Question

By the end of how many weeks, major organ systems formed during embryonic development?
A. 4 weeks.
B. 8 weeks
C. 12 weeks.
D. 24 weeks.

Answer 1

Hint: The fertilization of an egg cell (ovum) by a sperm cell initiates embryonic development (spermatozoon). Once fertilized, the ovum is known as a zygote, which is a single diploid cell. The zygote goes through mitotic divisions without significant growth (a process known as cleavage) and cellular differentiation, which results in the formation of a multicellular embryo.
All major organ systems develop by the end of the first trimester, or the 3rd/4th month. The genital organs are visible.

Step by step solution:
Human embryonic development, also known as human embryogenesis, is the process by which a human embryo develops and forms. It is distinguished by cell division and cellular differentiation processes that occur in the embryo during the early stages of development. In biological terms, the human body develops from a single-celled zygote to an adult human being.
In the third week, the inner cell or embryo begins to differentiate into three germinal layers: ectoderm, endoderm, and mesoderm. These cells transform and differentiate into all tissues and organs, including nerves, blood, muscle, bone, and the digestive tract.
The heart is the first organ to begin operating. Following the first month of pregnancy, the heart begins to develop.
Limbs and digits show up in the second month.
All major organ systems develop by the end of the first trimester or third month. The genital organs are visible.
During the fifth month, the embryo begins to move and hairs start to appear on the head.
Eyelashes are formed, eyelids separate, and the body is covered in fine hair by the end of the second trimester (24 weeks or 6 months).
The fetus is fully developed and ready for birth by the end of the ninth month.

So, option C is correct.

Note: Organogenesis is the process by which organs develop from the third to the eighth week of pregnancy and continues until birth. Sometimes, such as in the lungs, full development continues after birth. Different organs contribute to the development of the body's many organ systems.