I don't normally deal in biology, but I was able to integrate it into a discussion in class the other day and I thought it might make for a good story. Many of you know I probably should have been a middle school teacher as I love poop jokes and this is certainly no exception.
I was explaining synthesis to my students and was trying hard to come up with an analogy that would help them understand the true meaning of it. We were reading a chapter from the physics book and I was wanted students to not simply summarize what they were reading. I was asking them to make it their own writing. (in case you are wondering, I had some success with this strategy) I told them to read a section from the chapter and then write a single paragraph about it. I explained that I wanted them to synthesize and not simply summarize.
In a stroke of genius, I thought of poop as a synthesis process. I began to explain this. I said, "You know how you eat something? And then it comes out the other end as something different? Like it actually looks and is physically different?" (yes, there are a few exceptions to this). I said, "This is synthesis!" I continued, "I don't want you to vomit onto the page after consuming what is in your book." I explained that you can still tell what was eaten if you vomit; but rarely can you tell what you ate after you poop! Voila! Synthesis!
How do you explain synthesis to your students? I know my way is a bit crass, but I guarantee they won't forget it.