Problem 77 - Objective Biology for NEET

Question

Which of the following statement is incorrect with respect to bryophytes? (a) The plant body is thallus like, more differentiated than algae and attached to substratum by the help of rhizoids. (b) The antherozoids are released in water for fertilization. (c) Zygote formed undergoes meiotic cell division immediately. (d) They have leaf like, stem like and root like structures.

Step-by-Step Solution

Answer

The incorrect statement with respect to bryophytes is (c): 'The zygote formed undergoes meiotic cell division immediately.' The zygote undergoes mitotic, not meiotic, cell divisions.

Step 1: Understand Bryophyte Characteristics

First, understand what are bryophytes. Bryophytes are a group of plant species that are characterized by their thallus-like bodies that are more differentiated than algae, and are tethered to their substrate with the help of rhizoids. They have leaf-like, stem-like, and root-like structures. During their reproductive process, they release antherozoids into water for fertilization.

Step 2: Identify Incorrect Statement

Next, compare each of the given statements to the characteristics of bryophytes. (a) matches the description of bryophytes being thallus-like, more differentiated than algae, and held down by rhizoids. (b) is also correct as bryophytes do indeed release antherozoids into water for fertilization. (d) is also accurate as bryophytes have stem-like, leaf-like, and root-like structures.

Step 3: Confirm Incorrect Statement

The remaining statement (c) is incorrect. After fertilization, the zygote of bryophytes undergoes mitosis, not meiosis, leading to a new sporophyte individual. Therefore, statement (c) is the incorrect statement about bryophytes in this case.

Key Concepts

Plant body structure

Bryophytes are fascinating organisms primarily characterized by their unique plant body structure. Unlike higher plants that possess distinct roots, stems, and leaves, bryophytes have a thallus-like body. This means their structure is less specialized but still more differentiated when compared to algae.
This differentiation allows them to adapt to various terrestrial and semi-aquatic environments. In bryophytes, we observe structures resembling leaves and stems, known as leaf-like and stem-like structures, which offer them support and an interface for photosynthesis.
An essential point is the rhizoids, which are hair-like structures anchoring bryophytes to their substrate. These rhizoids do not absorb water or nutrients like true roots but serve mainly to stabilize the plant. Even though they don't possess the complexities of vascular plants, their simple yet effective structure is a testament to their resilience and adaptability.

Reproductive process

The reproductive process of bryophytes is quite intriguing and distinct from other plant types. Bryophytes rely on a combination of sexual and asexual reproduction. Their primary mode of sexual reproduction involves the formation of male and female gametes.
In the male structure, known as the antheridium, motile sperm cells called antherozoids are produced. These antherozoids are unique because they require a thin film of water to swim and reach the female reproductive organ called the archegonium.

• Water is essential for fertilization, highlighting the dependency of bryophytes on moist environments.
• Once the antherozoids reach the archegonium, they fertilize the egg, resulting in the formation of a zygote.

This process ensures genetic diversity that helps bryophytes adapt to changing environments.

Cell division in bryophytes

Understanding cell division in bryophytes is crucial in appreciating how these plants grow and replicate. Cell division occurs through mitosis and meiosis, but the role of each is distinct.
When a bryophyte zygote forms after fertilization, it does not undergo meiosis immediately. Instead, the zygote undergoes mitosis, leading to the development of a multicellular sporophyte.
The sporophyte generation is critical because it harbors spore-producing structures, where meiosis occurs later, producing haploid spores.

• These spores can disperse over distances.
• On reaching a suitable substrate, they germinate to develop into a new gametophyte.

Thus, bryophytes exhibit a life cycle alternating between gametophyte and sporophyte phases, a characteristic feature of their adaptation strategy in varying environments.

Differentiation from algae

Bryophytes hold a unique position in the plant kingdom, bridging the gap between aquatic algae and terrestrial plants. While they share some similarities with algae, particularly in being thallus-like, there are notable developmental differences.
Algae typically thrive in aquatic environments and are largely single-celled or simple multicellular organisms. In contrast, bryophytes have adapted to life on land, exhibiting more complexity.
In bryophytes:

• The presence of structures like leaf-like and stem-like entities signifies more differentiation.
• Rhizoids help in anchoring the plant, a feature not seen in algae.
• Reproductive strategies also differ as bryophytes depend on multicellular gametangia for reproduction.

These distinctive features mark bryophytes as an evolutionary step above algae, reflecting the gradual adaptation of plants from aquatic to terrestrial life environments.