Class 11 Biology Plant Kingdom Angiosperms

Angiosperms

  • In the angiosperms or flowering plants, the pollen grains and ovules are developed in specialized structures called flowers and the seeds are enclosed by fruits.

Class_11_Biology_Plant_Kingdom_Angiosperms1

Fig. Angiosperms

  • They are divided into two classes
  • The dicotyledons - characterized by having two cotyledons in their seeds.
  • The monocotyledons- have only one cotyledon.

Class_11_Biology_Plant_Kingdom_Dicot_Plant

Fig. A dicot plant

Class_11_Biology_Plant_Kingdom_Monocot_Plant

Fig. A monocot plant

  • The male sex organs in a flower is the stamen, consists of a slender filament with an anther at the tip and the anthers, following meiosis, produce pollen grains.
  • The female sex organs in a flower is the pistil or the carpel, consists of an ovary enclosing one to many ovules.
  • Within ovules highly reduced female gametophytes are present, termed as embryo sacs.
  • The embryo-sac formation is preceded by meiosis.
  • Each embryo-sac has a three-celled egg apparatus – one egg cell and two synergids, three antipodal cells and two polar nuclei, the polar nuclei eventually fuse to produce a diploid secondary nucleus.
  • Pollen grain, after dispersal from the anthers, are carried by wind or various other agencies to the stigma of a pistil this is termed as pollination.

Class_11_Biology_Plant_Kingdom_Pollination

Fig. Pollination

  • The pollen tubes enter the embryo-sac where two male gametes are discharged, one of the male gametes fuses with the egg cell to form a zygote (syngamy) and the other male gamete fuses with the diploid secondary nucleus to produce the triploid primary endosperm nucleus (PEN), termed as double fertilization.
  • The zygote develops into an embryo and the PEN develops into endosperm which provides nourishment to the developing embryo.
  • The synergids and antipodal cells degenerate after fertilization, during these events the ovules develop into seeds and the ovaries develop into fruit.

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