Features of the alveoli (Edexcel GCSE Biology & Combined Science)

This lesson describes how the alveoli are adapted for gas exchange by diffusion between the air in the lungs and the blood capillaries. The PowerPoint and accompanying resource are part of the second lesson in a series of 2 which have been designed to cover the content of point 8.2 & 8.3 of the Edexcel GCSE Biology and Combined Science specifications.

During the 1st lesson in this series, the students were shown how to calculate the surface area to volume ratio and so this lesson begins by challenging them to recall that the larger the organism, the smaller the ratio. This is done through the PLAY YOUR CARDS RIGHT format as shown in the cover picture, and leads into the key idea that complex multicellular organisms like humans have developed a range of different adaptations to increase this ratio at their exchange surfaces. Moving forwards, time is taken to consider and discuss how the following adaptations of the alveoli affect the rate of diffusion:

• large surface area
• lining of the alveoli consisting of a single layer of flattened cells
• maintenance of a steep concentration gradient

Each feature is related to diffusion and current understanding and prior knowledge checks are used to allow the students to assess their progress and to challenge them to make links to other topics of the course. All exam questions have mark schemes embedded into the PowerPoint