Plant Life Cycle And Alternation Of Generation Pdf

plant life cycle and alternation of generation pdf

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The life-cycle of a bryophyte shows regular alternation of gametophytic and sporophytic generations.

PLANT EVOLUTION AND DIVERSITY. TYPES OF LIFE CYCLES FOUND IN ALGAE

The life-cycle of a bryophyte shows regular alternation of gametophytic and sporophytic generations. This process of alternation of generations was demonstrated for the first time in by Hofmeister. Thereafter in Strasburger could actually show the periodic doubling and halving of the number of chromosomes during the life-cycle.

Image Courtesy : worldbotanical. The haploid phase n is the gametophyte or sexual generation. It bears the sexual reproductive organs which produce gametes, i. With the result of gametic union a zygote is formed which develops into a sporophyte. This is the diploid phase 2n. The sporophyte produces spores which always germinate to form gametophytes. During the formation of spores, the spore mother cells divide meiotically and haploid spores are produced. The production of the spores is the beginning of the gametophytic or haploid phase.

The spores germinate and produce gametophytic or haploid phase. The spores germinate and produce gametophytes which bear sex organs. Ultimately the gametic union takes place and zygote is resulted. It is diploid 2n. This is the beginning of the sporophytic or diploid phase.

This way, the sporophyte generation intervenes between fertilization syngamy and meiosis reduction division ; and gametophyte generation intervenes between meiosis and fertilization. In bryophytes, where the two generations are morphologically different, the type of alternation of generations is known as heteromorphic.

In the case of bryophytes the gametophyte generation is conspicuous and longer-lived phase of the life-cycle in comparison to that of sporophyte generation. Here, the gametophyte is quite independent whereas the sporophyte is dependent somehow or other on the gametophyte for its nutritive supply. The gametophyte gives rise to sporophyte and sporophyte to the gametophyte and thus there is regular alternation of generations.

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Life Cycles in Plants and it Types (With Diagram)

All plants undergo a life cycle that takes them through both haploid and diploid generations. The multicellular diploid plant structure is called the sporophyte, which produces spores through meiotic asexual division. The multicellular haploid plant structure is called the gametophyte, which is formed from the spore and give rise to the haploid gametes. The fluctuation between these diploid and haploid stages that occurs in plants is called the alternation of generations. The way in which the alternation of generations occurs in plants depends on the type of plant. In bryophytes mosses and liverworts , the dominant generation is haploid, so that the gametophyte comprises what we think of as the main plant.

Alternation of generations is a reproductive cycle of those plants , fungi and protists in which a sexual reproductive phase alternates with an asexual reproductive phase. The term can be confusing for people familiar only with the life cycle of a typical animal. A more understandable name would be "alternation of phases of a single generation" because we usually consider a generation of a species to encompass one complete life cycle. The life cycle of organisms with "alternation of generations" is characterized by each phase consisting of one of two distinct organisms: a gametophyte thallus tissue or plant , which is genetically haploid , and a sporophyte thallus or plant , which is genetically diploid. A haploid plant of the gametophyte generation produces gametes by mitosis.

Evolutionary Developmental Biology pp Cite as. Photosynthetic organisms are found in most of the branches of the eukaryotic tree of life, and these organisms have diverse life cycles. There has been a tendency toward dominance of the diploid phase of the life cycle in the land plant lineage, and recent analyses suggest a similar trend in the brown algae. A number of hypotheses have been proposed to explain the evolutionary stability of different types of life cycle, and in some cases these hypotheses are supported by empirical studies. Molecular analyses are elucidating the regulatory molecules that control life cycle progression and are providing insights into the developmental pathways associated with the construction of each generation of the life cycle. Skip to main content.


Spore mother-cells undergo meiosis to produce haploid spores. • Spores are shed and develop into gametophytes. • And so the cycle continues. • Increasingly​.


Alternation of Generations

Alternation of generations , also called metagenesis or heterogenesis , in biology, the alternation of a sexual phase and an asexual phase in the life cycle of an organism. The two phases, or generations, are often morphologically, and sometimes chromosomally, distinct. In algae , fungi , and plants , alternation of generations is common. It is not always easy to observe, however, since one or the other of the generations is often very small, even microscopic.

The life cycles of all sexually reproducing plants follow a pattern of alternation between a haploid, sexual generation called gametophyte with a diploid, asexual generation called sporophyte. This phenomenon of alternation between gametophyte n and sporophyte 2n in the life cycle of a plant is called alternation of generations Hofmeister, Alternation of generations is of two types- isomorphic and heteromorphy. In isomorphic or homologous type both the alternating generations are morphologically similar, while in heteromophic or heterologous type of alternation of generations both the generations of life cycle are morphologically dissimilar.

Alternation of generations also known as metagenesis or heterogenesis [1] is the type of life cycle that occurs in those plants and algae in the Archaeplastida and the Heterokontophyta that have distinct haploid sexual and diploid asexual stages. In these groups, a multicellular haploid gametophyte with n chromosomes alternates with a multicellular diploid sporophyte with 2 n chromosomes, made up of n pairs. A mature sporophyte produces haploid spores by meiosis , a process which reduces the number of chromosomes to half, from 2 n to n. The haploid spores germinate and grow into a haploid gametophyte.

Different plant groups representing gametophytes and sporophytes differ in the following patterns:.

The Life Cycle of Plants

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First, they possess a sexual life cycle that requires an alternation between a multicellular haploid generation, which produces sperm and egg.


Alternation of Generations in Plants and Algae

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The Life Cycle of Plants

Какой немец. - Тот, что был в парке.

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Life perpetuates itself through reproduction, which is the transfer of genetic information from one generation to the next. This transfer is our definition of life cycle.

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