Question

Egg with large amount of yolk is
A. Microlecithal
B. Mesolecithal
C. Oligolecithal
D. Macrolecithal

Answer 1

Hint: The egg has a yellow part in the centre that is well centered in the albumen, the white part of the egg and it is surrounded by vitelline membrane that is transparent. Other parts of egg are shell, membrane, aircel, egg white, egg yolk and chalaza.

Complete answer:
Yolk is the nutrient bearing portion of the egg and it supplies food to the developing embryo. In a large egg there is 17 grams of yolk and a yolk makes almost 33% of the liquid weight of the egg. Amount of yolk varies in eggs as in some eggs the amount of yolk is very less and in other yolk is present in large amounts than the amount of the cytoplasm.

> Option A- Microlecithal- In these eggs the amount of yolk is much less than the amount of cytoplasm. Such eggs are found in flatworms, roundworms, marine arthropods etc.

> Option B- Mesolecithal – In mesolecithal eggs there is comparatively more yolk than the macrolecithal. In such eggs cell cleavage is uneven, yolk is concentrated in one part of the egg with the cell nucleus and most of cytoplasm on other part of egg.

> Option C- Oligolecithal- These eggs have little yolk in the cytoplasm. Such eggs are found in higher mammals and some invertebrates.

> Option D- Macrolecithal: The egg that have large amount of yolk is called macrolecithal. These eggs have large concentrated yolk, such eggs are found in crocodile, aves, chelonian etc.

Hence, the correct answer is option (D).

Note: Human eggs are alecithal eggs that have negligible amount of yolk or mainly no yolk present in the human egg. As yolk provide nutrition to the developing embryo it is important for organisms that are oviparous to have yolk in their eggs.