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  1. 2. <ul><li>Gaseous exchange : uptake of O2 from the environment and the discharge of CO2 to the environment. </li></ul><ul><li>Takes place in respiratory structures. </li></ul><ul><li>Movement of the respiratory gases between the respiratory surface and the external environment is by diffusion . </li></ul><ul><li>Characteristics of respiratory structures: </li></ul><ul><ul><li>The respiratory surface is moist </li></ul></ul><ul><ul><li>Cells lining the respiratory surface are thin </li></ul></ul><ul><ul><li>The respiratory structure has a large surface area. </li></ul></ul>
  2. 3. <ul><li>Small organisms do not need any special respiratory structure. </li></ul><ul><li>Respiratory surface for unicellular organism such as Amoeba sp. is the entire plasma membrane. </li></ul><ul><li>Surface area per volume depends on the size of organism. </li></ul>
  3. 4. <ul><li>Respiratory system of insects known as tracheal system ; composed of air tubes called tracheae . </li></ul><ul><li>Air enters the tracheae through spiracles. </li></ul><ul><li>Spiracles of insects such as grasshopper have valves which allow them to open and close, so that air can go in and out of the body. </li></ul><ul><li>Tracheae branch into fine tubes </li></ul><ul><li> called tracheoles. </li></ul><ul><li>Large number of tracheoles </li></ul><ul><li>provides large surface area for </li></ul><ul><li>diffusion of gases. </li></ul>
  4. 5. <ul><li>Air travels through the tracheoles reaches the fluid filled tips, O 2 diffuses directly from the tracheoles into the cells, while CO 2 diffuses from the cells into the tracheoles. </li></ul><ul><li>Larger insects have air sacs which speed up movement of gases to and from tissue. </li></ul>
  5. 6. <ul><li>Air is drawn into and out of tracheae by rhythmic movements of abdominal muscles that compress and expand tracheae to speed up diffusion of gases into the cells. </li></ul><ul><li>Insect inhales; </li></ul><ul><ul><li>Abdominal muscle relax </li></ul></ul><ul><ul><li>Spiracles are open </li></ul></ul><ul><ul><li>Air pressure inside is lowered </li></ul></ul><ul><ul><li>Air is drawn in </li></ul></ul><ul><li>Insect exhales; </li></ul><ul><ul><li>Abdominal muscles contract </li></ul></ul><ul><ul><li>Increase air pressure </li></ul></ul><ul><ul><li>Forces air out </li></ul></ul>
  6. 7. <ul><li>Respiratory structure: gills </li></ul><ul><li>Each gill composed of filaments. </li></ul><ul><li>Filaments : </li></ul><ul><ul><li>have numerous thin-walled named lamellae. </li></ul></ul><ul><ul><li>Have thin membranes </li></ul></ul><ul><ul><li>Rich supply of blood capillaries </li></ul></ul>
  7. 9. <ul><li>Gaseous exchange enhanced by countercurrent exchange mechanism. </li></ul><ul><ul><li>The blood in the capillaries flow in the opposite direction to the flow of water. </li></ul></ul><ul><ul><li>ensures maximum intake of O 2 (80%) by the blood. </li></ul></ul><ul><ul><li>Deoxygenated blood enters the capillaries, it encounters water with higher O 2 content </li></ul></ul><ul><ul><li>Thus, along the capillaries, the diffusion gradient allows the transfer of O 2 into the blood. </li></ul></ul><ul><li>Ventilation increases the flow of water over respiratory surface by swimming and opening and closing the operculum. </li></ul>
  8. 10. <ul><li>Gaseous exchange occurs through skin and lungs . </li></ul><ul><li>Skin: </li></ul><ul><ul><li>Thin </li></ul></ul><ul><ul><li>Highly permeable to respiratory gases. </li></ul></ul><ul><ul><li>Kept moist by secreting mucus </li></ul></ul><ul><ul><li>Beneath skin, large number of blood capillaries </li></ul></ul>Facilitate rapid and efficient exchange of gases between skin and environment.
  9. 11. <ul><li>Lung: </li></ul><ul><ul><li>Consists of a pair of thin walled sacs </li></ul></ul><ul><ul><li>Thin </li></ul></ul><ul><ul><li>Moist </li></ul></ul><ul><ul><li>Covered by network of capillaries. </li></ul></ul><ul><li>Breathing mechanisms </li></ul><ul><ul><li>Filling buccal cavity with air </li></ul></ul><ul><ul><ul><li>Bucco-pharyngeal floor lowered  glottis closes  nostril open to suck air  air is drawn into bucco-pharyngeal cavity. </li></ul></ul></ul><ul><ul><li>Forcing air into the lungs </li></ul></ul><ul><ul><ul><li>Glottis open  nostrils closed  bucco-pharyngeal floor raised  air pressure increased  air is forced into the lungs </li></ul></ul></ul><ul><ul><li>Frog repeat steps (a) and (b) to take in more air, pumping up itself to a considerable size </li></ul></ul><ul><ul><li>Expiration </li></ul></ul><ul><ul><li>the frog opens its nostrils and glottis  air flows out of its lungs. </li></ul></ul>
  10. 15. <ul><li>Breathing mechanism involves: </li></ul><ul><ul><li>Inhalation </li></ul></ul><ul><ul><li>Exhalation </li></ul></ul><ul><li>Inhalation: </li></ul><ul><ul><li>External intercostal muscles contract  internal intercostal muscles relax  rib cage move upwards and outwards  diaphragm contracts and flattens  increases volume of thoracic cavity  reduced air pressure  air is drawn into the lungs through nostrils and fill the alveoli. </li></ul></ul>
  11. 16. <ul><li>Exhalation </li></ul><ul><ul><li>External intercostal muscles relax  internal intercostal muscles contract  rib cage move downwards and inwards  diaphragm relax and returns to original shape  decreases volume of thoracic cavity  increased air pressure  air is forced out of the lungs. </li></ul></ul>