exchange surfaces

• Small organisms like amoeba have a very large surface area compared to their volume, allowing for efficient substance exchange through simple diffusion
• Large organisms have a smaller surface area compared to their volume, requiring adaptations to increase the efficiency of substance exchange across their surface
• Adaptations for substance exchange in organisms

  Structures with projections or folded membranes to increase surface area, ventilation or good blood supply to maintain concentration gradients, single layer of cells to reduce diffusion pathway
• Structures for substance exchange in organisms

  • Gills in fish
  • Alveoli in humans
  • Tracheal system in insects
• Trachea

  • Has c-shaped rings of cartilage for support, lined by ciliated epithelial cells with goblet cells producing mucus, contains smooth muscle that can contract to reduce airflow
• Bronchi and Bronchioles

  • Contain cartilage for structural support, branching tubes connecting to the lungs
• Alveoli


  • Located at the end of bronchioles, site of gas exchange in the lungs
• Structures in the mammalian gas exchange system

  • Trachea
  • Bronchi
  • Bronchioles
  • Alveoli
• Smooth muscle contraction in the trachea

  Reduces airflow to the lungs
• Smooth muscle relaxation in the trachea

  Dilates the airway for increased airflow
• Lung anatomy

  Lungs split into smaller tubes (bronchioles), end in alveoli where gas exchange occurs
• Bronchioles


  • Contain cartilage within their walls to provide structural support
• Gas exchange in alveoli

  Oxygen diffuses into the blood, picked up by red blood cells; carbon dioxide diffuses into alveoli and is exhaled
• Features providing large surface area, short diffusion distance, and maintaining concentration gradient

  • Large number of alveoli providing large surface area
  • Alveoli and capillary walls made up of single layer of squamous epithelial cells for short diffusion distance
  • Each alveolus surrounded by a capillary network for maintaining concentration gradient
• Ventilation


  Mechanism of breathing involving diaphragm muscle and antagonistic interactions between external and internal intercostal muscles
• Inhalation (inspiration)


  Volume of thorax increases, pressure decreases, air flows into lungs
• Exhalation (expiration)

  Volume of thorax decreases, pressure increases, air is forced out of lungs
• Muscle actions during inhalation and exhalation

  Diaphragm contracts during inhalation, relaxes during exhalation; external intercostal muscles contract during inhalation, relax during exhalation; internal intercostal muscles contract during exhalation, relax during inhalation
• Volume of air inhaled and exhaled can be measured using a spirometer
• Graph from spirometer shows peaks and troughs representing vital capacity, tidal volume, and residual volume
• Vital capacity is the maximum volume of air an individual can inhale and exhale during a deep breath
• Tidal volume is the air inhaled and exhaled when at rest
• Residual volume is the volume of air that always remains in the lungs to prevent collapse
• Breathing rates can be calculated by counting repeating patterns on the spirometer graph
• Ventilation rates can be calculated by multiplying tidal volume by breathing rate
• Oxygen uptake increases when ventilation rate increases, such as during exercise
• Ventilation and gas exchange in fish

  Fish swim with mouth open to allow water to flow over gills for gas exchange
• Less oxygen dissolved in water than in the atmosphere poses challenges for fish in maintaining the concentration gradient
• Ventilation in fish

  1. Fish swim with their mouth open so that water can flow in and over the gills

  2. Gills are the site of gas exchange

  3. Fish lower their buccal cavity to increase its volume, causing water to flow in

  4. Simultaneously, the operculum valve shuts and the operculum cavity expands, causing a decrease in pressure

  5. Fish raise the floor of their buccal cavity to force water over the gills and out of the operculum

  6. When the fish raise the buccal cavity and close their mouth, the pressure is high, opening the valve for water to flow over
• Ventilation in fish ensures a constant flow of water over the gills for gas exchange
• Components of gills in fish

  • Gill filaments
  • Gill lamellae
• Gill filaments


  • Longer parts sticking out in the gills
• Gill lamellae

  • Semi-circle structures covering the gill filaments, the exact location of gas exchange
• Counter current flow mechanism

  • Water flows over the gill lamellae in the opposite direction to the flow of blood in the capillaries to maintain the concentration gradient for diffusion
• Gas exchange in insects

  1. Insects have a tracheal system made up of spiracles, trachea, and tracheals

  2. Spiracles are valve-like structures that allow gases to move in and out and help prevent water loss

  3. Tracheals branch into many branching tracheals, the site of gas exchange

  4. Insects can contract and relax abdominal muscles to create a pumping mechanism for gas exchange

  5. The large surface area is maintained by many branching tracheals

  6. Short diffusion distance due to the wide reach of branching tracheals across the abdomen

  7. Concentration gradient is maintained by cells respiring and the pumping mechanism
• When insects are in flight, the rapid contraction and relaxation of muscles lead to anaerobic respiration, producing lactate which lowers the water potential, causing water to move into abdominal cells by osmosis
• Decrease in tracheal fluid volume due to osmosis causes a decrease in pressure, allowing air from the outside to move in through the spiracles