life cycle of gymnospermae and angiospermae

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 life cycles of gymnosperm and angiosperm such that its example characteristics and there life cycles and the thing if you want to know anything related to biology so please let me know down in the comment section and please follow my blog to show your great support so
                           lets start 
CLASS GYMNOSPERMAE
introduction 
*such that gymno means naked and spermae means seed
*so gymnosperms are defined as such of the plants that produces naked seed such that seed is present outside of their body without any of the protection so that is the reason they are known as the naked seed plants 
characteristics 
*gymnosperms are one of the most successful group of seed plants such as that plants that produces seeds such that these type of plants are found all over the world 
*these type of plants contribute to about one third of the worlds forests 
*the gymnosperms are heterosporous plants which produces seeds bot no fruits the two kind of spores that are found in the are the microspore and the other one is known as the megaspore which than develops microsporophyll and megasporophyll respectively that than forms the male and female reproductive parts and cells respectively 
*the ovules in these type of plants are usually borne on the exposed surface of the fertile leaves megasporophyll these ovules unlike those of angiosperms are not enclosed but lie naked on tthe surface of fertile leaves 
*they show regular heteromorphic alternation of generation such that in them different generations are found that alters with each with other they have independent dominant sporophyte but less conspicuous dependent gametophyte the female gametophyte is permanent retained within the ovule 
*the megasporangium bearing ovules are not folded and joined at the margins to form an ovary 
classification 
some of the important genera of class gymnosperms are 
*Cycas (sago palm)
*Pinus  (pines)
*Taxus  (yew)
*Picea  (hemlock)
*Cedrus (deodar)
*Ginkgo 
*etc 
life cycle of pinus
introduction 
pinus is a conifer which belongs to the class gymnosperm conifers are heterosporous 
life cycle 
in the life cycle of pinus the dominant diploid sporophyte generation alternates with inconspicuous gametophyte generation 
the main plant body is sporophyte 
steps of life cycle with characteristics features 
formation of cones 
such that in them male and female cone are produced on the same plant 
*male cones are small in size and produced in clusters on an axis 
*female cones are large in size and are conspicuous 
formation of megagametophyte 
the megasporangium is located on the female cone each of the female cone is composed of large number of spirally arranged scale leaves megasporophyll which are woody in texture at the base of each scale is an ovule an ovule is actually a megasporangium which is protected by two integuments each of the megasporangium has a single diploid megaspore mother cell the megaspore mother cell divides meiotically to produce four haploid megaspores the functional megaspore (n) undergo mitosis to produce the female gametophyte or an embryo sac the embryo sac contains one to several archegonia the archegonia contains the female gamete or an egg
formation of microgametophyte 
microspore are formed in the microsporangium which are present on the microsporophyll the microspore germinates with in its own wall to form a small inconspicuous male gametophyte by meiosis such a microspore of seed plant that contains the microgametophyte or the male gametophyte including the gamete is known as the pollen grain 
pollination 
pollen grain in pinus has two wings attached to the lateral sides pollen are produced in great number and are  carried by wind due to the presence of wing they can float a long distance during the pollination the pollen lands directly on the ovule 
fertilization 
only a few pollen are able to germinate to form the pollen tubes through which male gametes are transferred to the embryo sac for the fertilization more than one egg can be fertilized to form several zygotes but only one of the zygote survives to form a single embryo after the fertilization the ovule becomes the seed 
germination of new sporophyte plant 
the seed contains a embryo along with some of the stored food material the seed upon the germination give rise to a new sporophyte plant 
in the life cycle of pinus the dominant diploid sporophyte generation alternates with the inconspicuous haploid gametophyte generation 
CLASS ANGIOSPERMAE
introduction 
angio means closed and sperm means seed 
such plants that have their seed protected by the parent body are known as the angiosperms such that the word angiosperm means enclosed seeded plants 
features 
*angiosperms make about 235000 of the 360000 known species of plants 
*they are heterosporous autotrophic plants 
*they are the most abundant and the most successful of all the plants present on the earth 
*they produce flowers fruits and seeds 
*in these plants fertile leaves bearing ovules are folded and joined at the margins to form ovaries the ovary after the fertilization is changed into a fruit containing fruit 
life cycle of an angiosperm plant 
introduction 
angiospermic plants show heteromorphic alternation of generation 
features 
*the adult plant is diploid sporophyte mostly differentiated into roots stems and leaves 
*at maturity sporophyte plant produces flowers 
*the flower is a modified shoot that consist of pedicel thalamus that is also known as the torus and the floral leave that are sepals petals stamens and the carpels thalamus and the floral leaves especially the stamen and carpels are so modified that they dont even look like stem and leaves respectively
*the sepals and petals are the non essential or non reproductive parts sepals protect the inner parts while petals attracts the insects for the process of pollination when the pollination is over the petals and sepals usually fall off
*stamens and carpels are the essential or reproductive parts of the flower the stamen consist of a filament and an anther it is male reproductive part of the flower 
*the carpels consist of a basal broader part the ovary the style and the terminal part of the style the stigma carpel is female reproductive part of the flower 
life cycle 
different steps occurring through the life cycle of an angiosperm are as following 
formation of megasporangium 
the ovary contains ovule which consist of an integument covering and the tissue and the nucellus present inside 
inside a ovule a megaspore cell (2n) is present which on meiosis produces four haploid megaspores (n)
*one of the remaining functional megaspore divides by the mitosis to form the eight cells two group of three cells each move towards opposite pole each the remaining two central cells join to form the diploid fusion nucleus 
out of three cellspresent near the microphyle one is the egg central 
the seven celled structure containing the egg and the fusion nucleus is called as the female gametophyte  
formation of pollen grains
inside the pollen sac several microspores are produced by meiosis each of the microspore consist of two nuclei generative and the tube nucleus the microspore is than also known as the pollen grain 
pollination 
during the process of pollination the pollen grain is transferred from anther to stamen to stigma of carpel 
formation of microgametophyte 
the pollen tube grow through the style enters the ovule and then reaches the female gametophyte here it discharges the male gametes the sperms 
*one of the sperm (n) combines with the egg(n) to form the zygote 2n 
*other sperm combines with the fusion nucleus 2n to form the endospermic tissues 3n 
                  thanks for reading                             

    
               
       

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