What route does air take through an insect's tracheal system to reach respiring cells?
Air passes through spiracles into tracheae, which branch into fine tracheoles that reach close to respiring cells.
AQA A-Level Biology - (7402) · 3.3.2
Revise AQA A-Level Biology - (7402) specification point 3.3.2, Gas exchange, with free active-recall flashcards. Flip through the set or review every question and answer below.
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What route does air take through an insect's tracheal system to reach respiring cells?
Air passes through spiracles into tracheae, which branch into fine tracheoles that reach close to respiring cells.
What two features make insect tracheoles effective for gas exchange?
They provide a large exchange surface and short diffusion paths.
In which directions do oxygen and carbon dioxide diffuse in an insect's tracheal system?
Oxygen diffuses towards cells; carbon dioxide diffuses in the opposite direction.
How can insect body movements help gas exchange?
They help ventilate the tracheal system and maintain concentration gradients.
What is the trade-off when an insect closes its spiracles?
Closure reduces water loss but also restricts gas exchange.
How do gill filaments provide a large surface area for gas exchange?
They carry numerous gill lamellae.
How do gill lamellae provide a short diffusion distance between water and blood?
The lamellae are thin.
How do water and blood flow relative to each other at the gill lamellae?
Water flows over the lamellae and blood flows through them in opposite directions.
How does counter-current flow support oxygen uptake in fish gills?
It maintains an oxygen concentration difference along the exchange surface, so oxygen continues to diffuse from water into blood.
In which direction does carbon dioxide diffuse across fish gills?
From blood into water.
Where do gases mainly enter and leave a dicotyledonous leaf?
Through stomata in the epidermis.
What surface do the mesophyll air spaces expose to air?
A large surface of moist cell walls.
How do interconnected mesophyll air spaces aid gas diffusion between stomata and cells?
They allow gases to diffuse over short distances.
What are the directions of carbon dioxide and oxygen diffusion associated with photosynthesis in a leaf?
Carbon dioxide can diffuse in for photosynthesis; oxygen produced can diffuse out.
Which gases are used and produced by leaf respiration?
Respiration uses oxygen and produces carbon dioxide.
What determines the net movement of oxygen and carbon dioxide in a leaf?
The relative rates of photosynthesis and respiration.
What is the consequence of stomatal opening for water loss?
It allows water vapour to escape.
How does a thick waxy cuticle help a xerophyte conserve water?
It reduces evaporation through the leaf surface.
How do sunken stomata, leaf hairs and rolled leaves reduce water loss in xerophytes?
They retain humid air near stomata, reducing the water vapour concentration gradient and slowing water loss.
What is the trade-off of stomatal closure in xerophytes?
It limits water loss but also restricts carbon dioxide entry, which can limit photosynthesis.
What overall compromise do xerophyte adaptations make between water conservation and gas exchange?
They limit water loss while retaining some gas exchange; they do not completely separate gas exchange from water loss.
What route does air follow from outside the body to the alveoli?
Trachea → bronchi entering the two lungs → progressively narrower bronchioles → alveoli.
What are alveoli?
Small air-filled structures where gas exchange with the blood occurs.
How does gas exchange occur between alveolar air and blood?
By diffusion across the alveolar and capillary walls.
In which directions do oxygen and carbon dioxide diffuse during alveolar gas exchange?
Oxygen: alveolar air → blood. Carbon dioxide: blood → alveolar air.
How do numerous alveoli help gas exchange?
They provide a large surface area for diffusion.
How does the thin alveolar epithelium help gas exchange?
It gives a short diffusion distance between air and blood.
What role does the moist alveolar surface play in gas exchange?
It allows gases to dissolve before diffusing.
How does a rich capillary supply help alveolar gas exchange?
It helps maintain concentration gradients.
How does ventilation help maintain concentration gradients in the alveoli?
It replenishes alveolar air.
What do the diaphragm and external intercostal muscles do during inspiration?
The diaphragm contracts and flattens; the external intercostals contract and raise the ribs.
How do volume and pressure changes drive air into the lungs during inspiration?
Thoracic volume increases, lung pressure falls below atmospheric pressure, and air enters.
What happens to the diaphragm and external intercostal muscles during expiration?
Both relax.
How do volume and pressure changes drive air out of the lungs during expiration?
Thoracic volume decreases, pressure rises, and air is driven out.
What do the internal intercostal muscles do during active expiration?
They contract to help lower the ribs, acting antagonistically to the external intercostals.
Is resting expiration active or passive?
It is largely passive.
What does lung disease incidence measure?
New cases in a defined population over a stated period.
What can lung disease incidence data be used to examine?
Associations between lung disease and risk factors, such as smoking and pollution.
What three aspects must be considered when comparing lung disease incidence data?
The populations, time periods, and exposure measures used.
What does a correlation between two variables mean, and what does it not establish?
The variables vary together, but this alone does not establish that one causes the other.
How can other factors confound an association between an exposure and lung disease incidence?
They may influence both the exposure and disease incidence.
What should be considered when interpreting a risk factor–disease association causally?
Study design, possible confounding, and the strength and consistency of evidence.
What is a statutory restriction?
A legal measure that restricts an activity or source.
When using experimental data to consider restrictions on lung disease risk factors, what three aspects of the evidence should be evaluated?
How should a proposed or adopted restriction on a lung disease risk factor be assessed?
Consider the source of exposure and how much reducing that exposure is expected to reduce risk.
Does evidence of an association between an exposure and lung disease conclusively prove causation?
No. An association alone is not conclusive proof of causation.