To construct a 3D model of a plant cell, acquire a rectangular container to house the organelles and represent the cell wall, such as a Tupperware container or aluminum baking pan. Line the inside of the pan with plastic wrap to represent the cell membrane. Make clear gelatin using half the recommended quantity of water, and chill it inside of the container to represent the cytoplasm. Carefully insert objects shaped like the various organelles into the chilled gelatin.
Insert a ball about the size of a ping pong ball into the gelatin to serve as the nucleus of the plant cell. This is the organelle that houses the DNA. For added detail, slice the ball in half, and glue pieces of yarn to the inside to represent the DNA. Allow the glue to dry before inserting the nucleus into the cytoplasm.
Gummy worms or cooked spaghetti noodles are some options to represent the endoplasmic reticulum. Dip some of the worms or noodles into a clear paste, and attach candy sprinkles to serve as the ribosomes on the rough endoplasmic reticulum.
Other organelles to include in the model are the mitochondria, lysosomes, Golgi apparatus, large central vacuole and chloroplasts. Pinto beans or raisins work well to represent the mitochondria, and M&Ms or other small, circular candies can represent the lysosomes. Use folded ribbon for the Golgi apparatus and a sealed plastic sandwich bag filled with water for the large central vacuole. Add green beads for the chloroplasts.
It is helpful to reference a diagram of a plant cell in a textbook or online to ensure all organelles are in the correct places.