What is Gametophyte? Female & Male Gametophyte and Sporophyte

Gametophyte, is a stage that all plants and certain algae species in their life cycle. Sporophyte, a multicellular diploid generation, and Gametophyte, a multicellular haploid generation, are both involved in this process. The primary function of the gametophyte is to produce gametes. The gametes generated are haploid reproductive cells like sperm and eggs. Male and female organs (gametangia) mature and generate eggs and sperm (gametes) for sexual reproduction during the gametophyte phase, which is haploid (has a single pair of chromosomes). Here we will be learning about gametophyte in depth and discussing some important questions.

Read more: Megasporangia

Key Terms: Gametophyte, Sporophyte, Male Gametophyte, Female Gametophyte, Types of Gametophyte, Alteration of Generation.

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Reproductive Organs of Gametophyte

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In the gametophyte process, two types of sex organs (male and female) are identified.

• Archegonium: 

Archegonium is an egg-producing multicellular female reproductive organ. This organ produces haploid egg cells, similar to the ovary.

• Antheridium:

Antheridium is a male reproductive organ that resembles gonads and helps in the production of haploid sperm cells.

Antheridium

Archegonia and antheridia are both microscopic structures. Bisexual gametophytes are gametophytes that have both male and female organs. The gametophytes with only one type of sex organ or gametangium are known as unisexual gametophytes. Male and female reproductive organs, on the other hand, are tiny structures. The term 'diploid' refers to cells with two sets of chromosomes, and is usually written as '2n'. Haploid cells have only one pair of chromosomes and are denoted as 'n'.

Read more: Difference between sporophyte and gametophyte

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Haploid

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If a cell has just one pair of chromosomes, it is said to be haploid. The number of chromosomes in the gametes, which could be eggs in females or sperm cells in males, is also referred to as haploid. Human gametes are haploid, meaning they have 23 chromosomes. Each of these chromosomes is found in a pair in diploid cells. The number of chromosomes in a single set is symbolised by the letter 'n,' which is also known as the haploid number. n=23 in the case of humans.

Haploid

Half of the chromosomes seen in normal diploid cells of the body are found in gametes. Somatic cells are the diploid cells that make up the body. Haploid gametes are generated during meiosis. It is a type of cell division during which the number of chromosomes in the parent diploid cell is decreased by half. In the life cycle of some organisms, such as algae, haploid segments exist. Male ants, for example, live their whole lives as haploid organisms.

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Female Gametophyte: Embryo Sac

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Embryo sac is the term given to the female gametophyte organ. The female reproductive organ of gymnosperms is relatively big and multicellular because it not only sustains the gametes but also contributes to the growth of the embryo.

The female gametophyte of angiosperms, on the other side, is a tiny, eight-nucleated structure that primarily regulates the gametes. Female gametophytes produce female gametes, which serve as the molecular foundation for fertilisation and seed development. This mechanism is supported by both gene and cellular activities, thus accessory cells can be genetically activated in the case of gamete failure.

Read more: Sexual Reproduction in Flowering Plants

Female Gametophyte Development

Female gametophytes have two distinct stages of development. Megasporogenesis is the initial step in the formation of tetrad haploid megaspores from a single diploid cell. Only one megaspore survives and begins to grow inside an embryo sac, while the other three are destroyed.

The functional haploid megaspore generates the female gametophyte – embryo sac in the second phase, megagametogenesis. The female gametophyte has a 7-celled, 8-nucleate structure. Only the polar nuclei of these eight nuclei move and unite to form a diploid cell in the middle. This diploid cell becomes a triploid endosperm after fusing with the sperm. Three nuclei produce antipodal cells, whereas the remaining two produce synergid cells. All of these cells, however, eventually dissolve.

Read more: Asexual reproduction

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Male Gametophyte: Pollen Grain

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A pollen grain, which is transformed from the microspore mother cell, is the basic gametophytic structure. Pollen grain germination evolves pollen grain into male gametophyte before pollination. The pollen mother cell divides into four microspores inside the microsporangium during meiosis cell division, and these microspores eventually grow into the pollen grain.

Taptum is the inner layer of microsporangium that caters again for growing microspores. When the microsporangium matures, it splits open and releases the pollen. The pollen grain of a male gametophyte is made up of two cells, one generative and one vegetative, as well as two layers. The thick outer coat is the exine, whereas the thin inner layer protects the pollen.

Male Gametophyte Development

By moving the nucleus to one side, germination in the pollen sac generates a central vacuole structure. Mitosis later splits the nucleus into two nuclei. A vegetative cell is the large cell, whereas a generative cell is the little cell.

