Egg - synergids, Biology

Assignment Help:

Egg - Synergids

The three cells of the egg apparatus are arranged in triangular fashion with the egg sharing a common wall with the two synergids and the central cell. In the egg the wall is thicker at the micropylar end and is absent at the chalazal end. At this end the lateral walls of the egg cell appear to join the central cell wall. The egg cell wall is traversed by plasmodesmata on the sides of the two synergids and the central cell but not at its outer face. The egg cell becomes highly polarized early in its development. Polarity is expressed by the aggregation of cytoplasmic elements at the chalazal end of the cell. The micropylar end of the cell is occupied by a large vacuole. Thus, the distribution of the vacuole and cytoplasm in the egg cell is just the opposite of that in the synergids.

The ultra structure of the egg cytoplasm indicates that it is inactive. The mitochondria show only a few cristae. But for Zea mays, dictyosomes are either absent (Epidendrum) or are only a few in numbers. Where present, the dictyosomes exhibit an inactive state. Plastids are present in the egg; they often contain a striking difference from the male gametes. The egg cytoplasm is rich in ribosomes. In Plumbago capensis where the embryo sac lacks synergids. However many finger- like wall projections arise at the micropylar end of the egg cell. They resemble the filiform apparatus of the synergids. In this plant the egg cell seems to have taken over the role of synergids in addition to its own gametic function.


Related Discussions:- Egg - synergids

Why do fats have thermal isolation properties, Why do fats have thermal iso...

Why do fats have thermal isolation properties? Triglycerides are weak heat conductors and in addition they form thick layers of fat tissue when accumulated by the organism. Tha

Precautions for estimation of sucrose by fehling soxhlet, Explain Precautio...

Explain Precautions for Estimation of Sucrose by Fehling Soxhlet Method? 1. Maintain proper temperature of the water bath for complete hydrolysis. 2. Add distilled water to

Determine some guidelines for cancer prevention, Determine Some Guidelines ...

Determine Some Guidelines for Cancer Prevention? The guidelines for cancer prevention focus on the following: 1. Include plant-based diet, limiting red meat in particular.

Explain about climate regulation, Q. Explain about Climate Regulation? ...

Q. Explain about Climate Regulation? By giving off moisture through their leaves and providing shade, plants help keep us and other animals cool. Forests are especially good cl

Johne’s disease, Johne’s disease The disease, discovered by Heinrich A....

Johne’s disease The disease, discovered by Heinrich A. Johne, a German bacteriologist and veterinarian, in 1905, is caused by a bacterium named Mycobacterium avium subspecies p

Rules of nomenclature classification, Q. Rules of Nomenclature classificati...

Q. Rules of Nomenclature classification? The Rules of Nomenclature prescribed the categories into which plants should be classified. These categories constitute the units of cl

Can you show downsloping st-segment, Q. Can you show Downsloping ST-Segment...

Q. Can you show Downsloping ST-Segment? The long term follow-up information suggests that patients whose ST depression evolves to downsloping have more severe disease than tho

Promotion - stages of carcinogenesis, Promotion - Stages of carcinogenesis ...

Promotion - Stages of carcinogenesis The second stage or promotion is reversible and does not include changes in structure of DNA but rather in the expression of the genome of

How will this increase survival, Why would we evolve so that when we are st...

Why would we evolve so that when we are stressed our immune system is suppressed? How would this increase survival?

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