Question

Eggs which have yolk in the center surrounded by cytoplasm are called as
A. Centrolecithal
B. Homolecithal
C. Microlecithal
D. Alecithal

Answer 1

Eggs are organic constituents and consist of zygotes that develop into an embryo. The yolk present in the egg provides nutrition to the embryo for its growth and development.

Complete step by step answer: The eggs are classified on the basis of the distribution of yolk in the cytoplasm and the quantity of yolk inside the egg are as follows:
A. Centrolecithal eggs- These are eggs that have their yolk placed in the center of the cytoplasm of the ova. Many arthropods, hydrozoa, some insects, and coelenterates are determined to have centrolecithal eggs. Centrolecithal eggs are determined to have a great amount of yolk and are large and elongated. Coelenterates are aquatic invertebrate animals such as corals, sea anemones, and jellyfishes.
B. Homolecithal eggs- Homolecithal eggs are also known as isolecithal eggs. These eggs have
very little or no yolk present in the cytoplasm of the ovum. Some examples include echinoderms, mammals, amphioxus, and sea urchins.
C. Microlecithal eggs- Eggs that are small in size and contain less amount of yolk are termed as
microlecithal eggs. These small eggs are produced over large quantities in animals with high egg mortality. Cell cleavage divides the egg into small portions and the yolk is evenly distributed. Cartilaginous fish, roundworm Toxocara, flatworm Paragonimus westermani, etc., are some examples of animals that consist of microlecithal eggs. Microlecithal eggs are also described as oligolecithal eggs or alecithal eggs by some Embryologists. These eggs have very little yolk present in them. Marsupials, eutherian mammals, and amphioxus comprise these types of eggs.
D. Alecithal eggs- Whereas, mammalian eggs are termed as alecithal eggs. Alecithal eggs do
not contain any yolk in them. They comprise a negligible amount of yolk in them. In conclusion, eggs which have yolk in the center surrounded by cytoplasm are called centrolecithal eggs.
Therefore, the correct answer is option A, i.e., Centrolecithal.

Note: The yolk present in an egg is necessary to provide nutrients for the development of the
embryo. Hence, it is important in oviparous animals such as birds, reptiles, amphibians, etc. Some other types of eggs based on their yolk quantity include: mesolecithal egg and macrolecithal eggs