Make the gelatin according to the package directions. Place less water in the mixture than directed on box; this will cause the gelatin mixture to be stiffer.
Open a large plastic resealable bag and place it inside a glass bowl. Pour the gelatin into the plastic bag and seal. Place the gelatin into the refrigerator. Allow the gelatin to cool in the refrigerator for one hour.
Remove the gelatin bag from the refrigerator. Open the bag and place the plum into the center of the mixture. Place the candies and remaining fruit throughout the gelatin bag -- these will represent the organelle. Close the bag and place it in the refrigerator. Allow to set up completely.
Using the markers and poster board, make a key that lists which fruit or candy represents which organelle in the cell. List the organelle as follows: cell membrane -- plastic bag, cytoplasm -- gelatin, centrosome -- gumball, Golgi body -- Laffy Taffy, lysosome -- M&M's, mitochondrion -- raisins, nuclear membrane -- plum peel, nucleolus -- plum pit, nucleus -- plum, ribosomes -- candy sprinkles, rough endoplasmic reticulum -- sour gummy worms, smooth endoplasmic reticulum -- gummy worms and vacuole -- jaw breakers.