Question

Which of the following shows isogamy with non-flagellated gametes?
A. Sargassum
B. Ectocarpus
C. Ulothrix
D. Spirogyra

Answer 1

Hint: It is a filamentous charophyte green algae of the order Zygnematales.
It is named for the helical or spiral arrangement of the chloroplasts that is characteristic of the genus. It is commonly found in freshwater habitats.

Complete answer: Sargassum: Sargassum is a genus of brown (class Phaeophyceae) macroalgae (seaweed) in the order Fucales.
Some species of sargassum have berry-like gas-filled bladders that help the fronds float to promote photosynthesis.

Ectocarpus: Ectocarpus is a genus of filamentous brown algae.
Ectocarpus is a cosmopolitan marine brown seaweed found mostly as free-floating filaments in intertidal to sublittoral zones of temperate regions.
It can easily grow as epiphytes on other seaweeds.

Ulothrix: Ulothrix is a genus of green algae in the family Ulotrichaceae.
Ulothrix is a genus of non-branching filamentous green algae, generally found in fresh and marine water. The cells are normally as broad as they are long, and they thrive in the low temperatures of spring and winter. Reproduction in Ulothrix takes place by means of vegetative, asexual, and sexual methods.

Spirogyra: Spirogyra is also known as water silk, mermaid's tresses, and blanket weed.
Spirogyra can reproduce both sexually and asexually. It is isogamous.
In vegetative reproduction, fragmentation takes place, and Spirogyra simply undergoes intercalary cell division to extend the length of the new filaments.

  

So, the answer is D. Spirogyra

Note: Sexual reproduction is of two types: Scalariform conjugation and lateral conjugation.
The essential difference is that scalariform conjugation occurs between two filaments and lateral conjugation occurs between two adjacent cells on the same filament.
They reproduce sexually by conjugation in which two non-flagellated morphologically similar but physiologically different gametes (isogamous) fuse together.