flowers

The stamen is the male reproductive organ of a flower. It consists of an anther and a filament. The anther contains pollen sacs where pollen grains develop, while the filament supports the anther and positions it for pollen release. The carpel is the female reproductive organ; petals and sepals mainly assist in attraction and protection.

The anther is the pollen-producing part of the stamen. It contains microsporangia, or pollen sacs, in which diploid microspore mother cells undergo meiosis and produce haploid microspores. These develop into pollen grains. Egg cells form in ovules, while fruits and seed dispersal are associated with later reproductive events, not the main function of the anther.

A typical anther is bilobed, meaning it has two pollen-bearing lobes. Each lobe normally contains two microsporangia, also called pollen sacs. Thus, the total number in one complete anther is 2 × 2 = 4. Option A counts only one lobe, while six and eight are not the usual number in a typical anther.

In the anther, microspore mother cells undergo meiosis and produce haploid microspores. Each microspore develops into a pollen grain, which represents the male gametophyte in angiosperms. Egg cells, synergids, and antipodal cells are parts of the female gametophyte inside the ovule, so they cannot develop into pollen grains.

The exine is mainly made of sporopollenin, an exceptionally resistant biological polymer. It protects pollen from desiccation, decomposition, enzymes, and other environmental stresses during transfer from anther to stigma. The inner intine contains mainly cellulose and pectin. Cellulose, lignin, and chitin are therefore not the best answer for the principal material of the exine.

Autogamy is the transfer of pollen from the anther to the stigma of the same flower, so option B is correct. Geitonogamy occurs between two flowers on the same plant, while xenogamy occurs between flowers on different plants of the same species. Double fertilisation is a fertilisation event after pollination, not a type of pollen transfer.

Geitonogamy is pollination between two different flowers of the same plant. It appears functionally similar to cross-pollination because pollen moves between flowers, but genetically it is self-pollination because both flowers belong to one plant. Autogamy occurs within one flower, xenogamy between different plants of the same species, and cleistogamy in closed flowers.

Pollination carried out by wind is called anemophily. Wind-pollinated flowers commonly produce abundant, light, and dry pollen that can travel on air currents; their stigmas may be exposed or feathery to trap pollen. Hydrophily uses water, entomophily uses insects, and ornithophily uses birds, so those options describe different agents.

Pollination by water is called hydrophily. It occurs in some aquatic plants, where water carries pollen to the stigma or to the female flower. Anemophily is pollination by wind, entomophily by insects, and cleistogamy is self-pollination within flowers that remain closed. Thus, only hydrophily identifies the water-based pollination agent.

Pollination by insects such as bees, butterflies, and beetles is called entomophily. Such flowers often have colour, fragrance, nectar, or suitable shapes that attract insects. Hydrophily is water pollination, anemophily is wind pollination, and ornithophily is bird pollination. Therefore, entomophily is the only option matching insects as the pollinating agent.

Wind transfer is random, so only a small fraction of pollen reaches a suitable stigma. Wind-pollinated flowers compensate by producing very large quantities of light, dry pollen that can be carried by air. Colourful petals, nectar, and strong fragrance usually attract animal pollinators, especially insects, and are not the typical adaptations for anemophily.

Insect-pollinated flowers commonly have colourful petals, fragrance, and often nectar. These features attract insects, which pick up pollen while feeding and carry it to another stigma. Very light, dry pollen is more typical of wind pollination. Cleistogamy refers to self-pollination in flowers that remain closed, so it is not the general insect-pollination feature.

After landing on a compatible stigma, a pollen grain germinates and produces a pollen tube. The tube grows through the style toward the ovule and carries the male gametes to the embryo sac. The ovule later develops into a seed, the ovary into a fruit, and the zygote into an embryo. Therefore, pollen tube is the immediate product asked for here.

The small opening left in one or both integuments of an ovule is called the micropyle. The pollen tube commonly enters the ovule through this opening during fertilisation. The chalaza is the end opposite the micropyle, the nucellus is internal ovular tissue, and the embryo sac is the female gametophyte containing the egg apparatus and central cell.

The megaspore mother cell is diploid and undergoes meiosis to produce four haploid megaspores, usually arranged as a tetrad. Meiosis reduces the chromosome number by half and creates reproductive spores. Mitosis generally maintains chromosome number, while fertilisation joins gametes and pollination transfers pollen; neither produces megaspores from this mother cell.

Double fertilisation is a defining reproductive feature of angiosperms. One male gamete fuses with the egg in syngamy to form the diploid zygote. The other fuses with the two polar nuclei in triple fusion to form the usually triploid primary endosperm nucleus. These two linked fusions distinguish angiosperm reproduction from the usual patterns in the other listed groups.

Syngamy is the fusion of one male gamete with the egg cell. It produces a diploid zygote, which later develops into the embryo. Fusion of the other male gamete with the two polar nuclei is called triple fusion and contributes to endosperm formation. Synergids and antipodal cells do not participate in syngamy, so option A is unambiguous.

Triple fusion occurs when one male gamete fuses with the two polar nuclei in the central cell of the embryo sac. The resulting primary endosperm nucleus is usually triploid and begins endosperm development. The egg-cell fusion is syngamy, while the two polar nuclei may first fuse with each other to form a secondary nucleus but that event alone is not triple fusion.

Syngamy is the fusion of a male gamete with the egg cell, and its immediate product is the diploid zygote. The zygote later undergoes divisions and differentiates into an embryo. Endosperm begins after triple fusion involving the second male gamete and polar nuclei. Pollen grains are formed earlier in the anther, so they cannot be the product of syngamy.

Triple fusion produces the primary endosperm nucleus, usually with triploid chromosome number. This nucleus divides and develops into endosperm, a nutritive tissue that supports the developing embryo, often by supplying stored nutrients. The embryo develops from the zygote, the seed coat from integuments, and the anther is a pre-existing floral organ.

Sporopollenin is the main material of the pollen exine and is highly resistant to decomposition, desiccation, enzymes, and environmental stress. This durable layer protects pollen during transport. Germ pores are regions where exine is thin or absent, allowing the pollen tube to emerge. Cellulose and pectin are associated mainly with the intine, not the exine.