Where are the generative cell present in the male gametophyte of an angiosperm? Mention the function of it.

The male gametophyte of an angiosperm is the pollen grain. It is the haploid cell that undergoes mitotic division to form a small generative cell and a large vegetative cell. Hence, the generative cell is located in the pollen grain. During development, the generative cell gives rise to male gametes through mitotic division.

Self pollination is fully ensured if

The style is longer than the filament

The time of pistil and anther maturity is different

Where are the sporopollenin present in the male gametophyte of an angiosperm? Mention the function of it.

Pollen grains or male gametophyte is made up of two wall layers: outer exine and inner intine. The exine is the outermost layer that is made up of the most resistant organic material called sporopollenin. Hence, sporopollenin is present in the exine of the male gametophyte of an angiosperm. It can withstand high temperatures and strong acids and alkali. No enzyme that degrades sporopollenin is so far known. Therefore, it provides protection to the pollen grains and protects the male gametes located in the pollen grains.

Where are the germ pore present in the male gametophyte of an angiosperm? Mention the function of it.

Pollen grains are the male gametophyte in angiosperms. It is covered by outer exine and inner intine. The exine is made up of sporopollenin. The place where exine and sporopollenin are absent is called germ pore. It is the site from which the pollen tube emerges and the contents of the pollen grain move into the pollen tube.

Explain the events up to double fertilization after the pollen tube enters one of the synergids in an ovule of an angiosperm.

The process of transfer of pollen grains from the mature anther to the stigma of a flower is called pollination. After germination of pollen grains, the pollen tube penetrates the solid part of the stigma and style and enters one of the synergids in the ovule inside the ovary. Each pollen grain carries two male gametes. It releases two male gametes into the embryo sac. One of the male gametes moves towards the egg cell and fuses with it to form a diploid zygote. This process is called generative fertilization or syngamy. The other male gamete fuses with the two polar nuclei (or a diploid secondary nucleus formed by the fusion of polar nuclei) located in the central cell of the embryo sac and forms a triploid primary endosperm nucleus (PEN). This is termed as a triple fusion or vegetative fertilization. Thus, in angiosperm, two acts of fertilization occur in the same embryo sac. This phenomenon is called double fertilization.

Describe any two devices in a flowering plant which prevent both autogamy and geitonogamy.

Autogamy and geitonogamy are the types of self-pollination. Autogamy is the transfer of pollen grain from the anther to the stigma of the same flower. Geitonogamy is the pollination between different flowers within a plant. Flowering plants developed different outbreeding devices to prevent self-pollination (both autogamy and geitonogamy). (i) Self-incompatibility (self sterility): It is the genetic mechanism. The mature pollen grains fall on the receptive stigma of the same flower or different flower within the same plant but fail to produce a pollen tube due to the presence of similar self-sterile genes. (ii) Dioecious plants: The male and female flowers are produced by different plants. Thus, the plant is either male or female. The male plant only produces pollen grains or male gametes and the female plant produces an egg. Thus, in dioecious plants, both autogamy and geitonogamy did not occur.