Question

Hormogonia are vegetative reproductive structures of
A. Ulothrix
B. Oscillatoria
C. Spirogyra
D. Chara

Answer 1

Hint: The cellular filaments which are motile and are formed in certain cyanobacteria, and are produced as a result of vegetative reproduction is known as hormogonia. These structures in some cases may contain heterocysts involved in nitrogen fixation.

Complete answer: Oscillatoria is a cyanobacterium, which is filamentous. Hormogonia are present in these organisms, which have the ability to produce new filaments vegetatively under favorable conditions. The Hormones in these organisms arise as a result of separation disc formation. This structure also facilitates the nitrogen fixation process.
Considering the other options:
-Ulothrix is a filamentous green alga, which is aquatic in nature. Even though the most prominent type of reproduction is through vegetative means, the methods of reproduction are by fragmentation and formation of akinete which acts as a food reserve and gives rise to new plants under favorable conditions.
-Spirogyra is also an aquatic green alga, which undergoes vegetative reproduction by fragmentation, in which the parent organism breaks down into different fragments, and each fragment gives rise to new organisms.
-Chara is also an alga, in which both sexual and vegetative reproduction takes place. The vegetative reproduction is through the production of tubers and amylum stars.
Thus, the most appropriate answer is B, i.e., Oscillatoria which has Hormogonia as the vegetative reproductive structures.

Note: The blue-green algae or cyanobacteria are prokaryotic autotrophic organisms. These organisms exist in a symbiotic relationship with higher plants since they have the ability to convert the atmospheric nitrogen into usable forms such as ammonia. They exist within the legumes, formed on the root surfaces of these plants.