We as humans need a way to gather oxygen from our enviroment to survive. In response our body has a system that carries out respiration which is the distrubition of oxygen to the blood and the disposal of the waste product carbon dioxide. In the human breathing process the first step is the breath in. First we open the mouth and expand our lungs to bring in air. The first place the air travles into our mouths which is an opening in the human body used for taking in air, food, and the releasing of carbon dioxide this is the first place the air travles through. Then it must pass the epiglottis which is a skin flap in the back of your mouth that closes for food and opens for air. It is used to keep food and other materials from entering your trachea. The air then passes down the trachea which is a long “windpipe” that is lined with constantly moving cilia. These cilia whip back and forth and trap foregin objects and keep them from entering the lungs. The air completes its path down the trachea when it reaches the bronchus which is a speration of the trachea into the two different lungs it is used to carry oxygen to different parts of the body. These bronchus break into many bronchioles which then branch into many many microscopic tubs that cary the oxygen to every part of the lung till they meet the thin sacs called aveoli. Aveoli are thin sacs in the lungs that carry oxygen in and carbon dioxide out of the blood stream. They diffuse the oxygen into the blood cells that need it and in turn diffuse carbon dixoxide out. Diffusion is an easy method for the transfer of oxygen because it dosent take any energy and since the walls of the aveoli are only 1 cell thick it diffuses without any problems. After the oxygen is diffused into your blood it is then used for cellular respiration and many other things. But there is a waste product to this activity which is what we exhale carbon dioxide. Now carbon dioxide diffuses back into the blood which carries it to the lungs and since there is a high level of oxygen in the lungs and a low one in the blood and a high level of carbon dioxide in the blood and a low level of it in the lungs the oxygen simply diffuses into the blood and the carbon dioxide into the lungs where it is exhaled and the process begins again. We humans and other mammals are known as tidal breathers, which much like the tide come in and goes back out and come in and so forth. With us though all our respiatory action goes on trhough one opening in our body, our mouth with fish its very different.
Since fish are aquatic animals and cannot breathe air they must use a different system to somehow get the oxygen out of the water. But fish have a major problem as to getting oxygen from the water. The water only contains about 1/30 as much as oxygen per volume than air. This means that the fish have to find a more efficent way of getting oxygen to there blood. You see since we are tidal breathers we can only diffuse 50% of the oxygen into our blood stream because once 50% has diffused in it is equal on both sides and cannot diffuse anymore. So fish rather than tidal breathing pass water by there gills by moving them and since the waters constantly running through the gills it is able to diffuse about 99% of the oxygen into the bloodwhich makes it more efficent than tidal breathing and able to get a suffient amount of the oxygen in it for survival. In a fish first the oxygen is pumped by the flapping of the outer gills to where it quickly moves by them it is then brought into the gills which are the entry way for oxygen in a fishes respiration and the oxygern that is in the water diffuses into the fishes blood stream. Then the newly oxgenated blood passes through the aorta which is a large tube that carries blood. It is used to