Alternation of generation - class-XI

Three types of life cycle patterns are seen in the Saccharomyces (yeasts).

(i)         Haplobiontic life cycle (Saccharomyces octopus)

(ii)        Diplobiontic life cycle (Saccharomyces ludwigii)

(iii)       Haplodiplontic life cycle (Saccharomyces cerevisiae)

The correct option is C.

• Fucus (rockweed) is a type of brown alga and it displays the diploid life history. 
• The zygote becomes the embryo and develops into the mature Fucus. 
• The receptacles are reproductive branches and so contain many cavities with external pores. These pores contain antheridia (male) and oogonia (female)
• The correct option is C.

In a haplontic life cycle, the plant body is a gametophyte and dominant a dominant phase. The reproductive cell undergo mitosis to form gametes that are haploid, the gametic fusion results in a diploid zygote, which undergoes meiosis to form haploid spores.

Ustilago is a genus of around 200 smut fungi parasitic on the grasses. In the haplontic life cycle, the haploid stage is multicellular whereas the diploid stage is a single cellular. The zygote undergoes meiosis to form the haploid spores. Each spore germinates are being divided to form gametophyte. The other three are not having this life cycle.

So, the correct answer is option D.

Haplo-Diplontic life cycle observed in 8 in following plants. This life cycle present only in Bryophytes and pteridophytes. So, sphagum, polytrichum, marchantis and riccia belongs to Bryophyta and selaginella, pteris, dryopteris and polysiphonia belongs to pteridophyta. That's why they consists Haplo-Diplontic life cylcle. 

In Bryophytes, sexual reproduction is oogamous, but the gametes are often described in terms of their fusion. Isogamy is a primitive form where gametes are identical, but Bryophytes generally exhibit more advanced forms.

In many pteridophytes, especially heterosporous ones, the gametophytes are dioecious (separate male and female gametophytes). This is a general characteristic of the group's reproductive strategy.

Answer is option C i.e. "Bryophytes"
The zygote does not undergo meiosis immediately in bryophytes to form the sporophyte (a multi-cellular body). Some cells of the sporophyte undergo meiosis to form haploid spores. Spores further germinate to produce the gametophyte.

Bryophytes are known as amphibians of the plant kingdom because they require water for the movement of male gametes to the archegonia. Option B is wrong because sex organs in bryophytes are multicellular. Option C is wrong because the plant body is a thallus, not differentiated into true roots, stems, or leaves. Option D is wrong because Polytrichum is a moss, not a liverwort.

In pteridophytes, the spore germinates to form a small, inconspicuous, multicellular, free-living, photosynthetic thallus called a prothallus. This structure represents the reduced gametophyte stage of the plant.

Statement (A) is wrong because the sporophyte in mosses is more elaborate than in liverworts. Statement (D) is wrong because Pinus is monoecious, meaning male and female cones are borne on the same tree. Statements (B) and (C) are correct.

In bryophytes, the main plant body is the gametophyte (n), which produces gametes through mitotic division since the cells are already haploid and do not need to undergo reduction division.

Apospory is the development of a gametophyte directly from the vegetative cells of a sporophyte without meiosis. Since the sporophyte is diploid (2n), the resulting aposporously formed gametophyte is also diploid, and therefore its gametes will be diploid.

In alternation of generations, the haploid plant is the gametophyte and the diploid is the sporophyte. Algae showing haplontic cycles have a dominant gametophyte. Bryophytes and pteridophytes exhibit a haplodiplontic life cycle.

Following are the correct statements: 

In mosses, when antheridia and archegonia are on different branches of the same plant, the condition is monoecious (since both sexes are on one plant) and specifically paroicous (if they are on the same branch) or autoecious (if on different branches). Given the options, 'monoecious and paroicous' is the standard classification for this specific arrangement.

Mosses have neither pollen nor flowers and rely on water to carry the male gametes (the sperm) to the female gametes (the eggs). The spore capsules are produced after the sperms have fertilized the eggs. As they are produced after fertilisation, these spore capsules are diploid.

In bryophytes and pteridophytes and gymnosperms the male and female gametophytes to not have an independent free-living existence. They remain within the sporophyte. The gametophytes are quite large in Bryophytes as compared to other phyla like pteridophytes or angiosperms.