Reproduction In Plants

Somatic hybridization fuses protoplasts (cell walls removed) of distantly related species (e.g., Pomato from potato + tomato).
Overcomes sexual incompatibility barriers.

Somatic hybridization is a process in plant biotechnology that involves the fusion of two different plant cells (somatic cells) to create a hybrid plant with characteristics from both parent plants. Unlike traditional hybridization, which involves the fusion of gametes (sperm and egg cells), somatic hybridization bypasses sexual reproduction by fusing somatic (non-reproductive) cells, typically from the tissue or cells of two different species or varieties.

Other options:

• (A) Artificial pollination: Fails due to incompatibility.
• (C) Conventional breeding: Requires compatible species.
• (D) Mutation breeding: Alters genes within a species.

Correct Answer: (B) Somatic hybridization

(A) Antipodals - Haploid: Correct. The antipodal cells, along with the egg apparatus (egg cell and synergids), are part of the mature embryo sac (female gametophyte) which is haploid (n) in angiosperms.

(B) Zygote - Diploid: Correct. The zygote is formed by the fusion of haploid male and female gametes (n + n = 2n), making it diploid.

(C) Synergids - Diploid: Incorrect (Mismatch). Synergids are part of the egg apparatus in the embryo sac and are haploid (n) like all other cells of the female gametophyte.

(D) Primary Endosperm Nucleus (PEN) - Triploid: Correct. The PEN is formed by the fusion of one haploid male gamete (n) with two haploid polar nuclei (n + n), resulting in a triploid (3n) nucleus in most angiosperms.

Thus, the mismatch is (C) Synergids - Diploid, as synergids are actually haploid cells.

The formation of the Primary Endosperm Nucleus (PEN) is a key event in the process of double fertilization, which is unique to angiosperms.

Let's review the structure of a typical female gametophyte (embryo sac) in angiosperms:

• It is usually a 7-celled, 8-nucleated structure.
• It contains:
  • The egg apparatus at the micropylar end (consisting of one egg cell and two synergids).
  • Three antipodal cells at the chalazal end.
  • A large central cell containing two polar nuclei.

During double fertilization:

1. One male gamete (haploid, ) fuses with the egg cell (haploid, ) to form the diploid zygote ( ). This process is called syngamy and leads to embryo development.
2. The second male gamete (haploid, ) travels to the central cell and fuses with the two polar nuclei (each haploid, ) located within it. This fusion event, involving three haploid nuclei ( ), is called triple fusion.

The product of triple fusion is the Primary Endosperm Nucleus (PEN), which is typically triploid ( ). This nucleus is formed within the large central cell, which subsequently becomes the Primary Endosperm Cell. The PEN undergoes mitotic divisions to form the endosperm, a nutritive tissue for the developing embryo.

Therefore, the cell of the female gametophyte that is involved in the formation of the PEN (by hosting the triple fusion event) is the Central cell.

Pollination by water is known as hydrophily. It is relatively rare in flowering plants, even among aquatic species. We need to determine which of the listed aquatic plants uses a different pollination mechanism.

• Vallisneria: This is a submerged freshwater plant. It exhibits epihydrophily, where male flowers detach, float to the water surface, and pollinate the female flowers which reach the surface via long stalks. It is pollinated by water.
• Hydrilla: Similar to Vallisneria, Hydrilla is a submerged freshwater plant that also typically uses water for pollination (epihydrophily). It is pollinated by water.
• Water hyacinth (Eichhornia): This is a free-floating aquatic plant. Its flowers are large, colorful, and emerge above the water surface on an inflorescence stalk. These characteristics are typical of plants pollinated by insects (entomophily) or sometimes wind (anemophily). Water hyacinth relies primarily on insect pollinators. It is not pollinated by water.
• Zostera (Seagrass): This is a submerged marine plant. It exhibits hypohydrophily, where pollination occurs entirely underwater. The pollen grains are long and ribbon-like, carried by water currents to the feathery stigmas. It is pollinated by water.

Therefore, the aquatic plant among the options that does not show pollination by water is Water hyacinth.

Let's analyze each statement regarding megasporogenesis and female gametophyte development in angiosperms:

"Only one megaspore present towards chalazal end remains functional."

