Sexual Reproduction in Flowering Plants

The process of formation of microspores from a pollen mother cell (PMC) through meiosis is called microsporogenesis.

The correct developmental sequence related to microsporogenesis will be -

Sporogenous tissue $(B) \rightarrow$ Pollen mother cell $(D) \rightarrow$ Microspore tetrads $(A) \rightarrow$ Pollen grains $(C)$

Synergid is haploid, Zygote is diploid, Central cell initially contains two polar nuclei which fuse just before fertilization to form a secondary nucleus $(2 n)$.

Primary endosperm cell (PEC) is triploid.

Transfer of pollen grains from anther to stigma of a different plant is known as Xenogamy. This is the only type of pollination which brings genetically different types of pollen grains to stigma. Cleistogamy flowers are invariably autogamous.

Non-albuminous seeds have no residual endosperm as it is completely consumed during embryo development. E.g. Pea.

Wheat, maize and barley are the examples of albuminous seeds.

Synergids guide the entry of pollen tube for fertilizing the eggs, in a typical angiospermic embryo sac.

The endosperm is triploid, if the diploid chromosome number of typical angiosperm is 36

$ \begin{aligned} \text { So, }3 n & =n+n+n \\ & =18+18+18 \\ & =54 \end{aligned} $

A typical anther is bilobed with each lobe having two theca i.e. they are dithecous.

A typical Angiosperm embryo sac, at maturity is 7 -celled and 8 nucleate.

Polar nuclei are situated below the egg apparatus in the large central cell.

Three cells are grouped together at micropylar end and constitute the egg apparatus.

Hence, A is true but R is false.

Both wind and water pollinated flowers are not very colourful and do not produce nectar, this is because they rely on wind and water to carry their pollen. Wind and water pollinated flower do not need to attract insect, so they did not evolve to produce bright coloured flower.

To develop a mature female gametophyte, or embryo sac, from a megaspore mother cell in an angiosperm plant, the process involves a sequence of cell divisions. Initially, the megaspore mother cell undergoes one meiotic division. This meiotic division results in the formation of four haploid megaspores. Out of these, typically only one megaspore survives and continues to develop, while the others degenerate.

Following the meiotic division, the surviving megaspore undergoes three successive rounds of mitotic division, without cytokinesis. This series of mitotic divisions leads to the formation of an eight-nucleate structure. Subsequently, these nuclei organize to form a mature female gametophyte, or embryo sac, which is ready for fertilization.

Thus, the complete development from a megaspore mother cell to a mature female gametophyte in an angiosperm plant involves 1 meiotic division followed by 3 mitotic divisions. This sequence ensures the proper formation of the structures necessary for reproduction in flowering plants.

Statement I says that fig fruit is a non-vegetarian fruit because it has enclosed fig wasps in it.

This statement is incorrect in the biological sense used in NCERT. A fig is a fruit of a plant, and it is not classified as "non-vegetarian." Although fig wasps are associated with figs and may enter the fig during pollination, the statement as given is not scientifically correct.

Statement II says that fig wasp and fig tree show a mutual relationship because the fig wasp completes its life cycle in the fig fruit and the fig gets pollinated by the wasp.

This statement is correct. This is a classic example of mutualism, where both organisms benefit:

• the fig wasp gets a place to reproduce and complete its life cycle,

• the fig tree gets pollinated.

So, the correct answer is:

$\boxed{\text{Option B: Statement I is incorrect but Statement II is correct}}$

Both statements are correct, and the multinucleate condition of tapetal cells (R) directly explains why they have dense cytoplasm and multiple nuclei (A)—it boosts their synthetic and secretory activity to nourish microspores.

Answer: Option C

The correct one is Option C:

A → II

B → III

C → IV

D → I

Explanation:

• Scutellum is the cotyledon of a monocot seed (II).

• Non-albuminous seeds (endosperm absent at maturity) include groundnut (III).

• Epiblast is a vestigial (rudimentary) cotyledon (IV).

• Perisperm arises from the persistent nucellus (I).

