Question

What is the correct observation regarding the size of egg, blastula, and gastrula of a frog?

• A. There is progressive increase in size from zygote to blastula to gastrula.
• B. All the three are of same size.
• C. Zygote is small while blastula and gastrula are larger.
• D. Gastrula is larger while zygote and blastula are of same size.

Answer 1

Answer: (D)

Gastrula is larger while zygote and blastula are of same size.

• The zygote is covered by zona pellucida and the cleavage results in the formation of morula which is of the same size because the cells do not grow and just divide.
  
• The morula changes in structure and forms the blastula which is similar to the size of zygote because the zona pellucida is still intact which inhibits the increase in size.
  
• The zona pellucida degrades after the implantation and as gastrulation takes place after it, the gastrula is larger in size as compared to both zygote and blastula.
  

So, the correct option is 'Gastrula is larger while zygote and blastula are of the same size'.