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UNIT 2 The nutrition function RESPIRATION IN DIFFERENT ANIMALS Natural Science 2. Secondary Education UNIT 2 What is diffusion? Diffusion in living things • Diffusion is the transfer of gases between the external environment and the circulating liquid, through tissues that are thin enough to allow these gases to pass. • When the circulating liquid reaches the respiratory organs, it is carbon dioxide-rich and oxygen-poor. When air reaches the respiratory organs, on the other hand, it is oxygen-rich and carbon dioxide-poor. • This is when diffusion occurs: oxygen will move from the area of high concentration to the area of low concentration (from the air to the circulating liquid), and carbon dioxide will do the same (it will move from the circulating liquid to the air). Air with O2 CO2 Air with CO2 Exchange tissue Blood with CO2 Natural Science 2. Secondary Education O2 Blood with O2 UNIT 2 What is diffusion? Diffusion in living things • Diffusion can occur: • Through the body surface. This occurs in sponges, polyps, worms and some amphibians. • Through gills: This occurs in molluscs, crustaceans, fish and some amphibians. • Through tracheae: In insects. • Through lungs: In amphibians, reptiles, birds and mammals. Natural Science 2. Secondary Education UNIT 2 How some animals take oxygen from the water RESPIRATION IN WATER is carried out THROUGH THE BODY SURFACE THROUGH GILLS Click on each box to find out more Natural Science 2. Secondary Education UNIT 2 How some animals take oxygen from the water Respiration through the body surface • This is seen in animals that live underwater or in very wet environments, like the soil. • Sponges, cnidarians (polyps and jellyfish), worms and some amphibians absorb air in this way. O2 CO2 O2 CO2 Wet environment Body surface The animal absorb O2 through its surface Respiration through the body surface in an annelid. Natural Science 2. Secondary Education The animal eliminates CO2 through its surface Go back to the Start menu UNIT 2 How some animals take oxygen from the water Respiration through gills • Gills are very thin sheets or filaments full of capillaries. • When water passes through the gills, carbon dioxide from the circulating liquid inside the organism is exchanged for oxygen from the water. • Gills are the respiratory organs of aquatic molluscs, crustaceans, fish and some amphibians. Blood with O2 Blood with CO2 CO2 Water Water with O2 Natural Science 2. Secondary Education O2 Water with CO2 Respiration through gills in a fish. Go back to the Start menu UNIT 2 How some animals take oxygen from the air RESPIRATION IN AIR is carried out THROUGH TRACHEAE THROUGH LUNGS Click on each box to find out more Natural Science 2. Secondary Education UNIT 2 How some animals take oxygen from the air Respiration through tracheae • This type of respiration occurs in almost all insects. • Tracheae are very thin tubes that branch out to provide the animal’s tissues with oxygen. • They lead out of the body through pores called spiracles. The insect’s tissues Spiracle Trachea CO2 O2 Exoskeleton Respiration through tracheae in an insect. Natural Science 2. Secondary Education Go back to the Start menu UNIT 2 How some animals take oxygen from the air Respiration through lungs • This type of respiration occurs in amphibians, reptiles, birds and mammals. • Lungs are made up of millions of tiny tubes or cavities called alveoli, which are full of capillaries. This is where oxygen passes into the blood. • Lungs are connected to the external environment by the rest of the respiratory tract (airways). Blood with O2 Blood with CO2 Airways O2 CO2 Lungs Respiration through lungs in a mammal. Natural Science 2. Secondary Education Go back to the Start menu