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

Briefly explain what is the leaf, Briefly explain what is The Leaf? In a ...

Briefly explain what is The Leaf? In a typical dicot, leaf primordia arise from the apical meristem, which is housed within the terminal bud on a shoot. The leaf cells are produc

Genetic diversity of population, Genetic Diversity of Population The b...

Genetic Diversity of Population The biological diversity of animals, plants, and microorganisms is of fundamental importance to human survival. The term "gene resources" may b

Krebs cycle, Krebs Cycle The acetyl  group  of acetyl   co A  is now co...

Krebs Cycle The acetyl  group  of acetyl   co A  is now completey  degraded  stepwise  into  carbon  and hydrogen atoms  in the mitochondria  by a cyclic  sequence of  eight ma

Contractile vacuoles - excretion, Normal 0 false false fals...

Normal 0 false false false EN-IN X-NONE X-NONE MicrosoftInternetExplorer4

Explain subclavian flap aortoplasty, Explain Subclavian Flap Aortoplasty ? ...

Explain Subclavian Flap Aortoplasty ? Initial steps are same as for resection and end-to-end anastomosis. After exposing a the entire length of intra thoracic segment of left s

What are the main techniques of genetic engineering, At the present level o...

At the present level of the biotechnology what are the main techniques of genetic engineering? The main methods of genetic engineering today are: the recombinant DNA technology

Kangroo rat, Kangroo Rat Kangroo rat Dipodornys merriami, a native of ...

Kangroo Rat Kangroo rat Dipodornys merriami, a native of South-West America is a classical example of how small mammals survive in desert. It exhibits all the osmoregulatoryad

Explain feeding schedule in infancy, Explain Feeding Schedule in Infancy? ...

Explain Feeding Schedule in Infancy? 1) Milk feed 5-6 times/day. Continue breast-feeding. Exclusive breast-feeding up to 6 months even during illness. Follow demand feeding.

Adrenal medulla, ADRENA L MEDULLA The adrenal medulla develops from th...

ADRENA L MEDULLA The adrenal medulla develops from the neuroectoderm of the embryo. Medulla consists of chromaffin cells or phaeochromocytes. These cells are connected wi

What are the responsibilities of cber, Question 1: Explain how drug app...

Question 1: Explain how drug approval is obtained through various Regulatory Bodies in India using a flow diagram? List out the different regulatory bodies in India L

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