Question

The correct sequence of various stages in embryonic development is

• A. Fertilization --> Cleavage --> Morula --> Blastula --> Gastrula
• B. Cleavage --> Fertilization --> Gastrula --> Blastula
• C. Blastula --> Cleavage --> Gastrula --> Fertilization
• D. Gastrula --> Fertilization --> Cleavage --> Blastula

Answer 1

Answer: (A)

Fertilization --> Cleavage --> Morula --> Blastula --> Gastrula

When sperm and ovum fuses with each other, fertilization takes place and forms zygote. After fertilization, zygote undergoes rapid cell divisions (cleavage) to form morula, which is an 8 cell mass in a spherical shape which undergoes further cell divisions to form a spherical ball of cells; blastula, which is hollow sphere of cells. Blastula finally forms gastrula, which is three layered structure known as ectoderm, mesoderm and endoderm. Hence, correct sequence is Fertilization --> Cleavage --> Morula --> Blastula --> Gastrula.