A few years back, my son had to make a 3D plant cell for science class. Instead of making a styrofoam mock-up that would just end up in the trash, we decided to make it from cake. Here is what I (you didn't actually believe he would help me did you?) came up with.
Step 1: What You Need and Creating the Cell Wall
I didn't take any step-by-step pics along the way. Had I known I would've needed them, I would have. I omitted the adjoining cell wall sections when I made my cake.
Here's the "verbal" how-to:
What you need:
1- 9"x13" sheet cake (I used chocolate)
Fondant - purchased or home made
Corn Syrup or Glucose
Gel Icing Colors (Pink, Orange, Purple, Blue, Green, Brown & Yellow)
Small Artist's Paintbrush
Foil (to cover the board)
Piping bags or ziploc bags
Diagram of Plant Cell (2 follow)
1) Cover your board with foil. Center cooled cake on board and using sharp knife, cut off any "hump" to make your cake surface level.
2) Using diagram as a guide, use knife to cut the cake into the basic cell shape.
3) Cover cake with buttercream.
4) Using Gel Icing Colors, color fondant to desired color depths of Orange, Purple, Dark Purple, Dark Pink, Pale Pink, Dark Green, Pale Green, Dark Blue, Pale Blue & Yellow. Make a small batch (about 1/4 cup) each of Light Brown, Brown & Dark Purple buttercream.
5) Sprinkle counter with powdered sugar. Roll out pale blue fondant into a 1/16" thick by 2 1/2-3" wide strip long enough to wrap around the outside edge of your cell cake to create the Plasma Membrane. Keep moving the fondant and lightly sugar the underside as needed to prevent it from sticking. It's OK if you need to do it in sections as it will be covered by the pink outer layer that is to be the Cell Wall.
6) Roll out the pale pink fondant as in step #5 and making the pink just about a 1/4" wider. Wrap the pink strip around the pale blue layer using the paintbrush and the water to adhere. Be sure to leave a section of the blue on the left side exposed so you can see the underlying Plasma Membrane. Just use a thin coat of water over the blue or the pink layer won't stick but instead slide off.
7) Using the pale blue fondant, make small discs and adhere to the outer pink layer using water to represent the Plasmodesmata. Using the handle of the paintbrush, indent the upper edge of the pink to make cross-sections. Using small pieces of the pale blue, adhere with water into the indents and again indent with the brush handle. Cut off any overhang.
This completes the Cell Wall.
Always keep your work surface dusted with powdered sugar when rolling out your fondant to prevent sticking. Also remember to dust your rolling pin and move your fondant as this will also prevent your fondant from sticking.
If you don't have a piping bag, ziplocs work just as well. Place your buttercream into the corner of the bag. Remove excess air, zip shut and snip off a tiny section of the corner. You don't want to snip off too big of a section as you only want to pipe tiny dots.