Sexual Reproduction in Flowering Plants

Sexual reproduction in flowering plants involves the participation of both male and female gametes and takes place through different parts of the flower. The process also relies on external agents like wind, water or insects to transfer pollen for successful fertilisation, making it a coordinated and important biological function.

This Story also Contains

1. Reproductive Structure of Flowering Plants
2. Megasporogenesis and Microsporogenesis
3. Pollination In Flowering Plants
4. Fertilisation in Flowering Plants
5. Embryogeny and Post-Fertilisation Events in Flowering Plants
6. Seed and Fruit
7. Recommended Video on "Sexual Reproduction in Flowering Plants"

The chapter includes many detailed concepts and diagrams and requires time to revise during final preparation. However, it has high importance in competitive exams such as NEET and also in paramedical and pharmacy entrance tests. Therefore, studying this chapter will guarantee you scores in the exams. Sexual Reproduction in Flowering Plants is one of the most important topics in biology.

Reproductive Structure of Flowering Plants

The flower is the reproductive organ of the plant, which includes both the male and female reproductive organs. These gametes are responsible for the reproduction of the plants. Some important parts of the flowering plants are given below:

1. Androecium (Male Reproductive Organ)

• Stamen: Contains filament and anther; helps in pollen production.

  • Filament: A stalk-like structure that supports the anther.

  • Anther: Produces and stores pollen grains (male gametes).

2. Gynoecium (Female Reproductive Organ)

• Carpel / Pistil: Made up of stigma, style, and ovary; responsible for egg production.

  • Stigma: The top part that receives pollen during pollination.

  • Style: Connects stigma to the ovary and helps in transferring pollen.

  • Ovary: Contains ovules where eggs (female gametes) are produced.

Also Read

• Difference between Somatic and Zygotic Embryogenesis

• Difference between Gametogenesis and Embryogenesis

• Dithecous anther

Megasporogenesis and Microsporogenesis

The process of microsporogenesis and megasporogenesis is described below-

• Microsporogenesis is the process by which microspores, which are male gametophytes, are formed from the pollen mother cell inside the microsporangia of the anther.
• Each anther contains four microsporangia arranged in pairs, and each microsporangium has a well-organised structure with multiple layers, such as epidermis, endothecium, middle layers and tapetum inside the microspore.
• All the outer 3 layers help to protect the pollen grains and the inner parts, and the innermost layer, the tapetum, helps in the nourishment of pollen grains.
• The diploid pollen mother cells undergo meiosis to produce a tetrad of four haploid microspores. These microspores mature into pollen grains, which later take part in fertilisation.
• On the other hand, megasporogenesis occurs in the ovule within the megasporangium, also called the nucellus, which is surrounded by protective layers called integuments.
• Inside the nucellus, a single megaspore mother cell undergoes meiosis to produce four haploid megaspores, of which usually only one remains functional.
• This functional megaspore gives rise to the female gametophyte, also known as the embryo sac. The ovule’s structure includes the funicle (stalk), hilum (attachment point), micropyle (opening for pollen entry), and chalaza (base of the ovule), all helping in the development and the fertilisation process.
• Together, microsporogenesis and megasporogenesis ensure the formation of male and female gametes required for sexual reproduction in flowering plants.

Pollination In Flowering Plants

Pollination is an external process that involves the transfer of pollen grains from the anther to the stigma. There are two types of pollination - self-pollination and cross-pollination. There are certain differences between self-pollination and cross-pollination. Both of them are discussed below in the table:

Types of Pollination Based on Pollinating Agents

The abiotic agents of pollination are described below-

1. Entomophily (Pollination by Insects):

• Pollinating agents: Bees, butterflies, moths, beetles, etc.

• Flowers are usually brightly colored with fragrance and nectar to attract insects.

• In entomophily, pollen sticks to the insect’s body and is transferred from one flower to another.

