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Q1. How many sperms will be produced from 10 primary spermatocytes and how many eggs will be produced from 10 primary oocytes?

Solution

10 primary spermatocytes will produce 40 sperms and 10 primary oocytes will produce 10 eggs. 

Q2. Describe the functions of human placenta.

Solution

Functions of human placenta: 1. Nutritive organ: Food materials pass from the mother’s blood into the foetal blood through the placenta. 2. Digestive organ: The trophoblast of the placenta digests proteins before passing them into foetal blood. 3. Respiratory organ: Oxygen diffuses from the maternal blood into foetal blood through the placenta. Carbon dioxide diffuses from the foetal blood into the maternal blood also through the placenta for elimination by the mother’s lungs. 4. Excretory organ: Nitrogenous wastes pass from the foetal blood into the maternal blood through the placenta for elimination by mother’s kidneys. 5. Endocrine organ: Placenta secretes (hCG), estrogen, progesterone and human placental lactogen. 6. Storage organ: The placenta stores glycogen for the foetus before liver is formed. 7. Barrier: Many substances pass from the mother to the foetus via placenta and cause abnormal development in the developing foetus.

Q3. Breast fed infants have a better immunity than bottle fed ones. Why? 

Solution

The first secretion from the breast, colostrum, is rich in antibodies, which provide passive immunity to the child. So, breast fed infants have a better immunity than bottle fed ones. 

Q4. Assuming a spermatogonial cell has 30 chromosomes, how many chromosomes will be formed in: a) The primary spermatocyte b) a spermatid derived from the cell  Justify your answer.   

Solution

a) 30 chromosomes will be formed in the primary spermatocyte since primary spermatocyte is formed by mitosis of spermatogonial cell. b) 15 chromosomes will be formed in spermatid derived from the cell since spermatids are formed by meiosis of spermatocytes.

Q5. Give a schematic labelled diagram to represent oogenesis (without description).

Solution

Stages in oogenesis      

Q6. Give reason for the following: (a) The first half of the menstrual cycle is called follicular phase as well as proliferative phase. (b) The second half of the menstrual cycle is called luteal phase as well as secretory phase.

Solution

(a) During follicular phase, primary follicles transform into Graafian follicle under FSH stimulation. Graafian follicles secrete estrogens with stimulate enlargement of endometrium of uterus. So, the first half of the menstrual cycle is called follicular phase as well as proliferative phase. (b) During luteal phase, corpus luteum is fully formed and secretes a large quantity of progesterone. So, the second half of the menstrual cycle is called luteal phase as well as secretory phase.

Q7. Given below are the events in human reproduction. Write them in the correct sequential order. Insemination, Gametogenesis, Fertilization, Parturition, Gestation, Implantation.

Solution

Correct order of events in human reproduction: Gametogenesis, Insemination, Fertilization, Implantation, Gestation, Parturition.

Q8. (a) Draw a diagram of the structure of a human ovum surrounded by corona radiata, label the following parts: (i) Ovum (ii) Plasma membrane (iii) Zona pellucida (b) State the function of zona pellucida.  

Solution

(a) Structure of a human ovum       (b) Function of zona pellucida: A capacitated sperm passes through the corona radiate to reach the zona pellucida. One of the glycoproteins of zona pellucida, ZP3 functions as a sperm receptor and binds a complementary molecule on the surface of the sperm head. Binding of the sperm head to the receptor molecule ZP3 induces the acrosome reaction of the sperm to release its hydrolytic enzymes by exocytosis.

Q9. Where are fimbriae present in human female reproductive system? Give their function.

Solution

The funnel-shaped proximal part of the fallopian tube is called infundibulum. Its margin bears motile, finger-like processes called fimbriae. The fimbriae bear cilia that beat towards the operature (called ostium) to direct the release of egg (from ovary) into the infundibulum.

Q10. Mention the name and role of hormones which are involved in regulation of gamete formation in human males.

Solution

Hormones involved in regulation of gamete formation in human males: GnRH: Gonadotropin-releasing hormone (GnRH) stimulates adenohypophysis to secrete gonadotrophins. GSH: Glutathione (GSH) stimulates Sertoli cells to secrete factors while help in spermatogenesis. ICSH: Interstitial Cell Stimulating Hormone (ICSH) stimulates interstitial cells to secrete testosterone.

Q11. What is colostrum?

Solution

Colostrum is a thin, yellowish, opalescent fluid released after birth from the mother’s breast for 2 to 3 days. It is also called foremilk.

Q12. Explain why all copulations do not result in pregnancy. 

Solution

Fertilization takes place in the fallopian tube. The copulation is timed such that the sperms reach the fallopian tube when ovum is still there and will then only be able to cause effective fertilization. Hence, all copulations do not result in pregnancy.

Q13. Differentiate between menarche and menopause.

Solution

The beginning of first menstrual cycle at puberty in human females is called menarche. The cessation of menstrual cycle in women around 50 years of age is called menopause.

Q14. Where is morula formed in humans? Explain the process of its development from zygote?

