Difference Between Morula and Blastula

Main Difference – Morula vs Blastula

Morula and blastula are two early stages of an embryo in animals. After fertilization, a rapid cell division occurs in the zygote by mitosis. Small, spherical cells are formed from the zygote during this process, which is known as cleavage. These cells are called blastomeres. The morula develops into the blastula in the process known as blastulation. Blastula later becomes the embryo. The main difference between morula and blastula is that morula is a spherical mass of blastomeres, which are formed following the splitting of a zygote whereas blastula is an early developmental stage of the embryo, consisting of a spherical layer of cells filled with fluid.

Key Areas Covered

1. What is Morula
      – Definition, Structure, Formation
2. What is Blastula
      – Definition, Structure, Formation
3. What are the similarities between Morula and Blastula
      – Common Features
4. What is the difference between Morula vs Blastula
      – Comparison of Key Differences

Key Terms: Blastocoel, Blastocyst, Blastoderm, Blastomeres, Blastula, Blastulation, Cleavage, Embryoblast, Morula, Trophoblast, Gastrula, Endometrium, Embryo

What is Morula

Morula represents an early developmental stage of an embryo in animals. It comprises a solid ball of cells, which is a result of the rapid cell divisions of a zygote by mitosis. The small, spherical cells in the morula are referred to as blastomeres. Usually, the first cell cleavage by mitosis occurs 24 hours after fertilization. Morula is formed in eggs with a little yolk, which undergoes complete cleavage. Morula consists of 10-30 cells. The collection of spherical cells resembles a mulberry.

Blastulation refers to the formation of blastula from morula. A fluid-filled cavity known as blastocoel is developed from morula. Once the cavitation is complete, the embryo is referred to as the blastula. Morula stage can be seen 4-5 days after fertilization.

Figure 1: Early stages of the mammalian embryo
a – Two-cell stage, b – Four-cell stage, c – Eight-cell stage, d, e – Morula stage

What is Blastula

Blastula is a hollow ball of cells of an animal embryo in its early stages of development. Once morula consists of about hundreds of cells produced by cleavage, it develops into the blastula. Blastula consists of a spherical cell layer known as blastoderm. The blastula in mammals develops into the blastocyst. The blastoderm surrounds the fluid-filled cavity known as blastocoel. Blastocyst contains an inner cell mass (ICM), which is distinct from the blastula. The spherical cell layer of the blastocyst is called the trophoblast. The ICM in the blastocyst is referred to as the embryoblast. The trophoblast develops into the placenta nourishing the embryo. The embryoblast is differentiated into different types of cells in the organism’s body in the process called gastrulation.

Figure 2: Blastulation
1 – Morula, 2 – Blastula

Similarities Between Morula and Blastula

Morula and blastula are two early stages of embryonic development of animals.

During embryonic development, morula develops into blastula.

Both stages of morula and blastula are protected by zona pellucida.

Definition

Morula: Morula is a solid ball of cells resulting from division of a fertilized ovum, and from which a blastula is formed.

Blastula: Blastula is a hollow ball of cells of an animal embryo in its early stages of development.

Occurrence

Morula: Morula forms 4-5 days after fertilization.

Blastula: Blastula forms 5-10 days after fertilization.

Structure

Morula: Morula is a solid cell mass.

Blastula: Blastula is a hollow structure.

Composition

Morula: Morula consists of a ball of small, spherical cells formed by the rapid cleavage of the zygote.

Blastula: Blastula consists of a spherical cell layer of blastomeres and a fluid-filled cavity called blastocoel.

Number of Cells

Morula: Morula consists of more than a hundred of cells.

Blastula: Blastula consists of 128 cells.

Develops into

Morula: Morula develops into the blastula in a process called blastulation.

Blastula: Blastula develops into the gastrula in a process called gastrulation.

Applications in in-vitro Fertilization (IVF)

Morula: Transferring of morulas on the fifth day after fertilization results in a reasonable pregnancy rate.

Blastula: Transferring of blastulas results in a lower pregnancy rate compared to that of morula.

Conclusion

Morula and blastula are two early stages of embryonic development in animals. The main difference between morula and blastula is in their structure. Morula is a solid cell mass, which develops from the zygote due to rapid mitotic cleavages. The cells in the morula are called blastomeres. These blastomeres arrange in a spherical cell layer known as blastoderm in the process called blastulation. The resultant hollow structure is referred to as a blastula. The blastula compromises of a fluid-filled cavity called blastocoel. The blastula develops into the blastocyst, consisting of an ICM called embryoblast. The embryoblast develops into different types of cells in the body.

Reference:

1.”The cleavage divisions up to the morula stage.”5.1 The cleavage divisions and the migration of the embryo through the tube. N.p., n.d. Web. Available here. 10 June 2017.
2. Sherbahn, Richard. “Morula stage IVF embryos.”In Vitro Fertilization Picture of a Morula Stage Embryo – Day 4 Human IVF Embryo. N.p., n.d. Web.Available here. 10 June 2017.
3. “Cleavage, the Blastula Stage, and Gastrulation – Boundless Open Textbook.” Boundless. N.p., 08 Aug. 2016. Web. Available here. 10 June 2017.

Image Courtesy:

1. “Gray9′ By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body (Public Domain) via Commons Wikimedia
2. “Blastulation” Public Domain) via Commons Wikimedia