The generative cell, confines to a smaller section of the pollen grain. Whereas, the vegetative cell containing cytoplasm serves as preserved fuel for male gametophytes. The growing pollen grain falls on the stigma during this phase and gets nutrition through the germ pore. By pushing out the intine through the germ hole, this absorption enlarges the vegetative cell and finally produces the pollen tube. The nuclei travel to the pollen tube during this stage. The nuclei move to the pollen tube during this stage, and the generative cell is split into two haploid cells: non-motile and one-celled male gametes.

Read more: Bryophytes and Pteridophytes

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Sporophyte

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The nonsexual phase (or an organism representing the phase) in the alternation of generations—a phenomena in which the organism's life history is divided into two separate phases, each of which produces the other. The gametophyte is the sexual phase. A diploid (two sets of chromosomes) plant body develops in the sporophyte phase and ultimately generates spores through meiosis. These spores divide mitotically to generate gametophytes, which are haploid (containing just one pair of chromosomes) gamete-producing organisms. During fertilisation, two gametes combine to form a diploid zygote, which divides mitotically to form a new sporophyte.

The type and relative size of the two stages varied substantially between plant and algal groupings. The sporophyte stage has grown increasingly important throughout evolution. Thus, in the higher (i.e., vascular) plants the sporophyte is the dominating phase in the life cycle, but in the more primitive nonvascular plants (bryophytes) the gametophyte stays dominant. Although some species have determinant life cycles and are commonly gametophyte-dominant, the dominant phase in algae often is dependent on the surrounding.

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Difference between Gametophyte and Sporophyte

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Due to genetic variability, all plants reproduce both sexually and asexually. Plant genetic components are used to make gametophytes and sporophytes. Mosses differ from complex vascular plants include that typically spend extra duration as sporophytes. The gametophyte stage of these species is the most visible section of the plant.

Difference between Gametophyte and Sporophyte

Haploid gametophytes have just one copy of each chromosome in each cell, which is why they must reproduce asexually. Gametophytes eventually generate gametes, which unite to form a diploid zygote that develops into the sporophyte. As diploid sporophytes have two copies of each chromosome, they may support meiosis and generate haploid spores that develop into gametophytes. Different plants go through both phases. The amount of complexity and significance, on the other hand, varies each phase.

The following are the differences between Gametophyte and Sporophyte:

Also read: Double Fertilization in Angiosperms

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Alternation of Generations

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In biology, the alternating of a sexual and asexual phase in an organism's life cycle is known as generation alternation, also known as metagenesis or heterogenesis. Both physically and chromosomally, the two stages, or generations, are typically unique.

Alteration of Generations

Alternation of Generations is prevalent in algae, fungus, and plants. However, because one or both generations are generally very small, if not microscopic, it is not always simple to witness. The gametophyte generation, or sexual phase, generates gametes, or sex cells, whereas the sporophyte generation, or asexual phase, produces spores. The gametophyte is haploid (has a single pair of chromosomes), whereas the sporophyte is diploid (has two sets of chromosomes) (has a double set). The gametophyte is the dominant life phase of bryophytes, such as mosses and liverworts, whereas the sporophyte is dominant in angiosperms and gymnosperms. In mushrooms, the haploid phase is also prevalent. Although some algae have distinct life cycle stages, many species change over and forth from sexual and asexual phases in response to environmental factors.

Also read:

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Things to Remember

• During the alternation of generations of plants and a few algae, the gametophyte is the sexual phase. This stage generates gametes that are passed down across generations. It is a haploid phase that produces the zygote that gives rise to sporophytes.
• The sporophyte produced from the zygote and is the diploid phase of the plant life cycle. Sporophytes produce spores from which gametophytes develop.
• At the two-celled stage, pollen grains are discharged from pollen-sacs. The generative cell splits again, resulting in two male gametes. These male gametes are discharged into the embryo sac, where they will fuse with the egg and central cell.
• The embryo-sac and the female gametophyte are same. Female gametes are produced at the haploid stage. Inside the ovule, the female gametophyte is present.
• The major distinction between gametophyte and sporophyte is that the first is the sexual phase of the plant life cycle, while the latter is asexual. Gametophytes are haploid and generated by meiosis, whereas sporophytes are diploid and generated through mitosis.
• The two forms of gametophytes are Male gametophytes and Female gametophytes. Female gametes are the embryo-sac, whereas male gametophytes are pollen grains.
• Gametophytes are multicellular haploid creatures. When the gametophyte reaches maturity, it generates one or more gametangia. This is where haploid gametes are produced.
• Some examples of Gametophyte are mosses and hornwort.