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

Define r and k strategists, Define r and K Strategists? Ecologists have...

Define r and K Strategists? Ecologists have identified two major types of reproductive strategies among species. Characteristic patterns can be seen among species relating the

Determine about the sense of contrast, Determine about the Sense of  Contr...

Determine about the Sense of  Contrast It is  the ability to  perceive  slight changes  in  luminance between  regions which  are not  separated by  definite borders. This  is

Health promotion for the general population, Q. Health Promotion for the Ge...

Q. Health Promotion for the General Population? Targeted to have a healthy, risk free population and involves development of an effective communication strategy to modify indiv

Differentiate between osseointegration and osseointegration, Q. List the pa...

Q. List the parameters used to differentiate between osseointegration and fibro osseointegration. The parameters used are: a) Pain b) Rigid fixation - mobility scale, pe

What is the neurotransmitter of the neuromuscular junction, What is the neu...

What is the neurotransmitter of the neuromuscular junction? How does the nervous system trigger muscle contraction? The nervous cells that trigger the muscle contraction are th

What are the physical signs of mitral stenosis, Q. What are the Physical Si...

Q. What are the Physical Signs of mitral stenosis? A typical malar flush is described in mitral stenosis. It is difficult to appreciate in Indians. Pulse is normal or low volum

What is the salivary digestive enzyme, What is the salivary digestive enzym...

What is the salivary digestive enzyme? Which type of food does it digest and into which smaller molecules does it transform the food? The salivary hydrolase is called as saliva

Ameoba, locomotion in amoeba

locomotion in amoeba

What are the main structures of chloroplasts, What are the main structures ...

What are the main structures of chloroplasts? Chloroplasts are included by two membrane layers, the outer and the inner membranes. Inside the organelle the formative unit is kn

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