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Explanation for children:
The cell wall is the outermost layer of a bacterial cell, in the figurative sense the peel of the orange. Its main function is to protect and stabilize the inside. You can see that an orange peel has many small holes through which air and water can pass. This is why our oranges sometimes dry out and no longer taste good. The cell wall of the bacteria also has many small holes through which many molecules simply pass. Therefore, there is another layer under the cell wall, the cell membrane, which controls exactly what gets inside and what doesn't.