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Sunday, 26 September 2021

Stamen, Microsporangium and Microsporogenesis l Sexual reproduction in flowering plants l NEET l Class XII l NOTES


Stamen, Microsporangium and Microsporogenesis 



·         There are two parts of a typical stamen –


      the long and slender stalk called the filament, and


      the terminal generally bilobed structure called the anther.


·         The proximal end of the filament is attached to the thalamus or the petal of the flower.


·         Anther & filament are attached together with help of small region,  called connective.


·         A typical angiosperm anther


      is bilobed

--- with each lobe having two theca,

                           i.e., they are dithecous.

·         Often a longitudinal groove runs lengthwise separating the theca.


·         The bilobed nature of an anther is very distinct in the transverse section of the anther.

·         The anther


      is a four-sided (tetragonal) structure

      consisting of four microsporangia (tetrasporangiate)


Ø  located at the corners,

Ø  two in each lobe.


·          The microsporangia

      develop further and


      become pollen sacs.

Ø  They extend longitudinally all through the length of an anther and

Ø   are packed with pollen grains.


Structure of microsporangium:


·         In a transverse section, a typical microsporangium appears near circular in outline.


·         It is generally surrounded by four wall layers


1.       Epidermis,

2.       Endothecium,

3.       Middle layers

4.       The tapetum


·         The outer three wall layers


      perform the function of protection and

      help in dehiscence of anther to release the pollen.


·         The innermost wall layer is known as tapetum.


      It  nourishes the developing pollen grains.


       Cells of the tapetum possess dense cytoplasm


      It generally have more than one nucleus.


·         Tapetal cells  become bi-nucleated by endoploidy.



·         When the anther is young,


      a group of compactly arranged homogenous cells called the sporogenous tissue


                                                       occupies the centre of each microsporangium.


Microsporogenesis :


·         As the anther develops,


      the cells of the sporogenous tissue

---  undergo meiotic divisions


                      ---- to form microspore tetrads.


·         Cells of the tetrad are haploid.


·          As each cell of the sporogenous tissue


      is capable of giving rise to a microspore tetrad.

      Each one is a potential pollen or microspore mother cell (PMC).


·          The process of


      formation of microspores from a pollen mother cell


F  through meiosis

               is called microsporogenesis.


·         The microspores, as they are formed, are arranged in a cluster of four cells–the microspore tetrad .


·         As the anthers mature and dehydrate, the microspores dissociate from each other and develop into pollen grains .


·         Inside each microsporangium


      several thousands of microspores or pollen grains are formed


F  that are released with the dehiscence of anther




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