
The carbon (IV) oxide produced as a by-product is harmful to cells and has to be constantly removed from the body.
Most animals have structures that are adapted for taking in oxygen and for removal of carbon (IV) oxide from the body. These are called “respiratory organs”.
The process of taking in oxygen into the body and carbon (IV) oxide out of the body is called breathing or ventilation.
Gaseous exchange involves passage of oxygen and carbon (IV) oxide through a respiratory surface by diffusion.
Types and Characteristics of Respiratory surfaces
Different animals have different respiratory surfaces.
The type depends mainly on the habitat of the animal, size, shape and whether body form is complex or simple. Cell Membrane:
In unicellular organisms the cell membrane serves as a respiratory surface. Gills: Some aquatic animals have gills which may be external as in the tadpole or internal as in bony fish e.g. tilapia.
They are adapted for gaseous exchange in water. Skin: Animals such as earthworm and tapeworm use the skin or body surface for gaseous exchange.
The skin of the frog is adapted for gaseous exchange both in water and on land. The frog also uses epithelium lining of the mouth or buccal cavity for gaseous exchange. Lungs: Mammals, birds and reptiles have lungs which are adapted for gaseous exchange.
Characteristics of Respiratory Surfaces
- They are permeable to allow entry of gases.
- They have a large surface area in order to increase diffusion.
- They are usually thin in order to reduce the distance of diffusion.
- They are moist to allow gases to dissolve.
- They are well-supplied with blood to transport gases and maintain a concentration gradient.
Gaseous Exchange in Amoeba
Gaseous exchange occurs across the cell membrane by diffusion. Oxygen diffuses in and carbon (IV) oxide diffuses out. Oxygen is used in the cell for respiration making its concentration lower than that in the surrounding water.
Hence oxygen continually enters the cell along a concentration gradient. Carbon (IV) oxide concentration inside the cell is higher than that in the surrounding water thus it continually diffuses out of the cell along a concentration gradient.