A day or two before the class drop a bean per student into a shallow dish of tap water. Dry on paper towels before handing to students.
Ask students what they might expect to find in a seed (maybe they have already grown plants from seeds, and so have some good guesses).
Students split open their seed and look for the tiny root sticking out (more visible when the seed is pre-soaked a day longer), and the tiny leaf next to it. (Older students: the root and shoot make up the plant embryo)
The other parts are food for the growing plant, until it has leaves and can make it's own food. (Older students: the cotyledon where the plant gets it's food from as it germinates.)
Give students one dandelion seed (with an intact parachute).
Have them look really closely at the seed hanging from the parachute, and how they get carried in the wind.
(Good segue into Wind blown seed design activity.)
Page 10 from the resource book has a good image of the inside of a seed.