2.38 understand the role of diffusion in gas exchange

When plants photosynthesise, they use up CO2 and produce O2. When plants respire, they use up O2 and produce CO2. This means there is a lot of gas exchange in plants, this happens by diffusion.

When a plant is photosynthesising it uses up CO2 (so there is barely any left in the leaf). This causes more CO2 to enter the leaf (by diffusion) - from an area of high concentration (outside the leaf) to an area of low concentration (inside the leaf). At the same time, O2 is being produced (as a waste product of photosynthesis), some of this is used for respiration whilst the rest diffuses out of the leaf (through the stomata) - moving from an area of high concentration (in the leaf) to an area of low concentration (outside the leaf).