
Introduction:
During pre-embryonic stage, the zygote starts multiplying into more than hundreds of cells. These cells establish into primary germ layers, and the conceptus attaches to the uterine wall. This process is divided into cleavage, implantation, and embryogenesis.

Answer to Problem 1TYR
Correct answer:
The conceptus reaches the uterus about 72 hours after ovulation. It consists of more than 16 cells and resembles a mulberry. Hence, it is called a morula. Therefore, option b is correct.
Explanation of Solution
Justify reasons for the correct statement:
The morula is smaller than the zygote. Small blastomeres are produced by cleavage. Cleavage also initiates the production of large amounts of cells, by which the embryonic tissues are formed. Meanwhile, the morula produces identical twins and divides into two cell masses.
Option (b) is given as, “morula”.
In the uterine cavity, the morula lies freely for 4 to 5 days and starts multiplying into more than 100 cells.
Hence, option (b) is correct.
Justify reasons for the incorrect statements:
Option (a) is given as, “zygote”.
Zygote multiplies into hundreds of cells. These cells are established into three primary germ layers, and the conceptus is attached to the uterine wall firmly. Hence, it is a wrong answer.
Option (c) is given as, “blastomere”.
After fertilization, the first cleavage produces two daughter cells or blastomeres. These cells proliferate at shorter time intervals. Hence, the number of blastomeres is increased. Hence, it is a wrong answer.
Option (d) is given as, “blastocyst”.
During embryonic development, a hollow thin structure consists of a group of cells (inner cell masses) called blastocyst. The embryo arises from the blastocyst. Hence, it is a wrong answer.
Option (e) is given as, “embryo”.
Fertilized egg is called as an embryo. Hence, it is a wrong answer.
Hence, options (a), (c), (d), and (e) are incorrect.
Morula is a spheroidal stage, and it consists of more than 16 blastomeres.
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Chapter 29 Solutions
Anatomy & Physiology: The Unity of Form and Function (Standalone Book)
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