Question

Egg which contains very little amount of yolk are called as
A)Alecithal
B)Microlecithal
C)Mesolecithal
D)Polylecithal

Answer 1

Hint: The egg is the organic vessel composed of the zygote in which an embryo develops awaiting it can survive on its own, at which point the animal hatches. An egg will result from the fertilization of an egg cell. Most of the arthropods, vertebrates except live bearing mammals, and mollusks lay eggs, even though some, such as scorpions, do not.

Complete answer:
An alecithal egg is one which has a very little amount of yolk or no yolk. Yolk gives the nutrition needed for the development of the embryo and therefore its presence is necessary for organisms that are oviparous
Small eggs which have little yolk are called microlecithal eggs. The yolk is equally distributed, so the breakdown of the egg cell cuts through and divides the egg into cells of reasonably similar sizes
Microlecithal eggs necessitate minimal yolk mass. Such eggs are generally found in flatworms, roundworms, annelids, bivalves, echinoderms, the lancelet and in most marine arthropods.
Mesolecithal eggs have more yolk when compared to that of the microlecithal eggs. The yolk is concentrated in one part of the egg with the cell nucleus and most of the cytoplasm in the further. The cell cleavage is irregular, and is mainly concentrated in the cytoplasm rich animal pole.
The larger yolk present in the mesolecithal eggs allows for a longer fetal development.
Eggs with a large yolk are called macrolecithal. The eggs are usually few in number, and the embryos have enough food to go through full fetal development in most groups. Macrolecithal eggs are only found in selected representatives of two groups: Cephalopods and vertebrates.
Macrolecithal eggs go through a diverse type of development than other eggs. Owing to the large size of the yolk, the cell division cannot split up the yolk mass. The fetus as an alternative develops as a plate-like structure on top of the yolk mass and only covers it at a later stage. A part of the yolk mass is still present as an external yolk sac at hatching in many groups. This type of fetal development is general in bony fish, although their eggs can be quite small. In spite of their macrolecithal structure, the small size of the eggs does not permit for direct development, and the eggs hatch to a larval stage. Rather than the bony fish and cephalopods, macrolecithal eggs are generally seen in cartilaginous fish, reptiles, birds and monotreme mammals. The eggs of the coelacanths are about a size of 9 cm in diameter, and the young go through complete development even as in the uterus living on the copious yolk.

Hence, the correct answer is option (A)

Note: Generally the mammals have little egg yolk .In the case of human beings they are alecithal it means that it is totally absent in yolk. Yolk is necessary for providing nutrition and also for the development of the embryo. So their presence is very important in oviparous.