Sexual Reproduction in Flowering Plants: Structure & Functions

Content Writer | Updated On - Jul 23, 2024

Flowers are the reproductive parts of the plant that contain the male and female gametes for reproduction. Although plants can reproduce both by sexual and asexual modes, but majority of the flowering plants reproduce sexually.

In a flower, both male and female gametes fuse to form a zygote.
The male gamete involved in reproduction is called the androecium, and the female gamete is called the gynoecium.
Flowers, also called angiosperms are the main site where sexual reproduction takes place in flowering plants.

In this article, we will discuss sexual reproduction in flowering plants of subject biology class 12 chapter 2.

Table of Contents

Structure of Flower
Stages of Sexual Reproduction in Flowering Plants
Functions of a Flower
Things to remember
Sample Questions

Structure of Flower

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Flowering plants are also called angiosperms and account vast majority of the animal kingdom. The structure of flower consists of both vegetative and reproductive parts. In this section, we will discuss these parts in detail.

Vegetative Parts of a Flower

The vegetative part of a flower is usually not involved in sexual reproduction. They are mainly used in reproduction by asexual means. These parts contain the corolla (petals) and the calyx (sepals).

Corolla

A corolla is defined as a group of petals that surround the flower to protect its reproductive organs.

They contain nectaries, a structure that secretes nectar to attract insects to the flower for the process of pollination.
The petals are brightly colored due to the presence of pigments like anthocyanins, carotenoids, and anthoxanthin.

Calyx

A Calyx is defined as the special leaves present below the petals. They are also sepals.

They protect the flowers and fruit from predators when they are in the budding stage.
Sepals help in the process of photosynthesis.

Reproductive Parts of a Flower

The reproductive parts of a flower are those parts that are mainly involved in sexual reproduction. Rose, hibiscus, Mustard, Gulmohar, etc are some examples of flowering plants that reproduce sexually. The male part and the female part are the two reproductive parts of a flower.

Androecium

The androecium is the male reproductive part of the flower, also called the stamen which is the third whorl of a flower, it has two parts: anther and filament.

Anther

It is that part of the stamen which contains the pollen grains.

The anther is present at the end of a tube-like structure called a filament.
It consists of two lobes in which microsporangium or pollen sac is present.
Microsporangium is responsible for producing microspores that grow into male gametes.

Filament

It is a thread-like stalk that supports the anther.

Filaments make it easy for the pollinators to access the pollen grains.
It also carries the nutrients to the anther for the development of pollen grains and anther.

Microsporangia and Microsporogenesis

Microsporangia are bi-lobed structures that produce microspores and gametes. They are present at the end of the stamen that act as pollen sacs in anther.

Tapetum, middle layer, endothecium, and epidermis are the four layers of microsporangia.
The process of formation of microspores (pollen grains) inside the microsporangium (pollen sac) is called microsporogenesis.

Anther

Figure: Structure of a Stamen

Gynoecium

The gynoecium is the female reproductive part of a flower that is used for the production of ovules and is located at the central position of the thalamus. The gynoecium consists of the stigma, style, ovary, and ovules.

The reproductive part of the flower where the pollen lands is called the stigma.
The stigma and the ovary are connected with a long-tube-like structure called style.
An ovary is that part of a flower where fertilization takes place.
Ovules are confined within the ovary. It develops into a seed when fertilization occurs.
Megasporangium is responsible for producing megaspores that grow into female gametes.

Figure: Structure of Flower Diagram

Megasporangia and Megasporogenesis

The structures that produce megasporocytes yield megaspores. The process of arrangement of the megaspore of the mother cell is called megasporogenesis.

Out of three megaspores only one is utilized and the others are degenerated.
The only megaspore which is functional forms the female gamete.

Stages of Sexual Reproduction in Flowering Plants

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Pollination of Flowering Plants

Pollination is the equivalent of reproduction, where the transfer of pollen grains occurs from one potent flower to the stigma of another flower or the same flower.

Pollination is considered as the first step of sexual reproduction in flowering plants.
Here, pollen grains have a male gamete, which is present in the anthers of the flower part.
The process begins when pollen grains from flowers land on the stigma.
It connects the stigma and ovary of the flower.
The pollen grains transmit sperm from the grain to the ovary.

Types of Pollination

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There are two types of pollination: Self pollination and Cross polination

Self-Pollination

Self-pollination is a process where pollen from the anther of one flower lands to the same flower's stigma. Examples of self-pollination include hermaphrodite or dioecious plants.

They contain both male and female sexual reproductive parts in the same flower.
Self-pollination can further be divided into two types: autogamy and geitonogamy.

