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ADAPTATIONS FOR GAS EXCHANGE We will be studying the diversity of adaptations for this process in four organisms: Fish Mammals Insects Plants Definitions Respiration Gas exchange Ventilation AN OVERVIEW Cellular respiration requires O2 and produces CO2 : C6H12O6 + 6O2 6CO2 + 6H2O glucose + oxygen carbon dioxide + water Gas exchange provides a means of supplying an organism with O2 and removing the CO2 THE SOURCE OF OXYGEN Air • about 21% oxygen • thinner at higher altitudes • easy to ventilate Water • Oxygen content varies but is always much less than air • even lower in warmer water/salt water • harder to ventilate GAS EXCHANGE SURFACES Gases move by diffusion. Diffusion Diffusion is greater when: • the surface area is large • the distance travelled is small • the concentration gradient is high Gas exchange also requires a moist surface • O2 and CO2 must be dissolved in water to diffuse across a membrane GAS EXCHANGE SURFACES Therefore, an efficient gas exchange surface will… • have a large surface area • provide a small distance for gases to diffuse across • be moist …and will be organised or operate in a way that maintains a favourable concentration gradient for the diffusion of both gases. A circulatory system may operate in tandem with the gas exchange system to maintain the concentration gradient. STRUCTURE OF THE GAS EXCHANGE SURFACE Depends on: • the size of the organism • where it lives – water or land • the metabolic demands of the organism – high, moderate or low TYPES OF GAS EXCHANGE SURFACE INSECT TRACHEAL SYSTEM Air tubules (tracheae & tracheoles) throughout the body which open to the environment via spiracles. INSECT TRACHEAL SYSTEM • • • • Tracheae kept open by circular bands of chitin. Branch to form tracheoles that reach every cell. Ends of the tracheoles are moist. Oxygen delivered directly to respiring cells – insect blood does not carry oxygen. ENHANCING THE EFFICIENCY OF INSECT TRACHEAE • Oxygen delivered directly to respiring cells. • Can pump abdomen to move air around in tracheal system. BUT • Size of animal limited by relatively slow diffusion rate. During prolonged activity, the muscle will start to respire anaerobically. This causes a build-up of lactate, which draws water into the muscle. Diffusion distance for oxygen is reduced. Now complete the worksheet!