3.2 Gas Exchange Flashcards
Explain how the body surface of a single - called organisms is adopted for gas exchange
- thin,flat shape and large surface area to volume ratio
- short diffusion distance to all parts of cell -> rapid diffusion e.g. of O2 / CO2
Describe the tracheal system of an insect
- Spiracles = pores on surface that can open / close to allow diffusion
- Tracheae = large tubes full of air that allow diffusion
- Tracheoles = smaller branches from tracheae, permeable to allow gas exchange with cells
Explain how an insect’s tracheal system is adapted for gas exchange
Tracheoles have thin walls
- so short diffusion distance to cells
High numbers of highly branched Tracheoles
- so short diffusion distance to cells
- so larger surface area
Tracheae provide tubes full of air
- so fast diffusion
Contraction of abdominal muscles (abdominal pumping) changes pressure in body, causing air to move in / out
- maintains concentration gradient for diffusion
Fluid in end of Tracheoles drawn into tissues by osmosis during exercise (lactate produced anaerobic respiration lowers water potential of cells)
- as fluid is removes, air fills Tracheoles
- so rate of diffusion to gas exchange surface increases as diffusion is faster through air
Explain structural and functional compromises in terrestrial insects that allow efficient gas exchange while limiting water loss
- thick waxy cuticle / exoskeleton -> increases diffusion distance so less water loss (evaporation)
- spriacles can open to allow gas exchange and close to reduce water loss (evaporation)
- hairs around spiracles -> trap moist air, reducing water potential gradient so less water loss (evaporation)
Explain how the gills are adapted for gas exchange
- gills made of many filaments covered with many lamellae
- increase surface area for diffusion
- thin lamellae wall / epithelium
- so short diffusion distance between water / blood
- lamellae have a larger number of capillaries
- remove O2 and CO2 quickly so maintains concentration gradient for diffusion
Explain the counter current flow:
- Blood and water flow in opposite direction through / over lamellae
- So oxygen concentration always higher in water ( than blood near )
- So maintains a concentration gradient of O2 between water and blood
- For diffusion along whole length of lamellae
Explain how the leaves of dicotyledonous plants are adapted for gas exchange
- many stomata (high density) -> large surface area for gas exchange (when opened by guard cells)
- spongy mesophyll contains air spaces -> large surface area for gases to diffuse through
- thin -> short diffusion distance
Explain structural and functional compromises in xerophytic plants that allow efficient gas exchange while limiting water loss
Xerophyte = plant adapted to live in very dry conditions e.g. Cacti and marram grass
- thicker waxy cuticle
- increases diffusion distance so less evaporation
- sunken stomata in pits / rolled leaves / hairs
- trap water vapour / protect stomata from wind
- so reduced water potential gradient between leaf / air
- so less evaporation
- spines / needles
- reduces surface area to volume ratio
Describe the gross structure of the human gas exchange system
Explain the essential features of the alveolar epithelium that make it adapted as a surface for gas exchange
- flattened cells / 1 cell thick -> short diffusion distance
- folded -> large surface area
- permeable -> allows diffusion of O2 / CO2
- moist -> gases can dissolve for diffusion
- good blood supply from large network of capillaries -> maintains concentration gradient
Describe how gas exchange occurs in the lungs
- oxygen diffuses from alveolar air space into down its concentration gradient
- across alveolar epithelium then across capillary endothelium
Explain the importance of ventilation
- brings in air containing higher conc. of oxygen & removes air with lower conc. of oxygen
- maintaining concentration gradients
Explain how humans breathe in and out (ventilation) - inspiration
- Diaphragm muscles contract -> flattens
- External intercostal muscles contract, internal intercostal muscles relax (antagonistic) -> rib cage pulled up / out
- Increasing volume and decreasing pressure (below atmospheric) in thoracic cavity
- Air moves into lungs down pressure gradient between leaf
Explain how humans breathe in and out (ventilation) - expiration
- Diaphragm relaxes -> moves upwards
- External intercostal muscles relax, internal intercostal muscles may contract -> rib cage moves down / in
- Decreasing volume and increasing pressure (above atmospheric) in thoracic cavity
- Air moves out of lungs down pressure gradient
Explain why expiration is normally passive at rest
- internal intercostal muscles do not normally need to contract
- expiration aided by elastic recoil in alveoli
Suggest his different lung diseases reduce the rate of gas exchange
- thickened alveolar tissues (e.g. fibrosis) -> increases diffusion distance
- alveolar wall breakdown -> reduces surface area
- reduce lung elasticity -> lungs expand / recoil less -> reduces concentration gradient of O2 / CO2
Suggest how different lung diseases affect ventilation
- reduce lung elasticity (e.g. fibrosis - boiled up of scar tissue) -> lungs expand / recoil
- reducing volume of air in each breath (tidal volume)
- reducing maximum volume of air breathed out in one breath (forced vital capacity)
- narrow airways/reduce airflow in & out of lungs (e.g. asthma - inflamed bronchi)
- reducing maximum volume of air breathed out in 1 second (forced expiratory volume
- reduced rate of gas exchange -> increases ventilation rate to compensate for reduced oxygen in blood
Suggest why people with lung disease experience fatigue
- cells receive less oxygen -> rate of aerobic respiration reduced -> less ATP made
