Animals

• Gas exchange follows the same general trend in animals as in plants.
• Oxygen and carbon dioxide diffuses across moist membranes.
• . The exchange happens directly with the environment in simple animals.
• The exchange between the environment and the blood happens with complex organisms, such as mammals.
• The blood transports oxygen to deeply embedded cells and transports carbon dioxide out of the body.
• Oxygen and carbon dioxide are transferred by earthworms directly through their skin.
• Oxygen diffuses into tiny blood vessels on the surface of the skin where it mixes with hemoglobin, a red pigment.
• Hemoglobin loosely binds to oxygen and brings it across the bloodstream of the animal.
• Hemoglobin transports carbon dioxide back to the blood.
• Terrestrial arthropods have a set of openings on the surface of the body called spiracles.
• Spiracles open into tiny air tubes called tracheae, which grow into fine branches that reach into all areas of the body of the arthropod.

   
• Fishes use external extensions of the surface of their body, called gas exchange gills.
• Gills are tissue flaps which are richly supplied by blood vessels.
• This attracts water into its mouth and through the gills as a fish swims.
• Oxygen spreads through the gill's blood vessels from the water, while carbon dioxide exits the blood vessels and enters the water flowing through the gills.
• There are well-developed respiratory systems with lungs for terrestrial vertebrates such as amphibians, reptiles, birds, and mammals.
• In their lungs, frogs swallow air, where oxygen diffuses the blood to bind with hemoglobin in the red blood cells.
• . By means of their skin, amphibians can exchange gases as well.
• To provide increased surface space for gas exchange, reptiles have folded lungs.
• Rib muscles aid the expansion of the lungs and protect the lungs from damage.
• Birds have in their lungs large air spaces called air sacs.
• The rib cage spreads apart when a bird inhales, and a partial vacuum is created in the lungs.
• Air flows into the lungs and then into the air sacs, where much of the exchange of gas takes place.
• This method is the adaptation of birds to the rigors of flight and their enormous metabolic requirements.
• Mammalian lungs are classified into millions of microscopic air sacs called alveoli (the singular is alveolus).
• A rich network of blood vessels for transporting gases surrounds each alveolus.
• Furthermore, mammals have a dome-shaped diaphragm that separates the thorax from the abdomen, providing a separate the chest cavity for breathing and blood circulating.
• The diaphragm contracts and flattens to create a partial vacuum in thelungs during inhalation.
• With air, the lungs fill, and gas exchange follows.