Autogamy

Autogamy is a type of self-pollination where the pollen is transferred from the anthers of one flower to the stigma of the same flower.

Geitonogamy

Geitonogamy is a type of self-pollination where the anthers are transferred from one flower to another flower's stigma, but it occurs on the same flowering plant.

What are the advantages of self-pollination?

Self-pollination has the following advantages.

There is no diversity in self-pollination; hence, the complete purity of the plant race is maintained.
Self-pollination removes the recessive characters.
The plants does not have to depend on external factors for sexual reproduction.
A small quantity of pollen grains provides a tremendous success rate.

Cross-Pollination

Cross-pollination is a process of sexual reproduction in flowering plants where the pollen is transferred from anthers to the stigma of another flower. Both flowers, in the process, are genetically different.

They are dependent on another agent for the transfer to occur.
Here, the agents of pollination are birds, insects, water, wind, and animals.
Different types of flowers are pollinated by different biotic and abiotic agents.

Types of Flowers	Agents
Hydrophilus	Pollinated by water agents
Anemophilus	Pollinated by wind
Zoophilous	Pollinated by birds, bats, human beings
Entomophilous	Pollinated by insects
Ornithophilous	Pollinated by birds
Spores	Non-Spore forming

What are the advantages of cross-pollination?

The advantages of cross-pollination are as follows:

Cross-pollination is very important to every plant as it introduces new genes.
It improves the resistance of future generation plants because it will be more adaptive to the surroundings.
Cross-pollination is the only way for unisexual plants to reproduce.
If there are any flawed characters in the lineage, they will be eliminated due to genetic recombination.
The seeds produced from cross-pollination are amazing in vitality.

Fertilization in Flowering Plants

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Fertilization is the second stage of sexual reproduction in flowering plants. It occurs immediately after pollination. In this stage, the pollen is transferred to the ovary through the pollen tube. It includes the fusion of male gametes with the female gametes. Fertilization occurs in three steps:

Endosperm
Embryo development
Seeds and Fruit Development

Endosperm

An endosperm is a part of a seed that act as a reserve for food materials that is later utilized by the embryo for nutrition. It is formed after a male gamete fuses with the two polar nuclei in the central cell. Examples of endosperm include peas, coconut, beans, etc.

Embryonic development

After the transfer of pollen to the ovary, one male gamete fuses with the female gamete and the remaining gamete connects with the polar nuclei.

The zygote is further developed into an embryo.
The gametes that are transferred to polar nuclei will form endosperm nuclei.
The fertilization process results in the formation of seeds from ovules.

Seed and Fruit Development

Once the fertilization stage is complete, the ovary develops into fruit and the ovules into seed.

The ovary wall converts into the wall of the mature fruit called pericarp.
The pericarp helps in the protection of the developing embryo.
The seeds are made up of a single or a double cotyledon and are formed from the ovules.
It takes up its nutrients from the endosperm.
The tough protective seed coats are a result of hardened integuments of ovules.
The micropyle is also present as a small pore on the hard coat of the seed.
It facilitates the flow of water and oxygen into the seed.

Figure: Fertilisation in Flowering Plants

What is Asexual Reproduction?

Asexual reproduction in plants happens through vegetative propagation, budding, and spore formation. The plants which are produced by asexual reproduction thrive in controlled environments.

It does not involve the actual fusion of female and male gametes.
The method occurs both naturally as well as artificially.
The plants that use asexual reproduction are ginger, dahlia, potato, onion, and buds.
Artificial methods of reproduction include cutting, layering, grafting, and micropropagation.
The plants produced by asexual reproduction thrive much stronger than those produced by any other method.

Functions of a Flower

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The reproductive structures of flowering plants are the flowers. The following are the important functions of a flower:

Various species of flowers play an important role in reproduction.
Flowers produce nectar that helps the pollinators to transfer pollen from one flower to the next.
It helps in the development of pollen tubes and results in the formation of gametes.
The green leafy portion called sepals protect the flowers from extreme conditions.
Flowers provide a wide range of resources for various species and support pollinators.
The ovarian portion of the flower develops into a mature fruit.
Some fruit-bearing flowers mature into fruits to nourish and protect the seeds, making it more attractive to animals for dispersion

Things to Remember

Sexual reproduction in flowering plants takes place when male and female gametes are present in the flower.
The male reproductive part is referred to as the androecium, and the female part is the gynoecium.
The male organ of a flower comprises different parts such as filament, anther, and pollen grains.
Microsporogenesis is the process by which the formation of microspores or pollen grains takes place.
The process of arrangement of megaspores in a mother cell is called megasporogenesis.

