Question

Male gametes are flagellated in
A. Ectocarpus
B. Spirogyra
C. Polysiphonia
D. Anabaena

Answer 1

Hint: Ectocarpus is a filamentous marine brown alga which is heterotrichous in nature. The male gametes of the alga characteristically contain a single chloroplast with a pyrenoid and a distinct prominent concave eye spot, into which the flagellum gets fit.

Complete answer:
Different species of Ectocarpus are found throughout the world. They grow in marine habitat, either free-floating, lithophytes (on rocks) or epiphytes (on other sea plants). They are commonly found in both tropical and temperate seas. In Ectocarpus, sexual reproduction is both isogamous and anisogamous type. Oogamy is absent. Biflagellate gametes are liberated from the plurilocular gametangia through apical or lateral aperture. During the process of fertilisation, many male gametes surround the female gamete and get entangled by their anterior large flagellum therefore a clamp-like structure is formed. Out of many male gametes, only one male gamete gets fused with the female gamete and the remaining gametes gradually get destroyed. The uniting gametes then form zygote through plasmogamy and karyogamy. The zygote undergoes germination and develops into a sporophytic (2n) plant.
Among the other given options:
In Spirogyra, sexual reproduction occurs through conjugation in which more active male gamete passes through a conjugation tube and fuses with female gamete of the cell of the adjacent filament. Here, the male gametes are non-flagellated and show amoeboid movement.
Polysiphonia is a small upright bushy marine alga that also produces non- flagellated spermatia.
Anabaena is a cyanobacteria. It does not reproduce sexually. They mostly reproduce asexually by binary fission, fragmentation, endospore formation, etc.

Note: Ectocarpus produces biflagellate gametes. During fertilization, the flagella of male gamete plays a very important role in establishing initial sexual contact with the female gamete.