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Exchange of Gas What you intend the students to learn about this idea? 1/ Gases are exchanged across surfaces to enable survival of organisms Organisms cannot survive without gas exchange Oxygen and carbon dioxide are needed for energy-transforming processescellular respiration and photosynthesis. Cellular respiration produces energy (uses oxygen and produces carbon dioxide) whereas respiration is the movement of gases between the environment and the cell Diffusion is the process which carbon dioxide (waste product of respiration) is expelled and oxygen is obtained. This process is passive and depends on the concentration gradient. Gas exchange in organisms can occur in different ways: Animals- special surfaces in their respiratory system, Mammals – respiratory surfaces in their lungs, Fish – gas exchange surfaces in their gills, Insects – air-filled tubes (trachea) send oxygen to respiratory surfaces Aerobic organisms are oxygen dependent – the amount of oxygen effects amount of energy. Anaerobic organisms are not oxygen dependant. 2/ The respiration of mammals occurs across well developed respiratory structures There is plenty of oxygen in atmospheric air (21%). While it also consists of carbon dioxide the majority of air is nitrogen. Larger animals which have high metabolic rates need lots of oxygen. Animals have well developed respiratory mechanisms linked closely to the circulatory system. Lungs are internally expanded respiratory structures & must remain moist. Breathing air uses less energy than water. Mammalian respiratory system consists of the pharynx, trachea, bronchi, bronchioles and alveoli Gas exchange occurs at the alveoli were capillaries facilitate diffusion. Haemoglobin (respiratory pigment) carries large amounts of O2 in the blood. Inspiration occurs when the diaphragm and muscles contract to draw air into lungs. Expiration occurs when they relax and air is forced out of the lungs. Page 1 of 4 Adequate gas exchange requires a large moist surface area, thin membrane and enough supply of substances What can hinder respiration and how? Emphysema and asthma. 3/ Organisms can breathe in water using gas exchange surfaces in gills The amount of oxygen dissolved in water is very low and depends on temperature, salinity and depth. Organisms living in water do not have a high demand of oxygen because they use less energy Gills allow exchange of gases in water & are expanded respiratory surfaces Water passes over gills in one direction and small amounts of oxygen are efficiently gained because of the counter-current flow of blood and water Gas exchange occurs across membranes in the gills called lamellae. 4/ Smaller organisms and plants exchange gas directly with their environment. Small organisms need little oxygen especially inactive organisms Small organisms have a high surface area to volume ratio so exchange of gas occurs directly with their environment. This occurs with plants however they can regulate this process. Plants use up carbon dioxide produced by cellular respiration as well as additional carbon dioxide from the environment during the day in photosynthesis which produces oxygen. Flowering plants don’t have specialised organs for gas exchange but have openings called stomata which allow passage of oxygen and carbon dioxide Insect have a network of fine internal air-filled tubes (tracheae) along its body with openings (spiracles). Air moves along these tubes. Insect blood usually plays no part in gas exchange. Gas is diffused straight to the body cells. Why is it important for students to know this? 1/ In facilitating knowledge of the world students need to understand that all organisms require gas exchange and do this in different ways. Respiration is interlinked with how other systems function and understanding gas exchange will assist with learning about bodily function as a whole. 2/ Students need to understand why we need to obtain oxygen/carbon dioxide to survive and how this process occurs. Understanding respiration, the effects of Page 2 of 4 asthma and the implications of smoking will inform student so they can make wiser life choices. Students need to understand that the body’s absorption of oxygen can be hindered by not meeting the body’s iron requirements. 3/ In facilitating knowledge of the world students need to understand how organisms are able to breathe in aquatic environments. Understanding the requirements of gas exchange in fish will assist in students providing appropriate care for aquatic pets. 4/ Understanding the requirements of gas exchange in plants and small organisms will assist in students providing appropriate care for plants and other pets. Having an understanding of plant respiration will assist students in thinking about global warming. Understanding flowering plants use of stomata for gas exchange will help students understand differences when looking at plants in different habitats. What else you know about this idea (that you don’t intend students to know yet)? 1/ Regulation of respiration. Respiration physiology in detail. Details of the anaerobic process as well as cellular respiration. 2/ How inspiration works in detail. Detailed knowledge of respiratory diseases. The development of the respiratory system in young. 3/ How pollution can affect the ability of marine life to breathe. Details of the process of gas exchange in swim bladders. 4/ The effect of air pollution on the respiration of plants and insects. Detailed knowledge of how plant respiration could work to reduce global warming. Knowledge about students’ thinking/difficulties connected with teaching this idea 1/ Vernacular misconception - ‘respiration’ is different from ‘cellular respiration’ 2/ Tidal volume can be perceived to be fixed and that it cannot increase with breathing frequency. All air in the lung is expelled in exhalation. Dependency of gas exchange on concentration gradients 3/ Gills are the only structure involved in gas exchange of fish (swim bladder/cutaneous respiration). 4/ Gas exchange in plants occurs at night. Insect blood has a major role in gas exchange like mammals and fish Teaching procedures (& particular reasons for using these to engage with this idea) Page 3 of 4 Build a spirometer– by building spirometers using plastics tubes and bottles in buckets of water students can measure how much air can fit into their lungs and the amount they would normally inhale and exhale. This can be very useful in allowing students to visualise tidal volume and the capacity of lungs which can often be confused. Dissection of fish – students are shown how water flows across the gills and get to see the gill structure. This can be helpful to students as they get to visualise the gill structure with their own eyes instead of relying on textbook diagrams. Students will be able to investigate the gill structure and identify different components. Models of fish versus human respiration– Students build paper models of fish and human respiratory systems showing tissues, blood flow and gas exchange. This highlights the differences in respiratory structures and how they function. It also can assist kinetic and visual learners to better understand how these systems are put together and how they function. Concept map – By allowing student to construct concept maps their understanding of the concept is show. This can enable any misconceptions to be addressed. It will also help student to visualise the different aspect and how they link together to form a functioning system. Specific ways of ascertaining students’ understanding or confusion around this idea (include likely range of responses) Firstly students’ misconceptions can be determined through worksheets, quizzes or class discussions. Then teaching approaches to gas exchange can be focused on carefully addressing any aspects which may lead to confusion. Assessment of understandings can be achieved through worksheets, activities, quizzes, class discussion, predict observe and explain, concept maps and probing understanding. Common misconceptions of gas exchange are: 1/ Vernacular misconception of the term ‘respiration’ 2/ Tidal volume is fixed. All air in the lungs is expelled in exhalation. The dependency of gas exchange on concentration gradients 3/ Gills are the only structure involved with respiration of fish (swim bladder/cutaneous respiration) 4/ Gas exchange in plants occurs at night. Insect blood is involved with respiration. Page 4 of 4