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Which one of the following has haplontic life cycle?
A
Wheat
B
$Funaria$
C
$Polytrichum$
D
$Ustilago$
Detailed Solution
In a haplontic life cycle the dominant, free-living phase is haploid; the zygote is the only diploid cell and it undergoes meiosis directly (zygotic meiosis).
Wheat is an angiosperm: the dominant phase is the diploid sporophyte, so its life cycle is diplontic.
$Funaria$ and $Polytrichum$ are mosses (bryophytes): they have a dominant haploid gametophyte alternating with a multicellular diploid sporophyte, i.e., a haplo-diplontic life cycle.
$Ustilago$ (smut fungus) is a fungus; its vegetative phase is not diploid, and the diploid stage is restricted to the fusion nucleus, which undergoes meiosis. Its life cycle is therefore taken as haplontic.
Hence the organism with a haplontic life cycle is $Ustilago$.
Wheat is an angiosperm: the dominant phase is the diploid sporophyte, so its life cycle is diplontic.
$Funaria$ and $Polytrichum$ are mosses (bryophytes): they have a dominant haploid gametophyte alternating with a multicellular diploid sporophyte, i.e., a haplo-diplontic life cycle.
$Ustilago$ (smut fungus) is a fungus; its vegetative phase is not diploid, and the diploid stage is restricted to the fusion nucleus, which undergoes meiosis. Its life cycle is therefore taken as haplontic.
Hence the organism with a haplontic life cycle is $Ustilago$.