The diagram above represents an animal cell. What is the function of X? It controls energy released.
It regulates the transport of materials.
It produces proteins.
It synthesizes cellulose.

X in the diagram represents the cell membrane and performs the function of regulates the transport of materials.

Explanation:

The cell membrane, marked with X in the diagram, is a lipid bilayer with hydrophobic properties, which acts as a semi-permeable membrane to the passage of substances.

This membrane, that covers the cell and keeps it isolated from the extracellular space, has the function of controlling or regulating the passage of materials from the extracellular to the intracellular space, as well as the exit of substances from the interior of the cell. To fulfill this function it has several alternatives of transmembrane transport.

The other options are not correct because:

i am going to guess that it is co2.