exchange surfaces

• Describe how diffusion distance, SA, Volume and SA:Vol ratio vary with increasing organism size

  As organism gets bigger, all dimensions increase. Diffusion distance by a linear factor, SA by a factor^2 and volume by a cubed factor. This means that volume increases faster than SA so the SA:Vol ratio decreases.
• Describe how the level of activity of an organism is related to demand for oxygen and glucose

  As activity increases, demand for energy increases. This requires a higher rate of respiration and therefore a higher demand for oxygen and glucose.
• Explain how volume is related to demand and surface area is related to supply and how this means adaptations are required in larger organisms

  Larger volumes require more oxygen and glucose as they have many more respiring cells. Exchange takes place across surfaces so larger surface area increases the ability to supply. In organisms with large volumes, simple surface area is not adequate to meet the demand of the cells so adaptations occur to increase surface area and have large exchange surfaces.
• Suggest some reasons why some organisms need specialised exchange systems

  Larger volumes so SA:Vol ratio too small to meet demand. High activity levels
• State the 4 features of efficient exchange surfaces. For each feature explain how it increases efficiency of the exchange surface

  Large surface area - Overcome SA:Vol problems

  Thin - short diffusion distance

  Well ventilated - Helps maintain conc. gradients

  Good blood supply - Helps maintain steep conc. gradient
• State Fick's law and show how the importance of each of the 4 features of efficient exchange surfaces can be explained by Fick's law


  Rate of diffusion is proportional to

  (SA x conc. gradient)/Thickness of Barrier

  Ventilation and blood supply affect conc. grad.
• Draw and label a diagram of the human gaseous exchange system

  
• Describe the structure of the nasal cavity, the trachea, the bronchi, bronchioles and alveoli and how they are adapted for their function


  Nasal Cavity:

  Large surface area with good blood supply warming gases to same temp as inside lungs

  Hairy lining which secretes mucus to trap dust and bacteria and protect delicate lining of lungs

  Moist to increase humidity and reduce evaporation from exchange surfaces

  
  

  Trachea + Bronch + Large Bronchioles:

  Cartilage rings to stop collapsing

  Cilia and mucus to trap dust etc. and sweep up and out

  Smooth muscle + elastic fibres to allow tube size to change - wider for more oxygen, smaller to reduce chance of infection

  
  

  Smaller Bronchioles:

  Smooth muscle and elastic fibres

  Squamous epithelium - some gas exchange occurs

  
  

  Alveoli:

  Elastic fibres - spring back when breathe out to push air depleted in oxygen out

  Sacs - high surface area

  Squamous epithelium - very thin, Moist - dissolve gases for increased diffusion

  Good blood supply - capillaries only one cell thick - maintain coc. grad. and short dist.
• Describe the importance of elastic fibres and lung surfactant in the function of alveoli

  Elastic fibres - spring back when breathe out to push air depleted in oxygen out

  Lung surfactant - reduces surface tension, stopping the walls of the alveoli sticking together
• Explain how the mammalian gaseous exchange system is adapted to be an efficient gas exchange surface

  Large surface area (alveoli)

  Short distance

  Good blood supply (network of capillaries)

  Ventilated
• Define the terms breathing, ventilation and gas exchange

  Breathing - behaviour/action - muscle contraction/relaxation

  Ventilation - flow of air in/out of lungs

  Gas exchange - diffusion of oxygen and carbon dioxide between the alveoli and the blood
• Define the terms inspiration, expiration, active process and passive process

  Inspiration - breathing in, inhalation

  Expiration - Breathing out, exhalation

  Active process - Uses energy for muscle contraction

  Passive process - Relaxing of muscles
• Describe the process of inspiration linking the action of muscles, to the movement of structures, the change in pressure within the lungs and the direction of airflow

  External intercostal muscles and diaphragm contract

  Ribs move up and out, diaphragm flattens

  Volume in lungs increases

  Pressure in lungs decreases

  Pressure in lungs is lower than atmospheric pressure

  Flow of air into lungs
• Describe the process of normal expiration linking the action of muscles, to the movement of structures, the change in pressure within the lungs and the direction of airflow

  External intercostal muscles and diaphragm relax

  Ribs move down and in, diaphragm becomes domed

  Volume in lungs decreases

  Pressure in lungs increases

  Pressure in lungs is higher than atmospheric pressure

  Flow of air out of lungs
• Describe how the process of forced expiration is different from normal expiration and suggest when it might be used

  Internal intercostal muscles contract using energy (active process) forcing ribcage down and in and decreasing volume in lungs

  Used to blow out a candle etc.
• State 3 pieces of equipment used to measure the functioning of the lungs. For each outline how they work.

  Peak flow meters - measure maximum rate at which air can be expelled from lungs

  Vitalographs - peak flow meters that calculate and graph the volume of air expelled as you breathe out as quickly as you can. One measure used to asseess lung function is 'forced expiratory volume in 1 second' (FEV1)

  Spirometers- Floating chamber on water with a pivot so that it moves down when you inhale and up when you exhale connected to a recording pen which draws a trace on a rotating drum.

  
• Describe how a spirometer measures change in lung volume and explain why it cannot measure absolute lung volume

  Can calibrate trace for a known volume of air.

  Cannot ever completely empty lungs so always some residual volume that is not measured.
• Define the term tidal volume

  The volume of air moved into or out of the lungs in one breath during normal breathing (in dm^3.breath^-1)
• Define the term vital capacity

  The volume of air breathed out after the deepest inspiration. It is the maximum volume of air that can be exchanged in one breath.
• Define the term inspiratory reserve volume

  The maximum extra volume that can be inhale after normal inspiration
• Define the term expiratory reserve volume

  The maximum extra volume that can be exhaled after normal expiration
• Define the term residual volume

  The volume of air remaining in the lungs after a maximal expiration
• Define the term total lung capacity

  The volume in the lungs at maximal inspiration
• Define the term breathing rate

  The number of breaths per minute
• Define the term ventilation rate

  The volume of air moved into or out of the lungs per minute
• Label the spirometer graph

  
• Explain how a spirometer trace is different to a graph of the changes in lung volume during breathing

  Spirometer trace does not show the residual volume and therefore doesn't show total lng capacity. Inspiration and expiration are the opposite way up as floating chamber moves down as lung volume increases, not up.
• Write an equation to link ventilation rate with breathing rate and tidal volume

  Ventilation rate = breathing rate x tidal volume
• Describe how a spirometer trace would differ during exercise as compared to the trace before exercise started

  Peaks and troughs larger and closer together
• Describe how tidal volume and breathing rate link to oxygen uptake and explain the importance of the change in tidal volume and breathing rate during exercise

  Increased tidal volume and breathing rate means more air and therefore more oxygen is entering the lungs and available to be taken up by the RBCs. During exercise more oxygen is needed for respiration so uptake more air must enter and leave the lungs at a faster rate.
• Define the term exoskeleton

  An external skeleton of some organisms e.g. insects
• Define the term spiracle

  Small openings along the thorax and abdomen of an insect that open and close to control the amount of air moving in and out of the gas exchange system and the level of water loss form the exchange surfaces
• Define the term tracheae

  The larger tubes of the tracheal system. They are held open by rings of chitin.
• Define the term tracheoles

  The smallest tubes of the tracheal system. They supply air to each cell. Cells often surround them so oxygen is effectively delivered into the centre of the cell. Carbon dioxide diffuses into them from the cells.
• Define the term tracheal fluid

  fluid found at the end of the tracheoles in insects that helps control the surface area for gas exchnge and water loss
• Outline the structure of the insect gas exchange system and describe the way oxygen reaches the body cells

  Spiracles open allowing gases to enter. Branching network allows diffusion of oxygen and carbon dioxide directly to/from cells
• Explain why insects will tend to keep spiracles closed when oxygen demands are very low

  To reduce water loss
• Describe adaptations that make insect gas exchange system that make it an efficient gas exchange surface

  Large surface area - lots of branching and vast numbers of tracheoles

  Short diffusion distance - tracheoles very small and in between cells - every cell very close to a tracheole

  Concentration gradient maintained by the use of oxygen within cells (for the most part, some also use abdominal pumping etc.)
• Describe ho activity changes the volume of tracheal fluid in the tracheoles ad explain the value of this occuring

  As activity increases, anaerobic respiration takes place due to lack of oxygen. The lactic acid produced causes water to leave the tracheal fluid by osmosis, reducing its volume and leaving a larger gas exchange surface available for diffusion
• Describe adaptations that insects with very high energy demands have to increase the efficiency of their gas exchange system

  Large insects use abdominal pumping to move air in/out

  When active, muscular movements of the thorax and abdomen ventilate tracheal system and force air in and out of the air sacs