3.3.2 gas exchange Flashcards
Adaptations of gas exchange surfaces
Single-celled organism
Thin flat shape so, large SA:V
Short diffusion pathway
For rapid diffusion
Gas exchange in tracheal system of an insect
Air moves through spiracles (pores) on the surface of insect
Air moves through tracheae
Gas exchange at tracheoles directly from cells
- oxygen diffuses down conc gradient to respiring cell
- CO2 diffuses down conc gradient from respiring cells
Adaptations of gas exchange in tracheal system of insect
Lots of thin, branching tracheoles so, short diffusion pathway and SA:V so, rapid diffusion
Rhythmic abdominal movements increase the efficiency of gas exchange by increasing the amount of O2 entering > maintains greater conc gradient for diffusion
gas exchange across gills of fish
Counter current flow
Blood flows through lamellae and water flows over lamellae in opposite directions
Always a higher conc of O2 in water than the blood it is near
Hence, concentration gradient of O2 between the water and blood is maintained along the whole length of lamellae > equilibrium not met
Maximises diffusion of oxygen
Adaptations of gills
Made of gill filaments (thin plates) which are covered in many lamellae > gill filaments provide a large surface area, lamellae increase surface area
Vast network of capillaries on lamellae, remove oxygen to maintain a concentration gradient
Thin/flattened epithelium, shorter diffusion pathway between water and blood
Gas exchange in leaves
CO2/O2 diffuse through the stomata
Stomata opened by guard cells
CO2/O2 diffuse into mesophyll layer into air spaces
CO2/O2 diffuse down conc gradient
Adaptations of leaves for gas exchange
Lots of stomata that are close together > large surface area for gas exchange, don’t have to pass through cells to reach mesophyll
Interconnecting air space in mesophyll layers> gases come in contact with mesophyll cells
Mesophyll cells have a large surface area > rapid diffusion of gases
Thin > short diffusion pathway
Xerophytic plants
Thick waxy cuticle which increases diffusion distance > less evaporation
Stomata in pits/grooves which trap water vapour > water potential gradient decreased so less evaporation
Rolled leaves which trap water vapour > water potential gradient decreased so less evaporation
Spindles/needles reduce surface area to volume ratio
Hairs trap water vapour > water potential gradient decreased so less evaporation
Terrestrial insects
Thick waxy cuticle which increases diffusion distance so, less evaporation
Spiracles can open and close > open to allow oxygen in, close when water loss too much
Lungs
Trachea
Splits into 2 bronchi
Each bronchus branches into smaller tubes called bronchioles
Bronchioles end in air sacs > alveoli
Gas exchange in alveoli O2
Oxygen diffuses from alveoli
Down its conc gradient
Across the alveolar epithelium
Across the the capillary endothelium
Into the blood (in haemoglobin)
Gas exchange in alveoli CO2
CO2 diffuses from capillary down conc gradient
Across capillary endothelium
Across the alveolar epithelium
Into the alveoli
Why is ventilation needed
Maintains an oxygen concentration gradient - brings in air containing higher conc of O2, removes air containing lower conc of O2
Features of alveolar epithelium
Squamous epithelium - one cell thick: short diffusion pathway > fast diffusion
Large surface area to volume ratio > fast diffusion
Permeable
Good blood supply from network of capillaries - maintains conc gradient
Elastic tissue allows it to recoil after expansion
Surfactant
How are the lungs adapted for efficient gas exchange
Many alveoli/capillaries - large surface area > fast diffusion
Short distance between alveoli and blood - short diffusion distance > fast diffusion
Ventilation/circulation - maintains concentration gradient > fast diffusion