The correct answer is Option A: Nucellus. Here's why:

The ovule is the structure within the ovary of a flower that develops into a seed after fertilization. Let's break down the parts of an ovule and their functions:

1. Nucellus:

• This is the central core of the ovule.
• It is composed of parenchyma cells, which are specialized cells that store nutrients.
• The nucellus provides nourishment to the developing embryo sac (female gametophyte) and ultimately the developing embryo.

2. Integuments:

• These are protective layers that surround the nucellus.
• They develop into the seed coat (testa) after fertilization, protecting the seed.

3. Placenta:

• This is a tissue within the ovary that connects the ovule to the ovary wall.
• It plays a crucial role in the transport of nutrients and water to the developing ovule.

4. Funicle:

• This is the stalk that attaches the ovule to the placenta.

In summary, the nucellus is the part of the ovule that specifically stores reserve food materials to support the development of the embryo within the seed.

The correct answer is Option C: Exine layer. Here's why:

Pollen grains are incredibly resilient and often survive fossilization due to their tough outer layer called the exine. Let's break down why the exine is so important:

Exine:

• Structure: The exine is composed of a complex, highly resistant polymer called sporopollenin. This substance is incredibly durable, resistant to degradation by chemicals, enzymes, and even extreme temperatures.
• Function: The exine acts as a protective barrier for the pollen grain, shielding it from environmental damage and ensuring its survival during transport to the stigma of a flower.
• Preservation: The exine's robust nature allows it to withstand the pressures of fossilization, making it a common element in the fossil record.

Let's examine the other options:

Option A: Epidermal layer: While the epidermal layer of a plant does contribute to its structure, it's not the primary reason for pollen preservation.

Option B: Tapetum: The tapetum is a layer of cells within the anther that nourishes developing pollen grains. It doesn't directly contribute to the fossil record.

Option D: Intine layer: The intine is the inner layer of the pollen grain, composed of cellulose and pectin. It's less resistant to decay than the exine and is less likely to be preserved as a fossil.

In conclusion, the exine's unique composition and robust nature make it the crucial factor in the preservation of pollen grains as fossils.

The given figure is of the false fruit, strawberry and ‘x’ represents the thalamus.

To determine the correct set of statements, we need to analyze each statement individually based on the characteristics of water-pollinated plants and specific examples given:

Statement A: "The flowers of Vallisneria are colourful and produce nectar."

This statement is incorrect. Vallisneria is an example of a water-pollinated (hydrophilous) plant. Unlike insect-pollinated flowers, which are often colorful and produce nectar to attract pollinators, water-pollinated flowers typically lack bright colors and nectar because they do not need to attract insects or other animals. Vallisneria flowers are small and inconspicuous.

Statement B: "The flowers of water lily are not pollinated by water."

This statement is correct. Water lilies are typically pollinated by insects, not by water. The large and colorful flowers of water lilies are adapted to attract insect pollinators, contrasting starkly with the typical features of water-pollinated flowers.

Statement C: "In most of water-pollinated species, the pollen grains are protected from wetting."

This statement is correct. In water-pollinated plants, the pollen grains often have a covering or are structured in a way that prevents them from becoming waterlogged and sinking. This adaptation allows them to float on the water's surface and reach the female parts of other plants.

Statement D: "Pollen grains of some hydrophytes are long and ribbon like."

This statement is correct. In some water-pollinated plants, such as seagrasses (e.g., Zostera), the pollen grains are indeed elongated and ribbon-like, which helps them to be transported more effectively by water currents.

Statement E: "In some hydrophytes, the pollen grains are carried passively inside water."

This statement is also correct. Many hydrophytes have pollen grains that are transported by water currents, rather than being actively carried by animal pollinators or the wind. This passive transport is typical in water-pollinated species.

Based on the analysis, Statements B, C, D, and E are correct, while Statement A is incorrect. Therefore, the correct answer is:

Option D: B, C, D, and E only

The given diagram shows a wind pollinated plant showing compact inflorescence and well exposed stamens.

Stamens are exposed so complete autogamy does not occur.

In some members of Rosaceae, Solanaceae, Leguminosae pollen maintain viability for months.

In some cereals like rice and wheat belonging to Poaceae family to pollen loose viability within 30 minutes of their release.

