The diffusion lab has been a yearly activity in my biology class as part of a unit on cells and cell transport. Students fill a bag with starch and water and then submerge it in a solution of iodine and observe what happens. The iodine diffuses across the plastic bag and turns the starch purple. With the 2020 pandemic, it will not be possible to do this lab in person, so I created a virtual lab that explores the phenomenon.
In this lab, students progress through Google Slides, watch videos showing the set-up and observe a time-lapse video showing the starch turning purple. This document can be shared over on Google Classroom or other LMS. A dialysis tube was used instead of a plastic bag because the process does occur faster with the dialysis tube. In class, with freshman, the tubes can be difficult to work with, so I would usually prepare the starch filled bags ahead of time.
Admittedly, it is not the same as the hands-on experience, but I think it does an okay job of demonstrating the principles of diffusion, and how substances move from an area of high concentration to a low concentration across a semipermeable membrane. If you have a hybrid class, you could certainly do the experiment live while remote learners complete the virtual version.
The answer key is available on TpT which also includes downloadable PPT versions of the lab, though you can always convert google slides to PPT.