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Diversity Gas exchange and Circulation Assignment Human Humans have a closed system where the blood is contained entirely in the vessels. They also have a double circuit where the blood flows from one circuit to the other. Gas exchange is carried out in the lungs. The oxygen that we inhale is passed through the trachea which then splits into two bronchi. The bronchioles branch of the bronchi and divide into smaller branches. The oxygen passes through the bronchiole and into the alveoli (air sacs).The alveolar surface is very close to the lung capillary which will let the oxygen for rapid diffusion. The capillary which carries red blood cells the oxygen binds with the red blood cells by a protein called haemoglobin. As the oxygen travels with the red blood cells the body tissue capillary is very close to the body cell which allows rapid diffusion of oxygen and carbon dioxide back and forth. The oxygen diffuses into the body cell from the capillaries and the carbon dioxide is diffuses into the capillaries. As the capillary travels back to the lungs the carbon dioxide is expelled by the lungs and out your mouth. Fish Fish use gills for gas exchange underwater. Fish have a closed circulatory system where the blood is entirely contained within the vessels. Fish have a single circuit system where the blood goes directly to the body from it gills and only flows once through the heart. Gas exchange occurs by diffusion between the water and the blood that flows across the gill membrane and capillaries. The operculum (gill cover) prevents the exit of water and acts as a pump drawing water past the gill filament. As the water flows over the gill filaments in the opposite direction to the blood flows through the gills. This is called countercurrent flow. As the blood flows in the opposite direction to the water the oxygen from the water is absorbed into the blood which carries the gases to and from the cells. As the blood carries the carbon dioxide back around the circuit the carbon dioxide is diffused out of the gills and into the water. Insects Insects have an open circulatory system where the Haemolymph does not carry the oxygen. The open system allows the Haemolymph to flow freely through body cavity. Gas exchange occurs through their tissues and the air system of air –filled tubes called tracheae. The tracheae open to the outside through a small hole called Spiracles. The spiracle opens on the side of the body that allow air to enter and exit the body. As the air travels through the tracheae tube network in the body the tube branches of into smaller tubes called the tracheoles. When the tube ends and makes contact with the cells this is when the gas exchange occurs where the oxygen is taken into the cell and carbon dioxide is out of the cells and travels up the tube network and out of the Spiracles. This tracheal system is only good for small bodies such as the insect. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/T/Trach eal_Breathing.html Heart Humans The human heart has 4 chambers separated into 2 separate pumps one for each circuit. As the right Atrium receives the deoxygenated blood from the body it travels through the Right Ventricle which pumps the http://www.heart-healthweightwatcher.com/images/HumanHeartDiagram.jpg deoxygenated blood to the lungs. When the oxygenated blood from the lungs travels through the Left Atrium and is pumped into the Left Ventricle where the blood is pumped to the body by the veins. As the veins carry the oxygenated blood to the capillaries the cells allow quick gas exchange to occur. Then the veins carry the deoxygenated blood back to the heart which then repeats the same cycle again. This human heart requires a higher oxygen rate then the fish or insects because it pumps more oxygen into our body which lets us do everyday activities. Fish The fish heart has 3 chambers connected in a series acting as a single pump. The Sinus Venosus receives http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/ F/fish_heart.gif deoxygenated blood from the body which is pumped to the Atrium and then pumped to the Ventricle which will then pump the deoxygenated blood to the gills. As the oxygenated blood travels from the gills the blood loses some oxygen as it travels to the tissues. When the blood arrives at the tissues less oxygen is absorbed into the cells. The deoxygenated blood is pumped back to the heart and repeats the cycle. This heart is only suitable for the fish as their oxygen needs are lower, as they are supported by the water. Insects The Dorsal Vein is a single tube that runs along the back of the insect. The Tubular heart is a series of chambers where it pumps the Haemolymph back towards the head. The Ostia are small holes that allow re-entry of the Haemolymph to the heart. The open system allows the Haemolymph to flow freely http://bugs.bio.usyd.edu.au/Entomology/ima ges/Topics/intAnatomy/heart2.gif through out the body and into the tissues where diffusion of oxygen and carbon dioxide occur. This open system is suitable for the insects as the short distances for diffusion throughout the body.