The alternation of generations in gametophytes

A protective covering called a calyptra surrounds this embryonic sporophyte. These fuse in a process referred to as plasmogamy and karyogamy to form a diploid zygote. Most mosses rely on the wind to disperse these spores, although Splachnum sphaericum is entomophilousrecruiting insects to disperse its spores.

Vascular plants that make two kinds of spores and gametophytes are called heterosporic. The living species of Equisetum are distributed worldwide except for Australia, New Zealandand Antarctica. Single-celled spores travel via wind and germinate only in a moist area; water is required for fertilization.

Karogamy produces a diploid zygote, which is a short-lived sporophyte that soon undergoes meiosis to form haploid spores.


The male conifer gametophyte exists as pollen, which is wind-dispersed. The diploid zygotesproduced by the fusion of haploid egg and sperm, divide mitotically and differentiate into mature sporophytes, completing the life cycle.

Some flowers have many pistils that are partially or wholly fused. Alternation of generations occurs in almost all multicellular red and green algae, both freshwater forms such as Cladophora and seaweeds such as Ulva.

A sporophyte of Dicksonia antarctica. Megaspores develop within the megasporangium; typically one of the four spores produced by meiosis gains bulk at the expense of the remaining three, which disappear.

The way in which the alternation of generations occurs in plants depends on the type of plant.


These are described at Plant reproductive morphology. Haploids contain one set of chromosomes in each of their cells. Megasporangia and microsporangia occur on the same sporophyte, which is then called monoecious.

Fern leaves used in floral arrangements are a major industry in Florida, and in some cultures tree fern stems are used to make elegant, naturally sculpted bowls.

Alternation of generations

The gametophytes are very small and cannot exist independent of the parent plant. The multicellular diploid plant structure is called the sporophyte, which produces spores through meiotic asexual division. Note that the chromosome number here doubles from 'n' to '2n'.

A pollen grain represents an example of a male gametophyte in vascular plants. The life cycle of a gymnosperm is similar. As the diploid phase was becoming predominant, the masking effect likely allowed genome sizeand hence information content, to increase without the constraint of having to improve accuracy of DNA replication.

Gametophyte and Sporophyte The life cycle of a plant involves the alternation of two generations: Evolutionary emergence of the dominant diploid phase[ edit ] It has been proposed that the basis for the emergence of the diploid phase of the life cycle sporophyte as the dominant phase e.

Although the genus includes two rather distinct groups, modern botanists recognize but a single genus. There is a rich fossil record showing that pteridophytes have ancestors dating back nearly four hundred million years.

Dioecy occurs in a wide variety of plant families. The reproductive structures of the sporophyte cones in gymnosperms and flowers in angiospermsproduce two different kinds of haploid spores: Land plants all have heteromorphic anisomorphic alternation of generations, in which the sporophyte and gametophyte are distinctly different.

This is the cycle which is known as alternation of generations or alternation of phases. A megaspore often but not always develops at the expense of the other three cells resulting from meiosis, which abort. The gametophyte comprises the main plant the green moss or liverwortwhile the diploid sporophyte is much smaller and is attached to the gametophyte.

All spores the same size homospory or isospory.Plants exist in alternation generations called sporophytes and gametophytes.


Sporophytes represent the diploid phase of plants. Gametophytes represent the haploid phase of plants. Land plants have alternation of generations, for which the sporophyte generation produces spores rather than librariavagalume.comly speaking, the sporophytes of land plants do not have either male or female reproductive organs.

The gametophytes of flowering plants are of a single sex; the male gametophytes are contained within the pollen, and the female gametophytes.

In terms of alternation of generations, the internal parts of the pollen grains of seed-producing plants are most similar to a a) fern sporophyte. b) moss sporophyte.

While considering gametophyte versus sporophyte generations, there are some stark points, such as sporophyte is a diploid phase, whereas gametophyte is a haploid generation. Sporophyte stage is asexual, while gametophyte stage is sexual.

Alternation of generations (also known as metagenesis) is the type of life cycle that occurs in those plants and algae in the Archaeplastida and the Heterokontophyta that have distinct sexual haploid and asexual diploid stages.

In these groups, a multicellular gametophyte, which is haploid with n chromosomes, alternates with a multicellular. The alternation of generations is an important concept in the evolution of plants.

All land plants have alternation of generations. In mosses and their relatives (Bryophytes), the haploid gametophyte is the dominant generation, and the diploid sporophytes are sporangium-bearing.

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The alternation of generations in gametophytes
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