Read the given passage and answer the following questions :
The average duration of human pregnancy is about 9 months which is called the gestation period. Vigorous contraction of the uterus at the end of pregnancy causes expulsion/delivery of the foetus. This process of delivery of the foetus (childbirth) is called parturition. Parturition is induced by a complex neuroendocrine mechanism. The signals for parturition originate from the fully developed foetus and the placenta which induce mild uterine contractions called foetal ejection reflex. This triggers release of oxytocin from the maternal pituitary. Oxytocin acts on the uterine muscle and causes stronger uterine contractions, which in turn stimulates further secretion of oxytocin. The stimulatory reflex between the uterine contraction and oxytocin secretion continues resulting in stronger and stronger contractions. This leads to expulsion of the baby out of the uterus through the birth canal – parturition. Soon after the infant is delivered, the placenta is also expelled out of the uterus. The mammary glands of the female undergo differentiation during pregnancy and starts producing milk towards the end of pregnancy by the process called lactation. This helps the mother in feeding the new- born. The milk produced during the initial few days of lactation is called colostrum which contains several antibodies absolutely essential to develop resistance for the new-born babies. Breast-feeding during the initial period of infant growth is recommended by doctors for bringing up a healthy baby.
Arrange the following events of human foetal development in the correct sequence:
A. The heart of the embryo is formed.
B. The foetus develops limbs and digits.
C. First movements of the foetus and appearance of hair on the head are observed.
D. The body is covered with fine hair, eyelids separate and eyelashes are formed.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A, B, C, D
A. The heart of the embryo is formed. — First. The heart is formed after one month of pregnancy. Its sound, heard through a stethoscope, is the first sign of a growing foetus.
B. The foetus develops limbs and digits. — Second. Limbs and digits appear by the end of the second month. By the end of 12 weeks most of the major organ systems are formed.
C. First movements of the foetus and appearance of hair on the head are observed. — Third. These are usually seen during the fifth month.
D. The body is covered with fine hair, eyelids separate and eyelashes are formed. — Fourth. This happens by the end of about 24 weeks (end of the second trimester).
NCERT Extract:
Pregnancy and Embryonic Development – “… In human beings, after one month of pregnancy, the embryo’s heart is formed. The first sign of growing foetus may be noticed by listening to the heart sound carefully through the stethoscope. By the end of the second month of pregnancy, the foetus develops limbs and digits. By the end of 12 weeks (first trimester), most of the major organ systems are formed, for example, the limbs and external genital organs are well-developed. The first movements of the foetus and appearance of hair on the head are usually observed during the fifth month. By the end of about 24 weeks (end of second trimester), the body is covered with fine hair, eye-lids separate, and eyelashes are formed.”