Bihar Board - Class 12 Biology - Chapter3: Human Reproductive Short Answer Question
Chapter- 3 Human reproduction
Short answer type
Q.1. In chronological sequence, list the following events related to human reproduction. implantation, gestation, parturition, gametogenesis, and fertilization.
A.1. Following is the sequence of events occurring in the process of human reproduction:
- Gametogenesis
- Insemination
- Fertilization
- Implantation
- Gestation
- Parturition
Q.2. State the significance of the cervix in the female reproductive system.
A.2. The cervix is a narrow opening through which the uterus opens up to the vagina. The cervical canal is the cavity of the cervix which alongside the vagina goes on to form the birth canal.
Q.3. What is the reason for the absence of menstrual cycles during conception or pregnancy?
A.3. During pregnancy, all the events of the menstrual cycle stop and there is no menstruation. Menstruation occurs only when the egg that is released is not fertilized. But in pregnancy, the released egg is fertilized and hence the uterus lining does not shed, instead nourishes the fetus. However, a woman may experience uterine bleeding during pregnancy due to various reasons. It is not due to the period.
Q.4. Name the hormone crucial in parturition. Does the parturition signal originate from the mother or the fetus?
A.4. The hormone is Oxytocin. The signal originates from the placenta and fully developed fetus which initiate the foetal ejection reflex triggering the release of the hormone, oxytocin.
Q.5. State the role of the epididymis in male fertility.
A.5. It is situated along the posterior surface of each testis where spermatozoa acquire motility and the capacity to fertilize the egg. The surface of the sperm is altered in response to secretions of the epididymis, which is key to achieve the ability to fertilize an egg.
Q.6. What are the events that cause the chromosome number of gametes to go from 2n, n, and again back to 2n during reproduction?
A.6. Chromosomes replicate once but divide twice. They undergo mitosis, first meiotic cell division and second meiotic cell division, the outcome of which is n number of chromosomes. They fuse with the haploid(n) sex gamete of the opposite sex to form a diploid(2n) cell during reproduction.
Q.7. How is a primary oocyte different from a secondary oocyte?
A.7. The primary oocyte is a diploid cell whereas the secondary oocyte is a haploid cell. The primary oocyte is formed when oogonia are at the prophase-I of the meiotic division in the foetal ovary whereas secondary oocyte is formed from primary oocyte after meiosis – I division to produce ova in females during the stage of puberty.
Q.8. State the role of the ampullary-isthmic junction in the female reproductive tract.
A.8. In the ampullary-isthmic junction, fertilization of the ovum takes place.
Q.9. How is polyspermy checked by the zona pellucida of the ovum?
A.9. The zona pellucida is a thick layer that is girdled by corona radiata cells. During fertilization, cortical granules are released from the egg which blocks fusing of multiple sperms with an egg.
Q.10. What is the significance of LH surge through the menstrual cycle?
A.10. It triggers the rupture of the Graafian follicle and causes the release of the ovum in the fallopian tube.
Q.11. State the significance of the following stages during the lifetime of a female.
Menarche
Menopause
A.11. The first menstruation or onset of menstruation at puberty is referred to as menarche. It indicates the attainment of sexual maturity and the commencement of the fertile period. Menstruation cycle is the cycle of events from one up till the next menstruation and is repeated for about 28 days on an average wherein one ovum is released. Menopause, on the other hand, is when the menstruation cycle comes to a halt, indicating the end of the fertile period as the process of ovulation stops. Cyclic menstruation denotes a regular reproductive phase stretching from menarche to menopause.
Q.12. a. How many spermatozoa does one secondary spermatocyte produce?
b. Where in zygote does the first cleavage division occur?
A.12. a. The secondary spermatocytes undergo meiotic division – II to generate four haploid spermatids which through the process of spermiogenesis are transformed into spermatozoa.
A.2. b. Cleavage occurs within the fallopian tube and is holoblastic, dividing the zygote completely into blastomeres. The first cleavage divides the zygote longitudinally into two blastomeres wherein one is slightly larger than the other.
Q.13. Why does corpus luteum stay active throughout pregnancy and in the absence of fertilization, is active only for 10-12 days?
A.13. During the luteal phase, the leftover parts of Graafian follicle transform into the corpus luteum. It discharges large quantities of progesterone hormone which is required for the maintenance of the endometrium. The endometrium is important for implantation of the fertilized egg and various other stages of pregnancy. Hence, corpus luteum has a long life in pregnancy. In the absence of fertilization, upholding of the corpus luteum is not required and thus it declines within 10-12 days, which causes the lining of the endometrium to menstruate and hence the onset of the new menstrual cycle.
Q.14. What is a foetal ejection reflex? How does it cause parturition?
A.14. Foetal ejection reflex is the mild uterine contractions that arise from the parturition signals from the fully developed fetus and the placenta. This reflex stimulates the release of oxytocin, which causes uterine contractions, in turn, stimulating the increased secretion of oxytocin. This action of uterine contractions and oxytocin secretion further results in stronger contractions leading to the dilation and hence expulsion of the baby out of the uterus through the cervical canal, expelling placenta along, thus the parturition or childbirth.
Q.15. What are the functions of placenta other than its endocrine function?
A.15. The placenta promotes the supply of nutrients and oxygen to the embryo. It also facilitates the elimination of excretory wastes and carbon dioxide produced by the embryo. Placenta aids in the transportation of substances to and from the embryo as it is connected to the embryo through the umbilical cord.
Q.16. Why is breastfeeding recommended during the initial stages of infant growth?
A.16. The mammary glands in females start producing milk towards the end of pregnancy through the process of lactation which helps the mother feed the newborn. Colostrum is the milk produced during the initial few days. Colostrum contains antibodies which are crucial in developing resistance in the newborns, hence it is recommended by doctors to bring up a healthy baby.
Q.17. What are the different stages of the follicular phase of the menstrual cycle taking place in the ovary and uterus?
A.17. In this phase, primary follicles transform into the fully mature Graafian follicle in the ovary. The endometrium of the uterus simultaneously regenerates through proliferation. Changes in the levels of ovarian and pituitary hormones induce changes in the uterus and ovaries. During this stage, the secretion of FSH and LH eventually increases and triggers the secretion and follicular development of estrogen by the growing follicles. In the middle of the cycle, both LH and FSH reach the peak level. This speedy secretion of LH at the maximum level during the mid-cycle causes rupture of the Graafian follicle and hence ovulation.
Q.18. Define Parturition.
A.18. Parturition refers to a process of delivering a baby from the uterus to the vagina to the outside world. There are three stages of Parturition:
Dilation.
Expulsion.
Placental.
Q.19. Define Fertilization.
A.19. Fertilization refers to the biological process of fusion of male and female gametes resulting in the formation of a zygote. In humans, the fertilization process takes place in the fallopian tube.
Q.20. Write the main functions of each testis and ovary?
A.20. Tests are also called the Testicles. It is a pair of oval-shaped organs masked in a pouch called the scrotum. They are responsible for the production of sperms and the male hormone testosterone.
The ovary is a ductless reproductive gland, which functions by producing a female sex hormone called estrogen and also involved in producing and storing the ovum or the egg cell.
हिंदी के सभी अध्याय के महत्वपूर्ण प्रशन उत्तर के लिए अभी Download करें Vidyakul App - Free Download Click Here
