3.3.2 - Gas exchange Flashcards
Topic 3
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
The tracheal system of an insect
- Spiracles
- Tracheae
- Tracheoles
Spiracles (tracheal system of an insect)
Pores on the surface that can open / close to allow diffusion
Tracheae (tracheal system of an insect)
large tubes full of air that allow diffusion
Tracheoles (tracheal system of an insect)
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 (abdominal
pumping) changes pressure in body, causing air to
move in / out
○ Maintains pressure/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)
○ 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 between surface of insect and air 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
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 of O2 into blood along whole length of lamellae
If there was a parallel flow instead of counter current flow…
Equilibrium would be reached so oxygen wouldn’t diffuse into blood along the whole gill plate
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
Xerophyte
= plant adapted to live in very dry conditions eg. Cacti and marram grass
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 - reduces water loss (evaporation)
Describe the gross structure of the human gas exchange system
- Trachea
- Bronchi
- Bronchioles
- alveoli
Does a capillary network surround alveoli?
yes
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
(opposite for CO2)
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
> inspiration
- Diaphragm muscles contract → flattens
- External intercostal muscles contract, internal
intercostal muscles relax (antagonistic) →
ribcage pulled up / out - Increasing volume and decreasing pressure
(below atmospheric pressure) in thoracic cavity - Air moves into lungs down pressure gradient
Ventilation
breathing
Explain how humans breathe out
> expiration
- Diaphragm relaxes → moves upwards
- External intercostal muscles relax, internal
intercostal muscles may contract → ribcage
moves down / in - Decreasing volume and increasing pressure
(above atmospheric pressure) 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 / 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
