3.1 SA:V ratio - agar blocks practical

https://www.savemyexams.com/a-level/biology/aqa/17/revision-notes/3-exchange-and-transport/3-1-adaptations-for-gas-exchange/3-1-2-agar-blocks-practical/

using agar blocks containing indicator to determine the effect of surface area to volume ratio and concentration gradient on the diffusion of an acid or alkali