The endoplasmic reticulum aids in the production and movement of proteins and other materials through the cell.
<span>Mucous membranes provide a mechanical barrier at body openings. They also line the respiratory, GI, urinary, and reproductive tracts. Mucous membranes secrete mucus, a slimy substance that traps pathogens. The membranes also have hair-like cilia.</span>
Pretty sure it is C) Oxygen
since it is produced in photosynthesis, and consumed in respiration.