AP Biology Why do we need a respiratory system? O2O2 food ATP CO 2  Need O 2 in  for aerobic cellular respiration  make ATP  Need CO 2 out  waste product from Krebs cycle

AP Biology Optimizing gas exchange  High surface area  maximizing rate of gas exchange  CO 2 & O 2 move across cell membrane by diffusion  rate of diffusion proportional to surface area  Moist membranes  moisture maintains cell membrane structure  gases diffuse only dissolved in water

AP Biology Gas exchange in many forms… one-celledamphibiansechinoderms insectsfishmammals endotherm vs. ectotherm size cilia water vs. land

AP Biology Counter current exchange system  Water carrying gas flows in one direction, blood flows in opposite direction

AP Biology  Blood & water flow in opposite directions  maintains diffusion gradient over whole length of gill capillary  maximizing O 2 transfer from water to blood water blood How counter current exchange works front back blood 100% 15% 5% 90% 70%40% 60%30% 100% 5% 50% 70% 30% water counter- current concurrent

AP Biology Gas Exchange on Land  Advantages of terrestrial life  air has many advantages over water  higher concentration of O 2  O 2 & CO 2 diffuse much faster through air  air is much lighter than water & therefore much easier to pump  Disadvantages  keeping large respiratory surface moist causes high water loss   Internal lungs

AP Biology Terrestrial adaptations  air tubes branching throughout body  gas exchanged by diffusion across moist cells Tracheae

Lungs Exchange tissue: spongy texture, moist epithelium  Air enters nostrils   Pharynx  glottis  larynx (vocal cords)  trachea (windpipe)  bronchi  bronchioles  air sacs (alveoli)  Epithelial lining covered by cilia & thin film of mucus

AP Biology Alveoli  Gas exchange across thin epithelium of millions of alveoli  total surface area in humans ~100 m 2

AP Biology Negative pressure breathing  Breathing due to changing pressures in lungs  pulling air instead of pushing it

Autonomic breathing control  Medulla sets rhythm & pons moderates it  measures pH of blood & cerebrospinal fluid bathing brain  CO 2 + H 2 O  H 2 CO 3 (carbonic acid)  if pH decreases then increase rate of breathing & excess CO 2 is eliminated in exhaled air Nerve sensors in walls of aorta & carotid arteries in neck detect O 2 & CO 2 in blood

AP Biology Diffusion of gases  Concentration gradient & pressure drives movement of gases into & out of blood at both lungs & body tissue bloodlungs CO 2 O2O2 O2O2 bloodbody CO 2 O2O2 O2O2 capillaries in lungscapillaries in muscle

AP Biology Hemoglobin  Why use a carrier molecule?  O 2 not soluble enough in H 2 O for animal needs  hemocyanin in insects = copper (bluish/greenish)  hemoglobin in vertebrates = iron (reddish)  Reversibly binds O 2  loading O 2 at lungs or gills & unloading at cells cooperativity heme group

AP Biology Cooperativity in Hemoglobin  Binding O 2  binding of O 2 to 1 st subunit causes shape change to other subunits  conformational change  increasing attraction to O 2  Releasing O 2  when 1 st subunit releases O 2, causes shape change to other subunits  conformational change  lowers attraction to O 2

AP Biology O 2 dissociation curve for hemoglobin Bohr Shift  drop in pH lowers affinity of Hb for O 2  active tissue (producing CO 2 ) lowers blood pH & induces Hb to release more O 2 P O 2 (mm Hg) More O 2 delivered to tissues pH 7.60 pH 7.20 pH 7.40 % oxyhemoglobin saturation Effect of pH (CO 2 concentration)

AP Biology O 2 dissociation curve for hemoglobin Bohr Shift  increase in temperature lowers affinity of Hb for O 2  active muscle produces heat P O 2 (mm Hg) More O 2 delivered to tissues 20°C 43°C 37°C % oxyhemoglobin saturation Effect of Temperature

AP Biology Transporting CO 2 in blood Tissue cells Plasma CO 2 dissolves in plasma CO 2 combines with Hb CO 2 + H 2 OH 2 CO 3 H+ + HCO 3 – HCO 3 – H 2 CO 3 CO 2 Carbonic anhydrase Cl–  Dissolved in blood plasma as bicarbonate ion carbonic acid CO 2 + H 2 O  H 2 CO 3 bicarbonate H 2 CO 3  H + + HCO 3 – carbonic anhydrase

AP Biology Releasing CO 2 from blood at lungs  Lower CO 2 pressure at lungs allows CO 2 to diffuse out of blood into lungs Plasma Lungs: Alveoli CO 2 dissolved in plasma HCO 3 – Cl – CO 2 H 2 CO 3 Hemoglobin + CO 2 CO 2 + H 2 O HCO 3 – + H +