Using 3D models of the parts of plant and animal cells can help students to understand the cell from a visual perspective. Both the mitochondria, which is known as the "powerhouse" of the cell, and the chloroplast, which is only found in the plant cell, can be represented using a styrofoam ball and different colors of clay. Making these models of organelles will allow students to see the inner workings of the components of the mitochondria and chloroplast.
Making the Mitochondria Model (Cross-sectional)
Slice the styrofoam egg in half using the craft knife (at a 45 degree angle from top to bottom). Place one half aside.
Paint the outside of the half styrofoam egg using a brown craft paint. This will represent the outer membrane of the mitochondria.
Roll the modeling clay out in long strands, about 1/5 of an inch (1/2 cm) in width. Super glue the strands of clay to the newly cut styrofoam. These strands will represent the inner membrane (you can look up pictures of the inner membrane of the mitochondria to model the wavy structure).
Paint the spaces in between the wavy structure of the inner membrane using blue craft paint. This will model the matrix.
Making the Chloroplast Model (Cross-sectional)
Paint the outside of the other half of the styrofoam egg green. This will represent the outer membrane of the chloroplast.
Paint the face of the egg using a light green craft paint. This will represent the inner membrane of the chloroplast.
Create quarter-sized "thylakoids" by rolling balls of modeling clay and flattening them until they are the size of a quarter. Stack these thylakoids to create granum. Make about three granum.
Super glue these granum to the inner membrane portion of the egg so that each thylakoid is attached to the inner membrane surface in their stack.
Create strands of modeling clay, about 1/5 of an inch wide (1/2 cm), and super glue them to the styrofoam. These strands need to connect the granum, which will represent a system of tubules.
TL;DR (Too Long; Didn't Read)
If you cannot find a styrofoam egg, you can get a styrofoam block and carve out a cylinder shape using a craft knife.
Use caution when cutting the styrofoam with a craft knife.