• During megasporogenesis, the diploid megaspore mother cell (MMC) undergoes meiosis to produce four haploid megaspores, usually arranged in a linear tetrad.
• In the most common type of embryo sac development (Polygonum type), three of these megaspores, typically those towards the micropylar end, degenerate.
• The single megaspore located at the chalazal end remains functional and develops into the female gametophyte (embryo sac).
• This statement is correct.

"3 megaspore present towards chalazal end degenerate gradually."

• As explained above, usually only one megaspore is present at the chalazal end, and it is the functional one. The three megaspores that degenerate are typically located towards the micropylar end.
• This statement is incorrect.

"Each megaspore mother cell, directly develops into a megaspore."

• The megaspore mother cell (MMC) is diploid ( ). It undergoes meiosis (a reductional division) to produce four haploid ( ) megaspores.
• It does not directly develop into a single megaspore; it divides to form four.
• This statement is incorrect.

"Each female gametophyte is 7-celled & 7-nucleated structure."

• The typical mature female gametophyte (embryo sac) in angiosperms develops from the functional megaspore through mitotic divisions.
• It consists of an egg apparatus (one egg cell and two synergids) at the micropylar end, three antipodal cells at the chalazal end, and a large central cell containing two polar nuclei.
• Counting the cells: 1 egg + 2 synergids + 3 antipodals + 1 central cell = 7 cells.
• Counting the nuclei: 1 (egg) + 2 (synergids) + 3 (antipodals) + 2 (polar nuclei in central cell) = 8 nuclei.
• Therefore, the typical structure is 7-celled and 8-nucleated.
• This statement is incorrect.

The only correct statement among the given options is: Only one megaspore present towards chalazal end remains functional.

Let's analyze each statement:

Statement 1: Innermost layer of microsporangium is tapetum.

• A typical microsporangium (pollen sac) in an angiosperm anther has several wall layers surrounding the central sporogenous tissue.
• These layers, from the outside inwards, are: the Epidermis, the Endothecium, the Middle layers, and the Tapetum.
• The Tapetum directly surrounds the sporogenous tissue (which develops into pollen mother cells and subsequently pollen grains).
• Therefore, the Tapetum is indeed the innermost wall layer of the microsporangium.
• Statement 1 is correct.

Statement 2: Cells of tapetum possess dense cytoplasm more than one nucleus and nourishes developing pollen grains.

• The primary function of the tapetum is to provide nourishment to the developing microspores or pollen grains. This part is correct.
• To perform this nutritive function effectively, tapetal cells are metabolically highly active and are characterized by having dense cytoplasm. This part is correct.
• Tapetal cells often undergo abnormal mitotic divisions where nuclear division occurs without cytokinesis (cell division), leading to a multinucleate condition (having more than one nucleus per cell) or polyploidy. This part is correct.
• Therefore, Statement 2 accurately describes the key features and function of tapetal cells.
• Statement 2 is correct.

Conclusion:

Since both Statement 1 and Statement 2 are correct descriptions related to the microsporangium and its tapetal layer, the correct option is that Both Statements 1 & 2 are correct.

Analysis of the Assertion:

The assertion states: "In Bryophytes & Pteridophytes the number of male gametes produced is several thousand times the number of female gametes produced."

• In both Bryophytes (like mosses, liverworts) and Pteridophytes (like ferns), reproduction involves distinct male and female reproductive structures.
• The male reproductive structure, the antheridium, produces numerous motile male gametes called antherozoids (or spermatozoids).
• The female reproductive structure, the archegonium, typically produces a single, non-motile female gamete called the egg (or oosphere).
• Since each antheridium releases many antherozoids, and each archegonium contains only one egg, the total number of male gametes produced by a plant or population of plants is vastly greater than the number of female gametes.
• Therefore, the assertion is correct.

Analysis of the Reason:

The reason states: "Large number of male gametes fail to reach the female gametes during transport."

• Fertilization in both Bryophytes and Pteridophytes requires water.
• The motile antherozoids are released into the external environment (usually a film of water) and must swim towards the archegonium to reach the egg.
• This transport process is subject to environmental factors and chance. Many antherozoids may get washed away, dry out, be consumed, or simply fail to locate the chemical signals guiding them to the archegonium.
• Consequently, a significant proportion of the male gametes produced do not succeed in reaching a female gamete.
• Therefore, the reason is correct.

