exchange surfaces and breathing

• how do single celled organisms transport substances

  diffusion across csm from external medium to cytoplasm
• what happens to organisms as they become larger

  • higher metabolic rate -> higher O2 and glucose demand
  • many layers of cells further away from where substances enter/exit
  • smaller SA:V
• how do larger organisms exchange substances

  diffusion is too slow -> specialised exchange surfaces needed
• factors that affect the need for an exchange surface

  • size
  • SA:V
  • level of activity
• how does size affect the need for specialised exchange surfaces

  small organisms -cytoplasm close to external medium -> short diffusion distance

  larger organisms - several layers of cells to diffuse to, would use up nutrients, distance too far for diffusion to be effective
• how does SA:V affect the need for specialised exchange surfaces

  small organisms - large SA:V -> SA large enough to supply cells with sufficient oxygen

  larger organisms - smaller SA:V -> SA too small for sufficient oxygen supply
• how does level of activity affect the need for specialised exchanged surfaces

  more active = more energy required -> O2 and glucose needed to form ATP in respiration
• features of an efficient exchange surface

  • large SA
  • thin b barrier -> short diffusion path
  • maintenance of concentration gradient
  • permeable
  • moist
  • ATP for active transport
• how is a concentration gradient maintained

  good blood supply
• adaptations of root hairs

  • short diffusion path
  • large SA
  • conc gradient maintained by transport of materials out of root
• how does the lung have a large surface area

  lots of alveoli -> 70m2
• how does the lung have a thin permeable membrane

  plasm membrane -> permits diffusion of O2 and CO2
• how does the lung have a short diffusion path

  alveolus wall is 1 cell thick -> squamous epithelial cells

  capillary wall is 1 cell thick -> squamous endothelial cells

  capillaries force RBC close to capillary wall
• how are the lungs moist

  surfactant

  • reduce cohesive forces
  • prevents alveoli from collapsing
• surfactant

  watery substance made of proteins -> produced by alveoli
• how do lungs maintain conc gradient

  pulmonary artery -> brings deoxygenated blood

  capillaries -> pick up and remove O2 from alveoli

  ventilation -> removes CO2 and replaces with O2
• cartilage

  • C shaped
  • in trachea, bronchi and some large bronchioles
  • keeps airways open
  • keeps air resistance low
  • allows flexibility
• smooth muscle

  • in trachea, bronchi and bronchioles
  • contract and relax to adjust diameter of airway
• elastic fibres

  • in trachea, bronchi, bronchioles and alveoli
  • allow alveoli to stretch and recoil in breathing
  • allow alveoli to expand
• ciliated epithelium

  • in trachea and bronchi
  • move mucus up airway
• goblet cells

  • in trachea and bronchi
  • produce mucus
  • catch dust, pollen, pathogens
  • ready for movement by cilia
• structure of trachea

  • c shaped cartilage -> prevents collapse
  • smooth surface area -> low resistance
  • flexible -> neck movement and swallowing
• structure of bronchi

  • similar to trachea
  • branch into brioches
  • contain: cartilage, smooth muscle, goblet cells, elastic fibres and ciliated epithelium
• structure of bronchioles

  • cartilage near bronchi end
  • lined with a thin layer of flattened epithelium
  • contain smooth muscle and elastic fibres
  • NO goblet cells or ciliated epithelium
• breathing rate 


  number of breaths per min
• tidal volume

  volume of air taken inhaled or exhaled per breath
• ventilation rate

  total volume of air breathed in for out in 1 min
• inspiratory reserve volume


  volume of air inhaled above tidal volume
• expiratory reserve volume

  volume of air exhaled above tidal volume
• vital capacity 


  volume of air exhaled after maximum inspiration -> depends on age, gender, size, level of regular exercise
• residual volume 


  volume of air which remains in the lungs after forced expiration -> can't be measure directly
• dead space

  air remaining in trachea, bronchi, bronchioles where gas exchanged doesn't occur
• total lung capacity

  vital capacity + residual volume
• precautions hone using spirometer

  • healthy subject
  • fresh soda lime to absorb CO2
  • no air leaks
  • sterilised mouthpiece
  • water at correct level
  • chamber filled with medical grade oxygen
• why does a person need to wear a nose clip for spirometer

  • ensure all air breathed comes from chamber
  • to prevent entry/escape of air through nose
  • ensure valid results
• other equipment for measuring ventilation rates

  peak flow meter -> measures how hard and fast you exhale

  puff bags -> measure tidal volume and vital capacity
• diaphragm when inhaling 


  contracts -> moves down and becomes flatter
• external intercostal muscles when inhaling

  contracts -> raises ribs
• volume of thorax when inhaling

  increased
• pressure in thorax when inhaling

  drops below atmospheric pressure