Previous Years Questions

Meiosis takes place in...[NEET 2013]
The sexual reproduction is absent in….[NEET 1995]
For union between stock and scion in grafting which one is the first to occur….[NEET 1990]
A clone is ......… [KCET 2011]
Animals which possess cleidoic eggs exhibit….[KCET 2011]
Which among these is not a post fertilization event ?...[KCET 2016]
Type of asexual reproduction found in Hydra is..[KEAM]
Which of the following is having longitudinal binary fission ?….[KEAM]
In grafting, the stock and scion should be joined….
The mode of asexual reproduction in Euglena is….[CUCET 2010]
Isogamy is found in...[CUCET 2010]
In these plants artificial vegetative reproduction is possible through….[GUJCET 2006]
Apomixis in plant means development of a plant… [BHU UET 2008]
Which one of the following plants reproduces vegetatively by epiphyllous buds?

Sample Questions

Ques. How is zygote formed in flowering plants? (1 mark)

Ans. In flowering plants, the zygote develops when a male gamete completes syngamy by fusing with the nucleus of the egg cell.

Ques. What is double fertilisation? (2 marks)

Ans. Double fertilisation is a unique process that takes place only in flowering plants. In this case, one of the male gametes after entering the synergid, fuses with the nucleus of the egg cell to form the zygote. The other male gamete fuses with the polar nuclei to produce primary endosperm nuclei. As both triple fusion and syngamy takes place, this process is termed as double fertilisation.

Ques. What is the difference between Geitonogamy and Xenogamy? (1 mark)

Ans. In case of geitonogamy, the pollen grains move from anther to stigma of another flower growing on the same plant. On the other hand, when pollen grains are transferred from anther to stigma of a different plant, it is known as Xenogamy.

Ques. What are the male and female reproductive organs of a flower called? (1 mark)

Ans. The male reproductive part is called Stamen which comprises the anther and filament. The female reproductive part is called Pistil which comprises three portions of stigma, style, and ovary.

Ques. Name some of the agents of pollination and which areas of pistil form the fruits and seeds?(2 marks)

Ans. The pollinating agents are intricate in shifting pollen grains from the male to the female area of the flower. Animals, birds, insects, wind, more biotic and abiotic agents are examples of pollinating agents. The ovary matures into a fruit. The ovule changes into the seed.

Ques. What is pollination? State its significance. (2 marks)

Ans. The pollination mentions the transfer of pollen grains from the anther of a flower to the stigma of a similar or a separate flower. Pollination is an important procedure as it benefits in fertilization by taking the male gamete nearer to the female egg and letting their fusion. Therefore, it benefits the production of seeds and fruits. Also helps in reproduction as the seeds shaped assists in the generation of new offspring. Cross-pollination helps in the introduction of new deviations in plants.

Ques. Explain what happens after the fertilization process? (2 marks)

Ans. Fertilization forms an important part of the sexual reproduction process in the reproducing organisms. In every flower bearing plants the process of fertilization occurs only after pollination and germination and the process that follows hence forth are:

The ovary turns into a fruit
The ovule turns into a seed
The other parts such as the corolla, calyx and the remaining structures of the androecium and gynoecium tend to fall off.

Ques. What are the various kinds of pollination? (3 marks)

Ans. Types of Pollination are of three types:

Autogamy – Pollination takes place within a similar flower wherein the pollen grains from the anther are moved to the stigma of the similar flower.
Geitonogamy – The pollen grains are moved from the anther to the stigma of a separate flower but of the identical plant.
Xenogamy – The transferring of pollen grains from the anther to the stigma of an individual plant is Xenogamy.

Ques. How does aquatic plants facilitate pollination? (2 marks)

Ans.There are two kinds of aquatic plants that facilitate pollination, one where the flowers grow above water and the other where they grow underwater.

For flowers that grow above water pollination takes place through insects and birds.
In case the plants grow under water, pollination takes place via water only.

Ques. What are the phases that take place after fertilization? (3 marks)

Ans. There are a number of different phases that occur post fertilization which are as follows:

The development of the endosperm.
The enhancement of the embryo
The ovule turns into a seed
The ovary turns into a fruit.

Ques. Give a description of the composition of a pollen grain. (3 marks)

Ans. The structure of the pollen grains are made up of double coating barriers formed in a spherical structure.

The external layer is known as exine which is made up of sporopollenin i.e.,organic substances that are highly withstanding in nature and are not present at the opening area known as germ pore.
The interior layer is composed of cellulose and pectin and is known as the intine.
A full grown pollen is composed of a generative as well as vegetative cell.

