lesson 3

• Gas exchange


  1. Uptake of molecular oxygen from the environment

  2. Discharge of carbon dioxide to the environment
• Gas exchange is often called respiratory exchange of respiration but it should not be confused with cellular respiration
• Oxygen is needed in tissues for aerobic cellular respiration to occur and extract ATP from food
• Carbon dioxide must be released to prevent physiological pH in tissues from being very acidic
• In plants, the carbon dioxide that is released as a by-product of cellular respiration may again be taken up for the process of photosynthesis
• Respiratory surface or organ

  • It must be moist, large enough, and protected from desiccation (drying)
• Partial pressure


  The pressure exerted by a particular gas in a mixture of gases
• Fick's Law


  The amount of diffusion of a gas across a membrane is proportional to the surface area and the difference in partial pressure between the two sides and inversely proportional to the thickness of the membrane
• As an animal grows

  The surface area increases at a lesser rate than its volume, making diffusion of gases into the interior more difficult
• Ventilation


  The movement of the respiratory medium (air or water) over the respiratory surface
• Respiratory pigments or proteins

  • Hemoglobin (vertebrates)
  • Hemocyanin (invertebrates)
• Blood cannot carry sufficient oxygen and carbon dioxide in dissolved form to meet the body's requirements; hemoglobin helps enhance its capacity
• Plants take in carbon dioxide from the environment and release oxygen
• Gas exchange in plants happens in stomata, lenticels, root hairs, and pneumatophores
• In contrast with plants, animals take in oxygen and release carbon dioxide
• Respiratory surfaces or organs in invertebrates

  • Cell surface or cell membrane
  • Integumentary exchange
  • External gills
  • Tracheal system
• Respiratory surfaces in vertebrates


  • External gills
  • Internal gills
  • Lungs
• Lungs


  • Provide a membrane for gaseous exchange, require a circulatory system to transport gases to the rest of the body
• Ventilation in vertebrates


  1. Positive pressure breathing (amphibians)

  2. Air sacs as blower (birds)

  3. Negative pressure breathing (mammals)
• Control of respiration in vertebrates


  Nervous system regulates oxygen and carbon dioxide levels by controlling rate and depth of breathing
• Animals that inhabit high altitudes have larger hearts and lungs, and hemoglobin with a high affinity for binding oxygen
• Many diving animals have unusually high hematocrite and muscles with high amounts of myoglobin
• Parts of the human respiratory system

  • Nose/mouth
  • Pharynx
  • Trachea
  • Bronchi
  • Bronchioles
  • Alveoli
• Alveoli


  • Very thin epithelial layer, surrounded by rich capillary network, roughly spherical shape, internal surface covered with fluid
• Respiratory problems in humans

  • Asthma
  • Emphysema
  • Smoking-related diseases
  • Pneumonia
• Oxygen transport


  1. Oxygen diffuses from lungs into blood plasma and binds to hemoglobin

  2. Hemoglobin gives up oxygen in tissues with low partial pressure, high temperature, high carbon dioxide, and low pH
• Carbon dioxide transport


  1. Carbon dioxide diffuses from tissues into blood plasma

  2. 7% dissolved in plasma, 23% binds to hemoglobin, 70% in bicarbonate form