I read something on another homeschooling site about apple units. They suggested buying several types of apples, and then tasting them to discuss their appearances, which ones were sweeter, softer, etc. You could also make up a graph for the results.
Sort them by size, or smallest to largest etc.
Estimate, and count the seeds of an apple
http://www.atozteacherstuff.com/Themes/Apples/
Something else I remembered from reading something to dd was to cut an apple in half horizontally, and you'll see a start in the middle of the apple.
I think we are goint to have to do an apple unit too!