Relationship between Assertion and Reason:

• The production of a vastly larger number of male gametes (Assertion) is an evolutionary strategy to compensate for the high probability of loss during transport (Reason).
• By producing thousands of male gametes for every female gamete, the chances of at least one male gamete successfully reaching and fertilizing the egg are significantly increased, despite the inefficiency of the water-dependent transport mechanism.
• Thus, the reason provides a valid explanation for the assertion.

Conclusion:

Both the Assertion and the Reason are correct statements, and the Reason correctly explains the Assertion.

Therefore, the correct option is: Both Assertion and reason are correct.

Dioecious plants are those in which the male and female reproductive organs are present on separate plants.

In the case of papaya, individual plants can be either male or female, and both male and female flowers are produced on separate plants.

Therefore, the correct answer for an example of a dioecious plant is (A) Papaya.

Step 1: Understanding Ploidy Changes After Fertilization After fertilization in plants, the egg cell and the central cell are the ones that undergo changes in ploidy:

• The egg cell is haploid (n) before fertilization and, after fertilization by the sperm, it becomes a diploid (2n) zygote.
• The central cell, which contains two polar nuclei, also undergoes fertilization by the second sperm cell, resulting in the formation of a triploid (3n) cell. This will give rise to the endosperm.

Step 2: Analyzing the Answer Choices

• Egg cell and central cell (Option A) is the correct answer because both of these cells undergo ploidy changes after fertilization.
• Other options, such as synergids, antipodals, and central cell, are not directly involved in this process of ploidy change.

The correct answer is (A) : Egg cell and central cell.

• Most species of bamboo flower only once in a lifetime. This phenomenon is known as gregarious flowering. After flowering, the bamboo typically dies. The flowering period for bamboo species can range from 10 to 120 years depending on the species.
• This rare event of flowering only once during their lifetime is a significant characteristic of bamboo plants.

The correct answer is (D) : Once in lifetime.

• The primary endosperm nucleus is formed during the process of double fertilization in angiosperms. It results from the fusion of two polar nuclei and one male gamete (sperm cell).
• This fusion creates the primary endosperm nucleus, which later develops into the endosperm tissue, providing nourishment to the developing embryo.

The correct answer is (B) : Two polar nuclei and one male gamete.

• In Bryophyllum, adventitious buds (buds that arise in an unusual place) typically form at the notches in the leaf margin. These buds can then grow into new plants.
• This unique method of vegetative reproduction is a common feature in some succulent plants like Bryophyllum.

The correct answer is (C) : Notches in the leaf margin.

Here's the step-by-step solution:

1. Identify the given information:
   • Number of stamens in the flower = 10
   • Structure of each anther = Bilobed and dithecous
   • Number of Pollen Mother Cells (PMCs) per microsporangium = 5
2. Determine the number of microsporangia per anther:
   • A bilobed anther has 2 lobes.
   • A dithecous anther means each lobe has 2 thecae (microsporangia).
   • Therefore, the number of microsporangia in one anther = microsporangia.
3. Calculate the total number of microsporangia in the flower:
   • The flower has 10 stamens, and each stamen has one anther.
   • Total microsporangia = (Number of stamens) (Microsporangia per anther)
   • Total microsporangia = microsporangia.
4. Calculate the total number of Pollen Mother Cells (PMCs) in the flower:
   • Each microsporangium contains 5 PMCs.
   • Total PMCs = (Total microsporangia) (PMCs per microsporangium)
   • Total PMCs = PMCs.
5. Determine the number of pollen grains produced per PMC:
   • Each Pollen Mother Cell (PMC) is diploid and undergoes meiosis to produce 4 haploid microspores (pollen grains).
   • Pollen grains produced per PMC = 4.
6. Calculate the total number of pollen grains produced by the flower:
   • Total pollen grains = (Total number of PMCs) (Pollen grains produced per PMC)
   • Total pollen grains = pollen grains.

Therefore, the total number of pollen grains produced by the flower is 800.

The correct answer is (D) : 800.