This set of Class 12 Biology Chapter 3 Multiple Choice Questions & Answers (MCQs) focuses on “Human Reproduction – Fertilisation”.
1. The population of vagina with semen during coitus is called as _______
Explanation: Coitus or copulation is the process that leads to the release of semen from the penis into the vagina. The sperms populate the vagina along with other contents of semen. This process is called insemination.
2. What is the correct order of travel of sperm through the female reproductive tract before it reaches the egg?
a) Vagina -> Fallopian tube -> Uterus -> Cervix
b) Vagina -> Cervix -> Uterus -> Oviduct
c) Vagina -> Uterus -> Cervix -> Oviduct
d) Vagina -> Fallopian tube -> Cervix -> Uterus
Explanation: Sperms are released into the vagina. From here, they travel through the cervix and uterus before reaching oviduct or fallopian tube, where they can encounter an egg.
3. The number of semen delivered by a male determines the number of babies the female can conceive.
Explanation: Males usually release millions of sperm at each coitus. However, the female tract prevents most of them from reaching the fallopian tube with only one sperm being able to fertilize the egg. However, in rare cases where female releases two eggs (one from each ovary), there’s a probability of conceiving twins. Thus it is the number of eggs and not the number of sperm that determines the number of babies that the female can conceive.
4. What part of the oviduct does the sperm encounter the egg?
Explanation: The egg is released and awaits in ampulla for the sperm. The sperms cross the reproductive tract barriers before reaching the ampulla to fertilize the egg.
5. During a menstrual cycle, copulation on which of the following phases has the least probability of fertilizing an egg?
a) Menstrual phase
b) Onset of follicular phase
c) End of the follicular phase
d) End of the luteal phase
Explanation: Fertilization occurs only when the egg and sperm are present in the ampulla at the same time. Hence the coitus should happen near the period of ovulation. Ovulation occurs at the end of the follicular phase or the onset of luteal phase.
6. What is fertilization?
a) Release of egg from ovary
b) Release of sperm from testis
c) Mixing of semen with vaginal fluid
d) Fusion of sperm with egg nuclei
Explanation: Ovulation is the release of egg from the ovary. Spermiation is the release of sperm from testis. Insemination is the release of semen into vagina. Fertilization is the process that leads to fusion of male and female gametes.
7. What layer of egg cell prevents entry of other sperms?
a) Corpus luteum
b) Zona pellucida
d) Corona radiata
Explanation: The sperm contacts the egg cell at zona pellucida. The zona pellucida then undergoes chemical changes which renders egg insusceptible to further encounters with another sperm. This is essential to ensure that only a single sperm fertilizes the egg.
8. What triggers the completion of meiosis of secondary oocyte?
a) Maturation of Graafian follicle
b) Entry of sperm into the egg cell
c) Release of estrogen
Explanation: The secondary oocyte released from the ovary has finished first round of meiosis. The second round of meiosis occurs in ampulla after the egg encounters the sperm. This leads to formation of large ovum and a tiny second polar body.
9. The haploid ovum is also called as _____________
Explanation: The haploid ovum is formed after the second round of meiosis is completed. This haploid ovum is also called as ootid. Oogonium is the egg mother cell that is diploid and undergoes meiosis to form egg.
10. The fusion of haploid sperm and egg nuclei during fertilization leads to formation of a __________
a) haploid zygote
b) diploid zygote
c) haploid embryo
d) diploid embryo
Explanation: The fusion of sperm and egg restores the chromosome number. The new cell is called zygote having the potential to develop into a new organism.
11. At what stage of development is the sex of the human baby determined?
Explanation: The sex, in humans, is determined by the chromosomes received by the zygote from the male and female nuclei. If it is XX, the zygote will develop into a female child. If it is XY, the zygote develops into a male baby.
12. Which of the following is the correct number of chromosomes based on the cell type?
a) Sperm: 23; Egg: 23; Zygote: 23
b) Sperm: 46; Egg: 46; Zygote: 46
c) Sperm: 23; Egg: 23; Zygote: 46
d) Sperm: 46; Egg: 46; Zygote: 23
Explanation: Sperm and egg are haploid cells hence have only one set of chromosomes. Zygote on the other hand is diploid thus has 46 chromosomes.
13. The sex of the human baby is male if ______
a) sperm has X chromosome
b) sperm has Y chromosome
c) ovum has X chromosome
d) ovum has Y chromosome
Explanation: The sex in humans is determined by the sex chromosome that the male gamete carries. The females are XX hence meiosis results in all ova having X chromosome. Males are XY and 50% sperms have X and 50% have Y. Thus the determining factor that makes a baby male is Y chromosome in the sperm.
14. The sex ratio is low owing to the inherent bias in the number of sperms that carry Y chromosome.
Explanation: The human males have XY as their sex chromosomes. Thus upon undergoing meiosis, the probability of sperm having an X chromosome is the same as that of having a Y chromosome. There is no natural bias here. The lower sex ratio hence cannot be accounted to such a biological phenomenon.
15. Which of the following is not a layer that the sperm has to encounter before reaching the egg nuclei?
a) Zona pellucida
b) Corona radiata
c) Perivitelline space
d) Zona radiata
Explanation: The egg nuclei and cytoplasm is enveloped by various layers which prevent desiccation and provides nourishment and suitable habitat for the development of the egg. The sperm has to break these barriers to reach the egg nuclei.
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