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Difficulty: EasyThallophytes, Bryophytes, and Pteridophytes

Arrange the following sequential events in the reproductive life cycle of a moss (Bryophyta), beginning with the germination of a haploid spore:

  1. 1Germination of the haploid spore into a green, filamentous structure called a protonema
  2. 2Development of erect, leafy gametophytes bearing antheridia and archegonia
  3. 3Transfer of flagellated sperm through water to fertilize the egg within an archegonium
  4. 4Growth of a diploid sporophyte (capsule and seta) attached to and dependent on the gametophyte

Answer

The correct sequence begins with the germination of a spore into a protonema, followed by the development of leafy gametophytes with sex organs, fertilization via swimming sperm in water, and lastly the growth of the dependent diploid sporophyte.
In mosses (bryophytes), the reproductive cycle starts when a haploid spore germinates into a filamentous protonema. This structure gives rise to the leafy gametophyte, which bears sex organs (antheridia and archegonia). Flagellated sperm swim through water to fertilize the egg inside the archegonium, forming a zygote that develops into the sporophyte generation attached to the parent gametophyte.

Step-by-Step Solution

1
Identify the initial developmental stage following spore dispersal.
A haploid spore germinates on moist soil to form a filamentous, algal-like green structure known as the protonema.
Spores are single-celled reproductive units that initiate the haploid gametophyte phase.
2
Trace gametophyte maturation and gamete container production.
Protonemal buds develop into adult leafy gametophytes that produce male (antheridia) and female (archegonia) reproductive structures.
The dominant haploid gametophyte produces gametes by mitosis.
3
Identify the fertilization mechanism.
Flagellated sperm released from antheridia swim through a surface layer of water to reach and fertilize the egg in an archegonium, forming a diploid zygote.
Bryophytes require liquid water for sexual reproduction because sperm are flagellated.
4
Determine the final stage of sporophyte generation formation.
The diploid zygote undergoes mitotic division to form a sporophyte consisting of a foot, seta, and spore-bearing capsule, which stays attached to the gametophyte.
In bryophytes, the diploid sporophyte is nutritionally dependent on the autotrophic gametophyte throughout its lifespan.

Key Concept

Bryophyte life cycle and alternation of generations
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Topics

Thallophytes, Bryophytes, and Pteridophytes

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