Question

A morula can be differentiated from blastula in
A. Presence of cavity
B. Presence of more yolk
C. Presence of yolk
D. Absence of cavity

Answer 1

A mammal develops from a single cell called a zygote, which results from an ovum being fertilized by a single sperm. The zygote is surrounded by a membrane of glycoproteins called zona pellucida. The zygote then undergoes cleavage, resulting in an increase in the number of cells within zona pellucida.

Complete answer:
Cleavage is division of cells in an early embryo. The early stages of mammalian development involve the processes following fertilization, such as cleavage, the morula formation and blastula formation.
Once the zygote is formed, cleavage begins, leading to the formation of morula. Morula contains 8-16 celled daughter cells known as blastomeres. The first division occurs about a day after fertilization, and subsequent division takes place every 12 to 24 hours after that. Morula can be categorized as being either internal or external. Morula divides to form a blastocyst which has a cavity called blastocoel along with an inner cell mass.
Blastula is a hollow sphere of cells produced during development of an embryo by repeated cleavage of an fertilized egg. Cells of blastula form an epithelial layer, known as blastoderm, which encloses a fluid-filled cavity called blastocoel. After the blastula develops, it undergoes transition to the gastrula and the process is termed as gastrulation.
Both morula and blastocyst differ from each other as a morula is a mass of totipotent cells in a spherical shape after 3–4 days of fertilization whereas a blastocyst has a cavity inside the zona pellucida along with an inner cell mass.

Therefore the correct answer is D, absence of cavity.

Note: Depending on the amount of yolk in egg, cleavage can be holoblastic or meroblastic. Holoblastic cleavage occurs in animals with little yolk in their eggs, example humans. Whereas, meroblastic cleavage occurs in animals whose eggs have more yolk such as birds and reptiles. Cleavage replicates the genome and then divides the cells in half by the process of mitosis. However, there is no growth phase during cleavage.