Problem 84 - Objective Biology for NEET

Question

The sex organ in bryophytes are (a) Reduced to single celled stage (b) Multicellular (c) Net cell developed (d) Formed in sporophyte stage

Step-by-Step Solution

Answer

The correct answer is (b) Multicellular. The sex organs in bryophytes are multicellular.

Step 1: Understanding bryophytes

Bryophytes are a group of non-vascular plants, including mosses, liverworts and hornworts. Understand that they reproduce sexually as well as asexually.

Step 2: Exploring bryophyte sexuality

Bryophytes have specific male and female reproductive organs. The male organs are called antheridia and the female organs are called archegonia. These organs produce gametes for sexual reproduction.

Step 3: Looking at sex organ development in bryophytes

Consider the structure and development of these reproductive organs. They are multicellular and not reduced to a single-celled stage, nor are they net cell developed. Furthermore, they are not formed in the sporophyte stage but rather in the gametophyte stage.

Key Concepts

Antheridia and Archegonia

In the world of bryophytes—mosses, liverworts, and hornworts—reproduction takes a unique turn from what we might see in flowering plants. The male and female reproductive structures, known as antheridia (male) and archegonia (female), play crucial roles in the sexual reproduction process of these non-vascular plants. Unlike some organisms that rely on single-celled reproductive structures, bryophyte sex organs are complex and multicellular.

Antheridia are typically spherical or elongated structures that produce and release sperm, which are determined to find and fertilize the female gametes. Archegonia, on the other hand, are flask-shaped structures that house the single egg ready for fertilization. During the appropriate conditions, usually involving moisture, sperm swim towards the archegonia, and fertilization occurs, leading to the formation of a new generation of plants.

Gametophyte Stage

To understand the gametophyte stage in bryophytes, we should look at their life cycle. In these plants, the gametophyte represents the dominant, photosynthetic stage of the lifecycle and is the stage that is commonly recognizable as the 'plant' itself. At this point in their lifecycle, bryophytes display a unique feature: they are haploid, which means they have a single set of chromosomes.

During the gametophyte stage, the antheridia and archegonia are developed and become the centers of reproduction, as previously discussed. This contrasts with the sporophyte stage, where bryophytes form spores for asexual reproduction. Moreover, it's worth noting that the transition between these stages marks significant events in the alternation of generations, an important concept to grasp when studying plant life cycles.

Non-Vascular Plants Reproduction

Bryophytes, as non-vascular plants, lack the complex systems found in vascular plants, such as xylem and phloem. This distinction has profound implications on how they reproduce. They rely heavily on their surrounding environment, particularly on the presence of water, for reproduction.

Sexual reproduction in bryophytes, as we've seen, involves the antheridia and archegonia. When environmental conditions are right—mostly wet—the sperm, which is flagellated, can swim towards the egg in the archegonium. Upon fertilization, a sporophyte develops, which will eventually release spores into the environment, perpetuating the lifecycle of the bryophyte. This reliance on water for reproduction is one of the reasons bryophytes tend to be found in damp environments. In contrast, their asexual reproduction can occur through fragmentation, where a piece of the plant breaks off and grows into a new organism—a simpler, yet efficient form of reproduction.