All questions of May Week 3 for NEET Exam

**Answer:**

The prominent phase in the life cycle of bryophytes is the **gametophyte**. Bryophytes are non-vascular plants that include mosses, liverworts, and hornworts. They have a unique life cycle that involves alternating generations of two distinct phases: the gametophyte and the sporophyte.

**Gametophyte Phase:**

The gametophyte is the dominant phase in the life cycle of bryophytes. It is the haploid (having one set of chromosomes) and gamete-producing phase. The gametophyte is the visible, leafy part of the plant that we commonly recognize as the moss or liverwort. It is the phase that carries out photosynthesis and produces the sex organs.

During the gametophyte phase, the moss or liverwort produces archegonia and antheridia. The archegonia are female sex organs that produce eggs, while the antheridia are male sex organs that produce sperm. The sperm requires water for fertilization to occur because they swim to the eggs through a film of water.

After fertilization, the zygote is formed, which develops into the sporophyte phase.

**Sporophyte Phase:**

The sporophyte phase is the diploid (having two sets of chromosomes) and spore-producing phase in the bryophyte life cycle. It is dependent on the gametophyte phase for nutrition and support.

The sporophyte phase develops from the fertilized zygote and remains attached to the gametophyte. It is a small, non-photosynthetic structure that consists of a foot, seta, and capsule. The foot is embedded in the gametophyte and absorbs nutrients. The seta is the stalk-like structure that elevates the capsule. The capsule contains sporogenous tissue, which undergoes meiosis to produce haploid spores.

When the spores are mature, the sporophyte releases them into the environment. These spores are dispersed by wind or water and, upon landing in a suitable environment, germinate to form new gametophytes. The spores give rise to protonemata, which are thread-like structures that develop into new gametophytes.

**Conclusion:**

In conclusion, the gametophyte phase is the prominent phase in the life cycle of bryophytes. It is the leafy, haploid phase that carries out photosynthesis and produces the sex organs. The sporophyte phase, although important for spore production, remains dependent on the gametophyte phase for nutrition and support.

Incorrect Statements in the Life Cycle of a Moss:
1. The protonema stage is the second stage of the gametophyte, which develops from the leafy stage.
- This statement is incorrect. The protonema stage is actually the first stage of the gametophyte, not the second stage. It develops from the germinated spore and eventually gives rise to the leafy stage.
2. The leafy stage develops from the secondary protonema as a lateral bud.
- This statement is incorrect. The leafy stage actually develops from the primary protonema, not the secondary protonema. It emerges from the protonema as a lateral bud, eventually forming the leafy structure of the moss plant.
3. The leafy stage is attached to the soil through multicellular and branched rhizoids.
- This statement is correct. The leafy stage of a moss is indeed attached to the soil through multicellular and branched rhizoids, which help anchor the plant and absorb water and nutrients from the environment.
Therefore, there are two incorrect statements in the given list regarding the life cycle of a moss.

Embryonic development in bryophytes takes place in the archegonium.

The archegonium is a multicellular structure found in bryophytes, which are a group of non-vascular plants including mosses, liverworts, and hornworts. It is the female reproductive organ and is responsible for the production and protection of the female gametes, or eggs.

Embryonic development in bryophytes refers to the process by which a zygote, formed by the fusion of a sperm and an egg, develops into a mature sporophyte. This process occurs within the archegonium.

Here is a detailed explanation of the embryonic development in bryophytes:

1. Fertilization: In bryophytes, the male gametes, or sperm, are produced in antheridia, which are male reproductive organs. The sperm are released into the environment and need water to swim to the archegonium. Once the sperm reaches the archegonium, it fertilizes the egg, resulting in the formation of a zygote.

2. Zygote Development: After fertilization, the zygote starts to develop within the archegonium. The archegonium provides a protective environment for the developing embryo. It nourishes the embryo and provides it with the necessary nutrients for growth.

3. Embryo Formation: As the zygote develops, it undergoes cell divisions and differentiation. The archegonium nurtures the developing embryo by supplying it with nutrients and water. The embryo grows within the archegonium and gradually develops into a multicellular structure known as a sporophyte.

4. Sporophyte Maturation: The sporophyte continues to grow within the archegonium until it becomes mature. The mature sporophyte consists of a stalk-like structure called a seta and a capsule, or sporangium, at the top. The sporangium contains spores, which are reproductive cells that can grow into new gametophytes.

5. Spore Release: When the sporophyte is mature, the sporangium releases spores into the environment. These spores are dispersed by wind or water and can germinate to form new gametophytes, starting the cycle again.

In summary, the embryonic development in bryophytes takes place in the archegonium. The archegonium provides a protected environment for the growth and development of the zygote into a mature sporophyte. This process is essential for the reproduction and survival of bryophytes.

Corrected Statements:

I. Bryophytes are also called amphibians of the plant kingdom because they are dependent on water for sexual reproduction.
- This statement is correct. Bryophytes, like amphibians, require water for the fertilization of their gametes.

