Female gametophyte, Biology

Assignment Help:

Female Gametophyte

The development of a female gametophyte is initiated with the enlargement of one of the megaspores (usually the one close to the chalaza in a linear tetrad) followed by three mitotic divisions. Thus, the female gametophyte, also called the embryo sac is almost always a 7-celled or 8-nucleate structure. The eight nuclei thus formed organize into the egg apparatus, central cell with two polar nuclei and three antipodal cells. This mode of embryo sac development occurs in the majority of flowering plants.

There are variations from this mode of female gametophyte development. In order to visualize these deviations let us recall the formation of megaspore tetrad. Out of the four megaspores, three degenerate and only one participates in the formation of embryo sac. This mode of development of female gametophyte is known as the monosporic type. In some plants, two megaspores out of four participate. For example, if after meiosis, the lower or the upper dyad produces the embryo sac and the other degenerates, the development is termed bisporic. Sometimes, cell plate formation does not occur after any of the meiotic divisions and all the four megaspore nuclei contribute to embryo sac formation. 'This is called tetrasporic type of development. Depending upon the orientation and subsequent behavior of the megaspore nuclei and their derivatives, the tetrasporic gametophyte may be of several types.


Related Discussions:- Female gametophyte

Systematics, How do we define an living organism

How do we define an living organism

Why o-h bond is a polar covalent bond, Describe how electro negativity can ...

Describe how electro negativity can explain why a C-H bond is a no polar covalent bond, but a O-H bond is a polar covalent bond.

Orifices of heart, Atrio-ventricular Orifices The right and left atrio-v...

Atrio-ventricular Orifices The right and left atrio-ventricular orifices are oval apertures. The openings lie in a plane that is almost vertical with a slight downward inclinati

Protozoans - body form, Protozoans - Body Form The protozoan body is ...

Protozoans - Body Form The protozoan body is usually bound only by the cell membrane called plasmalemma. In some protozoans such as in ciliates the rigidity and the flexibili

Hydrostatic skeleton, Hydrostatic Skeleton The functioning of the hyd...

Hydrostatic Skeleton The functioning of the hydrostatic skeleton in an animal depends upon the musculature being arranged around an enclosed volume of fluid. After that, cont

Define aortic regurgitation, Q. Define Aortic regurgitation? Aortic reg...

Q. Define Aortic regurgitation? Aortic regurgitation is a common valvular disease that may present chronically or acutely. Normally the integrity of valve closure depends upon

Corpus allatum and prothoracic gland, Corpus Allatum and Prothoracic Gland ...

Corpus Allatum and Prothoracic Gland Corpus Allatum The corpus allatum is situated in the neck region of insects. It is generally a rounded, solid and translucent struc

Determine the types of neuropsychology, Determine the types of neuropsychol...

Determine the types of neuropsychology The practise in neuropsychology is roughly divided into two approaches. Some practitioners use standard comprehensive neuropsychological

Sex-influenced traits, what are the examples of sex-influenced traits in hu...

what are the examples of sex-influenced traits in human?

What process occurred during the formation of the platelet, Removal of a pa...

Removal of a patient's peripheral intravenous catheter resulted in brief bleeding and the loss of a small amount of blood. Which of the following processes occurred during the form

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd