Question

In which of the following there is no sexual reproduction-
(a)Ulothrix
(b)Nostoc
(c)Aspergillus
(d)Volvox

Answer 1

Hint: It is a cyanobacterial genus found in different environments that forms colonies in a gelatinous sheath consisting of filaments of moniliform cells. It can be found on soil, damp rocks, lakes and springs at the bottom, and occasionally in aquatic habitats.

Complete answer:
Unbranched filamentous green algae are the Ulothrix species. In Ulothrix, reproduction takes place by vegetative, asexual and sexual methods. Nostoc is a free-living cyanobacteria that fixes nitrogen with cells organised in bead-like chains (trichomes) clustered into a gelatinous mass (Nostoc balls). Reproduction is through vegetative and asexual techniques only. Aspergillus is a genus of fungi in which asexual and sexual methods exist in reproduction. Volvox is a freshwater green algae genus. The majority of Volvox species reproduce both asexually and sexually.

Additional Information: Reproduction in Volvox- The females' gonidia evolve into new spheres, each of whose own gonidia grows into a pair of eggs. The sperm leaves the male parent and swims to the mother, where her eggs are fertilised. The zygotes form a stage of rest that helps Volvox to withstand harsh environments.
Aspergillus Sexual Reproduction: Via the formation of antheridium and ascogonium, sexual reproduction takes place. Ascogonium has a terminal trichogyne and is a multinucleate, elongated female form.
There is an isogamous mode of sexual reproduction in Ulothrix, and most of the plants are heterothallic. In large numbers, i.e. 32 to 64 in each gametangium, the gametes are found.
So, the correct answer is ‘Nostoc’.

Note: Nostoc, by spore formation, reproduces vegetatively or asexually. Vegetative reproduction is carried out by fragmentation. Small colonies may grow attached to a large colony and form distinct colonies later on. Hormogonia's filaments are short and open.