Columella is the specialized structure found in the sporangium of A. UlothrixB. RhizopusC. SpirogyraD. None of the above

The correct answer is B. Rhizopus.
The columella is a specialized structure found in the sporangium of certain fungi, particularly in Rhizopus.
1. Rhizopus:
o Rhizopus is a genus of fungi that is commonly known as black bread mold. In Rhizopus, the sporangium (a structure that produces spores) has a specialized internal structure called the columella.
o The columella is a sterile, central structure within the sporangium. It does not produce spores but supports the spore-producing tissues, helping to maintain the sporangium's integrity.
o The columella plays a role in the proper formation and release of spores from the sporangium.
2. Other Organisms:
o Ulothrix: Ulothrix is a genus of green algae. It does not have a sporangium with a columella. Instead, it typically reproduces by zoospores, and its reproductive structures are quite different from those in fungi.
o Spirogyra: Spirogyra is another genus of green algae. It reproduces primarily by fragmentation or conjugation and does not have a columella in its reproductive structures.
o Rhizopus: As previously mentioned, Rhizopus, a fungus, is the correct answer since it has a sporangium with a columella.
The columella is a specialized structure found in the sporangium of Rhizopus, not in Ulothrix or Spirogyra. Therefore, the correct answer is B. Rhizopus.