NCERT Class 12 Biology: Chapter –3 Human Reproduction Part 4

Doorsteptutor material for NSO Class-3 is prepared by world's top subject experts: fully solved questions with step-by-step explanation- practice your way to success.

Download PDF of This Page (Size: 150K)

Short Answer Type Questions

Question 1:

A human female experiences two major changes, menarche and menopause during her life. Mention the significance of both the events.

Answer:

Menarche is the beginning of menstrual cycle in a female’s life that starts at the age of puberty and marks the attainment of sexual maturity.

Menopause is the end stage of a woman’s menstrual cycle that marks the end of reproductive stage.

Question 2:

a. How many spermatozoa are formed from one secondary spermatocyte?

b. Where does the first cleavage division of zygote take place?

Answer:

(a) Two spermatozoa are formed from one secondary spermatocyte.

(b) The first cleavage division of zygote takes place in the fallopian tube or oviduct.

Question 3:

Corpus luteum in pregnancy has a long life. However, if fertilisation does not take place, it remains active only for 10-12 days. Explain.

Answer:

During pregnancy, corpus luteum releases a large amount of progesterone and oestrogen due to the neural signal given by the maternal endometrium to the hypothalamus.

This sustains the release of Luteinising hormone and maintains the embryo until the gestation period. If the fertilisation does not occur, corpus luteum would not be able to remain active for more than 10-12 days because of the lack of progesterone which is required to maintain the corpus luteum.

Question 4:

What is foetal ejection reflex? Explain how it leads to parturition?

Answer:

Parturition is the delivery of foetus into the outside world. Foetal ejection reflex are the signals given by the completely developed foetus and the placenta which causes mild uterine contractions.

1. When the foetal ejection reflex occurs, mild uterine contractions takes place.

2. These mild uterine contractions trigger the release of oxytocin.

3. The release of oxytocin in turn, leads to stronger uterine contractions. This process continues until a stronger contraction leads to the expulsion of baby through the birth canal or parturition.

Question 5:

Except endocrine function, what are the other functions of placenta.

Answer:

Placenta is the temporary organ that:

1. Attaches uterus to the uterine wall.

2. Provides nutrients to the growing foetus.

3. Provides oxygen to the foetus.

4. Helps in waste removal from the foetus.

Question 6:

Why doctors recommend breast feeding during initial period of infant growth?

Answer:

Doctors recommend breast feeding during the initial period of infant growth because for a few days during the start of lactation, the milk produced by colostrum (the female mammary glands), is full of antibodies. This improves the immunity of baby and provides resistance against various diseases.

Question 7:

What are the events that take place in the ovary and uterus during follicular phase of the menstrual cycle.

Answer:

The events that take place in the ovary and uterus during follicular phase of the menstrual cycle are:

1. The primary follicle matures into graafian follicle.

2. After this the secretion on oestrogen takes place.

3. The endometrium lining of the uterus regenerates through proliferation.

4. Shedding of the endometrium lining starts taking place.

Question 8:

Given below is a flow chart showing ovarian changes during menstrual cycle. Fill in the spaces giving the name of the hormones responsible for the events shown.

Changes during menstrual cycle

Changes During Menstrual Cycle

Changes during menstrual cycle

Answer:

A: LH and FSH (Follicle Stimulating Hormone)

B: LH (Luteinizing hormone)

C: Progestrone

Developed by: