exchange surfaces

• hi everyone and welcome to miss asterisk biology in this video we are going through the entire module 3 for OCR a biology including exchange services transport animals and transporting plants and it is a big one
• if you want to skip ahead to any of those chapters then just click the time codes along the bottom
• if you do want any extra support on top of all of these videos for ocra and I'd highly recommend my ocra notes and my flash cards
• the notes Here summarize all the key terms key marking points to give you a really full understanding and save you loads of time
• the flash cards are those are better if you need help remembering the key marking points and getting your head around the key terms to include in the exams
• I'll link them both below and for now let's get into it
• the three key sections that this topic is split into

  • exchange surfaces
  • transport in animals
  • transporting plants
• we're going to begin with the exchange surfaces
• surface area to volume ratio

  the importance of this for organisms
• 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 organism
• 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. Inhalation: Diaphragm contracts, external intercostals contract, volume increases, pressure decreases, air flows in

  2. Exhalation: Diaphragm relaxes, internal intercostals contract, volume decreases, pressure increases, air flows out
• Spirometer


  Device used to measure volumes and rates of breathing
• Measurements from a spirometer


  • Vital capacity
  • Tidal volume
  • Residual volume
  • Breathing rate
  • Ventilation rate
• Fish face the challenge of lower oxygen concentration in water compared to air
• Fish ventilation


  1. Open mouth to draw water in

  2. Buccal cavity expands, pressure decreases, water flows in

  3. Operculum valve closes, operculum cavity expands, pressure decreases

  4. Buccal cavity raised, water forced over gills and out operculum
• Fish gills


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


  Made up of spiracles, tracheae and tracheoles, site of gas exchange
• Insect tracheal system


  • Abdominal muscle contractions create pumping mechanism
  • Many branching tracheoles provide large surface area
  • Thin tracheole walls provide short diffusion distance
  • Concentration gradient maintained by respiration and ventilation
• Types of circulatory systems


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


  Transport medium (hemolymph) pumped directly into body cavity, few vessels, low pressure
• Closed circulatory system


  Transport medium (blood) remains in blood vessels, allows gas and small molecule exchange
• Types of closed circulatory systems


  • Single (fish)
  • Double (mammals)
• Single closed circulatory system

  Blood passes through heart once per cycle, one circuit
• Double closed circulatory system

  Blood passes through heart twice per cycle, two separate circuits
• Pigmented protein


  For example, hemoglobin
• Single closed circulatory system


  • Blood passes through the heart once per cycle
  • Only one circuit that the blood takes
• Single closed circulatory system

  • Fish
• Single closed circulatory system


  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 the blood to the body before returning it back to the heart