One of the areas that I noticed my students struggling with when I taught science in the past was diffusion and osmosis.  There were a few ways I could tell this was a topic rife with misconceptions:

1. They were concepts that most students struggled to define/explain adequately on tests.
2. Even high performing students had trouble differentiating the two.
3. Their hypotheses and reflections on labs showed a lack of understanding

I think one of the reasons is that they have difficulty with the scale that is involved and the concept of concentration gradients.  From a scale point of view, I think students have misconceptions about liquids because of their sensory observations.  They see liquids as homogenous substances, and struggle to understand that there are tiny atoms/molecules moving around and colliding.  With concentration gradients, I think they have a difficult time understanding why particles move from areas of high concentration to areas of low concentration.  Two prominent misconceptions I have noticed arise from some of the most popular ways of describing diffusion.  The first is the personification of particles – teachers often imbue consciousness on particles by describing diffusion in terms of particles ‘seeing’ the high concentration and ‘knowing’ that they must move to another place.  Another way of describing concentration gradients is the idea of a ‘downhill’ force that takes particles from high concentration to low concentration.  My students would often take this explanation and turn it into a misconception that diffusion was driven by gravity.

For the purposes of my T-GEM, I have ‘created’ a new tech tool –  an interactive demo/game in which particles move around the screen in a way consistent with kinetic molecular theory (please forgive my improvised attempt at showing this visually in my video!), and students can control the variables.  I think interacting with a demo/game like this would help dispel misconceptions and help students make meaning of the process.