Sexual reproduction is the process in which new organisms are created, by combining the genetic information from two individuals of different sexes. The genetic information is carried on chromosomes within the nucleus of specialized sex cells called gametes.
Most of the flowering plants reproduce sexually ultimately producing flowers. Flowers are vital in the process of sexual reproduction. This is why flowers are also referred to as the reproductive part of a plant. The complete flower typically consists of:
The male and the female reproductive structures in flowers, the androecium and the gynoecium differentiates and further undergoes development.
Stamen consists of two parts – filament, the slender and long stalk and the anther, the bilobed structure each lobe having two theca hence they are dithecous
Anther is a tetragonal structure comprising microsporangia situated at the edge, two per lobe
The microsporangia develop into the pollen sacs later on. Microsporogenesis is the formation of microspores through meiosis from a pollen mother cell
Pollen grains are the representation of the male gametophytes. Maturity of the pollen grains is indicated by two cells – vegetative cels and generative cells
The female reproductive part of the flower, the gynoecium may be monocarpellary or multicarpellary. Each pistil consists of – stigma(pollen grains landing site), style(long slender section below stigma) and the ovary(pistil’s bulged section)
The ovarian cavity present in the ovary comprises the placenta from where the megasporangia emerges, commonly referred to as the ovules
The ovule consists of the following structures- funicle, hilum, integuments, micropyle, chalaza, nucellus, embryo sac or the female gametophyte. An ovule is formed from a megaspore
Formation of megaspores from the MMC(megaspore mother cell) is referred to as megasporogenesis
Mostly, one of the four megaspores is functional which develops into the female gametophyte(embryo sac), the rest are degenerate
At maturity, a typical angiosperm embryo sac although depicts 8-nucleated but is 7-celled
Sexual reproduction in Flowering plants is divided into three stages:
Pollination is the act of transferring pollen grains from the male anther of a flower to the female stigma. The goal of every living organism, including plants, is to create offspring for the next generation. One of the ways that plants can produce offspring is by making seeds. Polination is three types:
When pollen grains reach the stigma of a flower's female structures, a pollen grain containing two sperm makes its way into the ovary. One sperm fertilizes one egg, which becomes a diploid zygote. The other sperm fuses with polar nuclei to form endosperm that will nourish the zygote as it matures into a seed.
After pollination and fertilization, carpels develop into the fruit tissue we eat (ovary) and the seeds within (ovules). Fruit development is initiated by growth regulating hormones produced by developing seeds. Flowers with one carpel only require fertilization of one of the two ovules to produce fruit.
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