gas exchange

• smaller the organism, the higher the SA:V ratio

  larger the organism, the lower the SA:V ratio
• single-cellular organisms:

  • diffusion is quick
  • short diffusion pathway
  • high SA:V ratio
  • could only diffuse by itself
• multiple-cellular organisms:

  • diffusion is slow
  • lower SA:V ratio
  • needs specialised organs to exchange substances
  • diffusion alone is insufficient
  • some cells to deep into body to interact with enviroment
• the rate substance exchange is determined by organisms SA:V ratio
• Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air in alveoli and blood in the capillaries around them (5)

  many alveoli provide a large surface area which allows fast diffusion

  alveoli have thin walls so short diffusion pathway

  capillaries and alveoli maintain a conc gradient
• describe the path by which oxygen goes from alveolus to the blood (2)

  through capillary endothelium, so longer diffusion pathway
• Describe how ventilation helps maintain differenvce in oxygen conc (2)

  bringing in air increase conc of oxygen breathing out removes air with lower conc
• Explain how the counter-current principle allows efficient oxygen uptake in the fish gas exchange system (2)

  blood and water flow in opposite directions

  concentration gradient maintained along lamella
• Describe and explain the advantage of the counter-current principle in gas exchange across a fish gill (3)

  water and blood flow in opposite directions

  maintains concentration gradient of oxygen

  diffusion occurs along lamellae
• Use your knowledge of gas exchange in leaves to explain why plants grown in soil with very little water grow only slowly (2)

  stomata closed

  less carbon dioxide uptake for less photosynthesis
• Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange.

  tracheoles have thin walls so short diffusion pathway

  large number of tracheoles provide large surface area

  tracheae provides tubes full of air so fast diffusion
• Explain two ways in which the structure of fish gills is adapted for efficient gas exchange

  many lamellae so large surface area

  thin surface so short diffusion pathway
• Explain how the counter current mechanism in fish gills ensures the maximum amount of the oxygen passes into the blood flowing through the gills (3)

  water and blood flow in opposite directions

  blood always passing water with high concentration of oxygen

  diffusion gradient maintained throughout length of gill
• ventilation:

  • inspiration, requires energy
  • expiration
• inspiration:

  • external intercoastal muscles and diaphragm contract
  • volume in thorax increases
  • lung pressure decreases below atmospheric
• expiration:

  • external intercoastal muscles and diaphragm relax
  • volume of thorax decreases
  • air pressure increases above atmospheric
• Forced expiration:

  • air forced out of lungs
  • external intercoastal muscles relax
  • internal intercoastal muscles contract
• Lung structure:

  A) larynx

  B) external intercoastal muscles

  C) trachea

  D) bronchus

  E) bronchioles

  F) intercoastal muscles

  G) diaphragm

  
• Alveoli:

  • alveolar walls = single layer of thin, flat cells (alveolar epithelium)
  • creating short diffusion pathway
  • walls of alveoli contain elastin = elastic = allow recoil
  • millions of alveoli = large SA
• pathway for oxygen:

  • trachea
  • bronchi
  • bronchioles
  • alveoli
  • alveolar epithelium
  • capillary endothelium
• Factors affecting diffusion:

  • thin surface = alveolar epithelium = short pathway
  • large SA = many alveoli
  • maintain steep conc gradient = ventilation and circulation
  • circulation- blood high in O2 replaced by blood low in O2
  • ventilation- breathing replaces air low in O2 with air high in O2
• lung function:

  • tidal volume - volume of air in each breath
  • ventilation/breathing rate - number of breaths per min
  • forced expiratory volume (FEV1) - maximum volume air breathed out in a second
  • forced vital capacity (FVC) - maximum volume of air possible to breathe forcefully out of lungs
• PVR = tidal volume X breathing rate
• Describe and explain one feature of the alveolar epithelium makes the epithelium well adapted for gas exchange (2)

  single layer of cells which shortens diffusion pathway
• suggest and explain how a reduced tidal volume affects the exchange of carbon dioxide between the blood and the alveoli (3)

  more carbon dioxide in lungs

  so reduced concentration gradient

  so more carbon dioxide stays in blood
• describe the path by which oxygen goes from alveolus to the blood (2)

  through alveolar epithelium through the capillary endothelium
• describe how ventilation helps maintain difference in oxygen concentration (2)

  air brought in contains higher conc of oxygen

  alveolus removes air with low conc of oxygen