Sexual Reproduction in Flowering Plants: An Overview and Explanation

We notice creatures all around us because they reproduce, which is self-evident. It's unlikely that we would have recognized the existence of a single, non-reproducing member of a species. The enormous number of organisms belonging to a single species is what draws our attention towards them. Now, how can we tell if two different organisms are members of the same species? We usually say this because they resemble each other. Hence, we can say that reproducing organisms produce new individuals that are in some way similar to themselves just like- Flowers.

Read More: Class 12 Reproduction

Sexual reproduction in flowering plants

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Flowering plants, often known as angiosperms, reproduce in a sexual manner. Plant reproduction is primarily centered on the flower, which contains both male and female gametes. Although some components of flowers are sterile, but they all help in the reproduction process.

Angiosperms' reproductive organs are found in the flower. Sepals, petals, stamens, and pistils are the different sections of a flower. The germ cells are contained in the stamens and pistil, which are the reproductive portions of a flower. The flower can be unisexual (papaya, watermelon) if only the stamens or pistil are present, or bisexual (Hibiscus, mustard) if both stamens and pistil are present. 

• The male reproductive portion of the flower, the stamen, generates yellowish pollen grains. You've probably seen the yellowish powder that sticks to our hands when we touch a flower's stamen. 
• The female reproductive portion of a flower is the pistil, which is found in the center. The ovary, which is bloated at the bottom, the style, which is elongated in the middle, and the stigma, which is sticky at the end, are the three parts. 
• Ovules are found in the ovary, and each ovule contains an egg cell. 
• The female gamete in the ovule combines with the male germ-cell formed by a pollen grain. 
• The zygote, which is capable of developing into a new plant, is formed through the fusion of germ cells or fertilization. 
• As a result, pollen must be moved from the stamen to the stigma.

Read More: Difference Between Cross Pollination and Self Pollination

Reproductive Structure of a Flower

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• Androecium

It is the third whorl of a flower's male reproductive portion, which consists of stamens. Each stamen is made up of two parts: 

1. Anther 
2. Filament. 

The filament supports the tip of the anther. Pollen is created here, by meiosis and finally vanishes.

1. Anther: An anther is a four-lobed sac-like structure that produces pollen.
2. Filaments: Filaments are thread-like structures that are attached to the anther and help to keep it in place.

Microsporangia is the transverse part of an anther that creates a pollen sac. Pollen grains are contained in the pollen sac.

• Gynoecium

It is the flower's final whorl and the female reproductive organ. It is made up of pistil and is located in the center of the thalamus. The style, ovary, and the stigma make up the pistil. Internally, the ovary creates ovules. Ovules form megaspores, which grow into female gametophytes, through the process of meiosis. Egg cells are formed as a result.

Gynoecium can be:

1. Monocarpellary: It consists of a single pistil. For eg., peas & beans.
2. Multicarpellary: There are many pistils in this gynoecium.
3. Syncarpous: It's the combined pistil gynoecium. Tomatoes and cucumbers are examples.
4. Apocarpous: It's a gynoecium that has a free pistil. Lotus Vinca, for example.

Pistil:- Each pistil has three parts:

1. Ovary: The ovary is a storage chamber for ovules (eggs) awaiting fertilization.
2. Stigma: It's linked to the carpel's top, where pollen from other flowers lands.
3. Style: The ovary and the stigma are connected by a tubular structure. It is in charge of transporting pollen from the stigma to the ovary as well as keeping the stigma in place.

Pollination

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Pollination is an ecological activity that all flowering plants engage in. The developed pollen grains are transmitted from the anther to the stigma in this process, which allows flowering plants to reproduce sexually.

Pollination can be divided into two categories: 

• Self-Pollination: The pollen grains from the anther are deposited on the stigma of the same flower, or another flower on the same plant, in this procedure.

• Cross-Pollination: When pollen grains from one flower's anther are transported to the stigma of another flower of the same species, this is known as pollen transfer.

Process of Self-Pollination

Self-pollination happens when pollen is transferred from one flower to another within the same flower. Cross-Pollination, on the other hand, occurs when pollen is transferred from one flower to another. 

• Pollen is transferred from one flower to another by forces like wind, water, and animals.
• The pollen must reach the female germ cells in the ovary after landing on an appropriate stigma. 
• A tube grows out of the pollen particle and passes through the style to the ovary to do this. 
• The zygote splits multiple times after fertilization to produce an embryo within the ovule. 
• The ovule develops a thick covering and transforms into a seed over time. 
• The ovary develops quickly and ripens into a fruit. 
• The petals, sepals, stamens, style, and stigma may shrink and fall off meanwhile. 
• The seed contains the embryo, which develops into a seedling under the appropriate conditions. It's known as germination.

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Fertilization

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• Pollen is delivered to the ovary by the pollen tube after pollination. 
• One of the male gametes unites with the ovule, or female gamete, after reaching the ovary (fertilization), and the other combines with the polar nuclei. 
• When a gamete combines with eggs, it produces a zygote, which grows into an embryo over time.
• The endosperm nucleus is formed when the second gamete combines with the polar nuclei. 
• The embryo receives nutrients from it. 
• Ovules become seeds after fertilization, while the ovary develops into the fruit.