Question

In which egg is the yolk found in the centre and the peripheral part is yolk-less?
(a)Homolecithal
(b)Microlecithal
(c)Centrolecithal
(d)Telolecithal

Answer 1

This type of egg is present in insects where the yolk is present in the centre of the cytoplasm. The name signifies the yolk position. Superficial cleavage occurs in this type of egg.

Complete answer:
Egg of the many arthropods and a few coelenterates are described as centrolecithal. They are relatively large and elongate and have a really large amount of yolk. The nucleus lies at the geometric centre of the yolk mass, surrounded by a little amount of cytoplasm.

Additional Information: Isolecithal or Homolecithal Egg:
In isolecithal eggs, the little or no amount of yolk present is uniformly distributed throughout the ooplasm eg. echinoderms, Amphioxus, mammals. This condition is typically observed in eggs with little or no amount of yolk.
Telolecithal Egg:
In eggs containing moderate or large quantities of yolk, the distribution of yolk is not uniform. lt is concentrated more towards the vegetal pole. Egg, in which the yolk is concentrated towards one pole, is called a telolecithal egg. Telolecithal eggs may further classified into three types:
-Slightly Telolecithal- this sort of egg contains only a little quantity of yolk which is distributed unevenly. The vegetal pole has the very best concentration and therefore the animal pole the lower e.g. eggs of fishes.
-Moderately Telolecithal -This type of egg contains a moderate quantity of yolk which is distributed unevenly. Due to high concentration of yolk in the vegetal hemisphere, the nucleus is shifted more towards the animal hemisphere eg. amphibian egg.
-Extremely Telolecithal -In this sort of egg, thanks to the heavy deposition of yolk, the whole vegetal hemisphere and a serious portion of the animal hemisphere are occupied by yolk.

So, the correct answer is, ‘Centrolecithal.’

Note: -Cleidoic egg - These eggs contain a hard shell that is permeable for gases. Yolk, Salts and Water is present in large amounts in cleidoic eggs. Cleidoic egg is a terrestrial adaptation. Such as, Birds & Reptiles, Prototheria mammals and insects.
-Non Cleidoic egg - Egg membranes are soft in these eggs such as. All viviparous animals and oviparous animals which lay eggs in water.