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)
Buttercream Icing
Fondant - purchased or home made
Corn Syrup or Glucose
Gel Icing Colors (Pink, Orange, Purple, Blue, Green, Brown & Yellow)
Powdered Sugar
Rolling Pin
Sharp Knife
Small Artist's Paintbrush
Water
Cake Board
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.

Tips:

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.

Step 2: Creating the Cell Cross Section

1) Making the Chloroplast - Using the pale green fondant, make 3 flat ovals about 1/8" thick. Make 1 oval about 1/3 bigger than the others. Next, roll the pale green fondant into a 1/4" wide by 1/8" thick strip and standing on edge, wrap around the ovals securing with water to the edges of the ovals. Leave to dry a bit before attempting to place them as they will likely fall apart before making it to the cake. Once set up and using the diagram as a guide, place them onto the cake where the Chloroplast are located.

Using the Dark Green fondant, create the Chloroplast innards. I just made little barrel shapes about 1/4" tall and used the back edge of the knife to score the ridges onto the sides. You'll need 28 of these. 8 for each of the smaller ovals and 12 for the larger oval. I used a thin snake of the dark green fondant to connect them. Just roll out a thin snake and adhere with water to the oval. Then adhere the "barrels" on top of the snake. Again, using the diagram as a guide for placement. Your Chloroplasts are now complete.

2) Making the Central Vacuole and Tonoplast - Using White fondant, roll out to 1/8" thickness and using the diagram as a guide, cut to shape. Roll the white fondant into a 1/4" wide by 1/8" thick strip and standing on edge, wrap around the Vacuole securing with water to the edge. Again, leave to set up before placing with the help of the diagram. Once in place, you can create the Tonoplast by filling the Vacuole with a thin layer of the Corn Syrup. I filled mine after I finished the entire cross section. Your Central Vacuole is now complete.

3) Making the Peroxisome - Using a bit of the Pale Blue Fondant, make a flat circle about 1" in diameter. Take a small bit of the yellow fondant and make into a 1/2'" ball & adhere to center of pale blue circle with a bit of water. Using diagram as guide, set in place. Your Peroxisome is now complete.

4) Making the Mitochondrion - Using the Orange fondant, make a flat oval about 1/8" thick. Next, roll the orange fondant into a 1/4" wide by 1/8" thick strip and standing on edge, wrap around the oval securing with water to the edge of the oval. Again, leave to set up before placing with the help of the diagram. Using the brush and a bit of water, paint a thin layer of water over the oval's surface. It will become tacky while performing the next step, that is a good thing. If necessary, roll the orange fondant into another 1/4" wide by 1/8" thick strip and standing on edge, arrange in a snake like pattern inside the Mitochondrion. The tack created by brushing the surface will adhere it to the oval. If it has dried, re-brush the oval or just brush the edge of the strip. Once in place, your Mitochondrion is complete.

5) Making the Golgi Apparatus - Using the Pink fondant, roll into a 1/4" wide by 1/8" thick strip and standing on edge, place on cake (again, using the diagram as a guide for placement) in a snaking pattern while very gently pressing it down into the buttercream to adhere. Make a small ring (use a dab of water to join the ends) from the strip and place onto the cake. Your Golgi Apparatus is now complete.

6) Making the Nucleus - Roll the Purple Fondant into a ball just a bit smaller than a baseball. Using the knife, cut a 1/4 wedge out of the ball to create the Chromatin. Smooth away any cut marks with your finger.

Using the dark purple fondant, make a small flat disc, gently fold in half to make a crease (do not mash the halves together!), open back up and adhere to the center of the Nucleus with a bit of water so that half is going up a cut side and half is laying on the opposite cut side. You've just created the Nucleolus.

Using pale pink fondant, make several small discs and adhere to the Nuclear Envelope (the outside of the Nucleus) with water. Using the end of the paintbrush handle, make indents in the centers of each disc. Make several tiny snakes of pale pink fondant and create the cross sections along the cut sides of the Chromatin adhering with water. Allow a bit of each to hang over the edge. Use the paintbrush handle to work the overhang into a circle and indent the edge. Using the Dark Purple buttercream, pipe the veins onto the surface of Chromatin starting at the Nucleolus and working out toward the edge.

Using the light brown buttercream, pipe tiny dots all over the exposed areas of the Nuclear Envelope (the outside of the Nucleus). Your Nucleus is now complete.

7) Making the Rough & Smooth Endoplasmic Reticulum - Take a bit of the Dark Blue fondant and mix with a smaller sized piece of white fondant. Once mixed, roll into a thin snake about 1/8" in diameter. Cut off 2 pieces about 2 1/2" long and (using the diagram as a guide) place the ends into the buttercream creating an upside-down "U" shape and leaving it stand up off of the cake. Using another piece about 4-5" long, repeat as with the smaller pieces. Your Smooth Endoplasmic Reticulum are now complete.

Using the Dark Blue fondant, roll into a 1/4" wide by 1/8" thick strip and standing on edge, place on cake (again, using the diagram as a guide for placement) in a snaking pattern while very gently pressing it down into the buttercream to adhere. Using the light brown buttercream, pipe small dots all over the exposed sides and top to create the Ribosomes. Your Rough & Smooth Endoplasmic Reticulum are now complete.

8) Making the Centrosome - Using the Yellow fondant, make a flat circle about 1" in diameter and place on cake (again, using the diagram as a guide for placement). Next, make very thin snakes with the yellow fondant each about 1" long (you will need about 16 of them). Evenly space them around your Centrosome in groups of 2 with the edges flush against the Centrosome itself. Your Centrosome is now complete.

9) Making the Cytoskeleton - Make very thin snakes of Purple, Yellow & Orange fondant. Using diagram as a guide, place purple snakes for the Intermediate Filaments, Yellow snakes for the Microtubules & Orange snakes for the Microfilaments.

Using the brown buttercream, pipe tiny dots in groups of 2 & 3 onto the exposed Cytoskeleton (the white buttercream) to create Ribosomes. Your Cytoskeleton is now complete.

Congratulations! You have just made an edible replica of a plant cell.