II. They play an important role in plant succession on bare rocks.
- This statement is correct. Bryophytes are pioneer plants that colonize bare rocks and help in soil formation, paving the way for other plant species.

III. They lack true roots, stem or leaves.
- This statement is correct. Bryophytes lack true vascular tissues and have simple structures that function in a manner similar to roots, stems, and leaves.

IV. The sex organs in bryophytes are multicellular.
- This statement is correct. Bryophytes have multicellular sex organs called archegonia and antheridia.

V. They produce biflagellate zoospores.
- This statement is incorrect. Bryophytes produce haploid spores, not zoospores.

VI. Archegonium is flask-shaped and produces a single egg.
- This statement is correct. The archegonium in bryophytes is flask-shaped and produces a single egg.
Therefore, out of the given statements, 5 are correct.

Understanding Moss Reproduction
Mosses, as non-flowering plants, primarily reproduce through vegetative methods, specifically via fragmentation and budding. This allows them to spread and colonize new areas effectively.
Methods of Vegetative Reproduction
- Fragmentation:
- Mosses can break into smaller pieces, where each fragment can grow into a new individual. This process often occurs naturally when environmental conditions are favorable, or through physical disturbances.
- Budding:
- In some moss species, small outgrowths or buds can form on the parent plant. These buds eventually detach and develop into new moss plants. Budding is a form of asexual reproduction, allowing for rapid population increases.
Advantages of Vegetative Reproduction
- Rapid Colonization:
- Mosses can quickly occupy new habitats, as each fragment or bud can establish itself independently.
- Genetic Uniformity:
- Since the offspring are clones of the parent, they are well-adapted to the same environment. This can be beneficial in stable habitats.
Comparison with Other Methods
- Seeds:
- Mosses do not reproduce by seeds; they primarily use spores for sexual reproduction.
- Bulbs:
- Bulb formation is not a characteristic of mosses; it is more common in certain flowering plants.
In conclusion, the correct answer to how mosses primarily reproduce vegetatively is by fragmentation and budding, making option 'C' the right choice. This reproductive strategy plays a crucial role in the survival and distribution of mosses in various ecosystems.

Statement 1: Each sperm of moss has two flagella.
Statement 2: Water is essential for fertilization in mosses.

Explanation:
The correct answer is option 'B' - Both statements 1 and 2 are correct but statement 2 is not the correct explanation of statement 1.

1. Importance of Water in Moss Fertilization:
- Mosses are non-vascular plants that reproduce through the process of fertilization.
- In order for fertilization to occur in mosses, water is essential.
- Mosses require a moist environment for the male and female gametes to come in contact with each other.
- The presence of water is necessary for the sperm to swim from the male reproductive structure (antheridium) to the female reproductive structure (archegonium) where fertilization takes place.
- Water acts as a medium for the movement of sperm and facilitates the union of gametes, leading to fertilization.

2. Flagella in Moss Sperm:
- Mosses are unique in that they have swimming sperm, unlike most other plants where fertilization occurs through passive pollen transfer.
- The sperm of mosses are flagellated, meaning they possess whip-like structures called flagella that enable them to move in a liquid environment.
- Each sperm of moss possesses two flagella, which provide the necessary motility for the sperm to swim through the water to reach the egg for fertilization.
- The flagella help the sperm to navigate in the water towards the female reproductive structure and increase the chances of successful fertilization.

Explanation of the Correct Answer (Option B):
Both statements 1 and 2 are correct, as moss sperm do have two flagella and water is indeed essential for fertilization in mosses. However, statement 2 is not the correct explanation of statement 1.
Statement 1 simply states a fact about moss sperm having two flagella, whereas statement 2 provides the reason behind the requirement of water for fertilization in mosses. The two statements are related but not interdependent on each other.

Incorrect Statement Analysis
The correct answer is option 'D', which states: "The sporophyte in liverworts is differentiated into a foot, seta, and rhizoid." This statement is incorrect due to the following reasons:
Structure of Liverwort Sporophyte
- Unlike true mosses and higher plants, the sporophyte of liverworts is not well-differentiated.
- In liverworts, particularly in the thalloid forms like Marchantia, the sporophyte consists mainly of a foot that anchors it to the gametophyte and a capsule where spores are produced.
- There is no seta (stalk) present as seen in more advanced plants.
Comparison with Other Bryophytes
- In contrast, in mosses, the sporophyte is clearly differentiated into a foot, seta, and capsule.
- The absence of a seta in liverworts signifies their simpler structure compared to other bryophytes.
Summary of Liverwort Characteristics
- Habitat: Liverworts thrive in moist, shady environments such as stream banks and damp soils.
- Plant Body: The plant body is typically thalloid and dorsiventral, as observed in Marchantia.
- Asexual Reproduction: Asexual reproduction occurs through fragmentation and the formation of gemmae, which are specialized structures for asexual propagation.
In conclusion, option 'D' is incorrect because liverworts do not possess a differentiated sporophyte structure akin to that of mosses, making it clear that their sporophyte is simpler and lacks a seta.

The kinetic energy of an electron in the second Bohr orbit of s H atom is [a0 is Bohr radius],