• Example: Sunflower, Rose, Marigold

2. Chiropterophily (Pollination by Bats):

• Pollinating agents: Bats

• The flowers pollinated by the process of chiropterophily are large, dull-colored, and strongly scented, usually blooming at night.

• They produce lots of nectar and have sturdy structures to support bats.

• Example: Kigelia (Sausage tree), Baobab

3. Ornithophily (Pollination by Birds):

• In ornithophily, the pollinating agents are birds like hummingbirds, sunbirds, etc.

• Flowers are brightly colored, especially red or orange, and odourless.

• They have tubular shapes and produce copious nectar.

• Example: Hibiscus, Callistemon (Bottlebrush), Bignonia

Fertilisation in Flowering Plants

Fertilisation occurs when pollen-pistil interaction occurs, and finally when pollen grains reach the ovary. Here, the male gamete combines with the female gamete, the ovule, to form a zygote. The ovary turns into a fruit, and the fertile ovules turn into seeds. Reproduction can also be done separately. They undergo a different process called double fertilisation. Detailed discussion is mentioned below:

• Flowering plants have a different type of fertilisation known as double fertilisation, where there is the formation of a zygote after fertilisation of the egg and pollen.

• Two polar nuclei, when they fuse with the sperm, form an endosperm, which nourishes the embryo.

• One sperm is fertilised in the egg cell of the pollen tube, which results in the formation of a diploid zygote. This is further developed into an embryo.

• The second sperm cell gets fertilised at the central cell, containing two polar nuclei which form a triploid endosperm.

• After fertilisation, the ovule matures and the seed containing the embryo develops into a fruit.

Embryogeny and Post-Fertilisation Events in Flowering Plants

• Post-fertilisation events begin right after fertilisation and include the development of the zygote, formation of the endosperm, embryogeny (development of the embryo), maturation of the seed, and transformation of the ovary into the fruit.

• The endosperm is formed before the embryo and serves as a nutritive tissue, providing nourishment to the developing embryo. It can be retained in mature seeds (as in cereals) or used up during development.

• Embryogeny is the process of development of the embryo from the zygote.

• Embryogeny in monocots differs slightly from that in dicots.

• In dicot seed embryos, the main parts formed are:

  • Radicle (future root)

  • Plumule (future shoot)

  • Cotyledons (two seed leaves that may store food)

  • Hypocotyl (part between radicle and cotyledons)

  • Epicotyl (part above the cotyledons)

• In monocots, such as grasses:

  • The embryo has only one cotyledon (called scutellum).

  • Other parts include coleoptile (covers the plumule), coleorhiza (covers the radicle), plumule, and radicle.

Seed and Fruit

• A seed is a mature ovule formed after fertilisation and contains the embryo, cotyledons, and seed coat. The parts of a seed help in the protection and nourishment of the embryo.

• Seed formation happens after fertilisation, and seed dispersal ensures the spreading of plants to new areas. Dispersal can occur through wind, water, animals, or mechanical force.

• Dicotyledonous seeds (like beans) have two cotyledons, while monocotyledonous seeds (like maize) have only one cotyledon. These help store food and support the embryo.

• A fruit is formed from the ovary of a flower after fertilisation. It has parts like the pericarp (fruit wall), and sometimes the seeds inside.

• Types of fruits include:

  • Simple fruits (from a single ovary),

  • Aggregate fruits (from multiple ovaries of one flower),

  • Multiple fruits (from many flowers).

• Fruit and seed formation without fertilisation is possible through parthenocarpy, where fruits develop without seeds.

  • Parthenocarpic fruits include banana and seedless grapes.

  • It can be natural or induced using plant hormones.

• Polyembryony is the presence of more than one embryo in a seed. It can happen naturally in some plants and leads to multiple seedlings from a single seed.

• The significance of seeds and fruit formation lies in helping plants reproduce, spread, survive unfavourable conditions, and provide food for animals and humans.

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