Solution

As the human zygote passes through the fallopian tube to the uterus, cleavage occurs. The cleavage is holoblastic and it divides the blastomeres completely into daughter cells. The first cleavage takes place about 30 hours after fertilization. It is meridional, coinciding with the animal-vegetal pole axis. It produces two blastomeres, one slightly larger than the other. The second cleavage occurs within 60 hours after fertilization. It is at right angles to the plane of the first, and divides each blastomere into two by forming a mitotic spindle in each. Third cleavage takes place about 72 hours after fertilization. Subsequent cleavage divisions follow one after another in an orderly manner, but in a less precise orientation. Cleavage produces a solid ball of small blastomeres. The embryo now looks like a mulberry, and is known as morula. It refers to the lobed surface of the embryo at this stage.      

Q15. Give the function of: (a) Corpus luteum (b) Endometrium

Solution

(a) Corpus luteum: It secretes progesterone which prepares endometrium of the uterus for implantation and normal development of the foetus. (b) Endometrium: It undergoes cyclic changes during menstrual cycle and prepares itself for implantation of the blastocyst.

Q16. Draw a labelled section view of seminiferous tubule of a human male.

Solution

Section view of seminiferous tubule of a human male      

Q17. Failure of testes to descend into scrotal sacs leads to sterility. Why?

Solution

High temperature of the abdomen kills the spermatogenic tissue of the testes. Thus, no sperms are formed. Hence, failure of testes to descend into scrotal sacs leads to sterility.

Q18. Draw a labelled diagram of the reproductive system in a human female.

Solution

Reproductive system in a human female    

Q19. Nature has developed its own mechanism to restrict the number of eggs fertilised per cycle in humans. Justify.

Solution

Only one mature ovum is released per cycle of menstruation in human females. In this way, nature has developed its own mechanism to restrict the number of eggs fertilised per cycle in humans.

Q20. Name the muscular and the glandular layers of human uterus. Which one of these layers undergoes cyclic changes during menstrual cycle? Name the hormone essential for the maintenance of this layer.

Solution

(i) The muscular layer of human uterus is called myometrium and the glandular layer is called endometrium. (ii) Endometrium undergoes cyclic changes during the menstrual cycle. (iii) Progesterone is essential for the maintenance of endometrium.

Q21. Both vaccine and colostrum produce immunity. Name the type of immunity produced by these.

Solution

Vaccine produces active immunity and colostrum produces passive immunity. 

Q22. What is parturition? Which hormones are involved in it?

Solution

Parturition is the act of expelling the fully developed young one (foetus) from the mother's uterus at the end of gestation period. Oxytocin and relaxin hormones are involved in parturition.

Q23. Three of the steps of neuro-endocrine mechanism in respect of parturition are mentioned below. Write the missing steps in proper sequence. (a) Signals originate from fully developed foetus and placenta. (b) _____________. (c) _____________. (d) Oxytocin causes strong uterine contraction. (e) Uterine contraction stimulates further secretion of oxytocin. (f) _____________.  

Solution

(b) Foetal ejection reflex (c) The reflex triggers release of oxytocin (f) Expulsion of the baby out through the birth canal.

Q24. T.S. of mammalian testis revealing seminiferous tubules shows different types of cells. (i) Name the types of cells of germinal epithelium. (ii) Name the cells scattered in connective tissue and lying between seminiferous tubules. Differentiate between them on the basis of their functions.

Solution

(i) Germinal epithelium shows the following types of cells: 1. Spermatogonia 2. Sertoli cells (ii) Leydig cells or Interstitial cells.   Functions: Spermatogonia: Undergo meiotic division leading to sperm formation. Sertoli cells: Nourish germ cells. Leydig cells: Synthesise and secrete hormone androgen.

Q25. In ovary, which structure transforms into corpus luteum? Name the hormone secreted by corpus luteum.

Solution

Follicular cells of empty Graafian follicle transform as corpus luteum. The corpus luteum secretes a hormone called progesterone.

Q26. Draw a labelled diagram of the microscopic structure of a human sperm.

Solution

Microscopic structure of a human sperm        

Q27. What is meant by LH surge? Write the role of LH.

Solution

Rapid secretion of LH leading to its maximum level during the mid-cycle is called LH surge. It induces rupture of Graafian follicle and thereby the release of ovum (ovulation).

Q28. From where parturition signals arise, mother or foetus? Mention the main hormone involved in parturition.

Solution

Parturition signals arise from the foetus and placenta. Oxytocin is the main hormone involved in parturition.

Q29. ‘Each and every coitus does not result in fertilisation and pregnancy’. Justify the statement.

Solution

It is important that the ovum and sperm reach simultaneously to the ampullary-isthmic junction. As most of the sperms and ova fail to do so, each and every coitus does not result in fertilisation and pregnancy.

Q30. Placenta acts as an endocrine tissue. Justify

Solution

Placenta secretes hormones such as human chorionic gonadotrophic (hCG), estrogen, progesterone and human placental lactogen. So, placenta is regarded as an endocrine tissue.