The trophosome of Riftia pachyptila was found to be full of sulfur crystals. Why were there sulfur crystals in the trophosom

 

Riftia pachyptila lives on the floor of the Pacific Ocean near hydrothermal vents, and can tolerate extremely high hydrogen sulfide levels with the help of their symbionts. These symbionts (billions of bacteria called Endoriftia) actively produce the large elemental sulfur crystals in the trophosome by sulfide oxidation. Sulfide oxidation is the process where the toxic hydrogen sulfide is is converted to elemental sulfur (crystals).

Step-by-step explanation

Trophosome is a vascualrized organ which houses symbiotic bacteria that provide food for their host. Riftia pachyptila do not eat as they have neither a mouth nor a stomach. Instead, billions of symbiotic bacteria living inside their trophosome produce sugars from carbon dioxide, hydrogen sulfide, and oxygen which are found in their environment. Because hydrothermal vents have high hydrogen sulfide levels, the symbiotic bacteria are responsible for oxidizing hydrogen sulfide to sulfur to avoid toxicity. This is the reason why there are sulfur crystals in the trophosome.