exchange surface

• exchange surfaces in organism have many similar adaptations to make transport across the surface more efficient
• small organisms such as amoeba have very large surface area in comparison on their volume

  • a big surface area
  • shorter distance
• large organism

  • higher metabolic rate
  • smaller SA:V
  • longer distance from outside of the organisms
• what is the rate of diffusion affected by?

  1. surface area
  2. concentration gradient
  3. length of diffusion pathway
• all large organism have adaptations to increase the efficiency of transport across their surfaces to maximise diffusion.
• what are part of mammalian gas exchange system?

  • Trachea
  • bronchi + bronchioles
  • Alveoli
• Trachea

  • c shaped rings cartilage for support
  • ciliated epithelium with goblet cells
  • smooth muscle within the walls of trachea
  • lumen of the trachea constricting and reducing airflow into lungs
  • stretches and recoil of lumen due the elastic fibres
• Bronchi


  The trachea splits into two tubes the bronchi which connect to the right and left ling
• Bronchioles 


  the bronchi split into smaller tubes and create bronchioles both contain cartilage
• alveoli

  • large surface area = large number of alveoli provided
  • short diffusion distance = the alveoli walls are also very thin, made up of squamous epithelial cells
  • maintains a concentration gradient = each alveolus is surrounded by a network of capillaries to remove exchanged gases
  • oxygen diffuses from the alveoli into the blood in the capillaries + carbon dioxide diffuses from the blood in the capillaries to the alveoli
• what is ventilation?


  the mechanism of breathing which involves the diaphragm and antagonistic interactions between the external and internal intercostal muscles bringing about pressure changes in the thoracic cavity
• Ventilation 


  maintains the concentration gradient for gas exchange at the alveoli
• ventilation

  • inspiration = increased volume of the thorax therefore the air pressure inside the thorax is reduced
  • causes air to go into the lungs
  • expiration = decrease in the volume of the thorax and increase in the air pressure in the thorax
  • air forced out
• spirometer - measures the volume pf air inhaled and exhaled

  
• vital capacity 


  the maximum volume of air an individual can inhale and exhale during a deep breath
• Tidal volume 


  the air inhaled (peaks) and exhaled (troughs) when at rest
• Residual volume 


  the volume of air that always remains in the lungs so they do not collapse
• Breathing rate 


  The number of breaths taken per minute
• Oxygen uptake 


  increase when the ventilation rate increases e.g. exercise
• ventilation rate 


  tidal volume x breathing rate
• Ventilation in fish

  • fish swim with their mouth open so that water flows over the gills
  • fish lower their buccal cavity and open their mouth, this increases the volume of the buccal cavity = decreases pressure
  • this results in water flowing into buccal cavity
• Ventilation

  the operculum valve will shut and the operculum cavity (where the gills are located) will expand

  • this causes an increase in volume of the operculum cavity and therefore decrease in pressure
  • the fish will then raise the floor of the buccal cavity forcing the water from the buccal cavity this forces the water from the cavity over the gills
• Gas exchange in fish

  • fish exchange gases through their gills
  • gills are made of gill filaments + gill lamellae
  • Large surface area = many gill filaments and lamellae which are stacked
  • short diffusion distance = gill lamellae and filaments are both thin and contain capillary network
  • maintain concentration gradient = counter current system
• Counter current flow mechanism

  • water has a lower dissolved oxygen concentration compared to the concentration in the atmosphere
  • counter current system = when water flows over lamellae in the opposite direction to the flow of blood in the capillaries
  • this allows a diffusion gradient is maintained across the entire length of the gill lamellae
• counter current mechanism

  
• what type of system do insects use for gas exchange?

  • tracheal system made up of spiracles and trachea
• insects contract and relax their abdominal muscles to move gases in and out the spiracles to the trachea
• Insects gas exchange affordances

  • large surface area = many branching tracheoles
  • short diffusion distance = many branching tracheoles reach muscle + thin walled tracheoles
  • maintaining a concentration gradient = when cells respire they use up oxygen and produce carbon dioxide = abdominal muscle contract to pump air
• what happens to gas exchange when insects fly?

  • muscle cells respire anaerobically to produce lactate
  • this lowers their water potential = water moves from tracheoles (tracheal fluid) into to cells via osmosis
  • decrease in liquid in the tracheoles causes more air from atmosphere to move in