Sexual Reproduction in Flowering Plants: Flowering plants, often known as angiosperms, reproduce sexually. Plant reproduction is primarily centred on the flower, which contains both male and female gametes. Although some components of flowers are sterile, they all help in the reproduction process.
How do flowering plants reproduce sexually?
Flowers contain both male and female gametes and are the reproductive components of a plant. In biology, the male reproductive component is called androecium, while the female reproductive part is called gynoecium. Both of these sections are frequently found in a single flower, and only very rarely in two distinct flowers from the same plant or two different plants.
Filament, anther, and pollen grains are all elements of the male reproductive organ. Microsporogenesis is the process through which male gametophytes are generated. The stigma style and ovary make up the female reproductive organ. The ovum or eggs are stored in the ovary of the flower. Megasporogenesis is the process by which the ovum is formed.
A plant’s reproductive organs
Androecium
The androecium is the male reproductive organ of plants. Androecium’s primary function is pollen generation and storage. The stamen is an androecium unit. Numerous stamens make up the androecium. The filament and the anther are the two sections of a stamen.
Filament-
Filament mimics the stalk of a flower and serves as a support for another.
Anther-
An anther is a pollen-producing component of a flower that is oval. Microsporangia are found in both chambers of each anther. Four microsporangia reside at the four corners of an anther.
Microsporogenesis
The microsporangium’s cells split, resulting in the formation of another microsporangium. Microsporogenesis is the process of meiotic division resulting in the development of microspores or pollen grains inside the microsporangia. Microspores are produced by the mother cells of microspores. In a tetrad, microspores are usually arranged in a tetrahedral or isobilateral pattern. Microspores are responsible for male gametophyte development. The male gamete’s inner layer is made up of cellulose and pectose, while the outer layer is made up of sporopollenin.
Gynoecium
The gynoecium is the female reproductive organ of plants. It is responsible for the internal production of ovules, which result in the formation of an egg. The stigma, style, and ovary are the three components of the gynoecium.
Stigma
The stigma is the portion of a carpel that germinates pollen.
Style-
The stigma and ovary are connected by a tube-like filament known as the style. It aids pollen transport from the stigma to the ovary.
Ovary-
The ovules are formed in a tiny chamber where the ovary operates. Gynoecium comes in a variety of forms.
- Monocarpellary: It consists of one carpel.
- Bicarpellary: It consists of two carpels.
- Tricarpellary: It consists of three carpels.
- Multicarpellary: It consists of many carpels.
The gynoecium can be apocarpous or syncarpous. Carpels are free in apocarpous gynoecium. Syncarpous gynoecium, on the other hand, has the carpels fused together.
Megasporogenesis
The production of megaspores within the megasporangium is known as megasporogenesis. Megaspores develop from ovules through the process of meiosis. Megaspores are responsible for the production of the female gametophyte. One megaspore transforms into a gametophyte, while the decay of the other. The embryo sac grows from the basal megaspore. Microsporogenesis and megasporogenesis produce male and female gametes, which are the basic units of sexual reproduction in flowers.
Pollination
Pollination is a process in which pollen grains are transferred from the anther to the stigma. Self-pollination and cross-pollination are the two types of pollination.
1. Self-Pollination
Pollen grains pass from the anther of a flower to the stigma of the same or genetically similar flower, resulting in self-pollination. It is mostly divided into two types:
The flower is pollinated by its own pollen in this sort of pollination. Three procedures can cause it:
Homogamy is a phenomenon in which the anthers and stigmas of flowers are exposed. Mirabilis is a good example of this.
Cleistogamy – Cleistogamous flowers have closed anthers and stigmas, thus their anthers and stigmas are hidden. It’s found in Balsam and Oxalis.
Pollen grains from one bloom are transmitted to the stigma of another flower that is either genetically identical plant in this sort of pollination.
2. Cross-Pollination
Cross-pollination is defined as pollination in which pollen grains are transmitted from one flower’s anther to the stigma of a genetically distinct plant. Wind pollination (Anemophily), water pollination (Hydrophily), insect pollination (Entomophily), bird pollination (Ornithophily), bat pollination (Chiropterophily), and other pollinating agents are commonly used.
Fertilization
occurs when pollen grains reach the ovary after pollination. To produce a zygote, the male gamete unites with the female gamete, the ovule. Fertilized ovules convert to seed, and the ovary becomes a fruit. Double fertilisation occurs in angiosperms when two acts of fertilisation occur at the same time.
