Problem 104 - Objective Biology for NEET

Question

The gametophyte of bryophyte develops from (a) A haploid spore (b) A diploid spore (c) Zygote (d) None of these

Step-by-Step Solution

Answer

The gametophyte of a bryophyte develops from a haploid spore.

Step 1: Understanding Bryophytes Life Cycle

Any life cycle that includes a multicellular diploid and multicellular haploid stage is called an alternation of generations. In the life cycle of a bryophyte, the majority of the cycle is spent in the gametophyte phase. The sporophyte phase grows from the gametophyte and is in general largely dependent upon it.

Step 2: Identifying the Origin of Gametophyte

Reflecting on the initial question, we want to determine from where the gametophyte develops. In the bryophyte life cycle, the gametophyte arises from a haploid spore. This stage of the life cycle begins after a meiotic division of the diploid sporophyte, producing haploid spores.

Step 3: Verifying the Choice

Cross verifying with the provided options, (a) A haploid spore corresponds with our deduction. This is the correct answer.

Key Concepts

Gametophyte

In the fascinating world of bryophytes, the gametophyte is a crucial stage in their life cycle. Bryophytes, like mosses, liverworts, and hornworts, are non-vascular plants that largely spend their life in the gametophyte stage. This stage is significant because it is the dominant, photosynthetic part of their life cycle where they carry out most of their biological processes.

The gametophyte stage begins when a haploid spore lands in a suitable environment and germinates. The spore grows through mitosis into a multicellular structure, which is the mature gametophyte. This part of the cycle produces gametes: sperm and eggs in special organs called antheridia and archegonia, respectively. Notably, these structures are visible to the naked eye as the leafy green plant you often encounter.

Key Characteristics of Gametophyte:

• Dominant, independent phase of bryophyte life cycle
• Photosynthetic, nutrient-absorbing structure
• Produces gametes through mitosis

Alternation of Generations

The concept of alternation of generations is a captivating phenomenon in plant biology, illustrating an evolutionary adaptation to terrestrial life. This life cycle involves two distinct stages: the gametophyte and sporophyte.

In bryophytes, alternation of generations means that there is a shift between the haploid (gametophyte) and diploid (sporophyte) stages. Unlike most plants, in bryophytes, the gametophyte is the dominant stage, meaning it is the most visible and photosynthetic. The sporophyte develops from the gametophyte and remains attached to it, getting nutrients and support.

Formation and Development:

• The sporophyte begins as a fertilized egg or zygote.
• It undergoes mitosis to become a diploid multicellular organism.
• Eventually, it produces haploid spores through meiosis to start the cycle anew.

Haploid Spore

Haploid spores play a vital role in the life cycle of bryophytes, marking the beginning of the gametophyte stage. These spores are produced by the sporophyte phase through meiosis, a type of cell division that reduces the chromosome number by half. As a result, each spore has a single set of chromosomes, hence the term haploid.

When conditions are favorable, these haploid spores disperse and germinate into new gametophyte plants. This dispersal can occur through water, wind, or other natural agents, enabling bryophytes to colonize new environments.

Importance of Haploid Spores:

• Critical for sexual reproduction in bryophytes
• Ensures genetic diversity through sexual reproduction
• Allows colonization of new habitats