Gametophyte: Definition, Structure, Formation, Types, Functions, Description, Characteristics

Definition Of Gametophyte

The plant or algae genotype alternates gametophyte with the sporophyte phase in the haplontic cycle. The gametophyte is a plant carrying out mitosis to produce either sperm or eggs. It has a key role in sexual reproduction, as it allows genetic diversity and adaptation to be achieved by receiving different types of gametes that unite to form a diploid zygote. This is characterised by two very different phases - a haploid gametophyte and a diploid sporophyte, which reproduces the gametophyte. A cycle of this nature ensures that there is a lot of variation and complexity in the development and reproduction of plants.

These plants have a life cycle that shows alternation of two phases: a haploid gametophyte and a diploid sporophyte. Such a process of alteration of generations guarantees genetic diversity and adaptation to changes in the environment. In this cycle, a sporophyte goes through meiosis to produce spores that develop into gametophytes. In another process, gametophytes form gametes which fuse to give a new sporophyte.

The Life Cycle Of Plants

The life cycle of plants is explained below-

Explanation Of Alternation Of Generations

Sporophyte vs. Gametophyte

The sporophyte would be the diploid phase of the plant life cycle of spores produced by meiosis; that is, the gametophyte is the haploid phase that gives rise to gametes by mitosis. In vascular plants, the sporophyte is the dominant visible generation, and the gametophyte generation is frequently reduced. In non-vascular plants, such as mosses, the gametophyte generation is the dominant phase.

Characteristics Of Gametophytes

The characteristics of gametophytes are explained below-

Haploid Nature

Gametophytes are therefore haploid, meaning that they possess one set of chromosomes. This generation is the one that is directly involved in sexual reproduction because its organs and tissues give rise to sperm and egg cells, which unite in fertilisation to generate a diploid zygote.

Differences In Mosses, Ferns, And Flowering Plants

Mosses: Dominant Gametophyte Stage

In mosses, the gametophyte is the dominant and photosynthetic phase and is nutritionally independent, while the sporophytes are nutritionally dependent on the gametophyte stage.

Ferns: Reduced Gametophyte Stage

In ferns, the gametophyte is reduced and free-living, being a small, typically heart-shaped plant called a prothallus. The sporophyte is the larger, more conspicuous phase.

Flowering Plants: Highly Reduced Gametophyte Stage

In flowering plants, the gametophyte is highly reduced, with the male gametophyte (pollen grain) consisting of only a few cells, and the female gametophyte (embryo sac) located within the ovule.

Gametophyte Development

The gametophyte development is explained below-

Formation From Spores

Gametophytes are the product of spores, which are the product of the sporophyte through meiosis. A spore produces, through mitotic divisions multicellular gametophytes.

Structures Involved

Archegonia and Antheridia in Non-Flowering Plants

Archegonia are female organs and antheridia are male organs. Mosses and ferns produce eggs and sperm from the archegonia and antheridia, respectively.

Embryo Sac and Pollen Grain in Flowering Plants

In flowering plants, for instance, the female gametophyte (embryo sac) is developed within the ovule, and the male gametophyte (pollen grain) develops in the anthers.

Function Of Gametophytes

The functions of gametophytes are explained below-

Role In Sexual Reproduction

Gametophytes are directly responsible for the process of sexual reproduction through the production of gametes (sperm and egg cells). At fertilization, these gametes join to form a zygote. This zygote then develops into a new sporophyte.

Fertilisation Process

In gymnosperms, the sperm swims to the egg cell in the archegonium. In angiosperms, the pollen grain reaches the stigma and the pore germinates, and the pollen tube conducts the sperm to the embryo sac.

Gametophytes In Different Plant Groups

The details are given below:

Bryophytes (Mosses)

Structure and Function

In mosses, the gametophyte is the main photosynthetic structure and the dominant plant form. It bears the dependent sporophyte generation. It is composed of leafy shoots and rhizoids.

Pteridophytes (Ferns)

Structure and Function

Fern gametophytes, or prothalli, become minute, heart-shaped structures that bear the sexual organs: the archegonia and antheridia simultaneously. These are free living and photosynthetic.

Gymnosperms

Structure and Function

Gymnosperm gametophytes are reduced in size and are found within cones. The male gametophyte is the pollen grain, and the female gametophyte develops inside the ovule.

Angiosperms (Flowering Plants)

In angiosperms, the pollen grain represents a male gametophyte, whereas the embryo sac in the ovule represents the female gametophyte.

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