Gas Exchange Flashcards
Suggest an advantage of calculating SA:mass for organisms instead of SA:V
Easier / more accurate because irregular shapes
What is metabolic rate? Suggest how it can be measured
Metabolic rate = amount of energy used up by an organism within a given period of time
Often measured by oxygen uptake → as used in aerobic respiration to make ATP for energy release
Explain the relationship between SA:V and metabolic rate
As SA:V increases (smaller organisms), metabolic rate increases because:
Rate of heat loss per unit body mass increases
• So organisms need a higher rate of respiration
• To release enough heat to maintain a constant body temperature ie. replace lost heat
Explain the adaptations that facilitate exchange as SA:V reduces in larger organisms
- Changes to body shape (eg. long / thin)
• Increases SA:V and overcomes (reduces) long diffusion distance / pathway - Development of systems, such as a specialised surface / organ for gaseous exchange e.g. lungs:
• Increases (internal) SA:V and overcomes (reduces) long diffusion distance / pathway
Maintain a concentration gradient for diffusion eg. by ventilation / good blood supply
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 02 / cOz
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 large surface area
• Tracheae provide tubes full of air
So fast diffusion
• Contraction of abdominal muscles abdomina 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 in anaerobic respiration lowers y 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 y 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 0, and bring CO, quickly so maintains concentration gradient
Counter current flow in fish
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 O, 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 eg. Cacti
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
• keauces surrace area to volume ratio
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 02 / cOz
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 how humans breathe in and out (ventilation)
Inspiration (breathing in)
Diaphragm muscles contract - flattens
2. External intercostal muscles contract, internal intercostal muscles relax (antagonistic) - ribcage pulled up / out
3. Increasing volume and decreasing pressure (below atmospheric) in thoracic cavity
4. Air moves into lungs down pressure gradient
Expiration (breathing out)
Diaphragm relaxes → moves upwards
2. External intercostal muscles relax, internal intercostal muscles may contract → ribcage moves down / in
3. Decreasing volume and increasing pressure (above atmospheric) in thoracic cavity
4. 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 02/ CO
Suggest how different lung diseases affect ventilation
• Reduce lung elasticity (eg. fibrosis - build-up of scar tissue) - lungs expand / recoil less
• 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 (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
Explain the difference between correlations and causal relationships
Correlation = change in one variable reflected by a change in another - identified on a scatter diagram
Causation = change in one variable causes a change in another variable
correlation does not mean causation → may be other tactors Involved
