The organelle that is the reason why plant cells are more rectangular than animal cells is the cell wall.
- Cell Wall: The cell wall provides structural support and rigidity to the plant cells, maintaining their rectangular shape.
- Cell Membrane: While it does provide some structure, it is flexible and does not determine the rectangular shape.
- Vacuoles: Large central vacuoles can take up space and provide some structural support, but they are not the primary reason for the rectangular shape.
- Nucleus: The nucleus is involved in cellular functions but does not play a role in the shape of the cell.
Therefore, the correct answer is cell wall.