Lay the tray on a flat surface. In the center of the tray, place a large piece of blue modeling clay. Spread it out into a circular or oval shape, approximately 8 inches in diameter and about 1/2 to 1 inch thick. This represents the cytoplasm.
Roll pieces of the yellow modeling clay into rods approximately 1/2 to 1 inch in diameter. Lay these rods end-to-end, wrapping around the cytoplasm to represent the cellular membrane.
Roll the red modeling clay into a ball approximately 2 inches in diameter. Press this into the middle of the blue clay to represent the nucleus of the cell.
Press your index finger into the blue clay at various locations around the model, making depressions. These empty spaces represent the vacuoles, or storage centers, of the cell.
Lay the end of the pink yarn on the blue clay, starting from the nucleus. Extend the yard outward from the nucleus to form the tubular structure of the endoplasmic reticulum. Continue outward from the nucleus, and then curve the tubular structure back to the nucleus. Trim the excess yarn with scissors.
Press several beads into the open areas of the cytoplasm. These represent ribosomes. Line some of the endoplasmic reticulum with ribosomes.
Lay the end of the orange yarn on the blue clay, starting in the middle of the cytoplasm. Form a tubular structure similar to the endoplasmic reticulum, only make this within the cytoplasm, not connected to the nucleus. Trim the excess yarn with scissors. This represents the golgi apparatus.
Press two or three dried kidney beans into the open areas of the cytoplasm. These represent mitochondria.
Tear a 2-inch strip of masking tape from the roll, and fold it in half over the end of a toothpick to make a tiny flag. Label this with one of the cell parts, such as "Cytoplasm." Stick the flag into or next to the labeled part. Repeat for each part of the cell.
Write a key to the model on a separate sheet of paper. Include the function of each part of the cell that is labeled.