Question

Types of cleavage in centrolecithal eggs is
(a)Spiral
(b)Superficial
(c)Discoidal
(d)Unequal holoblastic

Answer 1

Hint: This meroblastic cleavage in which a layer of cells is produced about a central mass of yolk, this type of cleavage is characteristic of insects that have centrolecithal eggs (i.e. the yolk is located in the centre of the egg cell).

Complete answer:
Centrolecithal eggs describe the location of the yolk within the centre of the cytoplasm of the ovum. The cytokinesis of centrolecithal zygotes undergoes meroblastic cleavage. It is a kind of the cleavage during which the cleavage plane extends only to the accumulated yolk and is superficial.

Additional Information:
Superficial cleavage is characterised by the process of karyokinesis which results in the formation of multiple nuclei but lacks the process of cytokinesis. With the yolk positioned within the centre of the ovum, the nuclei migrate to the periphery of the egg and therefore the cell wall grows inward, partitioning the nuclei into individual cells. Superficial cleavage takes place in the Phylum Arthropods (including insects) which have centrolecithal egg cells.

So, the correct answer is, ‘Superficial.’

Note:
-Eggs of cockroaches are centrolecithal. The zygotes will undergo the cleavage, that is meroblastic cleavage, in which the cleavage plane extends only to the accumulated yolk and is superficial and this happens when cytokinesis takes place. This is often because of the massive dense yolk found within centrolecithal eggs and helps in delayed embryonic development.
-The types of eggs based on yolk characteristics are of 4 types and is described as:
-Isolecithal: sparse evenly distributed yolk, eg. sea urchin, mouse
-Mesolecithal: a moderate amount of yolk, often unevenly distributed, eg. frog
-Telolecithal: dense yolk concentrated at one end, eg. bird, reptile
-Centrolecithal: yolk is observed to be concentrated at the middle of the egg, eg. fly