MODULE 3 VIDEO

• small organisms like amoeba have a very large surface area compared to their volume. this means they have a big surface area for the transport substances and a short distance between the outside and the Very middle of the organism. simple diffusion is sufficient to meet their metabolic needs
• large organisms have a smaller surface area compared to their volume and a larger distance from the outside to the middle of the organis. they also have higher metabolic rates meaning they require more oxygen for respiration. large organisms require adaptations to increase the efficiency of exchange across their surface
• adaptations to increase efficiency of exchange

  • Providing large surface area
  • Maintaining concentration gradient
  • Reducing diffusion pathway
• the adaptations we'll focus on are the gills in fish, the alveoli in humans, and the tracheal system in insects
• Trachea

  Also known as the windpipe, has C-shaped rings of cartilage to support it and keep it permanently open
• Trachea lining

  Epithelial cells that are ciliated and contain goblet cells to trap pathogens and dust
• Smooth muscle in tracheal walls

  Can contract to constrict the lumen and reduce airflow, then relax to dilate the lumen
• Structures of the mammalian gas exchange system

  • Trachea
  • Bronchi
  • Bronchioles
  • Alveoli
• Alveoli

  • Provide large surface area for gas exchange
  • Have a short diffusion distance due to single layer of squamous epithelial cells
  • Concentration gradient maintained by ventilation and capillary network
• Ventilation

  1. Diaphragm contracts and external intercostals contract to increase thorax volume and decrease pressure, causing air inflow

  2. Diaphragm relaxes and internal intercostals contract to decrease thorax volume and increase pressure, causing air outflow
• Spirometer

  Device used to measure volumes and rates of breathing
• Vital capacity is the maximum volume of air that can be inhaled and exhaled
• Tidal volume is the air inhaled and exhaled during normal breathing
• Residual volume is the volume of air that always remains in the lungs
• Breathing rate can be calculated from the spirometer graph
• Ventilation rate is tidal volume x breathing rate, and increases during exercise
• Fish have the challenge of lower oxygen concentration in water compared to air
• Fish ventilation

  1. Open mouth to increase buccal cavity volume and decrease pressure, causing water inflow

  2. Close operculum valve to increase operculum cavity volume and decrease pressure

  3. Raise buccal cavity floor to force water over gills and out operculum
• Fish gills


  • Provide large surface area with many gill filaments and lamellae
  • Short diffusion distance across thin lamellae
  • Counter-current flow mechanism maintains concentration gradient
• Counter-current flow

  Water and blood flow in opposite directions, preventing equilibrium and maintaining diffusion gradient
• Insect tracheal system

  • Provides large surface area with many branching tracheae
  • Short diffusion distance across thin tracheal walls
  • Concentration gradient maintained by respiration and abdominal muscle pumping
• Insects can respire anaerobically during flight, producing lactic acid that decreases water potential and draws water into cells, decreasing tracheal fluid volume and causing air inflow
• Types of circulatory systems

  • Open (invertebrates)
  • Closed (vertebrates and some invertebrates)
• Open circulatory system

  Hemolymph pumped directly into body cavity, transports food and waste but not gases
• Closed circulatory system

  Blood remains in vessels, transports oxygen, carbon dioxide, and other substances
• Types of closed circulatory systems

  • Single (fish)
  • Double (mammals, birds)
• Single closed system has blood pass through heart once per cycle, suitable for fish with counter-current exchange
• Double closed system has blood pass through heart twice per cycle, with separate pulmonary and systemic circuits, more efficient for gas exchange
• Pigmented protein


  For example, hemoglobin
• Single closed circulatory system

  • Blood passes through the heart once per cycle
  • Only one circuit that the blood takes
• Organisms with single closed circulatory systems

  • Fish
• Single closed circulatory system in fish

  1. Blood passes through two sets of capillaries immediately after being pumped out of the heart

  2. Blood flows through capillaries in the gills to become oxygenated

  3. Blood flows through capillaries delivering it to the body before returning it back to the heart
• Single closed circulatory system would not enable efficient gas exchange for mammals but it does work for fish because they have that counter current flow mechanism
• Double closed circulatory system

  • Blood passes through the heart twice per cycle
  • Two separate circuits the blood would take
• Organisms with double closed circulatory systems

  • Birds
  • Most mammals
• Double closed circulatory system

  1. One circuit is blood vessels carrying blood from the heart to the lungs for gas exchange

  2. Second circuit is blood vessels carrying the blood from the heart to the rest of the body to deliver oxygen, nutrients and collect waste
• Blood vessels

  • Arteries
  • Arterials
  • Capillaries
  • Venules
  • Veins
• Capillaries

  • Form capillary beds (many branched capillaries connected)
  • Narrow diameter to slow down blood flow so red blood cells are squashed against walls, maximizing diffusion
  • Made up of only one layer of squamous epithelial cells with small gaps between them
• Hydrostatic pressure


  Pressure exerted by a liquid
• Oncotic pressure


  Tendency of water to move into the blood by osmosis