3.2 Gas Exchange Flashcards
Explain how the body surface of a single-celled organism is adapted for gas exchange
● Thin ,flat shape and large surface area to volume ratio
● Short diffusion distance to all parts of cell → rapid diffusion eg. 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 cell
Explain how an insect’s tracheal system (tracheoles) are 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 and a large surface area
Explain how an insects tracheal system (trachea) are adapted for gas exchange
- trachea provide tubes full of air so fast diffusion
Explain how an insects tracheal system (abdominal muscles) are adapted for gas exchange
● Contraction of abdominal muscles (abdominal
pumping) changes pressure in body, causing air to
move in/out
○ Maintains concentration gradient for diffusion
Explain how an insects tracheal system (fluid in tracheoles) are adapted for gas exchange
● Fluid in end of tracheoles drawn into tissues by
osmosis during exercise (lactate produced in
anaerobic respiration lowers ψ of cells)
○ As fluid is removed, 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)
● Spiracles can open to allow gas exchange AND close to reduce water loss (evaporation)
● Hairs around spiracles → trap moist air, reducing ψ gradient so less water loss(evaporation
Explain how the gills of fish 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 large number of capillaries
○ Remove O2 and bring CO2 quickly so maintains
concentration gradient
Explain counter current flow
- Blood and water flow in opposite directions 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
How is counter current flow different to parallel flow?
In parallel flow, equilibrium would be met BUT in counter current flow equilibrium it is not met
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
Describe leaf cross section
Explain structural and functional compromises in xerophytic plants that allow efficient gas exchange while limiting water loss
● 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
What is a xerophyte?
plant adapted to live in very dry conditions eg. Cacti and marram grass
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 / 1cellthick → 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 blood 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 the process of inspiration (breathing in)
- Diaphragm muscles contract → flattens
- External intercostal muscles contract, internal
intercostal muscles relax (antagonistic) →
ribcage pulled up /out
3.Increasing volume and decreasing pressure
(below atmospheric) in thoracic cavity
- Air moves into lungs down pressure gradient
Explain the process of expiration (breathing out)
- Diaphragm relaxes → moves upwards
- External intercostal muscles relax, internal
intercostal muscles may contract → ribcage
moves down/in - Decreasing volume and increasing pressure
(above atmospheric) in thoracic cavity - Air moves out of lungs down pressure gradient
Suggest why expiration is normally passive at rest
● Internal intercostal muscles do not normally need to contract
● Expiration aided by elastic recoil in alveoli
Suggest how different lung diseases reduce the rate of gas exchange
●Thickened alveolar tissue (eg. fibrosis)→ increases diffusion distance
● Alveolar wall breakdown→ reduces surface area
● Reduce lung elasticity→ lungs expand/recoil less→ reduces concentration gradients of O2/CO2
Suggest how different lung diseases affect ventilation
● Reduce lung elasticity (eg. fibrosis-build-up of scar tissue)→lungs expand/recoilless
○ 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 air flow in& out of lungs (eg. asthma-inflamed bronchi)
○ Reducing maximum volume of air breathed out in 1 second (forced expiratory volume)
● Reduced rate of gas exchange→increased 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
