B6- 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 insects
- 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 and a 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 maintaining the concentration gradient for diffusion
● Fluid in end of tracheoles drawn into tissues by
osmosis during exercise (lactate produced in
anaerobic respiration lowers ψ of cells) so diffusion is faster through air (rather than
fluid) to gas exchange surface
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 increasing surface area for diffusion
● Thin lamellae wall / epithelium so short diffusion distance between water / blood
● Lamellae have a large number of capillaries removing O2 and bring CO2 quickly so maintains concentration gradient
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
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
Thicker waxy cuticle to increases diffusion distance so less evaporation
● Sunken stomata in pits / rolled leaves / hairs to ‘trap’ water vapour / protect stomata from wind so reduced water potential gradient between leaf / air causing less evaporation
● Spines / needles reduces surface 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 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
Inspiration
Diaphragm muscle contracts
External intercostal muscles contract, intercostal muscles relax and ribcage pull up and out
Increasing volume and decreasing pressure in thoracic cavity
Air moves into the lungs down the pressure gradient
Expiration
Diaphragm muscle relaxes
External intercostal muscles relax , intercostal muscles down and ribcage down and in
Decreasing volume and decreasing pressure in thoracic cavity
Air moves out the 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 / 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
Suggest why people with lung disease experience fatigue
Cells receive less oxygen → rate of aerobic respiration reduced → less ATP made
Suggest how you can analyse and interpret data to the effects of pollution, smoking and other risk factors on the incidence of lung disease
● Describe overall trend → eg. positive / negative correlation between risk factor and incidence of disease
● Manipulate data → eg. calculate percentage change
● Interpret standard deviations → overlap suggests differences in means are likely to be due to chance
● Use statistical tests → identify whether difference / correlation is significant or due to chance
○ Correlation coefficient → examining an association between 2 sets of data
○ Student’s t test → comparing means of 2 sets of data
○ Chi-squared test → for categorical data
Suggest how you can evaluate the way in which experimental data led to statutory restrictions on the sources of risk factors
● Analyse and interpret data as above and identify what does and doesn’t support statement
● Evaluate method of collecting data
○ Sample size → large enough to be representative of population?
○ Participant diversity eg. age, sex, ethnicity and health status → representative of population?
○ Control groups → used to enable comparison?
○ Control variables eg. health, previous medications → valid?
○ Duration of study → long enough to show long-term effects?
● Evaluate context → has a broad generalisation been made from a specific set of data?
● Other risk factors that could have affected results?
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 factors involved
