classification of bryophytes and alternation of generation

hi
hope well thanks for your great support in the previous segments of this blog so in this segment of the blog i would like to talk about classification of bryophytes means its types and each type characteristics habitat examples its dormant generation characteristics of sporophytes and of gametophyte so
                                 LETS START
such that bryophytes are divided into three classes that are 
*hepaticopside
*bryopsida 
*anthoceropsida
HEPATICOPSIDA
introduction 
bryophytes belonging to this group is known as the liverworts this class of bryophytes includes about 900 species liverworts are the simplest of all the bryophytes 
habitat 
such that they are confined to or found in moist rocks and on wet and shady places since they live near water so chances of drying out are greatly reduced 
examples  
some of the common examples of liverworts are marchantia & porella
alternation of generation
their main plant body is gametophyte 
features of gametophyte 
*in them the gametophyte is haploid
*it may be thalloid such that flat or ribbon like usually dichotomously branched 
*it is generally attached to the soil by the means of special structure known as the rhizoids such that marchantia other species tends to grow upright and are falsely leafy such that differentiated into false stem and leaves that is present in porella 
*the sex organs develop on the upper surface of the thallus near the tips of the branches 
*in some condition sometimes sex organs develop on special branches on gametophyte that are known as antheridiophores and the archegoniophore such as in marchantia 
features of sporophyte 
* in them the sporophyte is diploid 
*it is dependent on gametophyte
BRYOPSIDA 
introduction 
bryophytes belonging to this group are known as the mosses they usually grow to form cushions or mats 
habitat
like liverworts most of the mosses inhibit in damp places in contrast to other bryophytes they grow equally well in fairly dry places however water is essential in the reproduction of water
examples 
some of the common examples of them is funaria & polytrichum
alternation of generation 
the main body or the main generation in them is gametophyte 
features of gametophyte *gametophyte is haploid and always differentiated into structure which resembles stem and leaves 
*multicellular rhizoids are also present 
*sexual reproductive organs archegonia and antheridia develop on the tip of different branches on the same plant as in funaria or on different plants as in polytrichum 
*the archegonia and antheridia form clusters and are mixed with sterile hairs forming a structure known as the paraphyses
features of sporophyte 
*diploid sporophyte produces haploid spores through meiosis
*spores of a moss unlike of liverworts develop into a alga like structure called as the protonema 
*protonema produces a bud from a haploid moss plant gametophyte is formed 
ANTHOCEROPSIDA
introduction 
bryophytes belonging to this class or group are known as the hornworts this group is slightly advanced than bryopsida & hepaticopsida 
examples 
one very good example of anthoceropsida is anthocerous which is also found in hilly areas 
features of gametophyte 
*gametophyte is highly lobed and irregular in outline 
*antheridia and archegonia are partially sunken in the gametophyte tissues 
features of sporophyte 
*the spores of them also show many of the advanced characters than the other classes due to which it can better survive on land as compared to other classes 
*except for a little early stage of development the sporophyte is not dependent upon its gametophyte for the nourishment and for protection 
*it has stomata and chloroplast in epidermis and can thus photosynthesize it own food rather than obtaining it from the gametophyte 
*it has a thick and waxy cuticle to check excessive loss of water that can cause desiccation 
*at the junction of foot and spores producing region there is a band of meristematic tissue this type of tissue keep on adding cell towards the spore producing region during the formation maturation and dispersal of spores from the opposite end due to fast growth rate of this meristematic tissue the sporophyte keeps on increasing in length for an indefinite period of time
*due to these characteristics the sporophyte continues to survive as such even after the death and decay of the gametophyte 
alternation of generation 
*in the life history of liverworts mosses and hornworts there are two distinct multicellular phases or you can call it generations
*these two generations are haploid gametophyte and diploid sporophyte which regularly alternate with each other 
*the gametophyte is the dormant generation because it is more conspicuous
*a haploid spermatozoid fuses with a haploid egg to produce diploid oospore 
*the oospore does not produces the gametophyte directly but produces a totally different plant called as the  sporophyte 
*the sporophyte in bryophytes is a less conspicuous generation which is usually differentiated into foot seta and capsule and called as the sporogonium
*spores develop inside the capsule by reductive division that is meiosis from spore mother cell
*the sporophyte produces spores and is therefore called as the spore producing generation 
*these produced spores on germination does not develop into a new sporophyte but instead give rise to the gametophyte gametes producing generation 
*thus in the life history of a bryophyte plant the two generations the gametophytic and the sporophyte regularly alternate with each other 
*this phenomena of alternation of generation of gametophyte and sporophyte in the life history of a plant is called as the alternation of generation 
*it should be noted that gametophyte or haploid stage begins with spores and ends at the gametes whereas the sporophyte begins with oospore and ends at spore mother cell
SIGNIFICANCE OF ALTERNATION OF GENERATION   
some of the significantly important points of alternation of generation are as following 
source of genetic recombination 
during the formation of spores from the spore mother cell by meiotic division reshuffling of genes occurs as a consequence a great variety of spores with different genetic combination 
better chances of survival 
the gametophyte with better genetic make up will have a better chance of survival in the harsh environment where they occur on the other hand gametophyte with less better characters will be eliminated there would be no reshuffling of genes during gametogenesis in the gametophytes as the gametes are produced after the mitosis the oospore developing after fertilization now has a new genetic make up as compared to the parent this genetic variation passes to the new sporophyte which on maturity once again produces further genetic recombination which are transferred to the gametophyte in this natural process the sporophyte this provides a large amount of genetic variability and nature selects the best genetic combinations
evolution 
on the basis of variation natural selection acts on population and thus cause evolution 

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