AeroLab Reading room

Biology / AS level

Gas exchange and the respiratory system

Cartilage supports larger airways, mucus traps particles and cilia move material toward the throat.

Learning objectives

The big idea

Cartilage supports larger airways, mucus traps particles and cilia move material toward the throat. Ventilation results from pressure changes produced by thoracic volume changes, not from lungs actively pulling individual oxygen molecules.

Thin alveolar and capillary layers, a large exchange area and continuing ventilation and perfusion help maintain gas partial-pressure gradients. Surfactant reduces surface tension. Smoking can damage cilia and elastic tissue, so gas-exchange limitation involves both airway defence and mechanics.

Worked example

A model alveolar barrier increases from 1 to 2 arbitrary thickness units. With other factors fixed, what happens to diffusion rate in an inverse-distance model?

Follow the solution

An inverse relationship gives new rate/original rate=1/2 when diffusion distance doubles.

Investigate and explain

Using the worked example as supplied data, predict the effect of changing one condition. Draw a labelled model, record your reasoning and identify a variable that would need controlling. No human, animal or microbial experiment is required.

No exact PhET model is claimed for this topic. Use diagrams and supplied-data reasoning instead.

Open the interactive investigation

Check your understanding

1. What maintains the alveolar oxygen gradient?

  1. Ventilation and blood flow
  2. Oxygen production in alveoli
  3. A complete absence of membranes
Check the answer and reasoning

Ventilation and blood flow

Fresh air supplies oxygen and blood removes it, sustaining a gradient.

2. A model alveolar barrier increases from 1 to 2 arbitrary thickness units. With other factors fixed, what happens to diffusion rate in an inverse-distance model?

  1. It doubles
  2. It halves
  3. It remains unchanged
Check the answer and reasoning

It halves

An inverse relationship gives new rate/original rate=1/2 when diffusion distance doubles.

3. Is air movement into lungs the same physical process as oxygen diffusion into blood?

  1. Yes
  2. Only at low temperature
  3. No
Check the answer and reasoning

No

Ventilation is bulk airflow driven by pressure differences; gas exchange is diffusion across a barrier.