Shopping list for you:

Flan base

3 different color Jellos

A wide variety of fruits.

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Basically put some fruity goodness inside the flan base, then pour jello into it.

All you have to do after that is wait for it to set. No chef skills required :3

All the pieces become one giant cell.

The flan would be the membrane, one of the jello colors is the cytoplasm.

The fruits you want to assign to the other cell parts is up to you, but I'll give a few pointers.

Lysosome: Banana slices

Ribosomes: Blackberries

Rough & Smooth ER: Strawberries could be both. Placing some strawberry halves seed side up to make the rough ER, then have some mashed up strawberry for the smooth.

Mitochondria: Orange sections

Vacuole: Apple slices

Centrosome: Kiwi slice (If you do this, remember to peel the fuzzyness off.)

Golgi: Could mash up some of the orange you have left from the Mitochondria.

Nucleus & Nucleolus: Because buying too many fruits is ridiculous, a small idea for this is to get the two other different color jellos, and use small circular cookie cutters to pour them into.

I think that's everything.

Have fun