Question

Which of the following is a microlecithal egg?
a. Insects
b. Fishes
c. Birds
d. Mammals

Answer 1

Hint: There are three types of eggs according to the proportion of the yolk to the cytoplasm of the ovum. These are microlecithal eggs, mesolecithal eggs and macrolecithal eggs. Yolk of an egg plays a major role in the supply of energy and synthesis of products required for the embryonic body. Yolk helps in development of an embryo and influences size of an egg, patterns of cleavage, type of development of an egg, etc.

Complete answer:
- Microlecithal eggs are the eggs which contain very little yolk in it but the amount of cytoplasm is high. These eggs are generally small in size as compared to other types of eggs. The eggs of marsupials, amphioxus and eutherian mammals are of this category of eggs. Eggs of mammals contain very little yolk and are termed as alecithal eggs which mean egg without yolk.
- Mesolecithal eggs have a moderate amount of yolk in them and the distribution of yolk is unequal in the egg. Examples of mesolecithal eggs are sharks, amphibians, ganoid fishes, etc.
- Macrolecithal eggs are the eggs in which yolk is present in large amounts and cytoplasm is less in quantity. The size of these eggs can be small or big. Examples of macrolecithal eggs are reptiles, birds, etc.

Hence, The correct answer is option (D).

Note: According to the distribution of yolk in the egg, the egg is classified further into three types- Homolecithal eggs are the eggs in which yolk is uniformly distributed throughout the cytoplasm of an egg. Examples are mammals, amphioxus, etc. Centrolecithal eggs are the eggs which contain yolk at the centre surrounded by cytoplasm. Examples are insects, arthropods etc. Telolecithal eggs contain yolk concentrated in one hemisphere of an egg. Examples are fishes, reptiles, etc.