Question

Which one of these has a haplontic life cycle?
A. Wheat
B. Funaria
C. Polytrichum
D. Ustilago

Answer 1

Karyogamy refers to the fusion of the two cell nuclei. It is a pathogen of seeds and flowers of cereals, wheat, corn, and grasses that exhibit the haplontic life cycle.

Complete answer: Life cycle is a series of changes that an organism undergoes through its lifetime. The lifecycle can be haploid, diploid or alternating between the two and may either be haplontic, diplontic or haplodiplontic. In the case of a haplontic life cycle, the haploid stage is multicellular, but the diploid stage is single-celled. Ustilago shows haplontic life cycle.
Features of the haplontic life cycle:
a) The zygote undergoes meiosis and gametophyte is a dominant phase.
b) The sporophytic phase is represented by a single-celled zygote called zygospores.
c) Haploid spores are formed by meiosis in a zygote.
d) Each spore in favourable condition forms a gametophyte.
e) It is observed in algae like Volvox, Spirogyra, etc.
Hence, the correct answer is option D.

Additional information: The diplontic life cycle refers to the life cycle in organisms which is dominated by the diploid stage. Plants and algae show alternation of generation. Here, mitosis usually occurs at the diploid stage, i.e. zygote and gametes are produced by meiosis.

Note: Here, both haploid and diploid stages are multicellular. In some, the gametophyte is dominant and free-living and the sporophyte is a small and short-lived phase, which is dependent on gametophytes, e.g. Bryophytes.