Which structure provides a rigid layer that protects and supports the cell?

The cell wall is the structure that provides a rigid layer protecting and supporting the cell. This outermost layer is primarily found in plant cells, some fungi, and bacteria. Its main functions include maintaining the cell's shape, providing structural support, and acting as a protective barrier against environmental stresses.

The composition of the cell wall can vary; for instance, in plants, it is mainly made up of cellulose, while in fungi, it often contains chitin. This rigidity allows it to withstand turgor pressure from the cell's interior, which is essential for maintaining the cells' integrity and overall function. In contrast, the other structures listed do not fulfill this specific role of providing rigidity and support in the same way. The cell membrane, for instance, is flexible, allowing for selective permeability but does not provide the same level of structural support. The nucleus is primarily involved in storing genetic information and regulating cellular activities, and mitochondria are responsible for energy production.