Ques. What is the pre-fertilization procedure in flowering plants? (5 marks)

Ans. The two important pre-fertilization procedures are gametogenesis and gamete transfer. The female and male reproductive forms in flowers are the androecium and the gynoecium which distinguishes and goes through development. Mentioned below is clear information regarding the male and female parts:

(A) Stamen, Pollen Grains and Microsporangium

Stamen comprises two parts which are first, filament, the slender and long stalk, and second, the anther, the bilobed formation for each lobe taking two thecae hereafter they are dithecous.
Anther is a tetragonal form including microsporangia located at the verge.
Microsporangia progress into the pollen bags later on. Microsporogenesis is the structure of microspores over meiosis from a pollen mother cell.
Pollen grains are the illustration of the male gametophytes. The development of the pollen grains is designated by two cells which are vegetative cells and generative cells.

(B) Megasporium, Pistil, and Embryo bag/sac

The female reproductive portion of the flower is the gynoecium which may be multicarpellary. Individually, a pistil contains stigma, style, and the ovary.
The ovarian cavity existing in the ovary embraces the placenta from wherever the megasporangia appear, generally mentioned as the ovule.
The ovule contains the following forms which are funicle, hilum, integuments, micropyle, chalaza, nucellus, embryo sac, and the female gametophyte. An ovule is structured from a megaspore.
Structure of megaspores from the megaspore mother cell is discussed as megasporogenesis.
Generally, one of the four megaspores is functional which progresses into the female gametophyte, and the rest degenerate.
While developing a typical angiosperm embryo sac even though it describes 8-nucleated but is 7-celled.

Ques. List the features of flowers where pollination occurs through wind, water or insects. (5 marks)

Ans. Listed below are the features of flowers pollinated by various agents such as wind, water or insects:

(A) Wind:

These flowers are small in size and devoid of petals.
They neither have brilliantly coloured petals nor do they have any fragrance or nectar.
Their stamen and stigma are uncovered and can be blown by wind.
The texture of the pollen is smooth and in large quantities.
The stigma of such flowers are fluffy and can easily acquire pollen from air.

(B) Water:

They contain tiny male flowers which are not very evident.
Pollens are released in huge quantities which are attracted by the big fluffy stigma of the female flowers.
The pollen released by male flowers keeps on moving in the water unless attracted by the stigma of the female flower.

They are big in size and have brightly coloured petals which helps them to attract insects.
The flowers have a sweet smell and nectar in search of which insects get attracted.
The pollens are sticky in nature which helps them to attach to the body of the insects.

Ques. How does sexual reproduction occur in flowering plants? (5 marks)

Ans. Sexual reproduction in flowering plants occur in three ways:

Pollination

Pollination is a process of transporting the pollen grains through the anther and the stigma of a similar flower of a plant or to a flower of a dissimilar plant for the procedure of fertilization and the production of seeds. Its implicated to transfer the pollen grains which are birds, wind, animals, and water.

Formation of a Zygote

After the pollination, the male gamete is transferred down through the style of the pistil to the ovary and the male gamete is merged with the female gamete to shape a zygote. The zygote is situated nearby the embryo sac which was located at the micropylar end where the embryo grows. Normally, zygote differences only after a few numbers of endosperm are shaped. This guarantees nutrition is rendered to the emerging embryo.

Formation of Fruits and seeds

Afterward, the formation of a zygote is allowed to progress in an embryo. The ovules grow into seeds and the ovary grows into a fruit. The final product of sexual reproduction is seeded in angiosperms. Normally, the establishment of seeds proceeds from fruits. Seeds are beneficial structure in the following methods:

The procedure of seed development is responsible as other reproductive processes (fertilization and pollination) are water-dependent.
For diffusion to newer habitats, seeds have an enhanced adaptive strategy assisting species to colonize other parts.
Young seeds are self-nurtured up until photosynthesis as they have sufficient food reserves.
Creates new genetic combinations resulting in variations.
Seeds that are dormant and dehydrated can be put in storage for use during the year.

Ques. How do flowers reproduce asexually? (2 marks)

Ans. Flowers reproduce asexually via their vegetative parts i.e. calyx and corolla.

Budding, sporogenesis, vegetative propagation, and fragmentation are the types of asexual methods.
Asexual reproduction in flowering plants does not involve the fusion of gametes.

Ques. What are the advantages of sexual reproduction in flowering plants? (2 marks)

Ans. The following are the advantages of sexual reproduction in flowering plants.

They provide higher yields in agriculture.
Sexual reproduction leads to genetic variation.
Sexually reproducing plants generate huge amounts of seeds enhancing the likelihood of plant progeny.

Sexual Reproduction in Flowering Plants: Structure & Functions