The correct answer is :

Option A : Geitonogamy

Explanation :

Geitonogamy refers to the transfer of pollen from the anther of one flower to the stigma of another flower on the same plant. While this process involves pollination between different flowers, because it occurs on the same plant, it does not increase genetic diversity.

Here's a quick overview of the other terms :

• Xenogamy refers to the transfer of pollen grains from the anther of a flower to the stigma of a flower on a different plant. This is cross-pollination and promotes genetic diversity.




• Autogamy refers to the transfer of pollen from the anther to the stigma of the same flower. This is self-pollination.




• Cleistogamy refers to a type of automatic self-pollination where the flowers do not open and are therefore self-pollinated before they open.

The process of female gametophyte formation in angiosperms, also known as megagametogenesis, involves several steps :

1. 1. Meiotic division in the megaspore mother cell (megasporocyte) - This division leads to the production of four haploid cells, which are the megaspores.




2. 2. Degeneration of three of the four megaspores - Typically, three of these megaspores degenerate, leaving a single functional megaspore.




3. 3. Successive mitotic divisions (not meiotic) in the functional megaspore - These divisions are typically free-nuclear (the nuclear membrane does not break down between divisions), and result in a multinucleate cell.




4. 4. Migration of the nuclei to the cell periphery and formation of cell walls - This results in the creation of a seven-celled structure known as an embryo sac or female gametophyte.




5. 5. The final structure of the female gametophyte includes an egg apparatus (one egg cell and two synergids), two polar nuclei in the central cell, and three antipodal cells.

Given these steps, the correct sequence of events in the formation of the female gametophyte is :

Option D : (C), (B), (A), (D), (E)

Tassels in the com cob represents stigma and style which wave in the wind to trap pollen grains.

Synergids are the cells of gametophyte and hence these are haploid Zygote is formed by fusion of two gametes and thus it is diploid.

Primary endosperm nucleus is formed by the fusion of diploid secondary nucleus with a male gamete. Therefore, it is triploid.

The correct answer is Option B : A is true but R is false.

Assertion A is true. In gymnosperms, the pollen grains are indeed released from the microsporangium and are typically carried by air currents, a method of pollination known as anemophily.

Reason R is false. Although it's true that air currents carry the pollen grains, the pollen grains do not directly reach the mouth of the archegonia in gymnosperms. Instead, they land on the ovule, where they germinate and form a pollen tube that delivers the male gametes to the egg. Therefore, a pollen tube is formed in gymnosperms, contrary to what Reason R suggests.

Mostly nucellus is consumed after fertilisation due to absorption of food by developing embryo in a seed. Sometimes, the nucellus remains persistent in the seed and is called perisperm.

(b) There is no need to emasculate unisexual flowers of the selected female parent - This statement is correct because unisexual flowers do not have male reproductive parts (stamens), so there is no need to remove anthers (emasculate) to prevent self-pollination.

(c) Emasculated flowers are to be bagged immediately after cross-pollination - This statement is correct because, after cross-pollination with the desired pollen, the flowers need to be bagged to prevent further contamination from unwanted pollen or other pollinating agents.

(d) Emasculated flowers are to be bagged after removal of anthers - This statement is correct. The emasculated flowers should be bagged after anther removal and before cross-pollination. This prevents contamination with unwanted pollen. After cross-pollination, the flowers should be bagged again to avoid any further contamination.

The other options are incorrect :

(a) The female flower buds of plant producing unisexual flowers need not be bagged - This statement is incorrect because even unisexual flowers need to be bagged to prevent contamination from unwanted pollen or other pollinating agents.

(e) Bisexual flowers, showing protogyny, are never selected for cross - This statement is incorrect because protogyny (when the female reproductive part matures before the male reproductive part) can reduce the chances of self-pollination, making these flowers suitable for cross-pollination.

The egg apparatus of an embryo sac consists of one egg cell and two synergids.

Whereas the embryo sac consists of one egg cell, two synergies, three antipodals and two polar nuclei.

As per the question none of the option is correct however considering the composition of embryo sac the correct option should be 2.

Cleistogamous flowers does not open at all. In such flowers autogamy occurs. Lack of cross pollination is a disadvantage of cleistogamy.

Among the animals, insects, particularly bees are the dominant biotic pollinating agents.