exchange surfaces qs

• one feature of gaseous exchange surface

  squamous epithelial layers are thin for short diffusion distance
• Exhalation in a mammal?

  • ribcage moves downwards and upwards
  • external intercostal muscles relax
  • Diaphragm relaxes
  • volume in thorax decreases, then Pa increases
  • Pressure inside is greater than outside
  • Alveoli elastic fibres return to normal length
• Inhalation in mammals?

  • ribcage moves upwards and downwards
  • external intercostal muscles contract
  • Diaphragm contracts
  • volume in thorax increases, then Pa decreases
  • Pressure outside is greater than inside
  • Air moves in to equalise the PA
• what do internal intercostal muscle do

  contract air to force out of the lungs
• goblet cells


  release mucus into trachea
• Name two types of epithelial tissue found in the lungs and airways?

  1. Ciliated

  2. Squamous
• Explain how the alveoli create a surface efficient for gas exchange [5]

  - Wall is one cell thick for shorter diffusion distance

  - Squamous cells provide short diffusion pathway

  - They are elastic so recoil to repel air during ventilation

  - They are able to maintain a steep concentration gradient

  - A large number of alveoli provide a large surface area

  - Small size of alveoli provide a large SA:V

  - Cells secrete surfactant to maintain surface area and prevent the alveoli collapsing
• Why do the balloons in a glass bell jar model expand? [3]

  - Volume inside jar increases

  - Pressure inside jar decreases to below atmospheric pressure

  - Therefore air is forced inside balloons
• What is meant by Tidal Volume?

  Volume of air inhaled/exhaled in each breath during regular breathing
• Explain the meaning of Vital Capacity

  The maximum amount of air inhaled/exhaled in one breath
• How does the squamous epithelium help improve gas exchange efficiency?

  Provides a short diffusion distance
• How so the large number of alveoli help improve gas exchange efficiency?

  Increase surface area
• How does a good blood supply help improve gas exchange efficiency?

  Maintains a high concentration gradient and removes oxygen from lung surface
• How does good ventilation help improve gas exchange efficiency?

  Maintains a large concentration gradient and supplies oxygen to alveoli
• List three reasons why a large multicellular organism such as a mammal needs a gas exchange system [3]

  - Small SA:V

  - Diffusion is too slow as the distance is too great

  - To supply enough oxygen/nutrients

  - Or to prevent CO2 buildup

  - Due to high metabolic rate
• Why is it not possible to expel all air from lungs?

  - Thorax cannot be completely compressed

  - Cartilage rings in trachea stop it becoming flat
• What are the air sacs in mammalian lungs called and why are there so many?

  - Alveoli

  - To provide larger surface area
• Explain the role of elastic fibres within the air sacs during ventilation


  - They recoil and prevent bursting

  - They return the air sac to its original size

  - They help expel air
• Explain how refreshing the air in the air sacs helps maintain a steep concentration gradient

  - Increases concentration of oxygen in air sac

  - So concentration of oxygen in air sac is higher than in blood

  - Decreases concentration of CO2 in air sac

  - So concentration of CO2 in air sac is lower than in blood
• Describe and explain a way in which a steep concentration gradient is maintained in the lungs

  - Continuous blood flow in the capillaries

  - Brings in more CO2/removes more oxygen

  Or

  - Oxygen combines with haemoglobin

  - Which keeps concentration in blood plasma low
• Using the mammalian gaseous exchange system as an example, explain how the different cells and tissues enable the efficient exchange of gas

  - Thin squamous epithelium

  - Thin endothelium of capillary

  - Provides a short diffusion distance

  - Epithelial cells also have surfactant to reduce surface tension

  - Red blood cells transport gases to/from alveoli which maintains a steep concentration gradient

  - Ciliated epithelium cells remove dust and bacteria

  - Cartilage holds airways open

  - Smooth muscle controls the diameter of blood vessels and airways

  - Elastic fibres to aid ventilation by recoiling

  - Macrophages engulf pathogens
• Describe how a spirometer would be used to measure tidal volume

  - Subject breathe normally but through mouth (not nose) so they wear a nose clip

  - Measure amplitude of waves from trace

  - Measure 3 waves and calculate mean

  - As subject breathes in lid goes down

  - Movement of lid is recorded on the trace by data logger
• Describe how you could use a spirometer trace to measure the rate of oxygen uptake

  - Measure volume of oxygen used

  - Find difference in height from one peak/trough to another

  - Measure time taken to use this oxygen

  - Divide volume by time taken
• 2 factors to be considered when carrying out a risk assessment for an experiment using a spirometer

  - Check health of volunteer

  - Check soda lime is working

  - Sufficient oxygen in chamber

  - Water level not too high

  - Ensure valves are working correctly
• 2 effects of increased permeability on surrounding tissues

  - Increase in volume of tissue fluid

  - Increased pressure in tissues

  - Swelling or inflammation

  - More white blood cells pass into tissues

  - Larger molecules or proteins pass into tissue fluid
• Why can't fish breathe in and out via ventilation?

  Water is denser, more viscous and has a lower oxygen content than air, so requires too much energy to be efficiently moved by a 2-way ventilation system
• Why do larger, eukaryotic organisms need specialised exchange surfaces?

  Because they have greater metabolisms so need more resources and have lower SA:V ratios so cannot get all of these resources via simple diffusion, osmosis etc. as the substances need to travel further to get to our internal cells
• What are 4 things all good exchange surfaces should have/be?

  1. Large surface area

  2. Thin

  3. Good ventilation

  4. Good blood supply
• How does having a large surface area aid exchange surfaces?

  Allows more substances to travel across at a time, increasing exchange rate
• How does being thin aid exchange surfaces?

  Allows substances to travel across them more quickly, increasing exchange rate
• How does having a good blood supply aid exchange surfaces?

  Allows optimal concentration gradient to be maintained by bringing/taking away substances quickly
• How does having good ventilation aid exchange surfaces?

  Allows a steep concentration gradient to be maintained
• Why can a single-celled organism only reach a certain size?

  Because any larger and it's SA:V ratio would be too small for it to support its metabolism when only transporting materials via diffusion, osmosis etc.
• What is an exotherm?

  A cold-blooded organism
• What is an endotherm?

  A warm-blooded animal
• Why do mammals need excellent exchange surfaces?

  Because they have large metabolisms
• What is the biological name for the mouth?

  The buccal cavity
• What is the purpose of the nasal cavity?

  Increases the temperature and moisture content of inhaled air. It's hairy, mucus-secreting lining also traps pathogens and irritants
• What is the membrane on the surface of the lungs called?

  Pleural Membrane
• What are the muscles between the ribs called?

  Intercostal muscles