Question

Triphasic life cycle is present in
A. Red algae
B. Brown algae
C. Diatom
D. Dinoflagellate

Answer 1

Hint: Triphasic life cycle includes a gametophytic phase and two distinct sporophyte phases. Alternation of generation is defined as alteration of multicellular diploid and haploid forms in the organism’s life cycles regardless of whether or not these forms are free living.

Complete Answer:
The triphasic life cycle includes an alternation of two diploid or sporophyte generations. There are two diploid phases and one haploid phase. Red algae show a triphasic life cycle. Red algae also called rhodophyta is one of the oldest groups of eukaryotic algae.
Red algae with a complicated life cycle involves three phases.
No motile stage occurs during the entire life of red algae. The spores and gametes are transported by the water in a passive manner.
The sexual reproduction only oogamy is observed. In red algae the egg cell develops in a female gametangium called carpogonium. It is here that fertilization occurs. The sperms are produced in their own spermatogonia but lack their own motility apparatus.

The correct option is, A - Red algae.

Additional information: Brown algae are multicellular and all go through an alternation of generation, diploid and haploid phases alternate. The diploid form the diplont or sporophyte, is the dominating form in its life cycle.
In the presence of adequate nutrients and sunlight, diatoms doubles approximately every 24 hours by asexual multiple fission. The maximum life span of individual cells is about six days.
The dinoflagellate life cycle comprises of four main phases, growth (mitotic and asexual), sexuality (meiotic), quiescence (a sexual or asexual immobile stage with a low metabolic rate which is popularly named cyst) and senescence (population decline and death).

Note: There are two diploid phases and one haploid phase. Triphasic life cycle is present in Red algae. Some species show alternation of generations that have distinct haploid sexual and diploid asexual stages. The haploid spores germinate and grow into haploid gametophyte. Life cycles of plant and algae with alternating haploid and diploid multicellular stages are referred to as diplohaplontic.