The levels of biological organization from individual to biosphere are, subatomic particles,Atoms,Small Molecules,Macromolecules,Moleculer assemblies organelle cell tissue organ organ system organsim population species community ecosystem and Biosphere
The answer you are looking for is chitin.
According to a page that I found with info on the subject,
"All arthropods have bodies divided into segments and covered with a hard EXOSKELETON. This tough casing is made of a protein called chitin, which is also found in human fingernails."
https://www.factmonster.com/dk/encyclopedia/nature/arthropods
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The cell membrane. it protects the cell from outside substances. it controls what can enter and leave the cell.