Angiosperms
Angiosperms are the flowering plants, in which pollen grains and ovules are developed on a special structure called flower. The seeds are enclosed by fruits.
The plant body is well developed and differentiated into root, stem and leaves.
They have a well-developed conducting tissues.
The size varies from microscopic (Wolfia) to tall trees like Eucalyptus.
They are divided into two classes: the dicotyledons and the monocotyledons.
The dicotyledons have two cotyledons in seeds and monocotyledons have single cotyledon.
Flower is the organ of reproduction formed on a special branch of stem. It consists of male reproductive structure called stamen and female reproductive structure called pistil or carpel.
Each stamen consists of filament, connective and anther at the tip. In the anthers, meiotic division produces pollen grains.
Pistil consists of an ovary enclosing one or many ovules.
Each embryo-sac has three celled egg apparatus, which consist one egg cell and two synargid cells. Three haploid antipodal cells are present opposite to egg apparatus. Another two cells fuse themselves form diploid nucleus or secondary nucleus.
Pollen grain, after dispersal from the anthers, are carried by various other agencies to the stigma of a pistil. The transfer of pollen to the stigma of a flower is called pollination.
Pollen grain germinates on stigma and pollen tube grows towards ovule.
Pollen tube enters the embryo-sac and discharges two male gametes. One male gamete fuses with egg cell forms zygote (syngamy), another gamete fuse with diploid secondary nucleus forms triploid primary endosperm nucleus (PEN).
This process involves double fusion, hence this event is called double fertilization.
The PEN develops into endosperm, which provides nourishment to the developing embryo.
The synergids and antipodals degenerate after fertilization.
After fertilization, ovule develops into seed and ovary develops into fruit.
Life Cycle of an Angiosperm
Plant Life Cycles and Alternation of Generation
In plants both haploid and diploid cells divides mitotically, resulting in different plant bodies.
The haploid plant produce gametes by mitosis, such plant body represent gametophyte. The fusion of gametes forms zygote, the zygote divides mitotically and develops the diploid sporophyte.
In all sexually reproducing plants there is an alternation of generation between haploid gametophyte and diploid sporophyte.
Haplontic Life Cycle
The dominant, photosynthetic phase in such plants is the free-living gametophyte.
Fusion of gametes forms single celled diploid zygote, it represent sporophyte. There are no free living sporophyte.
Meiosis in zygote forms haploid spores. The haploid spores divide mitotically, forming gametophyte.
The gametophyte is dominant photosynthetic stage.
Ex: Volvox, Spirogyra
Diplontic Life Cycle
In this type diploid sporophyte is dominant. It is photosynthetic and independent.
The gametophytic stage is represented by single or many celled gametophyte.
Gametophyte divides meiotically producing haploid gametes. The fusion of gametes forms zygote.
Zygote divides mitotically producing dominant sporophyte.
Ex: Angiosperms and Gymnosperms
Haplo-Diplontic Life Cycle
Both sporophytic and gametophytic stages are multicellular and free living. They differ in their dominant stages.
The gametophytes are thalloid, independent, photosynthetic and haploid gametophytic stage.
It alternates with short living multicellular, diploid sporophytic stage, either partially or totally depend on gametophyte, for anchorage and nutrition. This type is seen in bryophytes.
In pteridophytes, sporophyte is dominant, independent, photosynthetic and vascular.
It alternates with multicellular, autotrophic, photosynthetic, short lived haploid gametophytic stage.
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Angiosperms are the flowering plants, in which pollen grains and ovules are developed on a special structure called flower. The seeds are enclosed by fruits.
The plant body is well developed and differentiated into root, stem and leaves.
They have a well-developed conducting tissues.
The size varies from microscopic (Wolfia) to tall trees like Eucalyptus.
They are divided into two classes: the dicotyledons and the monocotyledons.
The dicotyledons have two cotyledons in seeds and monocotyledons have single cotyledon.
Flower is the organ of reproduction formed on a special branch of stem. It consists of male reproductive structure called stamen and female reproductive structure called pistil or carpel.
Each stamen consists of filament, connective and anther at the tip. In the anthers, meiotic division produces pollen grains.
Pistil consists of an ovary enclosing one or many ovules.
Each embryo-sac has three celled egg apparatus, which consist one egg cell and two synargid cells. Three haploid antipodal cells are present opposite to egg apparatus. Another two cells fuse themselves form diploid nucleus or secondary nucleus.
Pollen grain, after dispersal from the anthers, are carried by various other agencies to the stigma of a pistil. The transfer of pollen to the stigma of a flower is called pollination.
Pollen grain germinates on stigma and pollen tube grows towards ovule.
Pollen tube enters the embryo-sac and discharges two male gametes. One male gamete fuses with egg cell forms zygote (syngamy), another gamete fuse with diploid secondary nucleus forms triploid primary endosperm nucleus (PEN).
This process involves double fusion, hence this event is called double fertilization.
The PEN develops into endosperm, which provides nourishment to the developing embryo.
The synergids and antipodals degenerate after fertilization.
After fertilization, ovule develops into seed and ovary develops into fruit.
Life Cycle of an Angiosperm
Plant Life Cycles and Alternation of Generation
In plants both haploid and diploid cells divides mitotically, resulting in different plant bodies.
The haploid plant produce gametes by mitosis, such plant body represent gametophyte. The fusion of gametes forms zygote, the zygote divides mitotically and develops the diploid sporophyte.
In all sexually reproducing plants there is an alternation of generation between haploid gametophyte and diploid sporophyte.
Haplontic Life Cycle
The dominant, photosynthetic phase in such plants is the free-living gametophyte.
Fusion of gametes forms single celled diploid zygote, it represent sporophyte. There are no free living sporophyte.
Meiosis in zygote forms haploid spores. The haploid spores divide mitotically, forming gametophyte.
The gametophyte is dominant photosynthetic stage.
Ex: Volvox, Spirogyra
Diplontic Life Cycle
In this type diploid sporophyte is dominant. It is photosynthetic and independent.
The gametophytic stage is represented by single or many celled gametophyte.
Gametophyte divides meiotically producing haploid gametes. The fusion of gametes forms zygote.
Zygote divides mitotically producing dominant sporophyte.
Ex: Angiosperms and Gymnosperms
Both sporophytic and gametophytic stages are multicellular and free living. They differ in their dominant stages.
The gametophytes are thalloid, independent, photosynthetic and haploid gametophytic stage.
It alternates with short living multicellular, diploid sporophytic stage, either partially or totally depend on gametophyte, for anchorage and nutrition. This type is seen in bryophytes.
In pteridophytes, sporophyte is dominant, independent, photosynthetic and vascular.
It alternates with multicellular, autotrophic, photosynthetic, short lived haploid gametophytic stage.
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